On 2025/05/28 at 8:42 AM, Toxxyc said:

So it looks like at least one of the batteries have got a faulty BMS. The problem is getting worse, so it also makes sense. It could be that at 42%, two of the batteries switched off, resulting in the remaining SOC halving to 20%. That's my best guess at this stage.

If the problem is getting worse then I would think it points to cell imbalances or faults as opposed to a potential BMS issue.

In all the troubleshooting that your installer did, was the cell voltages inspected to determine if there are potentially weak cells.

Poor fuse connections on the battery lines can sometimes cause low DC bus voltage failures, especially if each battery is individually fused through a common bus bar (if daisy chained normally not an issue).

Do you have access to monitor the individual cell voltages to see what the delta is at high SOC levels (above 3.5v per cell) and at the lower SOC levels (below 3.1v per cell).

If you don't have access to cell voltage data, you can also try to charge the batteries to 100% SOC, turn off the PV (switch off the breakers, under very low load) and then apply a large load to see if the batteries can carry this as a high SOC, if they can it is almost certain that the low voltage dc bus errors are caused by weak cells.

Another factor to consider is how often is the bank charged to 100% SOC in order for the cells to properly balance and to rest the BMS SOC counter. This needs to be done as frequently as possible, if not daily.

If the are cells imbalanced you can also try and charge up the bank at low C rates (0.2) for an extended period of time (4 weeks plus), charging at 3.5v per cell (56v for a 16 cell battery) and keep the float setting at 56v as well which should force the BMS to balance the cells at that level. Also just make sure that the 56v is within the battery specs per the supplier.

If there are weak cells, then nothing can really be done, apart from insiting on a warrenty replacement).

Switching to AGM mode will only mask the issue, it wont solve it

I am having an issue with a 8kw Deye connected to 2 Cfe batteries connected in parrallel it keeps crushing with an fault code 56 i have been trying all possible scenarios now am left with checking the bms. I even removed the coms cable which worked for some days but it started again. help me out.