Incorrect Battery SOC

[RWI]

My configuration has two 8.0 kW Deye Hybrid in parallel. They are new and have been operating for about 3 weeks. On one occasion i noticed that the SOC was changed (reduced downwards) during the night which required additional charging to recover the SOC the following day. They then operated for some days with the SOC following quite closely the actual charge/discharge as a % of the total capacity. Also the battery voltages looked about correct. I have Lead acid batteries. The system charges the batteries during the day and discharges once the sun goes down until an SOC of 55% is reached when the load is supplied from the grid. The batteries then charge up the next day and can reach about 100% with good sun. The problem is that last night at some time the inverters changed the SOC from 55% to 0%. Now today it is charging back again and has reached about 55% with the % matching closely the actual charge volume. The problem is that the batteries are now about 100% charged because the voltage has reached the absorption value of about 57.5 V. I have checked that the battery capacity is set correctly and the batteries are new valve regulated batteries. The system would have been working correctly if it had not reset the SOC to 0%. overnight which was a huge change. Has anyone had this problem. There does not appear to be any way to adjust the SOC which I guess is internally calculated.

 

[RWI]

For anyone interested. This morning the SOC jumped from 65 to 100% after the charging voltage had reached the absorption value and reduced the charge current for about one hour. For the rest of the day i will not benefit from my excess solar generation. it looks like it has basically gone back where it was a few days ago. Does anyone have an idea how the algorithms used to calculate SOC work.

 

[atothex]

Hey i had yesterday a similar experience. My SOC changed from 20% to 100% in one minute (well that was fast). I guess it had something to do with the calibration of the SOC

Whats your brand of your batteries?

 

[Chorlton]

The methods of calculating SOC are generally less accurate than you would think. It can take a full charge and discharge of a battery to reset it to be more accurate (Be careful doing this as some batteries/ bms do not keep a % as a reserve and this can cause damage If actually fully discharged). In my case one battery was at 69% during a dull day for our off grid system so I charged it from the mains and it very rapidly went from 69% to 100%. Tested its capacity with a known power draw back down again and the capacity was fine , no reduction.

 

[atothex]

Thx for the answer. I will monitor the behaviour of the bms.
My frst guess was this is a calibration routine. Because after some minutes its reported 0% and started to charge it again.

This happend after some days with rain, no top balancing and SOC in the range from 20%-30%