New and confused... battery SOC.

[Entwood]

Hi, very new to this and slightly confused.... if anyone can enlighten me I would appreciate it!!

My system is set for a minimum SOC of 10%. Yesterday, due to heavy cloud the battery never charged, not unexpected at all..... so it ran down early ( evening meal prep time) and we were on the grid, again not unexpected.... however, overnight the SOC continued to drop steadily but slowly, eventually reaching 6% when it suddenly charged back to 10% from the grid before dropping slowly again, until solar started again. Attached a screen shot of the app to show,hopefully what I mean.

Questions are 1) is this normal behaviour...dropping below set SOC and recharging when no charge period is selected? and 2) is dropping to 6% going to harm the battery, installers said not to go below 10%?

Sorry to be a nuisance, regards, Nige

[MaterialBarracuda48]

Hello Nige,

Well the SoC is just a 'construct' of the Cell Voltages, there is only a small mV difference between 'flat' 10% and 'full' 100% SoC. You will also see that the cell Voltage can drop below, then recover back what you would expect the min cell Voltage to be. Once your battery has been low for a few hours, the reported SoC can drop below the 10% minimum as the BMS recalculates.

[TonyGomm]

Hello Nigel,
I can't comment on your specific system, but I would say that if you keep an eye on tomorrows weather forecast, and can predict that you might have low battery late in the day, then you might benefit from setting-up a charge mode period earlier in the day, that you can switch on or off before the peak charging period depending on how you predict the coming weather. Or use a mode that fully charges the batteries in the low-charge nighttime period. That way you both eliminate the low battery problem, and use less 'bought-in' energy off the grid.
Thinking again about the weather forecast, I use it also to plan ahead energy hungry activities - laundry and drying for example - for days when strong PV can be predicted.
Tony

[Entwood]

Hi both. Thanks for the responses. So it looks like the "behaviour" is not abnormal, so I guess it is not harmful either. I'm presently on a fixed price/term tariff with no "peak" times, so it matters not when I go "ongrid", the cost is the same. Terms of my "fix" are pretty good and the penalty for changing mid-term pretty high, so, according to my calculations I'm actually better off staying where I am, things will probably change in time but then the "penalty" won't apply. I'm also still waiting for DNO so the option of charging cheap then feeding for revenue doesn't apply. My concern was primarily potential harm to the battery and why it suddenly charged from the gridwhen not set up. Searching the facebook Foxess pages for ideas found this.....https://github.com/TonyM1958/HA-FoxESS- ... oat-charge which was informative especially the bit about "float charge".

[MaterialBarracuda48]

I did speed read your question, and know I missed some of the answers you wanted, so thanks to Tony for filling in the gaps.

Good also that you did some extra research behind the scenes, there is also a cold emergency charge also that protects the cells during cold snaps for protection. The BMS is a clever part of battery tech, that keeps it healthy.

[Entwood]

Thanks for the follow-up, appreciate it. For me every day's a school day at the moment!! As you mention temperature, I was going to ask this later as it got colder, but now is as good a time as any I hope....

Installers have set my system heaters to come on at 8 C and go off at 13 C, no time zones set for the reasons stated previously. Do those values make sense for SW UK ??

Regards, and thanks again, Nige