FoxESS Community - Owners & Installers Forum

Is there a situation where an EP5 battery output is resticted to 50% of it's maximum rate?

Situation looked like this:

Load - 2972W
Solar - 640W
Battery - 1895W
SoC - 14%
Grid Importing - 487W

Looking back through my data it appears to limit output whenever it goes below 20% SoC. It would be good to know if this is the case as up to now I've expected full output until it hit a min SoC settings.

What was your battery temperature ? - that could restrict your discharge/charge.

The other thing to say is that you are only looking at a sample which is taken every 5 minutes, you need to look at the graph over time to see as it could have been a transient i.e. the grid filled in for a few seconds whilst the battery ramped up to meet the load.

Thanks Dave,

Temp was around 14degC and I was monitoring using my real-time app which can scan every second when I want it to. Here's the snap-shot I took at the time:
I also reviewed my database and I found several instances where the battery and PV was supplying house demand with battery output above 2000W and as soon as the SoC dropped to 20% battery output dropped to around 1900W and the grid had to take up the slack.

Are you running a modbus connection?, the BMS bases it’s decision on the lowest cell temperature - is that 14C coming from the Fox inverter or is it the ambient temperature.

The charge / discharge behaviour definitely adjusts with temperature, I believe with latest battery firmware the first reduction in current is at 20C and derating as it falls - and the SoC also plays a part in the throttling which it sounds like it is what you are seeing.

If you have modbus, the inverter reports the BMS charge / discharge rates (in amps) maximum power is that figure multiplied by battery voltage.

Will has done a video which explains some of the effects and it has the charge current table from latest firmware (discharge current is a different table but it shows how it does its maths) https://foxesscommunity.com/viewtopic.php?p=9592#p9592

Thanks Dave, Will's video was very useful.

Yes, I'm using a modbus connection to get all my data and as you can tell I'm still learning about system.

Battery temps are generally in the high 20's and not going below 25. Think I may need to add another EP5 battery to ensure it can supply the house's peak demands on it's own (at least up to the limit of the invertor)

Via ModBus the "battery temp" is reported by both the inverter and the BMS. I'm using Home Assistant and the temperature that affects the BMS charge rate is "BMS Cell temp low", not "Battery temp" as reported by the inverter.
As I type this "Battery temp" is reported as 26.1°C but "BMS Cell temp low" reports 14.4°C.(outside temp is 11°C)
Cloud app v2.0 also reports 14.4°C
Last night the lowest "battery temp" reported was 21°C when the outside air temp was 7°C and cell low temp was 9°C which resulted in charge throttling to 5.5A until the cell temp rose to 11°C

Thanks nrb501.

What's the modbus register for 'Bat Cell Temp Low' please?

I'm using a USB - RS485 connection and the main registrer set for most of the invertor read-only values start at 31000
and I can see the ambient and fin temperatures in 31018/19.

Try address 37618.

It seems 31023 is the BMS pcb temp.

That's great, thanks Dave and nrb501