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Upgrading Corinna's Electrical System
With Solar Power, Battery Monitoring, Sine Wave Inverter and Lithium Batteries

The initial document on the Upgrade to Corinna's Electrical System has got far too long so I have decided to cover this addition of a Gateway to allow remote monitoring using a Raspberry Pi onto new pages. There are currently two new parts: the straightforward addition of The Raspberry Pi using the Venus OS and The Extension to Venus OS Large with Node-RED to allow the addition of a dedicated Dashboard and additional smart management.


We have basically been using the same power system on our narrowboat Corinna since she was new. A major component is an independent 24 volt system used purely for an inverter providing 230 volt power which enables us to use a mains fridge. It worked well when we were traveling for long distances every day but we have always had problems with rapid battery degradation which has become more acute over the years. This is partly because modern basic Lead Acid 'Domestic' batteries have a lower specification in terms of life cycles and partly because, we suspect, the original fridge become less efficient as it aged. The result was that we increasingly needed to run the engine for a period in the evenings, especially if we have had a short day, to avoid running the batteries down to an unacceptable level overnight. Even then we are lucky to get a couple of years life out of the batteries for the 24V system. Just after another set of batteries started to fail I saw that Sterling were selling Lithium batteries at a more sensible price of ~£550 per 100 Ah battery. Such Lithium batteries are good for over 5000 cycles to an 80% depth of discharge and offer a life of up to 20 years. That provoked me to look at upgrading the electrical system on Corinna. Initially I looked at switching to a 12V system using Lithium batteries with a common bank for the housekeeping and inverter allowing me to have three Lithium batteries which would more than double my existing usable capacity and outlast Corinna but that was not to be.

There was little doubt in my mind that Lithium batteries would be the correct solution if one is starting a boat design from scratch but, to cut a long story short, they pose us considerable problems in location as they have a more restricted temperature range than Lead Acid batteries. We could not meet the temperature constraints with our current battery location in a tiny engine room with keel cooling tanks which means the existing batteries can reach over 50 deg C in the summer yet have little protection against low winter temperatures. Lithium batteries are also much less tolerant when it comes to charging etc. and despite most having a battery management system built in to protect them trying to charge a Lithium battery directly without additional hardware such as a battery to battery charger is a good way to destroy a standard alternator.

Despite rejecting an immediate switch to Lithium it started me thinking and a search for other alternatives to solve my immediate problems, such as solar, and options I should leave open for the future. For example, one of my main worries with my existing system is that my existing 24 volt alternator is probably no longer replaceable and a battery to battery charger could be a simple way to replace the alternator and provide an optimised charging environment at the same time preparing for a future upgrade to Lithium batteries or an engine replacement.

The write-up has turned out to be much more comprehensive than I initially expected and has been broken up into a main body and a series of Appendices, both with the background resources to design and implement a system and comprehensive measurements on an actual systems. It is a living document and is being continually updated as I learn and measure more.

Initial Objectives of the Upgrade

It is difficult to know the best order to document the way the new system has developed as there has been much iterations in design. However laying down ones objectives is always a good way to start! The requirements were comparatively soft (ie not quantitative initially) and could be satisfied in several ways. For a starting point, the main objectives were to:

Some of the main ways the first two objectives can be addressed are:

Background - Lead Acid Batteries

Before we can go further I have to give some background on Lead Acid batteries to cover the first two points above. The specified capacity of a Lead Acid battery is not fully available in practice for a number of reasons. Firstly the specification assumes a slow discharge rate, normally C/20 where C is the nominal capacity and even a C/10 rate reduces the capacity. When used with an inverter the demand rate will be much higher when, for example one is running a microwave or boiling a kettle. Secondly the life in terms of cycles is very dependent on the depth of discharge and discharging to 50% may only provide 70 cycles with a basic Lead Acid leisure battery and perhaps 300-800 with the much more expensive sealed AGM (Advanced Glass Mat) batteries. (NCC Verified Leisure Battery Scheme Information).

Charging also plays a major part. An alternator initially gives virtually its full rated charge rate then slows as it approaches the desired voltage then holds it. The final voltage should be chosen to be such that the current taken by the battery tails off to a few percent over time, any higher and the excess charge breaks down the electrolyte and produces hydrogen and oxygen, an explosive combination and this gassing also means the battery needs frequent topping up. The stage at which the fixed voltage charge is first reached corresponds to only ~80% of full charge if the battery has been significantly discharged and it may take several hours to complete the charge with a steadily decreasing current. Stopping the charging too early is not good for the battery if repeated often and we are only left with greatly reduced usable capacity if we stop charging as soon as voltage limit is reached. Overcharging breaks down the electrolyte into hydrogen and oxygen not only drying out the battery but producing an explosive mixture. Standard Alternators can not be adjusted to suit different types of batteries.

The best chargers will charge at their highest rate initially (Bulk charge), then maintain the fixed voltage (Absorption charge ) for a period calculated based on the discharge history to reach full charge and/or by monitoring the reducing charge current. Then one can change to a much lower voltage level to maintain the battery at full charge which can be continued for ever - months anyway - without gassing (Float charge). The voltages vary a little with different types of Lead Acid battery construction but typically '12V' batteries use an 'Absorption' level of 14.4V and a 'Float' of 13.8V. In addition the levels are temperature sensitive and better chargers will have temperature sensor on the batteries and a voltage measurement on the terminals to compensate for temperature and voltage drops in the cables.

There are alternator controllers which can provide the ideal behavior for Lead Acid batteries but they mostly require modifications to be made to the alternator. My 24V alternator has already been modified to have lorry controller which allows several voltages but it still takes a long time to add the final 20% of charge - fine if one is running most of the day but no good if you are stationary and want to minimise running time. An alternative to an alternator controller is a Battery to Battery charger. They usually sit between an engine start battery (charged by an alternator) and the Leisure batteries. Good battery to battery chargers are expensive but provide an optimised charging profile and can efficiently convert between voltages at the same time, for example from 12 to 24 volt. They are almost mandatory for Lithium batteries and in my case could remove the need for an extra alternator on a 24V system.

It is actually surprisingly difficult to find Good background and reference information on management of Lead Acid batteries with sufficient depth to be useful. One site which I have found useful is the Car and Deep Cycle Battery FAQ 2021 by Bill Darden which I have used for some of my reference information.

Adding Solar Power

I chose an approach for the first phase of my upgrades which helped several of the existing problems, namely to add some solar cells with a sophisticated controller which charges batteries with a multistage adaptive algorithm with temperature and voltage monitors on the main battery pack. The idea is that during much of the day the solar can keep the batteries charged in an optimum way and, if required, bring the charge up the last few percent before the end of the day. Running my alternator on its lower setting avoids overcharging. This involved a certain amount of experimenting to check if a reasonable area solar array would provide useful power during our main cruising season of Late April to early August, say 8 weeks either side of the longest day. The only non-discretionary 24V power demand is the fridge and hot days with maximum demand are like to have plentiful solar! The initial phase of upgrades was therefore to add some Solar Power and some battery monitoring to inform the next phases.

Solar Panels

I had heard good reports on Renogy Solar panels (available through Amazon) and they produced panels which were ideally sized to fit the two areas available on Corinna. My initial order was for two 100 watt Mono-cystalline panels to fit between the Pigeon box and first mushroom vent leaving space to walk down one side of the roof. They are connected in series to match a 24V system. After my initial assessment I added two more 80 watt panels. The roof is not flat and is 'planked' which ruled out flexible panels so my flat panels are spaced from the roof by 4 rubber doorstops bolted with wide washers to some of the many fixing locations. At present they can be moved round a little and for security are now attached by fine Stainless Steel chains to Eyes in the roof. The panels came with 50cm cables terminating in the universally used MC4 Solar connectors. I bought a kit with ten connectors, strippers and the special crimping tool from Amazon (Prostar Solar Crimping Tool, Stripper with 10 male and Female Connectors and two assembly spanners currently £27.99) I bought 10 m of 6mm2 solar cable as part of my initial order from OnBoardEnergy. Strip Fuses and Fuse Holders came from Midland Chandlers as we passed. The complete cost of the four panels, connectors, special tools and solar wiring was under £400 and the chain and fittings another twenty pounds.

Solar Controllers - The Victron SmartSolar MPPT 100/20 charge controller.

It is impossible to over emphasise the importance of the solar controller whose job is to match the completely different supply characteristics of solar panels with the demands of charging batteries with the highest efficiency. This requirement has lead to the creation of controllers which contain DC to DC converters so the maximum solar voltage times solar current point can be chosen at any solar input and converted to the required battery voltage required for the charge point reached. Compared to earlier chargers this gives about 30% more useful power than when any excess voltage was wasted. This can be seen when you are using a Maximum Power Point Tracker (MPPT) controller as the output current is typically about 30% higher than the current input from the solar array despite the losses in the DC to DC converter. Multiple arrays can now also be connected in series as well as parallel and the controllers can often handle a number of output (battery) voltages.

Wikipedia has a reasonable explanation of Maximum Power Point Tracking if you want to understand more of the details. Another good source of information I found recently is at Clean Energy Reviews and their explanation of MPPT controllers and their advantages is as easy to understand for a layperson as any I have found. They have reviews which seem relatively free of bias and include Victron and Renogy Devices but note they are Australia based so conditions are very different to UK!

I looked at two of the main manufacturers of marine inverters, solar controllers, battery to battery chargers etc: Sterling and Victron both have good reputations. Sterling have the most affordable Lithium batteries and seem to have an edge on battery to battery converters whilst Victron excel on Solar Controllers and Battery Monitoring as well as having excellent Sine Wave Inverters. Victron's more recent offerings are 'Smart' with built in Bluetooth for configuration and monitoring via an App. Suitable Victron Smart devices can be networked via bluetooth so a temperature and voltage monitor fitted on the battery pack can be used by a Solar controllers with no additional wiring. Many devices automatically sense the battery voltages and can be used in 12, 24 and sometimes 48 volt systems. Unfortunately, but not surprisingly, that does not extend to inverters and battery to battery chargers but does include the Victron Solar Controllers, Voltage and Temperature Monitors and their Smart Shunt for Battery measurements. This meant that I did not have to initially make a number of major choices and could make measurements to inform those choices. As well as Bluetooth, most Smart Victron devices can also be linked to controllers which allow network connctions to the internet. I have chosen to use Victron devices wherever possible.

My initial Victron order was from OnBoardEnergy who are based at Springwood Haven Marina near Nuneton. We had looked in whilst passing on Corinna and I gained a lot of useful information from Kevin as well as few initial purchases. OnBoardEnergy offer on their web site to match an genuine internet offers and Kevin Mascall has done very well by us on our initial and subsequent orders which have been delivered by a premium delivery service - DPD. During the design phase I fortunately worked up in solar controller size to the Victron MPPT 100/20 Smart tracking controller. This device automatically determines the system voltage on installation then continually adjusts the working point to optimise performance. The combination of Renogy panels and Victron controller has proved very satisfactory and has produced peaks of over 360 Watts from my horizontally mounted 360 watts of panels in July which far exceeds the output I expected from horizontal mounted panels.

The Victron Solar controller is small, lightweight and easy to mount and wire and can be extensively monitored and configured via Bluetooth even from the other end of the boat. It is directly networked via Bluetooth to a Victron Smart Battery Sense voltage-and-temperature sensor which is mounted directly on the batteries and came with an inline fuse and pre-crimped eyelets. The Solar Charger uses these measurements to optimise its charge parameters. The controller is capable of providing up to 480 Watts at 24 volts and larger arrays can be used to maintain performance in lower light conditions including series connection up to 100 volts. The existing panels have regularly provided 1000Wh/day and peaked at 1200Wh/day ie the equivalent of 2 standard 100 Ah leisure batteries discharged to 50% without even being in full sun on a clear day in late July. Since fitting the initial 200 Watts I have never needed to run the engine in the evening so the first of the objectives has easily been achieved and the full 360 Watts of panel were still giving adequate power well into September. See the Appendix for actual measurements. A good solar controller with temperature measurement will set one back almost £200. In our case for our initial £600 investment in solar we expect to reduce engine hours by 60-90 per year, extend our lead acid battery life significantly and have quiet evenings!

Monitoring - The Victron SmartShunt and SmartConnect App.

The final component in my first phase of upgrading was to add a Victron Smart Shunt. This proved very enlightening as it not only provides current, voltage and power for the batteries but also the Consumed Amp/hours and an estimate of State of Charge which is automatically kept synchronised. It also has an addition voltage input which, in my case, monitors the 12v leisure battery voltage but could also monitor the battery mid point to indicate if equalisation is required. The shunt goes in the negative (ground) lead to the battery and there should be no other connection to the battery, it handles up to 500 Amps at which it drops 50 millivolts so the losses are negligible provided the wiring is kept compact. The only input required to the device (once via the App) is the battery pack capacity. The Bluetooth range seems much less than my other Smart devices possibly because the Shunt is currently mounted right above the batteries to keep leads short. The short range is a pity as the outputs are arguably some of the most useful for controlling the system. Other users have also suffered from short range and have used the option to connect an external Bluetooth transmitter, an expensive but pragmatic solution.

I needed to modify and in some cases beef up my high current wiring for the SmartShunt which involves making crimp connections onto heavy duty cables. Wiring requirements and ratings are covered in an Appendix. I found that an impact crimping tool by Draper worked very well when used with a heavy mooring hammer - they are available from Amazon for ~£20 as is battery/welding cable and the crimp connectors. So, adding monitoring will cost from £125 to £200 depending on rewiring and requirements for tools - heavy duty Copper cable is very expensive.

The Victron SmartConnect App

Smart Victron devices are all accessed from the same Victron SmartConnect App over Bluetooth. Most of the devices have default configurations which allows them to be initially used but further configuration and monitoring is done via Bluetooth and the App. Overall I am very impressed with the Victron App, most device have a main Status display page, a History page and a page titled Trends where you can plot in real time almost any of the data available from the device. History shows information stored within the device for up to 30 days whilst Trends shows plots of the real time data from the device which are lost when you disconnect or the screen goes off both of which are irritating shortfalls. Fortunately there is the option in the settings menu to keep the screen on while SmartConnect is active, causing SmartConnect to stay connected but quickly flattening the android device batteries even with the screen turned to low brightness - I end up keeping them in the dark to save power and connected to a power brick!

In addition to accessing devices you can also run demos of every device so you can investigate all the configuration options available before you purchase the device or set it up. The App is also used to update the firmware in the devices - updates are downloaded to the App before any device updaing starts - once the App has been updated with new firmware for your device you can not change any settings until the Device has also been updated which ensures they are always kept in step - av very safe proceedure. The App also allows you to set up a Bluetooth network which is, for example, used to connect the Battery Monitor to the SmartSolar Controller and any other devices needing the information. If you have a controller with internet access linked to your device you can also access the devices remotely via the app over the internet. See the latter pages for how to add a Raspberry Pi to the system.

Its main shortfalls are that you can only connect to a single Smart device at a time from each App via bluetooth and can not currently leave the App running in the background so it is easy to lose all the real time data collected for the Trend graphs although the more important History is stored internally in the devices. This meant I rescued several old phones/pads from storage for my investigations so I can monitor several devices simultaneously. Although the instructions make it clear the devices have to be paired within the App rather than within Android it is worth repeating. If you have to remove the connection for any reason that is done within Android and I have found you must also take the phone or whatever well out of Bluetooth range. I have only had to do it once after a device became inaccessible because it seemed to be permanently locked to a particular 'phone' whilst they are normally shown on all the Android systems with some 'grayed out' if already in use on a different system. Once I had an even more comprehensive lock out of the Bluetooth system possibly provoked by the Android device shutting down through flat batteries but this was fixed by removing power for 30 seconds from the Smart Shunt by pulling the inline fuse for ten seconds then reconnecting.

Update: From Victron Energy BV August 4, 2021 "Hi, We are working on new firmware that stores the trends in the product so no need to keep VictronConnect open. If you want to try it you can manually install the current beta release: https://www.victronenergy.com/live/victronconnect:beta" I have not tried this as it changes the device firmware on most of my devices and I do not see a route back but it should be a major improvement when it is issued. It appears that the stored data is at a lower time resolution than the current live data (ie 2m at 1s interval (RAM only), 2h at 30s interval, 1d at 5m interval, 45d at 30m interval).

Actual System Power Usage Measurements

Once the Solar and the SmartShunt monitoring were connected I was able to get far more information on what was actually going on than I had ever had before with graphical displays (Trend graphs) available for all of the important parameters versus time. This confirmed what I suspected, the current Matchpower inverter with Power-saver drew negligible power until a load was applied but the idle (running but without load) power was huge at 73 watts and with fridge started at ~ 200 watts falling a little after about 5 mins as it 'warms up' consistent with fridge itself being ~100 watts. The Fridge labeling says 90 watt so the Matchpower inverter efficiency is under 90% plus the considerable no-load overhead. The cycle time is obviously very dependent on ambient temperature but seems to have an on off cycle of approx 20 to 35 minutes (~40%) overnight giving a daily usage of 190x24x0.4 = ~1800 Wh which alone requires an engine run in the evening to avoid taking the batteries below 50%. There are measurements for most of my 'appliances' in the Appendix below with power inputs measured using the SmartShunt and outputs from the Victron Phoenix 24/1600 Smart Inverter once it was available,

Input power measurements. The alternator does exactly what is on the tin and provides 25 Amps initially tailing off to stabilise at 28.8 volts on the high setting but taking several hours to complete the process. The charge current falls as the battery reaches full charge and the rate falls so it is approximately equal to the deficit in Ah which needs to be made up.

In contrast the solar controller does an excellent job and the output current is typically 30% higher than the input current from the cells (which are at a higher voltage) due to its MPPT feature. You can see on the Trend Graphs that it does an optimisation every ten minutes or so. It maintains the charge rate right to the point it goes into absorption mode and tailors the time in absorption based on the charge history. The Solar controller keeps a lot of valuable information in the daily summary (History tab) including the maximum power, total Wh and times in bulk, Absorption and float for the last 30 days which can also be output as a data file.

Solar Power Measurements

This section covers covers both my general experiences and specific measurements on the solar panels. There are a number of constraints for me when making measurements which are generally applicable, both in the installation and the site. Firstly I have flat panels which are positioned near horizontal on the roof of the boat so they will never produce full power as they are always at an angle to sun so their effective area is reduced and there will be increased reflections at low incidence angles. The other constraint is that there is a certain amount of shading after 1200 on my home mooring which will get very much worse in the winter. This will hopefully not be a problem as over the winter as Corinna is, by default, on a power hook-up so the batteries are just being maintained fully charged with very little solar input needed for the 24V system as the inverter is off. The major power requirement on shore-power is for the 12V domestic system powering water pump, lighting, hifi and internet.

So there were several regimes which needed to be understood:

The shore power hook-up makes test measurements of the maximum solar power available more challenging as the 24V batteries never have any significant load and kept fully charged - one has to deliberately change to battery power and discharge the batteries but remembering keeping significantly discharging the batteries will shorten their life. I use the kettle for an initial ~100 Wh discharge and then use the fridge via an inverter. The old inverter has an idle-power of 70 Watts which provides a useful background usage. Even with these tricks it is easy to end up with the batteries full and no idea of the solar input which could be available although keeping the SmartConnect App running and connected to the SmartSolar device provides good insights.

There is also a lot of very useful information in the History stored by the SmartSolar where the times in each phase are accessible along with a graphical display of the power used in each and the maximum solar power during the day. The History information data can also be stored in a file which can be emailed or otherwise transferred in a .csv format (comma separated) which can be input to any spreadsheet and build up a picture over time. It is helpful to know the regime for each day but it is usually fairly obvious when you look at the data. Sample periods of selected data from these files is shown in an appendix.

Perhaps the easiest regime to understand is maintenance on a shore hook-up. At the start of the day the charger become active once the voltage of the solar panel is 5 volts above the batteries and this occurs much earlier than I expected with solar availability often 15 hours or more in mid summer. The battery voltage when the charger starts is used to estimate the state of discharge and adjust how long an Absorption phase will be needed to fully charge the battery once the bulk level has been reached. The initial power will be low and it takes a while in Bulk charging to reach the voltage of ~29V and but the Absorption time when just maintaining the batteries seems to be only a few minutes before going to Float for the remainder of the day. The total solar power provided during a 'maintenance' day is only 20 to 30 watts which is unlikely to be overcharging the batteries with an initial time in 'Bulk' of about an hour at the start if the day, a short time in 'Absorption' and the remainder in 'Float'.

In the other two regimes the batteries will be at least partially discharged when the charger turns on in the morning and the Absorption phase timing depending on the state of discharge (estimated from the battery voltage at the time solar become available) - that could be up to 6 hours although I have never seen it that long, one hour seems more typical and I have once seen 3 hours. Note: the absorption phase is also terminated if the current falls to a low and programmable level and that seems to be the norm. I have rarely been able to keep sufficient load to know exactly what the solar array was capable of yielding but have certainly seen 1200 Wh on days which only had broken sunlight. In August it easily keeps up with the old fridges demands up till 1900 when I finished checking and had recharged the batteries and  entered 'float' by 1300. As I said earlier the SmartSolar controller records the maximum power during the day and I will be able to plot an envelope during the year of time solar is available and peak power. The figures I initially made indicated that the panels are capable of producing close to their specified power in July even though they are horizontal rather than oriented towards the sun. Sample measurements were:

Solar with the initial 200 Watt array when I first got the solar running up and running ~ 500 Wh/day (400, 560, 288, 410 in mid July with peak of 870 on clear day) which would scale to an average power of 900 Wh/day with a 360 watt array.

Solar with 360 Watt array on 4 broken days and one mostly sunny day on the garden mooring (with some shading during afternoons) at end July 950, 1030, 1110 and 1270 with max powers recorded of 309, 310, 305 and 325. Average power ~ 1087 Wh/day. When making these measurements I had to keep discharging the batteries using the techniques above otherwise the solar spends most of the time throttled back in 'Float'.

October Update - Solar with shaded panels and cloud cover: This is going to be typical situation in the winter due to shading by my trees. The results have been surprising in that the panels give power when the sky is overcast or the panels are completely shaded just from reflected light. On a day with broken cloud it is possible to get far more at the times when it is cloudy than clear over the panels and up to 60 watts has been seen in October with no direct sunlight as seen in the snaps taken with the phone below which also shows the arrangement of the panels on the roof in two pairs. Also note how the charging current is 30% higher than the Solar current showing how well the MPPT controller works and the comprehensive display.


November Update - 120 days of data plotted I now have 4 months of data and I have done some plots which make it much easier to show the overall envelope of the variations with time and have included the most informative below - note the increase in array size from 200 to 360 watts at about day 20 followed by a holiday to Lechlade where the solar was used to the full and rarely entered float. The gaps at days 111-112 were running battery test then you can see the batteries recharging for two days. I find it interesting that the time sufficient energy is being produced to fire up the solar charger is almost the same as that of daylight (the time between sunrise and sunset) even into November (7 July 988 mins, 1 Nov 568 mins) and on my shaded moorings where direct sun does not even reach the panels in November. Min and max sunlight during the year are 467 and 1001 mins.

There is a full data set for the 4 months with additional notes in Appendix F - SmartSolar History from the SolarConnect App.

Why do we have some anomalously high solar output peaks? I have recently seen outputs from the solar panels that seem to exceed the theoretical maximum - they occur when there is a sky with bright cumulus or similar clouds which scatter additional sunlight in addition to full illumination through a gap, the highest so far was 423 watts in 26 June 2022 from flat mounted 360 watt panels!

Victron Phoenix 24/1600 Sine Wave Inverter

The next and most expensive step so far was to add a Victron Phoenix 24/1600 Sine Wave Inverter (~£650) to the system. It has been well worth it as it is much more efficient and enables me to use far more electrical equipment such as an induction hob.

The initial tests and measurements were done with the inverter lying flat on the engine room floor and when I was satisfied it was mounted on the bulkhead. The inverter is heavy ~ 11 kgs so needs to be secured well to the bulkhead. The inverter is hung from a wide 'bracket' which has has three 6mm holes to fix to a wall. My bulkhead is only 16mm ply so I used 3 SS No 10 by 16mm pan head screws with a small flange and also drilled 3 holes for screws below the bracket overlapping the edge slightly to take additional load. The inverter was then lifted into place and hung on the bracket. There are then two additional mounting holes under the bottom cover to secure the bottom and prevent it lifting off. There may be two more holes at the top, they are shown on the drawing but are only accessible it the whole cover is removed which I have not done [yet] and only five screws were provided indicating they were not needed.

I have a heavy duty fuse of 125 Amp rating as recommended between the battery switch and Phoenix. The positive cable all the way to the main battery is 25mm2 which is what is recommended for wiring up to 6 metres in the handbook although the internet version recommends 35mm2 up to 5 metres. My wiring will be closer to 3 metres (two way) so I am intending to keep to the 25mm2 for the positive. During initial testing the negative was 1.2m of 16mm and although that gave no problems it has been changed to 35mm and connected directly to the Smartshunt to minimise loses.

The App does not offer any history or trend pages for the Phoenix which is disappointing, it is mainly used for configuration of the eco mode. The status page only displays load in Volt Amps and input voltage are useful information but the voltage allows one to see voltage drops in the cables compared to voltages from the SmartShunt.

Off Mode: It is possible to switch the inverter off over Bluetooth through the App or on the invertor using the button but there is a very important difference. When you switch off on the inverter you switch the inverter off completely including the interfaces to Bluetooth and the Victron Direct network interface (for computer control) so you can not turn it back on remotely. The same applies if you disconnect the input power so you have to turn it on manually on the inverter itself the first time after reconnecting power. This is done as a safety feature as it prevents the possibility of 230V power being turned on accidently over the network whilst one is working on the system.

Measurements on Phoenix Inverter

Idle: The idle is the 9 watts as in the specification. The eco mode works by turning on power briefly every few seconds. The levels for turn on and off can be set in the app as can the frequency. The power in eco mode is specified to be 1.3 watts but is changing so fast it is difficult to measure but looks about correct at the default 3 secs and .16 secs. It should be possible to change these to much longer numbers and look at the trend graphs to get a more accurate estimate for other settings.

