Getting to Grips with New System

[Malc]

Hi _ I'm a new owner of a Fox system consisting of 2 X 5.18kWh batteries and a 5kW inverter. it all seems to operate ok and at the moment I'm primarily charging them overnight to 100% and using the power during the day. Hopefully once the sun starts to shine I will be able to charge them from solar during the day. What I've noticed is that although my system was rated at 10.36kWh I only get out around 7kWh each day. My min SOC was set at 20% with 10% reserve capacity. The installer changed my min SOC to 10% remotely and that made a small increase to 7.4kWh. I was also told that reducing the min SOC could reduce battery life. So because it had made such a small difference I tried to reset the min SOC back to 20% using the Fox app but even though I confirm the setting it keeps going back to 10%. Does anyone have a view on the amount of power I should be able to get out of the batteries, I understood that I wouldn't get 10.36kWh due to the 90% depth of discharge limitations etc but thought it would be better than 7kWh. Should I be able to reset my min SOC using the app, I was able to set the charging schedule using it. Many thanks in anticipation. Rgds

[Will]

Hi and welcome to the forum, can you confirm exactly which battery model you have and how you're monitoring the discharge/charge kWh. Any screenshots would help.

[Malc]

Hi Will and thanks for your response. The batteries are 2 Fox ESS EP5, each rated at 5.18kWh. I read all the data from the Fox Cloud 2.0 app. In the inverter section it tells you what you have discharged each day. The total I've quoted (7kWh) was read on days when the sun wasn't shining as any solar generation can increase the discharge available by partially recharging the batteries during the day. Sorry no photos, I'm not much of a smart phone user. Rgds

[Dave Foster]

If you don’t have EPS fitted (emergency power supply) then you would be best setting both your minSoC and Battery reserve to 10% - The EP5 batteries are rated at 90% depth of discharge and as you’ve paid for it, you really should use it, you won’t affect their warranty.

If the system is new, the 2 batteries may not be in perfect balance yet, this is usually achieved over several weeks and will happen more quickly if you can do full cycles i.e. charge them to 100% and then discharge them until they get to 10% - the BMS will more quickly learn the limits of the batteries this way.

The EP5 batteries are rated at 5.18 kWh capacity at 25C but this will derate as the battery temperature drops - so at 10% minsoc on your 2 batteries you would expect 9.32kWh at 25C (with perfectly balanced batteries) but as the temperature falls towards 0C this would reduce to ~8kWh and so the time of the year and their ambient temperature will all play a part.

For now it is best to set your minsoc / battery reserve to 10%, allow the batteries to do a few full cycles over the next few weeks and preferably monitor their performance when the ambient temperature is higher.

[reef]

As Dave mentions above, the capacity will reduce as the batteries get colder. I have 6 HV25 batteries at 92% SOH, so about 13.2kWh usable, however at this time of year it's more like 11kWh when they are cold. Here's a trace showing how the BMS has to re-adjust the expected remaining capacity as the temperature changes. From around 2am they are at or near 100% SOC the whole time: