Rebalancing my pack?

[HughF]

I've got a 2 yr old generic aliexpress 13s pack, it's quite out of balance (as indicated by the bluetooth BMS I added to it the other day) - what are my options for rebalancing it easily? I expect it to have about 100 cycles on it.

I've tried charging it up off a low-current charger (1.5A) but the BMS isn't able to bleed enough current off and I get a cell overvolt before the pack is balanced.

Do I need to charge it to a lower voltage (4.0v/cell perhaps) to start with?

 

[E-HP]

You could manually charge the lower series groups through the BMS balancing wires, after disconnecting the harness from the BMS. If you need a 4.2V source, you could get a 2A 4.2V wall wart charger from ebay or Amazon for about $5, cut of the connector and add some pins. Use your voltmeter and proceed with caution.
https://www.amazon.com/iCreatin-Adaptor-Lithium-Battery-Automatically/dp/B07S21YNRG
Once you get them closer, you could plug in the BMS and let it do the rest.

 

[john61ct]

You can do it manually with an adjustable supply given access to the balance leads.

Or buy a balancer with a decent balance rate, "active" meaning works without an charge current input at all, and ideal also in the sense that it still shuttles the current between cell/groups at the same rate, even as the delta closes.

Or a resistance based (burning) BMS as usual (IMO stupid design) but at least with a faster rate.

The input voltage should be just above the point at which balancing starts, if that setpoint is not adjustable

Keeping the current very low will help avoid (too much) wear & tear on the cells.

 

[HughF]

I have easy access to the balance wires, I'll use my nightcore 4 bay charger, with some clip leads, to bring the back back into balance.

I didn't think of going in via the balance leads.. I actually have one of those imax B6 clones that works quite well, but I think that only supports 6S maximum?

 

[docw009]

IF you have a Imax clone, it's probably faster to charge the low groups one at a time.

I thought that my IMAX b6AC 6S charger could send current thru the balance wires, but it top balances slowly like a BMS. I was going to balance my 10S pack 5 groups at a time witha 5 pin balance cable adapter. It took a long time to equalize one cell that was .25V off. Would have been faster to hook up to it directly.

 

[john61ct]

Limit balance lead charging to 3-4A

Maybe 5-6A if monitoring heat gain, especially at the terminations