Efficiency: The efficiency in converting power from the battery to 230V AC input to a device can be thought of as being influenced by three components. The losses in wiring etc increasing roughly with the square of the power input, the fixed component of power to run the inverter which is independent of power output and the efficiency the power conversion which we do not know the shape of but Victron claim an overall efficiency of up to 94%. We can get an overall idea of the shape from measurements on a series of resistive loads as we have in the Appendix and the data points have been fitted to a model proposed by Victron which is covered in the following Appendix.

In summary: The end-to-end efficiency seems to rise to be over 94% from 180 to 480 Watts output and then reduces to ~90% at 1000 Watts and ~83% at 1600 Watts .

General impressions/conclusions on Phoenix inverter.

The change from the Matchpower Square Wave inverter to the Phoenix Sine Wave inverter has been a dramatic saving in power when running the old fridge. Solar power now easily keeps up with fridge consumption on a partially sunny day in early August and enabled 24 hrs from solar alone fully re-charging the batteries by 1300 in early August. I get the impression the fridge motor is slightly more efficient/powerful on a sine wave and runs with a lower duty cycle. By early October I have not yet had to run the engine to charge batteries.

Eco Mode: The mode of operation in Eco is very efficient but has idiosyncrasies which can leads to some strange effects. For example the pulse of power is sufficient to flash the fridge light every 3 secs but not hold the inverter on. In contrast my Bosch palm sander draws enough start up power to activate the inverter but once running it does not draw enough power to keep it the inverter on so it stops after a few seconds then restarts a few seconds latter. However for most applications it works fine provided you can tolerate the short and variable delay in starting, for example, power tools.

Some appliances reduce their power by alternately switching on and off every 10/20 seconds to vary the mark space, these include many microwave ovens and Induction hobs and it is also best to switch out of Eco when running them. It is easy to switch mode on the inverter or through the App.


Upgrades to the 12V Domestic system

It was looking possible that the combination of solar, an improved inverter and a lower consumption fridge wouldl allow us to go several days without needing to run the engine to charge the 24 volt batteries whilst away from home and should keep them charged in a an optimum manner throughout the year whilst on a shore line. That still leaves a problem with the 12V 'Domestic' supply which provides for Lighting, Water Pump, Mobile Wifi, HiFi, and charging for Laptops, Pads, Phones etc. Currently the only charging for the 'Domestic' leisure battery is from the engine's alternator - this never proved a problem whilst traveling and running the engine daily but care has had to be taken whilst on a shore hook-up not to use much lighting or water. Now we also have continuous Mobile Broadband provided through an old phone and a GiffGaff 100 Gbyte data package and far more use of phones and pads to monitor and control the new systems so we need to look at ways to keep the 12V systems charged.

The obvious way is to use solar but a separate 12V system would be expensive and we do not have an easily accessible area to fit even a small addition solar panel. However for much of the day there is excess power available from the 24V solar system and the batteries end up on Float charge. So what is needed is a means to charge the 12V Domestic battery from the 24 Volt batteries preferably whenever they are well charged and the solar is active, ie at the float voltage or higher.

The best way would be with a battery to battery charger with phased charging and temperature compensation. They tend to be higher power than we require and only the Sterling version has temperature compensation and they are large and expensive (~£280). Victron however make a simpler device which is intended more as a power source but they say can be used as a trickle charger - to quote "Because of the adjustable output voltage it can also be used as a battery charger, for example to charge a 12-Volt starter or accessory battery in an otherwise 24-Volt system". The smallest version provides 110 watts (approximately 9 Amps) which is far more than any current requirements for 12V (apart from a few seconds surge when the water pump starts and possibly the horn). It provides a fixed voltage which can be adjusted by a potentiometer to a suitable battery float level to keep it trickle charged when not in use or recharged after discharge by internal lights etc when solar power is available. Bulk/Absorption charging to full capacity will occur on days with the engine running. The device in question is the Victron Orion-Tr 24/12-9 isolated 110 watt DC-DC converter which is currently £65.

Using the Orion-Tr 24/12 isolated DC-DC Converter to trickle charge a leisure battery.

A Victron Orion -Tr 24/12 isolated DC-DC 9 Amp Converter (110 Watt) has been added to our system and is powered from the 'switched' load from the Victron SmartSolar Charger to trickle charge the 12 volt domestic battery at ~13.7V. The SmartSolar MPPT 100/20 was initially programmed to turn on the Load output once the 24 volt battery has been charged to the close to the Absorption level and disconnect when it drops significantly below Float level. This can be achieved using the App and there is a convenient delay time built into the load switching algorithms to avoid switching on surges. The Load switching algorithms can be overridden in the App to allow continuous or no charging. There are also connections to allow switching via a switch or relay from a controller such as a Raspberry Pi .

The settings may need to take into account a battery temperature range and it is not clear if the temperature compensation changes the levels for the SmartSolar load switching. I have set up the SmartSolar using the SmartConnect App load switching to User Defined Mode 1 switching a little below the bulk/absorption level and off below the float level. It is a bit difficult to test as it does not work exactly as expected as it switches on a transition so you can have to think of the effects if you manually switch the solar off and on. The delay is also stated to be 2 minutes but it seems to be quite a lot longer and initially I thought it was not working.

Initial set-up and measurements on joint Smart Solar MPPT 100/20 and Orion System for 12V

The Orion is not programmable so the output voltage had to first be set using the potentiometer accessible from outside the bottom of the box beside the terminals to a suitable voltage to 'Trickle charge' the battery. This has been initially chosen to be 13.7V ie just below a normal 'Float' level of 13.8V at 25 degrees C and we will watch the current under no load over time to get a compromise between keeping the battery charged over long periods without engine running and overcharging. When the Orion was first connected the leisure battery partially charged and reading about 12.4V. There is no direct measurement of current but the Load Output of the SmartSolar is available as both a current and power which means we have a good estimate of the '12V' current if we assume a figure for the Orion's efficiency. The SmartSolar load current started at about 2 amps and fell to 1.4 amps within minutes then continued to fall to 0.4 amp after a few hours.

The 12V system was the put under load by progressively turning all the lights on and the Load Output power from the SmartSolar limited at circa 123 Watts. This corresponds to what one would expect as the Orion is supposed to limit at 110 Watts/9 Amps and has been set to 13.7 volts. By full load the voltage had dropped to ~13.2V at the battery (measured by the auxiliary input to the SmartShunt), again roughly what one would expect as the limiting will not be abrupt. The voltage rose quickly to over 14.4V when the engine was running again as expected and the power into the Orion dropped to zero. In other words it works as expected although longer term measurements are required to determine an optimum voltage to maximise the battery life.

Some further checks were also made using the History tab in the SmartSolar App where the daily total of the solar power and load power are available. The inverter was turned off so all the power used was through the switched load output from the SmartSolar controller. All the lights were turned on for 2 hours giving a power usage of 250 Wh which was matched to a few percent by the Solar input power after time was allowed for the 12V battery to be fully recharged, the difference being consistent with the residual 'trickle' and 'float' charge currents over the period which had fallen back to under 0.4 amps after 3 hours for both 12 and 24V supplies. The solar power was not steady and high enough to provide all the power so it was often being drawn from the 24V battery which needed to be recharged at the end making the check more realistic but less accurate.

There is a table of my measured domestic (12V) power requirements in an Appendix which I keep updated with extra equipment and better measurements

Remote Switching the Orion-Tr 24/12 from the Raspberry Pi

This section is one of the only part of this page which refers to our latter additions to the system which depend on a system controller such as our Raspberry Pi with a relay output and and also refers to Node-RED and our Dashboard displays. It provides a more flexible alternative to controlling the load output within the SmartSolar MPPT device if you have a controller in the system and is especially desirable if you have Lithium batteries, which we finally upgraded to, for reasons given below.

The Orion has a Remote Switch used to enable the output which normally comes with a link fitted. It is possible to add a manual switch to switch the Orion output on and off or, more recently we have the ability to control it via a relay from our Raspberry Pi (see separate pages on The Raspberry Pi using the Venus OS and The Extension to Venus OS Large with Node-RED to allow the addition of a dedicated Dashboard and additional smart management). Control from the Pi offers more scope than using algorithms in the Victron solar controller as we initially set up and can be managed in Node-RED. So what are the considerations?

We therefore started with a a simple timer arrangement for switching to top up in the morning when solar is plentiful and the engine will have run or being run on many days, and a second linkage period in the evening when the majority of domestic power will be drawn by lighting and entertainment. I chose 10:00 to 12:00 and 17:30 to 22:00 BST (Note timers etc work in Zulu/GMT not BST so may need to be reset twice a year or just left as is over winter). This is currently under test and seems to have reduced the overall demand and is much closer to calculated figures.

Ideally we needed another SmartShunt so the periods can be optimised using information on the state of charge of the domestic battery and we finally invested in one so we additionally switch on the 24V main solar charged batteries to the 12V 'domestic' link if the State Of Charge (SOC) of the domestic battery falls to below 90%. The total costs of the Orion-Tr 24|12, SmartShunt and cabling were little more than the cost of a good replacement domestic battery and will (we hope) extend the life of our existing domestic battery very significantly. It has however become obvious after 2 months cruising that our estimates of Domestic power requirements were low, even in the summer, and 300 Wh/Day from the 24 V supply is not unusual.

The final step[?] - the change to Sterling 150Ah Lithium batteries and a battery to battery charger.

The first four months showed the possibilities of Solar combined with a more powerful and much efficient sine wave inverter without investing in any new batteries. However the existing batteries had already suffered greatly and I only had a mismatched set of well used batteries still mounted in extreme situations. They could not last for ever - the measurements above show they have already lost half their capacity. I therefore decided it was time to revisit Lithium and see if I can either switch to or augment the existing set up with Lithium batteries rather than potentially waste more money replacing like with like.

A major reason why I did not make the change initially was the environment. No batteries like extremes of temperature and Lithium batteries are considerably more demanding than Lead Acid however the latest requirements of the Sterling Lithium batteries now seem to be slightly relaxed at: Charge from 0'C to 60'C / Discharge from -20'C to 60'C as the battery Management System (BMS) now handles charging and discharging limits independently.

So my first decision was to initially site the Lithium batteries outside of the engine hole on the engine room floor (above the existing batteries), and strap them into a frame. I have used that location to place two standard size leisure batteries (35L x 34W x 22H cms) for periods whilst running tests and it is workable even without recessing the floor which remains a possibility. The maximum size area is 45L x 35W x 24H cms where the 45 cms is for and aft. This takes up to 2 x 150Ah Sterling Lithium AL12150 batteries which are 41.0L x 23.5H x 17.0W cms and and 15 Kgs each for 150AH compared to 25 Kgs each for a typical lead acid battery. The area is protected from direct rain and there will be a cover in any case. The downside is reduced engine room access without removing the Lithium battery pack.

The Sterling Batteries have a very comprehensive built in Battery Management System (BMS) with:

Sterling specify that up to 4 batteries can be connected in series and any number in parallel - I will have two 150 Ah batteries in series initially. If I wish to extend in the future a new location will be required but that will still increase my usable capacity by 50% and their life by at least 10 fold which should see Corinna out.

The Lithium batteries have to be charged by a suitable Solar charger or a Battery to Battery Charger - charging Lithium batteries directly from an alternator will likely blow up the alternator as well as not being ideal for the batteries. Likewise the outputs from the Lithium batteries should not be in parallel with any Lead Acid packs, however up to at least 4 Lithium batteries in series or parallel is permissible. The maximum charger current should be less than 70% of the alternator output to avoid overheating and permanent damage to the alternator. A 30A input (360 watt) charger is ideal for my 12V 50 Amp alternator. I had a very enlightening discussion with Charlie at Sterling he confirmed that there is no longer a requirement for use of a Sterling B2B to satisfy the Warranty requirements. More recently I have spoken with Charles Sterling himself and he indicated the temperature requirements and cut off have been further relaxed to 70 deg C.

The App used for Bluetooth control is the Smart BMS which is provided by Daly to control their Smart BMSs and Charles confirmed Sterling are using a programmable Daly BMS. These seem to be reasonably well thought of and are used a lot by enthusiasts building their own battery packs potentially giving a rich source of information.

The discussion with Sterling indicated that, as long as the battery had not been put back into a storage mode, the BMS should remain powered up and the disconnects should automatically clear. The charge and discharge disconnects are also independent. An external voltage is only required to exit from storage/sleep mode or on a new battery. If you ever end up in that situation it should be noted most modern chargers will not provide an output unless a load is connected but a brief connection to a lead acid battery via a fuse should wake the battery controller up.

Victron v Sterling battery to battery Chargers.

There is little to choose.

Is a battery to battery charger worth it?

The costs of a 15A (360 Watt) B2B (Battery to Battery) charger are:

Even without Lithium batteries the addition of a B2B will appreciably speed charging when using the engine, especially the final stage and give us redundancy in case of 24V alternator failure. The Victron looks the best bet when it gets to Lithium as it is easier to program. Is the faster charging worth the extra investment on my system without Lithium? Probably not because of the solar charger. Is the redundancy worth it? Probably yes as an engine change is also on the books. The fact that one is prepared for Lithium at any time swings it to an implement now even without the Lithium batteries!

How much Lithium to add at what cost?

