Battery SOC rapid changes
Hi,
We installed a 8kW hybrid inverter with 2 x BSL 172 Ah (8.8kWh) batteries. I have seen a few instances when the battery S.O.C jumps very suddenly and unrealistically. Two days ago, the battery S.O.C increased from 58% to 66% in one measurement and then from 67% to 93% in 10 minutes, which is not possible.
Does anyone have any ideas or experienced similar behaviour? The BMS page on the inverter seem normal. Max. charge rate is 80A, max. discharge rate is 180A. Charge voltage is 54.5V. The battery voltage seems to fluctuate slightly at this time, but I'm not sure whether that is the issue, as it returns again to previous value shortly after slight increase.
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I am not totally sure, but my understanding is that yes the BMS in each battery will look after iteslf, however there is communication between the inverter and each battery via the CAM bus, so it will depend on how the inverter and battery talk to each other. It will also depend on the BMS and inverter firmware versions. There are a lot of variables and each battery will most likely have it's own unique behaviour regarding charging rates due to manufactures specific design, battery charge levels, temperature etc
For example I am having problems right now with one of my two SSLB1 running outdated firmware, in that it will not charge below certain temperatures, and also beeps when it reaches 100% charge which is quite annoying.
I also remember when my system was first commissioned my master battery was faulty, and the inverter couldn't see the batteries as master / subordinate pair. Instead is saw them as two masters which also lead to the SOC levels jumping about as the inverter switched reporting between the two individual batteries rather than reporting them as one aggregated unit.