Batteries cluster parallel connection

Thread Starter

mbilal2022

Joined Jul 14, 2022
2
Hello everyone,

I have a question regarding the battery clusters connection parallel. There are six clusters each consists of 14 lithium batteries of 100 Ah in a 250 kW PV system. The problem is cluster 1 and 2 will charge with low current and discharge with a bit higher current around 1 to 2 Amps, which makes an impact on the SoC of the clusters. Among 6 clusters, cluster 5 charges with higher current than all others. Although all are in parallel but the problem persists. What could be the possible reason.

P.S: Cluster 1 and 2 were disconnected for sometimes due to a fault. But all are now operating together for more than a month now. The system was installed almost 8 months ago.

Looking forward to the experts opinion. Thank you
 

Martin_R

Joined Aug 28, 2019
116
How long were cluster 1 and 2 out of circuit? I wonder if those clusters had discharged below their minimum voltage for some reason. Below 3v the cells can become permanently damaged. That would explain why you can't draw any current out of them
 

Thread Starter

mbilal2022

Joined Jul 14, 2022
2
I am not fully sure but I think they were not connected for a month while others were operating. But I am quite sure that none of the cells were discharge below 3.1 volts. There is a great protection system in the high voltage box in each cluster.

The clusters 1 and 2 do work, but I don't know why do they charge and discharge with different currents than others and the current difference makes the SoC difference that I can see on the HMI. For instance, C5 would be 50%, so C1 and C2 will 25% and others will be 35%.
 

KeithWalker

Joined Jul 10, 2017
2,455
I assume that the 14 cells in each cluster are connected in series. Does each cluster have it's own charge control circuit with equalization? You obviously have some defective cells in some clusters. You should disconnect each cluster in turn and measure the terminal voltage of each cell to identify the faulty ones.
 
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