The most I can expect with the current space available to mount Lead Acid batteries is 190 Ah which would gives an initial usable 95 Ah but 80 Ah is a more reasonable figure (even with AGM type lead acid batteries) which would mean a minimum of 100 Ah of Lithium discharged to 80% (or preferably 150 Ahr discharged to 55%) to be equivalent. Looking at the SmartShunt history the maximum discharge has been 54 Ah and that was before the new inverter was added. 120 usable Ah would power the fridge for two days even without solar or engine running. Conclusion 120 or 150 Ah batteries improve on existing performance in normal use. Cost £1440 - £1680. £1200 matches existing best new Lead Acid battery performance and maintains that level for thousands of cycles instead of, at best, a couple of seasons.

After much soul searching I ordered 2 Sterling 150 AH batteries and a Victron Orion-Tr Smart 12/24 360 Watt DC-DC Isolated Charger.

I did a brief test at home with an old 12 V battery to power the Orion. The Bluetooth App was loaded into my phone and a typical example of the main display for my fully charged battery is shown below. Note the large differential voltage as the battery has not yet balanced - i will come back to that latter.

Detailed installation planning started based on the assumption that any use of existing 24v lead acid pack would be an emergency rewire although they need to be kept in place to provide a load to the alternator and also keep the unlikely option of adding another 24/24 Victron Orion-Tr Smart DC-DC Charger to speed up engine charging even more.

The two batteries were then placed in Corinna and connected to the Solar Charger. The existing wiring for the Lead Acid 24 volt batteries has been simplified and the wiring to the old inverter disconnected. The old lead acid batteries are still in place to avoid damage to the 24V alternator but not used. The SmartShunt has been moved to the new Lithium batteries and the extra monitoring input is now used for the mid-point.

It is worth showing a chart which shows the differences between Lithium and various types of Lead Acid batteries to indicate some of the changes in set-up which were required to re-optimise the system. This is a generic chart and batteries vary between manufacturers but note the much flatter curve for the Lithium batteries and the rapid increase in voltage for the last few percent of charge which is why balancing is so important, both internally and between packs.

Initial Experience with Sterling 150 Amp Hour Sterling Batteries

The two batteries supplied both showed 99% State of Charge on their internal measurements via the Bluetooth App but the voltages were quite different at 12.9 and 13.2 volts which approximately correspond to 20% and 70% charges. I contacted Sterling and was assured they would equal up over a few charge cycles!! I connected up to the solar charger and added battery monitoring via my existing Victron Smartshunt - it took several days to charge them using solar at which point the higher battery cut out charging via the internal Daly BMS (Battery Monitoring System). The Daly BMS has separate switching via high power MOSFETs for charge and discharge which also stopped the charge current to the lower voltage battery. It seems that every hour or so it does pass current for a short time which might help balance the batteries but it would be very slow.

That was the point where I started to add a load from a 20 Watt QI light bulb across the 'full' battery to get additional charge into the other battery. This took a while and a relative addition of 900 - 1000 Wh has required before the batteries were close to being balanced which ties in with my initial estimates of charge based on their voltages. Both now come up to 13.51 Volts virtually together before the higher battery charge is cut out its BMS after a very rapid rise in voltage of a single cell. It is very important to 'top balance' batteries in series to get the full potential capacity.

The Daly BMS and the 'SMART BMS by DalyBMS' Android App

Most commercial 12 V and higher Lithium Battery packs have Battery Monitoring System (BMS) built in. The BMS carries out two important functions, it monitors the cells and ensures that each cells is balanced with the others and it ensures that all other parameters are kept within safe limits and prevents charging and discharging if these limits are exceeded. These include high and low voltages on cells and the overall battery, excessive charge and discharge rates and high and low temperatures. The Daly BMS is more comprehensive than many in that it has separate MOSFET switches for charging and discharging. The Daly BMS built into the Sterling batteries also has a bluetooth connection to an Android App offering monitoring functions and a password protected settings menu. The password protection prevents changes but enables one to examine the internal set-up. The main screen has already been shown above and screen dumps of the most important set-up screens (as provided) are shown below.


Daly BMS Settings Screens

There are however a number of anomalies I have found with the Daly BMS Apps display, or possibly in the BMS itself. The first is in the display of current into or out of the battery. First note the sign is unusual in that charging has a negative sign. More importantly there is no display for small currents (many users report this as under 1.3 amps but it seems to be nearer 2.6 amps for my batteries) whilst for currents over a couple of amps there is a reasonable resolution and the figures are similar to those from my SmartShunt. One hopes that the figures used in the calculations of SOC (State of Charge) do not have the same feature! The displays of SOC in the App also seem strange and always seem to be close to 77% or 100% but never between. In fact when the batteries were delivered the SOC had not been initialised and showed 99% whilst the voltages indicated charges of about 20% and 70% - I hoped this would be corrected after a full charge and a few charge/discharge cycles but this has not occured yet, perhaps because they have never had a full discharge

I also had a worrying problem in that the Bluetooth suddenly stopped working on one of the batteries and it was no longer visible in the App. I contacted the Sterling Technical support, who are always very quick to answer the phone, helpful and knowledgeable who told me not to worry and it would come back to life after a period. This duly happened after being left overnight. There are many Victron bluetooth devices in the area and I had also been using multiple phones/pads with the BMS App so it is possible the Bluetooth was connected to a device and had timed out after a few hours. I have had a similar problem with Victron device where a device was visible but grayed out and I had to take every bluetooth device a great distance away as the low power bluetooth used by these devices never fully turns off. There is also a power saving mode in the batteries where the Bluetooth is turned off reducing the idle current from 10mA to 1mA which should be inhibited but might have got tripped. This has only occured once in the first 3 months so I am no longer concerned.

The limits set within the BMS seem more generous than I expect especially on the upper temperature limits and I may consult on the need to change them to more conservative settings for safety. I may also see if the level for internal balancing can be optimised for series connections.

I have put together a few notes on what I have found about the Daly series of BMSs - I do not know which version of controller is installed and software functions can vary with software version installed.

From https://diysolarforum.com/ and other internet information

Balancing Series Connected Lithium Batteries

Despite what Sterling initially indicated I believe that the batteries must be brought to a similar state of charge. If they are very different the various safety cut outs will reduce the available capacity. When charging the higher battery will cut out before the lower battery reducing the available capacity by the difference. When discharging the opposite will occur so you effectively lose twice in available capacity. In practice you do not take the batteries that low so you may retain some capacityat the bottom end but at the expense of battery life.

There are various techniques for individual cells and the normal way is called top balancing when you try to get all batteries to the fully charged level together. This is what the BMS does for the 4 cells within the 12V batteries by taking current from the highest battery at a slow rate once it approaches full charge. Similarly we need to take power out of the higher battery until we have both at the same voltage when fully charged. Until they are closely matched the higher battery increases its voltage very rapidly at the end of charging and immediately cuts out charging via its MOSFET switch and that prevents further charging of either battery. So what I did was to use a 12V 20 Watt bulb across the higher battery to discharge it and pass current to the lower battery when under charge. In total I have had the bulb connected for about 20 hours and have got progressively closer to the same voltage before the upper battery accelerates away whilst still at a voltage level well below where the charge goes into absorption mode. The loss of capacity is probably not huge but there is an important side effect in that the voltage at which internal balancing by the BMS has not yet been reached which accentuates the problem - in my case the top battery is internally quite out of balance which exaggerates the problem as an individual cell is tripping the BMS.

So the first change to make is to reduce the Absorption voltage for the two batteries so the top battery is high enough to balance but not cut out. Looking at the individual cells using the Daly App via bluetooth the rapid increase starts when the first individual cell reaches a voltage of ~3.400 which is equivalent to a total of 27.2 volts acraoss the pack. Depending a little on the rate of charge the battery is within a few percent of fully charged when this level is reached. It is very safe to take a cell to 3.60 (28.4 / 8) so an adsoption level of 27.4 should enable balancing of individual cells to take place whilst achieving a SOC of over 95%. In fact many people use an Absorption level of 3.400 as they believe that the battery life is extended if the SOC is restricted to the 10 t0 90% range. My initial trial and error tests had shown that I needed to reduce the Absorption level to closer to 27.35 (from 28.4) to allow a battery to balance internally without cutting out.

These levels of Absorption are far lower than even the float recommended float by Sterling and the default settings used by Victron. It is questionable whether the standard Bulk - Absorbtion - Float cycle is appropriate for Lithium batteries which are being continuously cycled so until I have better balanced batteries I intend to either have extended Absorption times or set the Absorption and float levels the same. It is convenient that most manufacturers specify voltages which are the same as typical Lead Acid battery chargers to show compatibility but the downside is that the internal balancing must be near perfect to avoid charging being terminated by the BMS rather than the charger!

Optimising the internal balancing by the Daly BMS

The Daly BMS apparently does an adequate job of maintaining balance if the cells once the cells are reasonably balanced but does have some shortfalls compaired to the latest BMSs. It is however very well established and offers a high degree of protection amd reliability are safety are by far the most important consideration.

It however seems to be taking far longer than I expected for balancing to take place with little indication of progress after the first month of actual use of the batteries whilst cruising. So I have been investigating. This has proved challenging and it took some time to actually find the balancer indicator active and showing in the App. There are two parameters which should control this: The balancer should only open once a cell voltage has been exceeded and when a differential has been exceeded. I have been able to confirm these work but there seems to be a further condition that charging is taking place. Unfortunately this seems to be linked to the displayed current as shown in the App rather than an actual charge. As stated above the App does not display charges under ~ 2.5 Amps so the balancing only takes place for a very limited time before the current is reduces to this figure by the charge controllers although the SmartShunt shows current flowing and the battery voltage is still rising. This means balancing is only occuring for 5-10 minutes every cycle. Measurements I have found on the internet imply that the balance current is only ~25 mA for typical Daly BMSs so the effect is minimal and may take years. Daly BMSs also only balance a single cell at any one time.

It is possible to change many of the settings but they are password protected and any changes should only be made after checking with Sterling and obtaining the correct password which I did. My changes bring in the 'opening' of balancing at a lower cell voltage of 3.34 volts from 3.50 and at lower differential of 0.02 volts from .03. Even after these changes I can see no evidence of an effect on the balance of my batteries after a month.

I am continuing to make more measurements and have had some interesting 'discussions' with Sterling who have very impressive and accessible technical support.

Setting up the Victron SmartShunt for Lithium batteries

Most of the set up is similar to Lead Acid as you are trying to ensure that the State of Charge is syncronised when the batteries are just fully charged ie a tad short of the absorption level (~ .2v below) and tail current below 4% for a few minutes. See above for the levels I am actually using for the Absorption level. The other adjustments needed reflect the fact that the Lithium batteries are more efficient so Victron recommend setting the efficiency to 99% (95%) and the Peukert coefficient to 1.05 (1.25). There is a good discussion of all the parameters in the first reference below and Victron have produced a video

Reference Info (for entire section)





https://www.powerstream.com/lithium-phosphate-charge-voltage.htm - Charge voltage experiments with lithium iron phosphate batteries showing how capacity varies with charge voltage and higher cycle life with lower charge voltage

Thoughts on Solar Safety, Switching and Fusing.

I am ending this first page with some cautions:

Firstly Lead Acid batteries are Dangerous, they produce hydrogen and can explode if not ventilated, short circuited even momentarily, or otherwise abused. Wear safety goggles - a frightening number of people are blinded by acid from Lead Acid battery explosions in the USA and probably elsewhere. Lithium batteries often have some built in protection but have even higher stored energy.

Systems with Solar Input need special care to work on safely. It is no longer sufficient to disconnect the batteries physically or by switches when working on the system, for example, changing batteries. In a conventional Solar Power system there are seldom physical switches to turn off the Solar Power feeding the batteries [which may be considerable] and control may only be possible via the controller, by remote control switches or by Bluetooth to enable work to be carried out on the system. Worse still Solar Controllers have direct connections to the batteries and many have outputs designed to provide considerable power even when there is no input from the Solar Arrays probably conditional on battery voltage. Even without Solar, modern systems often include battery to battery converters so disconnecting the 12V domestic battery can still leave the 12V domestic system powered from the engine start battery, or a 24V source itself powered by battery or solar input!

Fusing remains important but most high quality controllers and converters have, in theory, a lot of inbuilt short circuit, open circuit and overload protection and adapt to different system voltages so it may not be necessary to have fuses between every device. Fuses can also be a useful way to disconnect parts of a system but many high power fuses are not a plug in type making disconnecting by 'pulling a fuse' difficult or risky

When working on a system with a Solar Controller providing input it should be turned off as should be as many of the battery to battery converters/chargers but even so one should always assume the system is live. Just checking with a meter is insufficient as one must assume the electronic controllers could switch on at any time. This means that great care must be taken when changing batteries - even a brief short with a spanner or a spark can cause major damage, burn out wiring and even cause explosions from hydrogen gas. Insulate your spanners with self amalgamating tape! There should be warning notices for any engineers brought in to repair or service the engine or change batteries about all multiple power sources.

Bluetooth systems should be properly protected and passwords changed from the default ones to prevent accidental or malicious changes by other people and nearby systems. It may be necessary to have dedicated bluetooth device available for service personnel and very full instructions on how to disable as much as possible of the system.

