SOK BMS Incorrect (ABC-BMS on app store)

[FR Steve L]

I am having a hard time with accurate readings from the BMS for my 2 SOK 206Ah LiFePO4 batteries. First, when connecting to the 2 batteries via the BMS app (called "ABC-BMS"), each shows a completely different SOC (see screenshots attached). I know that over time when charging/discharging, the SOC will drift, but they drift VERY quickly. Printed on the casing of the batteries is a message about having to go through 2 charge cycles for an accurate BMS reading, which I've done (also in the screenshot) and it hasn't helped the SOC accuracy. In addition, when my batteries are low (not completely discharged), the BMS will show 0% for both batteries which obviously isn't correct given I'm still drawing power through the inverter for a good amount of time until the battery actual does die.

How can one battery show 13.12V, but only 9% SOC?
How can the other battery show 13.11V, but only 2% SOC?
Based on a 12V voltage chart, 13.1V should be ~40% SOC...

Also attached for reference is the battery at 100% SOC (notice C MOS is grey, which per the manufacturer confirms the battery is fully charged)

Thanks in advance!

 

[FilterGuy]

Based on a 12V voltage chart, 13.1V should be ~40% SOC...

Don't try to use voltage charts for SOC on LiFePO4 batteries. It is crazy inaccurate due to the extremely flat discharge curve for the majority of the time. The only time voltage is an indicator of SOC on LiFePO4 is when the batteries are nearly full (95% soc or more) or nearly empty. (10% of SOC or less).

The charts you see floating around are from people that do not understand LiFePO4.

 

[FilterGuy]

Printed on the casing of the batteries is a message about having to go through 2 charge cycles for an accurate BMS reading, which I've done

Did you charge till the BMS cut off and Discharge till the BMS cut off. That is what is needed for the BMS to fully calibrate itself. SOK claims that they are working on improvements that will eliminate the need to do this, but it won't be available for existing batteries.

SOK makes its own BMSs and it appears to me that they are still learning. There are other issues (such as when the balancer turns on & off on the 100Ah batteries) that they have acknowledged and will be fixed on future versions of the battery. (I do not know if the same issues exist on the 200Ah batteries, but I would not be surprised if it did)