Battery rapidly draining followed by recharge from grid

[bdbdbd]

Hi,

Sorry if this is the wrong place to ask this, but I feel I'm getting the run around from Sungrow (battery providers)

Our solar system has consistently been exhibiting the issues shown in the image below for the past few months. It was not doing this when we had the system installed about a year ago.

1. When it drains to about 10-15% it rapidly drops to 0%.
2. This is followed by a sudden (and significant) spike in power from the grid that seems to recharge the battery to about 6%. This is recorded by our electeicity provider.
3. When recharging, it jumps from about 85% to 100% immediately.

The battery supplier said it was a firmware issue. 3 firmware updates later and no improvement. They then said they would adjust the level so the battery could not drain below 5% and change a setting to make it unable to recharge from grid. No improvement. They are now saying it is a battery equalization issue and we should wait another two weeks.

Can someone provide a simple explanation and let me know what I should say to these guys so it can be fixed.

 

[sunshine_eggo]

If that's a LFP battery, that sort of behavior is typical of imbalanced cells and a confused BMS setting 0% when a single cell hits low cut off and then setting 100% when a single cell hits high voltage cutoff.

The only thing you can conclude here is that you have about 70% of the rated capacity as usable. If this is imbalance, it should improve over time. If this is due to cell degradation, this is end of life - warranty replacement type situation.

The BMS should balance the cells when charging and when held at peak voltage for extended periods. You should see small, progressive improvement. It might not be evident on a daily basis, but after a couple weeks, it should improve measureably.