Another problem is that there will be far more wiring directly to the batteries, much will be low power for sensors to measure battery voltages and temperatures or for shunts to measure currents. These still need to be protected by local fuses - Victron sensors have fine wires protected by local fuses but a diagram is required to ensure they are connected properly after a battery is changed and they are placed in the correct place. Photographs are a useful tool and I use the mobile phone to take pictures before disconnecting or modifying any wiring.

Inverters have large capacitors on the input and there are huge input currents when connection is initially made and sparks and pitting on the terminals is common and switches need to capable of handling the loads. Any inverter over 2000 watts should be initially connected via resistor to pre-charge the capacitors. I use a 500 ohm resistor for at least 30 seconds to precharge my 1600 Watt inverter before making connections from my Lithium batteries.

This section may be extended as we gain experience with our system.

Overall Summary and Conclusions

The changes we have made have exceeded even our most optimistic expectations. We ran the engine for less than an hour total for charging batteries in the 4 months since we fitted the solar and have simultaneously greatly reduced the depth of discharge of our batteries which, along with much improved charging profiles will greatly extend the battery life even of Lead Acid batteries. The improved monitoring has played a major part in understanding our problems and guiding our usage in the future. The new sine wave inverter almost halved the battery consumption of original fridge so we left fitting the new fridge till the spring. We can now use a microwave hob for cooking during the summer months to complement the squirrel stove during spring and autumn when solar is reducing. The new fridge is now in use and the power consumption is ~ two thirds of the old fridge.

The addition of the large Lithium batteries has completed the transformation of our lifestyle afloat. We now have stored power for several days including basic cooking using the induction hob, microwave and Remoska without significant solar input or running the engine. At the same time the domestic batteries can be kept topped up from the Lithium batteries maintaining lighting, water pump, HiFi, computers, phones and Internet access. In the first month of cruising the batteries have never been below 70% State of Charge ie we have only used one third of their useable capacity even when moored up in atrocious weather with minimal solar input. Hot water, which is heated by the engine, now runs out long before electrical power!

We hoped that solar and other changes would have an impact during our main touring season but it seems it will cover the time from Easter to the start of the stoppage season in November.


There is a lot of information in the appendices and they grow with time. The ordering and indexing is Work in Progress.

Appendix A - Wire Gauges, Current ratings, Resistance and example voltage drops.

Conductor area in mm2 AWG equivalent Normal Rating in Amps IEE Rating in Amps Resistance in mOhms/metre

The Table is for Hi-Flex multi strand battery cable ratings and ~ equivalent AWG (American Wire Gauge). First rating is from normal sales literature for battery and welding cables ie free air and spaced cable, second is the more conservative IEE ratings from table-4d1a column 6 and resistance from https://www.cse-distributors.co.uk/cable/technical-tables-useful-info/stranding-chart/

Inverter Calculations: 24V 1600 Watt

Calculations for typical inverter cable lengths 2 x 1.25 m of 25mm2 = 2 milli-ohms

Nominal inverter output of 1600 Watts at 24 volts = 67 Amps == .13v drop == .54% voltage drop (8 watts spread over 2.5 metres of cable ~warm)

Max 2000 watts at 25 volts = 80 Amps == .16v drop == .64% drop

The Solar Charger output is also~ 15 amps peak in sunlight = 1.1 Watts lost ~ .3% but losses on input from solar panels are more significant as longer 6 mm2 cable and need to be watched.

Smart Charger Calculations: Orion Smart 12/24 15

Input from alternator - 30 amps at 12v 2 x 1.25 m of 10mm2 = 5 mOhms = .15 v drop

Output to 24 v Battery 15 amps at 24 v 2 x 1.25m of 10mm2= 5 mOhms = 0.075 v drop

ie both are negligible as there is excess alternator power and the output has current limit.

Appendix B - Measurements on Matchpower 1 KW Square Wave versus Victron 1.6 KW Sine Wave inverters

The Matchpower Square Wave inverter does not have a stabilised output and the output voltage and hence power drops considerably due to internal losses and wiring losses. It also has a very large no-load power consumption but does have a power saver which only turns it on if a load is applied which works extremely well. The Victron Phoenix 24/1600 is a fully stabilised sine wave inverter so there are no output reductions when a high load is applied.

The input power from the batteries measurements are from the Victron Smart Shunt and the Solar input has been turned off temporarily in the Victron Smart Solar MPPT 100/20 settings. The Phoenix Smart 24/1600 also has a Volt Amp display available in the App which differs for non resistive loads such as the microwave and the motor in the fridge compressor because the phase of the current and voltage differ for capacitive and inductive loads. The Smart Shunt figures should be best for power drawn from the batteries whilst the VA is more appropriate for inverter load and wiring loss calculations. The figures for the Fridge have a VA figure which is 20% higher.

The quirks of the Matchpower make some of the comparisons seem odd, for example, the Matchpower looks to use less power than the Victron boiling a kettle but that is because the output voltage and power drop under high loads and the resulting power is less than from from the stabilised Victron. The difference between the SmartShunt measurements and the Victron VA readings gives an indication of overall efficiency but for Resistive loads only . The losses will come from the idle power, losses in wiring and actual efficiency above and beyond the idle power.

Device: Measured by Matchpower: SmartShunt (power input) Phoenix: SmartShunt (power input) Phoenix: Phoenix VA (output) Comments
No-Load, Idle
Power used when no load connected and power saving modes off.
750 Watt Kettle
Resistive Load
Cooker (Top only)
Resistive Load
Cooker (Top and Oven)
Resistive Load (1050 watts nominal at 230V)
Microwaves have a seriously reduced output power when driven with square waves
Resistive Load (500 Watts nominal at 230 volts)
Slow Pot High
Resistive Load
Slow Pot Low
Resistive Load
Light Bulb (40Watt)
Resistive Load
Light Bulb (100Watt)
Resistive Load

Induction Hob (1200 watts)



Sterling Induction hob can not be run on square wave
Induction Hob (1000 watts)
Sterling Induction hob can not be run on square wave
Induction Hob (800 watts)
Sterling Induction hob can not be run on square wave
Portable Washing machine
Tefal Washboy table top washing machine, very simple, largely manual. 290 watt nominal.
Portable Spin dryer
Tefal Spinmaster free standing vertical 2200 rpm.
Old Zanussi Fridge
202 falling to 194
106 falling to 90
130 falling to 126
Power reduces slightly as compressor warms up. *
New LEC Fridge
69 falling to 60
Power reduces slightly as compressor warms up.

The fridge is, of course, the most important as it is on 24/7 and is non-discretionary and the change to the Victron Inverter comes close to halving the power used every day.

* Some latter measurements show an even more dramatic fall in power input with time on the old fridge of 112 W falling to ~91 W after 15 mins.

Appendix C- Inverter Power loss and Efficiency (based on Victron paper)

Victron do not provide efficiency curves for most of their inverters but if you search you can eventually find https://www.victronenergy.com/upload/documents/Output-rating-operating-temperature-and-efficiency.pdf. It has some tables of measurements on similar but higher power inverters (3000 Watt) and the following (rather basic) justification for their calculated curves which gives a very reasonable starting point and a logical way to size an inverter.

Victron Model for Inverter Efficiency

Electric current generates heat in the conductor through which it flows. The basic formula to calculate the rate of heat generation, or power dissipation, is:

P = R x I2 (1)

where P stands for power (measured in Watts), R (Ohm) is the resistance of the conductor and I (Amps) the current.

In power electronic circuits the situation is much more complicated: one has to deal with DC losses and switching losses, losses in semiconductors and in high frequency transformers, etc. Very often, however, formula (1) appears to be a fairly good approximation of the overall losses in the circuit. The power dissipation P of the circuit can then be calculated by defining R as the overall resistance between input and output of the circuit and I as the output current.

An even better approximation is obtained if a factor is added to (1) to account for the no-load power consumption, the power dissipated by the circuit when it is switched on without any load connected. It is an important specification especially of inverters since in the long run it can drain a battery and dominates the efficiency at very low power outputs

Taking into account the no-load power consumption results in the following formula:

Ploss = Po + Rinv x Iout2 (2)

Ploss is the total power dissipation in the product; Po is the no-load power dissipation (and by definition also the no-load power consumption); R is the “resistance” between input and output; and Iout the output current.

With formula (2) efficiency, an important specification of inverters, can be calculated:

η = 100 x Pout / (Pout + Ploss ) (3)

where η is the efficiency in % and Pout the output power (Pout = Vout x Iout ).

Tests and extrapolations on Victron Phoenix Smart 24/1600 Inverter Data

The above analysis by Victron has a some physical basis but can also be regarded as a power series fit and it would be logical to try a quadratic fit to the losses from experimental data which would show if there is any significant linear term. I found an App https://play.google.com/store/apps/details?id=com.ashermobile.math.curvefitterfree&gl=GB which I used to do a basic quadratic fit to some of my data and it does look as if the Victron suppositions are true up to the 1000 Watt level (table-top oven), the maximum I had inputs for, and at that point the efficiency was ~89.2% and was 92% at the 750 watt 'kettle' level.

The peak efficiency is at just under 25% of maximum output and is ~94.7% which is very much what is specified by Victron (max 94%), in fact it stayed at over 94% from 185 to 480 Watts output. Finally extrapolating to the maximum inverter load of 1600 watts the efficiency would be ~ 83%.

It is worth noting that these are end to end figures from the SmartShunt measurements at the batteries to the 230V output VA measurement by the Phoenix and included the losses in the wiring, contacts, switch and fuse. These figures have been derived for resistive loads but should be indicative of the performance on loads such as motors.

Appendix D - Estimates of typical 230V weekly power usage.

Note these are nominal powers for planning purposes and do not use measured powers although most of these have now been confirmed by measurements.

TOTAL per day averaged over a week = ~650 watt hours plus the existing Zanussi 240V fridge @ 1000 Wh/day ~= 1650 Wh/day which requires 3 hours engine average without solar of which 2 hours essential for fridge. This ignores Solar contribution which should cover over half during mid summer. Recent actual measurements on the Zanussi fridge in September show an average overnight consumption of ~1.3 amps equivalent to ~820 Wh/day. That brings down the daily requirement to ~ 1500 Wh/day with the lower average temperatures in September. The change to the LEC fridge should reduce these figures significantly.

Appendix E Estimating Solar Power

This appendix will bring together various sources of information in the literature on measurements and ways of estimating the solar power available through the year for various configuration of panel installations. What immediately stands out to me is the variability of available solar power with wide variations on all time frames. There is, for example, a wide variation in sun hours per day and month from year to year by factors of close to two fold, for example, see https://www.statista.com/statistics/322602/monthly-average-daily-sun-hours-in-the-united-kingdom-uk/

Despite the wide variations between years it is possible to see a pattern emerging with May typically having the highest monthly hours of sunshine. The actual hours of sunshine is far from the whole story as the solar arrays can give reasonable output under cloudy conditions and the figures also vary considerably depending on location within the country.

Victron MPPT Tool: Victron supply an interactive tool for their MPPT Solar Controllers at https://mppt.victronenergy.com/ which includes a monthly forecast of yield per day at a chosen location in the world. This is useful for planning but does not contain information on how it has been derived or the panel configuration in use - I believe it represents the configuration used by most installations which are fixed and giving peak output when pointed South and angled at an angle determined by the latitude whilst ours is horizontal. Even so I wish I had found that page earlier on. It is also the only tool where you enter the detailed differences between solar panel technologies and manufacturers although I have not exploited that fully.

What the curve shows for Oxford is that the solar power available is almost flat from late April to the begriming of August but then falls more rapidly to approximately 80% at the end of August and 60% by the start of October. In other words it is flatter and less symmetric about the longest day than one might have expected without taking into account average weather patterns. It means that there could be almost constant power during during our main cruising period, late April to the start of the School holidays but considerably less in the period starting September after the Bank holiday when we start again to cruise on the Thames.

The EU PVGIS Tool: The EU produce a much more comprehensive/complicated system, the PVGIS, for estimating the energy from a solar array. PVGIS is a web application that allows the user to get data on solar radiation and photovoltaic (PV) system energy production, at any place in most parts of the world. It is completely free to use, with no restrictions on what the results can be used for, and no registration is necessary. A good starting point is the manual at https://ec.europa.eu/jrc/en/PVGIS/docs/usermanual - it looks very complex but is actually quite easy to use provided you have a doctorate in Atmospheric Physics. You must also remember to select a location before anything else. I chose to enter "Oxford, UK" It enables you to specify the azimuth and elevation of a fixed array and will even calculate the optimum elevation for your location. Most of the inputs have sensible options and you probably only need to input the specified peak power of your array before hitting the Visualise results button to get a graphical output. The following shows the difference between optimised position array and a horizontal array, the summer is little changed whilst the power is much reduced by the low incidence angles in winter. I have included a compromise angle of 20 deg as 39 deg is not ideal on a boat even when moored!

Horizontal 360 Watt Polycrystalline Array

Array at compromise angle of 20 degrees elevation.

Array at optimum angle of 39 degrees elevation.

