Battery management system(BMS) balance current rating

[santoshgurral]

Hi Guys

I am working on a 18650 Li-ion battery pack system. So I was scouting for a BMS for my battery pack. I see a specification called "balance current" for BMS what does this mean?
There are BMS boards with different balance current ratings like 40mA balance current 70mA, 100mA and so on...
What does this balance current rating on a BMS board signify? Which one should I choose? I want to understand what is this 40mA/70mA/100mA signify, is it like the BMS keep discharging a full charged battery(4.2v) with 40mA until the other cells in the system reach its full capacity(ie 4.2v)?

[abyrvalg]

Yes, mostly correct, the BMS on your picture will discharge overcharged (above some "balancing threshold voltage") cells with that current until these cells go below threshold. But this process doesn’t care about other (not overcharged) cells.

[santoshgurral]

so I better choose a BMS with a relatively high balance current so that my battery pack balancing process is fast. is this correct?

Thanks
Santosh

[santoshgurral]

Hi

Please see attached image

In 1S5P arrangement 5 cells in parallel for total 8514mA, Will each cell be charged to its full capacity or each cell charge is limited by the cell with the smallest charge capacity?
I mean, since c3 is the cell with the lowest charge capacity of 1166mA each among all other cells in the pack will this make the TP4056 module to charge all cells c1,c2,c3,c4,c5 only up to 1166mA irrespective of their full capacity and stop charging the pack after 1166*5=5830mA instead of 8514mA?

Thanks
Santosh

[Siwastaja]

Use the lowest possible balancing current so there is a smaller risk for thermal shit hitting the fan if something goes wrong and the balancer gets stuck on.

40mA is likely enough unless this is a massive (tens of kWh) battery pack, or a pack built from a nearly-dead (poor quality, or abused and reused) cells.