FoxESS Community - Owners & Installers Forum

Hi all, new user/ poster here.

I've been told that I can safely move the SOC minimum down to 10%, below that risks damaging the batteries.

Could someone explain the danger of going below 10% and whether anyone would recommend going down from 20% (my current setting) to 15% now (is it the length of the days/ hours of sunshine or ambient temperatures that dictate this?).

Sorry for the PV 101 questions but looking to learn!

Thanks in advance!

My installer left mine set at 20% , when I asked about changing to 10% they said that was fine, they said 20% was just the default!
When set to 20% mine would dip down to about14% anyway. Now it dips to 11% not 10% as it's set to.

I think the 20% is set as default in case you have the EPS setup so you always have a little power in case of an emergency.

If in doubt ask your installer that way you have it in an email!

I believe that installers were inclined to tell customers to leave the Min SoC on 20% due to the early firmware which could 'drift' a long way on SoC as a number of us have seen.

The newer BMS and battery firmwares are much better about this (albeit not perfect - it seems that this particular battery chemistry is quite challenging to monitor and control very precisely) and will pulse charge if SoC drops too low, so I think 10% is OK as long as you have fully updated firmware and a reasonably well balanced set of modules.

Yes totally safe to reduce it to 10% now, it will be fine like that until probably late November when you can lift it to 15% - 20%.

It won't let you set it below 10% regardless, so 10% is effectively the minimum you can have.

Thanks so much for the replies everyone, very much appreciated!

Dave Foster wrote: ↑Tue May 16, 2023 5:00 pm Yes totally safe to reduce it to 10% now, it will be fine like that until probably late November when you can lift it to 15% - 20%.

Are you thinking of the effect of the cold on the battery? Winter feels like the time I'd want the most capacity in my battery because the solar gain is so low, relatively speaking.

calum wrote: ↑Tue May 16, 2023 9:56 pm Are you thinking of the effect of the cold on the battery? Winter feels like the time I'd want the most capacity in my battery because the solar gain is so low, relatively speaking.

Yes it's temperature, sadly Winter being the time you need your batteries the most, is when they have to put up with the lowest temps which reduce their effective capacity, the 15% gives them that little bit of extra protection.

BUT if you charge overnight on a low tariff they self warm, or if they are in a warm space / insulated enclosure the 15% isn't necessary - I think all of that applies to you, so you're all good

Dave Foster wrote: ↑Wed May 17, 2023 5:20 pm

calum wrote: ↑Tue May 16, 2023 9:56 pm Are you thinking of the effect of the cold on the battery? Winter feels like the time I'd want the most capacity in my battery because the solar gain is so low, relatively speaking.

Yes it's temperature, sadly Winter being the time you need your batteries the most, is when they have to put up with the lowest temps which reduce their effective capacity, the 15% gives them that little bit of extra protection.

BUT if you charge overnight on a low tariff they self warm, or if they are in a warm space / insulated enclosure the 15% isn't necessary - I think all of that applies to you, so you're all good

I'm going to try to add some trace heating while the enclosure is dismantled over the summer months. Just now the battery is happy in the low to mid 20s celcius, with low cell temps in the high teens, but in the colder months I'm thinking the modules sat at the bottom of the stack will be pretty chilly on the concrete floor of the garage!

As an aside, depending on how much peak rate consumption you might avoid by keeping your batteries working capacity up in the winter, and what the price difference is, an insulated enclosure can be a very good investment (this applies to current delivery as well as capacity - colder batteries suffer in both respects).