Most of the solar radiation data used by the EU PVGIS have been calculated from satellite images. There exist a number of different methods to do this, based on which satellites are used. The default choice is the PVGIS-SARAH data set. This data set of hourly solar radiation estimates has been calculated by CM SAF and the PVGIS team with 11 years of hourly data from 2005 to 2016 on a 0.05° x 0.05° (~ 5 km) grid and covers Europe, Africa, most of Asia, and parts of South America. The data sets are available for download but are tens of Gbytes in size indicating the work that the EU put into this tool. It would be interesting to see the effects of more recent data now global warming is starting to change the weather patterns. The PV technology 'presets' should also separate mono-cystalline and polycrystalline silicon which is an increasingly important choice.

The full print out (pdf) from PVGIS for our configuration is here. Peak yield is calculated by PVGIS to be ~1500 Wh/day and an average of >1200 Wh/day during our main cruising period. Half power points seem to be mid March and end of September which should reduce or avoid use of the engine to top up batteries in the evening during that period.

Appendix F - SmartSolar History from the SolarConnect App.

The following table uses most of the output which is available from the SmartSolar History output starting with my original tests with 200 Watts of solar panels as well as the 360 watt panels. Yield is the total power provided by the Solar Array during the day to the Battery. Load is the power from the switched output from the battery in addition to the power to the inverter which is taken directly from the battery. The switched load is only used to top up the 12V battery when solar power is available.

Date         Yield (Wh) Load (Wh) Max Solar
Max Solar
Min Bat'
Max Bat'
11/1/21 70 30 16.00 42.71 25.64 29.34 260 4 323
10/31/21 70 30 51.00 41.95 25.64 29.37 215 11 311
10/30/21 110 60 41.00 42.24 25.60 29.33 273 4 286
10/29/21 110 50 68.00 41.92 25.67 29.25 180 7 372
10/28/21 100 40 36.00 41.32 25.72 29.26 212 1 351
10/27/21 100 40 33.00 41.37 25.73 29.28 217 1 374
10/26/21 120 20 44.00 41.82 25.74 29.38 165 2 415
10/25/21 130 30 60.00 42.57 25.79 29.33 353 3 253
10/24/21 150 20 51.00 42.17 25.85 29.24 409 1 214
10/23/21 220 80 67.00 41.93 25.72 28.86 118 20 347
10/22/21 300 0 93.00 40.85 25.16 26.12 627 0 0
10/21/21 160 0 94.00 41.88 24.65 26.13 631 0 0
10/20/21 0 0 8.00 43.01 23.88 25.86 40 0 0
10/19/21 0 0 2.00 42.24 24.17 25.86 30 0 0
10/18/21 150 20 54.00 38.45 25.82 27.67 605 0 0
10/17/21 130 220 64.00 42.11 24.15 28.30 307 4 316
10/16/21 210 120 115.00 43.33 25.29 28.69 307 2 308
10/15/21 190 150 72.00 41.90 25.74 29.20 369 3 262
10/14/21 240 220 100.00 41.54 25.88 29.08 215 50 370
10/13/21 160 0 96.00 43.24 23.55 28.59 373 46 215
10/12/21 300 0 141.00 40.42 24.68 28.67 574 19 0
10/11/21 170 20 75.00 43.09 23.73 28.84 401 24 231
10/10/21 310 400 167.00 42.89 23.74 28.36 262 42 359
10/9/21 540 0 191.00 42.88 23.96 28.73 365 20 277
10/8/21 110 0 36.00 40.83 23.96 28.23 362 1 288
10/7/21 340 0 140.00 40.10 24.10 28.00 667 0 0
10/6/21 180 0 191.00 43.61 24.95 28.99 219 16 443
10/5/21 160 0 124.00 44.31 23.90 28.41 184 20 456
10/4/21 140 60 194.00 43.31 2.86 29.22 303 4 370
10/3/21 130 80 69.00 43.62 25.53 29.24 212 3 467
10/2/21 110 30 27.00 41.14 25.54 29.30 586 3 97
10/1/21 140 60 100.00 43.55 25.58 29.26 203 33 450
9/30/21 100 60 30.00 42.60 25.68 29.27 204 1 476
9/29/21 140 80 119.00 43.64 25.80 29.23 162 5 529
9/28/21 170 20 95.00 42.89 25.42 29.19 174 42 459
9/27/21 430 380 135.00 42.24 25.29 29.12 620 23 51
9/26/21 200 240 103.00 42.67 25.31 29.18 483 2 222
9/25/21 240 30 52.00 39.77 25.60 29.09 629 1 69
9/24/21 450 40 188.00 39.91 24.79 26.92 718 0 0
9/23/21 550 0 182.00 40.96 25.03 29.17 720 1 14
9/22/21 20 0 17.00 42.69 25.86 29.21 49 1 682
9/21/21 30 0 17.00 42.70 25.90 29.16 70 1 671
9/20/21 30 10 15.00 42.60 25.88 29.12 50 1 691
9/19/21 20 0 16.00 42.03 25.86 29.24 123 1 607
9/18/21 30 0 35.00 43.02 25.76 29.16 72 3 664
9/17/21 30 10 31.00 42.96 25.80 29.17 59 1 697
9/16/21 110 0 58.00 43.12 26.06 29.35 225 1 520
9/15/21 310 50 194.00 42.60 24.16 28.28 246 40 473
9/14/21 340 20 124.00 39.98 23.73 28.57 611 60 0
9/13/21 500 70 190.00 42.33 24.04 28.60 430 115 182
9/12/21 590 120 262.00 42.38 24.22 28.43 546 21 196
9/11/21 570 90 259.00 43.22 24.17 28.32 498 21 258
9/10/21 520 140 275.00 43.24 24.20 28.53 374 20 342
9/9/21 460 100 255.00 42.83 24.19 28.33 578 30 151
9/8/21 1000 70 231.00 42.64 24.06 28.34 529 20 233
9/7/21 310 60 169.00 41.41 24.15 28.24 526 39 217
9/6/21 180 80 199.00 42.04 25.01 29.14 337 19 437
9/5/21 120 110 48.00 42.39 0.01 29.16 129 2 631
9/4/21 180 30 106.00 42.28 0.01 29.62 193 17 527
9/3/21 270 160 133.00 42.12 25.53 29.11 189 19 593
9/2/21 390 300 121.00 42.71 24.13 29.94 423 7 360
9/1/21 30 20 65.00 42.42 0.01 29.18 90 2 523
8/31/21 260 0 162.00 43.14 25.06 29.13 416 15 357
8/30/21 20 30 10.00 42.16 25.80 29.12 99 1 708
8/29/21 600 0 317.00 42.55 24.12 29.15 502 34 279
8/28/21 310 10 246.00 43.51 24.23 29.18 225 21 571
8/27/21 390 0 180.00 42.68 24.46 29.05 362 18 431
8/26/21 330 10 280.00 43.39 24.59 29.95 295 17 492
8/25/21 630 10 307.00 43.55 24.23 29.12 372 29 432
8/24/21 550 10 285.00 42.85 24.20 29.18 312 20 509
8/23/21 30 30 25.00 42.88 25.86 29.16 107 20 708
8/22/21 640 0 275.00 43.21 24.15 29.11 662 20 164
8/21/21 30 40 15.00 42.79 25.77 29.12 82 20 731
8/20/21 30 40 13.00 41.43 25.80 29.11 66 20 758
8/19/21 40 50 17.00 42.67 25.83 29.13 93 20 747
8/18/21 530 0 251.00 43.00 24.15 29.15 485 20 328
8/17/21 40 50 13.00 42.81 25.86 29.14 46 20 773
8/16/21 30 50 14.00 43.32 25.94 29.10 73 20 787
8/15/21 420 10 286.00 43.03 24.03 29.14 215 20 588
8/14/21 30 70 11.00 43.14 26.00 29.12 48 20 804
8/13/21 120 40 88.00 43.12 24.22 29.19 147 20 701
8/12/21 30 10 38.00 43.10 0.01 29.11 126 20 675
8/11/21 30 10 69.00 43.16 26.08 29.12 72 20 759
8/10/21 780 0 256.00 42.49 0.01 29.06 464 58 309
8/9/21 460 10 225.00 43.18 23.84 29.12 499 20 324
8/8/21 280 0 202.00 44.17 0.01 29.14 237 20 609
8/7/21 200 10 228.00 44.12 0.01 29.16 162 61 466
8/6/21 50 50 12.00 43.83 26.08 29.15 91 20 796
8/5/21 60 40 16.00 43.30 26.12 29.14 61 20 809
8/4/21 70 30 85.00 42.78 26.11 29.09 77 40 677
8/3/21 50 10 45.00 43.18 26.13 29.13 99 40 281
8/2/21 70 10 33.00 42.84 26.17 29.04 210 21 249
8/1/21 890 30 300.00 39.91 24.30 28.77 661 257 0
7/31/21 440 0 266.00 42.64 24.42 28.50 774 2 129
7/30/21 640 0 336.00 42.12 24.67 28.80 877 50 0
7/29/21 1270 0 305.00 41.15 24.07 29.01 908 22 0
7/28/21 950 0 305.00 42.57 24.57 29.01 842 46 44
7/27/21 1060 0 310.00 42.45 24.49 28.93 652 32 238
7/26/21 1110 0 309.00 42.05 24.47 29.01 796 20 118
7/25/21 270 0 149.00 42.73 25.57 28.98 225 4 682
7/24/21 150 0 60.00 42.20 25.81 28.97 331 15 602
7/23/21 270 0 174.00 42.57 25.60 28.88 386 1 485
7/22/21 90 0 14.00 41.97 26.17 28.89 139 1 802
7/21/21 90 0 14.00 42.03 26.17 28.88 145 1 810
7/20/21 110 0 14.00 41.96 26.19 28.88 179 1 769
7/19/21 350 0 133.00 41.31 25.93 28.93 475 60 418
7/18/21 810 0 144.00 42.17 25.52 28.97 840 64 40
7/17/21 410 0 119.00 42.01 0.01 28.92 435 62 293
7/16/21 540 0 131.00 41.73 24.13 28.47 406 196 351
7/15/21 440 0 190.00 39.83 24.09 28.11 935 0 0
7/14/21 230 0 159.00 43.49 24.45 29.03 600 17 346
7/13/21 290 0 158.00 43.96 25.67 29.07 496 24 403
7/12/21 110 0 28.00 43.62 26.25 28.87 234 1 701
7/11/21 170 0 117.00 43.53 23.60 28.87 241 64 646
7/10/21 360 0 122.00 42.42 23.81 28.21 905 34 20
7/9/21 600 0 164.00 43.31 23.72 28.86 711 72 193
7/8/21 530 0 194.00 42.19 23.72 28.18 747 62 151
7/7/21 410 0 232.00 44.38 23.83 28.19 714 60 180
7/6/21 280 0 134.00 45.26 24.11 29.58 514 65 367
7/5/21 560 0 142.00 41.21 24.81 26.56 970 0 0
7/4/21 400 0 141.00 42.98 25.02 29.77 788 3 172
7/3/21 110 40 68.00 43.45 24.90 29.01 399 5 558
7/2/21 120 20 120.00 40.31 23.97 28.83 49 87 206

Note 1: Patterns of use. Very few of the readings in table are from 'Normal' operation ie when traveling with a pattern of use involving use of the fridge overnight, a kettle early morning then the engine running for a few hours before depending on the solar keeping the batteries fully charged until sunset. Most days were on a shore hook-up so the solar was just 'Maintaining' the batteries in a fully charged state. A number of 'Testing' days involved switching to battery use during the day to make measurements of the solar and used fridge, kettle or other loads to discharge the batteries enough to activate full solar recharging to obtain peak power and solar yield measurements.

Note 2: Effects of Maximum Absorption Time and Tail Current settings. There were some configuration changes part way through the data set - the use of Tail Current to terminate Absorption was turned off and the maximum Absorption time reduced from 6 to 2 hours, then the use of Tail Current was restored after a few weeks. This resulted in a number of days in the first few weeks with an absorption time of exactly 20 mins or multiple. The reason was that the manual implied that when the switched load was in use it was used for tail current measurements whilst my configuration would only use the switched load for supplying power to the 12V system and the high currents for the inverter would be directly from the batteries as recommended. This did not turn out to be the case. When Tail Current is in use and the batteries are not being discharged overnight (ie when on shore supply) the current is very low already at the end of the Bulk phase initiated at sunrise and Absorption is terminated very quickly and a large number of short readings of 1 minute appear.

I have plotted much of this data and the plots have been placed in the main text.

Appendix G - Setting up Charging and Measuring systems

Both the SmartSolar Charge Controller and SmartShunt need some information to give optimum performance. I will first look at the SmartShunt which has a large number of parameters which can be adjusted to optimise its estimate of State of Charge (SOC). They fall into two classes: Information to detect and reset the State of Charge estimates so they do not 'drift and information to translate the measurements of current into and out of the battery to a figure for Consumed Ah and then to State of Charge.

Estimating the Battery Capacity of Lead Acid batteries [WIP]

The most basic input you really must make is the Capacity of the Batteries which sounds very easy as it is printed on the side, however that assumes they are new and properly formed. In practice with Lead Acid batteries the capacity is reduced quite rapidly with use and the degradation depends very much on the depth of discharge they are taken to. Any discharges below 50% will cause rapid degradation and, depending on type, may limit one to 70 cycles with a basic leisure battery and perhaps 300-800 with the much more expensive sealed AGM (Advanced Glass Mat) batteries. (NCC Verified Leisure Battery Scheme Information). So you really need to know what the actual capacity is to estimate how deeply you are discharging or feed in very conservative figures

This problem does not seem to be addressed in any places I could find but there are ways of estimating the State of Charge itself so I am looking at ways of working backwards from depth of discharge figures combined with the Consumed Ah to estimate the Capacity. There are two main ways to measure the State of Charge - for unsealed flooded batteries you can measure the Specific Gravity of the electrolyte, for sealed batteries you can only use the voltage with no load. The use of the Open Circuit Voltage (OCV) depends on knowledge of the type of chemistry of the battery, the temperature of the battery and the battery must be completely free of any load for ideally several hours. You really need information from the manufacturers to make a good estimate but if the battery manufacturer's State-of-Charge (SoC) specifications are not available for the battery there are tables available on http://www.batteryfaq.org for various generic types of batteries and I thank them for allowing use of their information and spreadsheets such as that below.

Temperature and Chemistry: These tables show that this is not going to be easy as there are significant differences due to temperature and type of chemistry which we will also need to address in the setting up the Solar Charge Controller. You will note that the 100% charge voltages are significantly higher for the various sealed batteries and the voltage change between 0 and 100% SOC is 32% greater which means that the chemistry plays a large part. In contrast the temperature change offsets seem to be the same for both. If we plot Open Circuit Voltage versus Consumed Amp hours it will give us the Chemistry from the the 0% consumption if we fully charge the battery and leave it for a few hours and the SOC from the slope for the appropriate battery type. At least it will be better than my current guess of 67% of new capacity. One problem will be the need to allow several hours between each reading, another is there are many other factors that can affect the voltage readings so every battery manufacturer will have a slightly different voltage performance curve under load. Note: The temperature coefficients for variations in Open Circuit Voltage in the table above are not the same as those recommended for setting up the Absorption and Float voltages for charging.

Another problem is surface charge. All the figures above indicate that at 100% the batteries should read between 12.64 and 12.78 times 2 for a 24V system at 20.1 degrees whilst a quick look at the output from the SmartConnect shows a minimum battery voltage which is much higher at ~25.84 (equivalent to 12.92V) on days on a shore supply when the load is small! This memory effect after a very full charge is well known and is due to surface charge. It occurs because Lead Acid batteries cannot convert lead sulphate to lead and lead dioxide quickly during charge so some of the charge activities to occur on the plate surfaces, resulting in an elevated state-of-charge on the outside. A battery with surface charge has a slightly elevated voltage and gives a false voltage-based SoC reading. It dissipates quite slowly especially at temperatures below 25 deg C. - it means we will either have to wait for weeks or carry out a small discharge then wait before starting any measurements.

The following the generic graph shows the typical surface charge effect on an almost new 105 Ah Flooded Lead Acid battery discharged at 5.25A ( ie C/20 ) over 20 hrs after an initial absorption level charge followed by a period under no-load. It shows a reading well over 13 volts at the start which did not fall to the expected voltage until over 1Ah had been taken out.

It is not only the State of Charge displayed by the Victron Smart Shunt that depends on an accurate value for the Battery Capacity, the accuracy of available Ah will also be affected as the Peukert Exponent corrections uses it (I have left them as default values) and we need to sure the battery is fully charged when starting the calibration. At least we have temperature measurements available! Overall I am not convinced I will improve on my guesswork by much but keeping an eye on battery voltage will still be useful and allow some subjective corrections to my guess.

Keeping the batteries above 24.5V after a short recovery time with no load at normal temperatures is a useful way of ensuring that most Flooded Lead Acid batteries are not going to seriously damaged and was, in retrospect the point at which my batteries used to degrade rapidly if regularly reached in the morning before I added Solar!

A method to measure the battery capacity.

Despite my reservations above I decided to try to develop a method to improve my estimates of battery capacity and hence state of charge optimised towards the 50% level where damage rapidly increases. Some of the ground rules for making measurements derived from the discussions above are:

So I have taken a number of sets of readings overnight when only the fridge is running with a duty cycle of ~40% and a cycle time of ~ 1 hour allowing 40 mins for the Open Circuit Voltage to stabilise. The discharge rate with the fridge running is 100 watts giving a relatively low discharge rate of ~ C/30 and the Open Circuit Voltages have stabilised within .01 V by the end of the off cycle from inspection of the voltage versus time plots in the SmartShunt trend screen. Readings are ignored until ~ 5% of capacity has been drawn to avoid surface charge effects. After much lose of sleep I ended up with 45 points in 8 data sets some of which are 'extended' by the additional consumption of boiling a kettle (4 Ahr) before solar kicked in. I have plotted the results which show scatter as one would expect but are reasonably consistent even so. Each series has been plotted individually with a different colour but a single best fit trend line is shown on the first plot shown below. The intercept with the 0 Ahr discharge axis is at 25.88 volts which indicates the batteries are behaving more like sealed cells and the intercept with the the 24.5 volt line (assumed to be ~50% discharge) is at 52 Ahr indicating a remaining battery capacity of only ~104 AHr. This is below the figure I currently assume and indicates my batteries are already at under 50% of new capacity. So further investigation of this data is required.

Data from 8 nights combined for a single trend line

Individual trend plots for selected short and long series and a second order polynomial fit to the whole data set

The second plot shown above has trend lines for some individual series which show a spread with the longer series in general having a higher intercept. If a second order fit is done there are further indications that the capacity would be higher - more readings at higher total discharges are required to confirm that.

The extra set of readings and and curve (bold orangey red) above comes from an independent set of measurements on a pair of Powermax batteries which were replaced after just under 2 years prior to our new system. They still show green on their built in 'magic eye' indicators and are still matched in voltage. These measurements, unlike those on our battery pack in use, were at a virtually constant temperature. The plot shows that their capacity is down to about 50% (27 Ah discharge to 24.5 Volts ~= 54 Ah Capacity instead of 110 Ah claimed when new). The intercept at 0% discharge is at 25.46 is almost the classic figure for a flooded lead acid battery which can be topped up, which they have been every 200 hrs. The batteries in the main pack however behave like sealed batteries with an intercept at 25.88V. Knowledge of the chemistry ought to allow us to refine the voltage used for 50% discharge of we have no information from the manufacturer. The considerable differences in the curves shows the potential problems of mixing batteries from different manufacturers and ages and use with simple alternators without adjustments pf charge voltages. NOTE May 2022. One of these batteries has been repurposed to replace a dead domestic 12V battery so these reading and estimates are of great interest!

There has also been no corrections for battery temperature which would bring down the initial readings in each set slightly as the batteries were still cooling again tilting the initial curves slightly to increase the capacity. I do not have the temperature data to correct the curves properly but the correction curve below is plotted from a table allegedly originating from The Battery Council and will be of use in the future.

Note: This has much larger corrections to those in the table above for SOC from batteryfaq.org

Discussion of results of tests so far. There is a reasonable consistency between the 8 sets of measurements such that a single set of overnight measurements allows one to estimate the Capacity to better than 10% without prior information on the battery chemistry. It showed my various batteries are already down to 50% of their claimed capacity. This will mean that the SOC (State of Charge) reading from the SmartShunt will be much more accurate and the Peukert correction improved. If one has an initial set of readings when the batteries are new one should be able to track the degradation with time.

Sources of error: Many of the assumptions made here have been investigated and documented in "Development of an algorithm for estimating Lead-Acid Battery State of Charge and State of Health" a thesis is presented as part of Degree of Master of Science in Electrical Engineering, Blekinge Institute of Technology in September 2013 by Mateusz Michal Samolyk and Jakub Sobczak where similar techniques were used for real time corrections in estimating SOC for fork lift trucks. They developed and tested a correction method based on OCV measured during intermittent periods without charging or discharging used in conjunction with Coulomb counting. Their method corrected for short periods when the OCV had not reached equilibrium allowing more regular updating. Their measurements however indicate the 35 to 40 minutes settling time we get during regular fridge cycles is adequate for our purposes without further corrections and potentially giving errors and are probably less than the resolution of the measurements.

Temperature corrections (which have not been made so far) of ~0.0086V/deg are however significant and the overnight measurements I have made could have a temperature difference of 15 to 20 degrees from start to finish as the batteries cool overnight in an engine room which can raise the battery temperatures to 50 deg C.

Even so the biggest source of error is likely to be in the assumption of the voltage applicable to 50% discharge as it is dependent on battery chemistry and varies between manufacturers. If curves are not available from the manufacturer then the best estimates will be from discharging a new battery to 50% and measuring the discharge curve using the same intermittent fridge cycles corrected for temperature - even then many battery manufacturers claim their batteries improve during first few cycles. The next option is to guess the chemistry from the the 0% discharge intercept and any other information one can glean from what data sheets they do make available.

The following are the actual manufacturers figures for a classic style Trojan Deep-Cycle Flooded/Wet Lead-Acid Battery which is the closest that I can find to the old set of flooded batteries I tested.

12V battery V
24V battery V
100 1.277
90 1.258
80 1.238
70 1.217
60 1.195
50 1.172
40 1.148
30 1.124
20 1.098

The figure for the fully charged voltage is almost the same and the 24.5 volt intercept of 27.5 Ah corresponds to 60% SOC giving a resultant battery capacity of 68 Ah - slightly better than I might have expected for an old battery taken out of service. Note the temperature was probably below the 25 deg assumed in the table but I have not corrected as the intercept of 25.46 was correct.

More to follow??

Appendix H - What is this Peukert’s law and the Peukert exponent?

I have refereed to Peukert's law above as important when Coulomb counting is used to calculate State of Charge as used by the Smart Shunt. There is a nice simple explanation of a very complex phenomenon on the Victron Web site at https://www.victronenergy.com/media/pg/SmartShunt/en/battery-capacity-and-peukert-exponent.html which I have simplified even more here.

Peukert’s law and the Peukert exponent

The apparent capacity of a battery depends on the rate of discharge. Basically the faster the rate of discharge, the less capacity will be available from a battery. The relation between slow or fast discharge can be calculated by Peukert’s law and is expressed by the Peukert exponent. Some battery chemistries suffer more from this phenomenon than others. Lead acid are more affected by this than lithium batteries are and a Lead acid battery discharged completely in two hours will only give about half the Amp hours (capacity) available if discharged over 20 hours. The battery monitor takes this phenomenon into account with the Peukert exponent. If the efficiency and Peukert's law were ignored counting Amp hours in and out (Coulomb Counting in technospeak) would not work.

The formula that states the Law in a usable format is as follows:

H is the rated discharge time, in (hours).
C is the rated capacity at that discharge rate, in (Ampere-hours).
I is the actual discharge current, in (Amps).
k is the Peukert constant (Victron recommends using a value of 1.25)
t is the actual time to discharge the battery, in (hours).

The formula can be reorganised and written in a form to enter a calculator as:

I*t = C*(C/(I*H))^(k-1)

I*t is the new AH rating (the discharge rate at the time to discharge).

which in my case gives a reduction from 160Ah to 160*(160/(20*40))^(1.25-1) = 107Ah for a 1 kW load.

Where does the charge go: It is worth noting that that is not the end of the story. It looks as if the charge has “disappeared” but that is an over-simplification. What happens is that the chemical process which generates the current is progressing too slowly to allow diffusion through the plates and only takes place at the surface, so the battery looks as if it has a smaller capacity. A 200Ah battery discharged with 200 A and “flat” in 30 minutes will therefore also be (nearly) full again after recharging with 100 Ah at a slow rate, while the same battery which is discharged with 10 A and is flat in 20 hours will be nearly fully charged after recharging with 200 Ah. In fact a battery which has been discharged at a very high rate will recover over time and most of the remaining capacity can be retrieved after the battery has been left at rest for several hours or a day.

Applicability of Peukert's Law. Peukert's law is not a law based strictly on the physics but is an experimental parameterization of a complex effect which is found to be useful at high rates of discharge but less so at low discharge rates. This can be seen by inputting a discharge current much less than that for the rated capacity which leads to an unreasonable increase in capacity, try a C/100 rate of 1.6 Amps in the above example.

There is lot more about all of this at https://www.victronenergy.com/upload/documents/Book-Energy-Unlimited-EN.pdf - the book is well worth reading in full.

Appendix I Detailed measurements on the Lithium batteries

These measurements are even more difficult than for Lead Acid as the curves are so flat, in the case of the upper end the knee where the voltage increases rapidly is only a couple of percent from fully charged and, unlike lead acid batteries the cells do not balance themselves and are damaged if overcharged by even a small margin hence the need for a batery management System (BMS) to protect and balance them. The following measurents use a mix of measurements from the Victron SmartShunt and the internal cell measurements from the BMS built into the batteries. The curves are so flat that corrections for internal resistance during charge and discharge are crucial.

My initial measurements, in fact most of my measurements have been at the upper end and the batteries were rarely discharged below 30% and concentraated on getting the batteries into region where they would be balanced by the BMS. That has not been achieved and current work is concentration on using the batteries in a way that potentially maximises life which is not consistent with balancing and assessing what difference that makes to usable capacity. I have discussed the problems in the main text.

The measurements here come from the first 'deep' discharge down to the lower knee, what this represents in true SOC is dependent on the detailed chemistry and the manufacturers curves are not available so one is using course generic data. what the Culomb counting SmartShunt indicates to be 25% corresponds to only 17% on the voltage v SOC curve form batteries taken by a friend on his narrowboat with electric propulsion over after 5 years of use. This means that my readings realy need to be extended but with liimited solar and 'alternator' charge this is not to be undertaken lightly, last time took several days and the curves have discontinuities from the overnight periods when they were discharging running the fridge. I will make a complete set available as a spreadsheet in due course and in the meantime insert a chart with raw data from two cells, one random from the 'lower' battery and the other from the cell with the highest charge in the 'top' battery with a third curve including an empirical correction for cell resistence. A figure of 1.8 milliOhm per cell seemed to give the best fit to a smooth curve.


It is clear that there are a number of different parameters effecting the voltage and other as the internal resistance does not take out all the variations and there are even sections which seem to show the voltage decreasing with SOC which is most unlikely. However the overall impression is that between 30% and 90% SOC there is and underlying smooth transition with an increase of ~ 1mVolt per 1% SOC. These measurements were taken on each cell using bluetooth. In contrast our resolution on the Victron SmartShunt and other Victron devices is only 10 mV on the battery which is 1.25 mV per cell as there are 8 cells in the 24V battery. We are never going to be able to get an accurate SOC reading from the battery voltages but we may be able to get an indication if the SOC reading has drifted so far the we need to do a full charge to synchronise with a full charge.

The best chance is to take readings when the system is in as steady a state as possible so we can reduce the effects of any time constants and hysteresis between charging and discharging. Basically there are only two inputs for charging and two outputs from the battery. The inputs are the Solar Panels via the MPPT controller and the engine via the 12 to 24V battery to battery charger and the power outputs are the inverter and the 24V to 12V supply to keep the domestic battery charged. In addition there are some very small idle currents for various Victron devices from the Lithium battery. Overnight there is no Solar or Engine charging and the inverter and 12V charging are lowest and most predictable. Between 0000 and 0300 the only loads should be the fridge via the inverter and 'idle' currents for devices which are low and steady. Even after the hottest day recorded in the UK the fridge was off for 25 minutes during the cycle so if readings are taken just before the fridge/inverter switches on one should have had a steady state for at least 20 mins. The 'Domestic link' is always made between 1730 and 2200 when the majority of the load from lighting, Hifi, internet etc is made so at 2200 the domestic battery is fully charged and the hysteresis is such that the link rarely comes back on (at a 4Ahr deficit) before 0400 even if all our devices are put on charge before going to bed but should be checked. So on a normal night we should get between 2 and 6 readings of SOC and voltage between 0000 and 0300.

I have tested the concept with a series of total battery voltage versus SOC taken with all sources disconnected and only the fridge running through the inverter. The reading were taken just before the fridge turned ongiving circa 20 minutes with no loads/sources active by which time the voltage had stabilised within the 10 mVolt resolution of the SmartShunt.

This data set is smaller but higher quality and more consistent than the earlier set but shows a multiple plateau behavior which can be seen in the earlier set - I have no explanation for this.

I have also now got some further data sets and the following shows that the technique of only taking stable data does not solve the problem as the history seems to also make changes - see the 'rogue' set in blue below which was taken between the green and orange sets with a day separating the sets. The puple set followa another day. It indicates a potential error of 10% in SOC making the technique useless the reason can be found. The green set itself has several overnights which have not been broken out [yet!].

Most recently the red set has been added which is continuous over several days following a full charge and reset of the SmartShunt and more 'automation' of the data collection. The solar was off and the gaps are when it was detected that the system was charging the 12V domestic battery and for a period of 45 mins after the domestic linkage had been terminated. This set is showing high consistency betwen measurements and a multi plateau charging and discharging curve is looking more likely to be the case although I have no understanding of the chemistry behind it.

I have been continuing the automation and now use data selected using 'inhibits' by solar data and 12V charging with delays in turning off the inhibits of 90 and 45 minutes respectively rather than a simple timer and also allow data to be gathered when the inverter is turned off for over 60 mins. The stable data is now added to a log file along with the time which will make future analysis much easier. The last stable value is also displayed in the dashboard.

Appendix J - Settings I used for the SmartSolar Controller, SmartShunt and Phoenix Inverter with Lead Acid Batteries.

The easiest way to show the current settings of the various devices (as of 14 October 2021) is to show screen dumps of their settings screens in the SmartConnect App. Only the SmartSolar Controller, SmartShunt, and Phoenix Inverter need to be configured via the App. The only other settings is on the Orion Tr which supplies power to the 12V domestic battery and that has to be set manually with a screwdriver and is set to 12.71V to trickle charge it

SmartSolar Settings Screens

SmartShunt and Phoenix Settings Screens

Appendix K - Power measurements in Domestic 12V system

The SmartSolar measures the power provided to the Load circuit, namely the Orion Tr 24/12 and knowing its efficiency is specified to be 85% allows us to calculate the power used by the various system components it feeds. Some of them turned out to be somewhat surprising to me: a 10Watt halogen light was exactly what was expected but that was not the case for an LED replacement which had so low a power consumption it could not be measured reliably (under 2 watts). Our main lighting is by fluorescent lights which each contain three tubes each of a nominal 8 watts but only drew half that expected but a single 13 watt tube drew significantly more than the nominal power. The Hifi drew a surprisingly high 12 watts playing a CD at low volume. The powers are that from the 24 volt supply as that is what is measured and actually matters in this case. Potentially the largest steady demand on the 12V system is when running or charging our laptops. The two most likely to be present have 45Wh batteries and run for ~4 hours on batteries so will consume about 10 watts when charged. When in use and charging this could be up to 40 watts which are their nominal charger ratings.

Item Nominal Power (Watts) 24V Load Power (Watts) Hours per day Wh/day Comments
Water Pump
Tunnel Light (LED)

620 Lumen LED - Occasional use only when engine running

LabCraft Lights (5)
3 x 4
3 x 8 Watt tubes
HLC Light 20"
Corridor Single Tube
HLC Light 11"
Bathroom and Bed-head Single Tube
Wall Light Halogen
Hardly used
Wall Light LED
Often used
Hifi playing CD
Medium Volume
Charging Phones
3 x 2
2 Samsung A6 phones 12Wh batteries discharged to ~50% daily
Samsung Tab S6
5 (Estimate)
Browsing or Streaming TV 27Wh battery discharged to ~50%
Multipurpose 12V PS (No Load)
Idle keeping lap tops charged
Laptop using 12V PS
10 (Estimate)
Chillblast Helios Laptop ( charged and in use) 40Wh battery provides ~4 hours use
S3 Mini or M32 Phone - Tethered for Internet
Provides Wifi 24 x 7 (Tethered 3G) 6Wh battery. Now also used by Raspberry Pi for remote control and monitoring when it can be run from shore supply over winter
Raspberry Pi 3B+
Late addition: Running Victron Venus OS to allow remote monitoring. Can be run from shore supply over winter

The 12V power consumption is dominated by lighting during winter cruising - most are Labcraft which seem to be quite low power consumption despite having up to 3 fluorescent tubes. We tend to operate daylight hours but after nightfall we normally have two lights on in the living area if reading and one or two in the kitchen whilst cooking plus occasional use on demand elsewhere. Wifi provision, charging of phones and tablets and laptop use is not greatly dependent on season. The total use would allow ~2 days use to 60% charge on a new 100Ahr battery out of season hence the need to link to a solar power source especially if on a shore supply to avoid running an engine just for a 12V supply. In practice the measurements from our system show that these figures err on the low side for totals as i believe we make more use of computers and laptops.

This table has been modified to include provisional figures on the addition of the Raspberry Pi used for remote monitoring and control assuming it uses the 12 V domestic supply rather than the 24 V supply.

Appendix L - LEC R5017W 230V fridge.

The fridge is our main (only) non-discretionary power consumer on the 24/230V system. We initially intended to change to a low voltage 12/24V fridge which thought would have a major impact when we looked at the power consumption of the modern 12/24 volt fridges available from chandlers. It turned out they were mostly modifications of standard fridges with a low voltage Danfoss compressor and had the same power consumption as their parent fridges. The were obviously still some savings as in did away with the losses in the inverter but in the end we decided to get a 230V version of the LEC fridge which forms the basis of the Inlander Rir405W which is well proven in marine applications.

The LEC R5017W 230v is a 50cm wide fridge with 4* freezer and A+ rating which the manufacturers allege only uses 167 units year which equates to 458 Wh/day. Assuming the Victron Phoenix 24/1600 inverter is 94% efficient plus idle power, in Eco mode and the fridge runs for 6 hours a day -> 458÷.94+6×9+18×1.3 = 564 Wh/day which would be ~1/3 of existing fridge/inverter combination. More recent measurements on the Victron Inverter Zanussi fridge combination give a consumption during a warm September of 820 Wh/day giving ~250 Wh/day or 30% calculated saving from changing the fridge which will still be useful.

In summary the reasons for choosing the 230V version via an inverter were:

Measurements on LEC R5017W in 'ideal' conditions on Mains before installation

Measurements on LEC R5017W set with Fridge 6 deg and freezer -18 deg C with room temperature 20 deg in free air has 9.5/42 on ratio = 22.5%. The compressor is a D53CY1 using R600a coolant which I found on the web to have a power input of 65 Watts (and a 80 watt cooling capacity). 65 x 24 x .225 = 351 Wh/day which looks low compared to the LEC data. It is also described as a 1/10 hp unit which gives 765 / 10 x 24 x .225 = 413 Wh/days. I wonder if this mean that manufacturers Energy Efficiency figures include factors for opening/closing the door and freezing/cooling of food or assume a different ambient temperature of say 25 deg C ?

In normal operation the sides of the cabinet quickly rise about 10 deg C above ambient and the compressor rises much more slowly towards 18 degrees above ambient. These measurements were taken with the fridge sited well away from any obstructions and sitting on tight weave kitchen tiles from Heuga. The measurements were taken with an IR remote thermometer I bought from Screwfix several years ago to check domestic radiators and also use for 'Covid' fever checks on a forehead.

Installation of LEC R5017W on Corinna

The manufacturers specify a clearance of 2.5 cm on the sides and top and 5 cm at the back when installed under a counter. The existing fridge has cooling coils on the back so there is much tighter fit at the sides with circa 3 cm total clearance available. At the back there is a gap at the bottom allowing cold air to be drawn from the bilges and from below the water line. The actual gap is however a bare 5 cms until the top where there is an exit gap upwards for hot air.

The cupboard beside the fridge is shallow front to back (30cm) so does not overlap the whole side and can and had to be moved back and sideways to increase the clearance by 2.5cm. The fridge is slightly forwards of the work surface to increase clearance at the back but will still be inset from the pillar on the work-surface end. I have a USB powered variable speed fan providing up to 50 cubic ft/min available which can be mounted to provide cool (river temperature air) over the compressor and aiding flow up the sides if required. I also have a small 40 deg thermostat which can be bonded to the compressor but it may be too slow to respond to be useful.

Performance of the LEC R5017W on Corinna

When the fridge was initially fitted in April the ambient temperature was below the specified range of 16 to 36 deg C so there was a very low duty cycle and freezer was often not cooled fully. Once the temperatures rose above 12 degrees the freezer temperature was acceptable.

Power consumption whilst running at 20 deg seems even lower than anticipated and drops to ~ 61 watts after a few minutes based on SmartShunt input measurement of 2.3A at 26.56V thus including all the losses in the inverter. Typical 'on cycle' is 11 Wh every 40 minutes ~ 400 Wh/day

More measurements are needed when temperatures in Corinna reach summer and heatwave levels but look promising at the time this was written in early May at <450 Wh/day. Since then we have had a few days in June which qualify as heat wave, over 28 deg C and the duty cycle hardly seemed to change with the fridge on just over twice an hour which is very satisfactory.

Update after the hottest days ever recorded in the UK: We have just had our first ever extreme temperature warnings and the highest temperatures ever recorded in the UK as a challenge. The boat temperature reached 41 deg C at head height as measured by my IR thermometer with the region behind the fridge about 37 degrees on our mooring, just outside the maximum normal operating range. The freezer temperature remained below -18 deg C and the fridge at a safe temperature without adjustment although I did try adjusting the thermostat slightly as LEC recommend. The consumption during the peak days of the heatwave rose to 520 - 550 Wh/day but the fridge cycle never exceeded 40% on. All very pleasing. Note however that the orientation of our home mooring is such that direct sunlight does not hit the side behind the fridge after 1130 and it would be prudent to avoid mooring with direct sun on the side behind fridge for for the whole day under such extreme conditions and to avoid extensive use. We had another period in August with 4 'extreme' days in a row with peak temperatures of 32 deg C and the fridge used under 420 Wh/day but was not in use and rarely opened, even so an extremely pleasing performance.

Appendix M - My Original 'Day-Book' for Reference

Whilst I was planting and implementing the upgrade I kept a 'day-book' with all my thoughts, references, measurements, planning etc. Much has ended up in the in a polished version above but there is always useful information and dead ends recorded, which may be useful - one should never destroy a day-book and original measurements. There are also a few draft sections for the document above kept as they show some extra background thinking.

You can Click to Expand or hide my original working document ( effectively a day-book kept as a text file in the cloud so accessible from the nearest machine). I have done a little formatting from the original text file to display better in HTML and new sections may, on occasion be transferred from the working document.

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