My two batteries reach different voltages in bulk charging.

[whatismouse]

I have 2x 24V A123 bateries in series, for 48V/100Ah.

I noticed recently that while they generally always have the same voltage, they can vary by as much as 2V at end of a bulk charge, with one of the packs getting to 29.6V versus the other at 27.6. Then they will be pretty much the same once they settle at float voltages or under load. I dont have a way to charge them individually so I can't top balance them.

I lowered my bulk voltage from 57.6V to 56.4V because I didn't want to be over-charging one of my packs.

It occurred to me that if I were actually to raise the bulk charge voltage, the BMS would theoretically stop charging one of the packs at the HVC, and continue charging the other pack. If I were to do this once every year or so, would it be an ok way to balance my two packs?

 

[snoobler]

It wouldn't continue charging the other pack. All current through both batteries would stop because the circuit is broken.

You need to disconnect them and reconnect them in parallel. Charge to 29.2V and then place back in series. Monitor them moving forward.

 

[time2roll]

Good that you have discovered this now. I recommend that a 24v charging system is needed so these batteries can periodically be charged in parallel.

It might be possible to get an active 48v balancer to overlay the entire set but I don't know enough to really recommend that.

 

[whatismouse]

should i just get one of these crappy chinese things to charge them individually?

https://www.amazon.com/Variable-4Digital-Adjustable-Regulated-Switching/dp/B08FT18FQL/ref=sr_1_2?dchild=1&keywords=60+volt+dc+variable&qid=1616727951&sr=8-2

 

[time2roll]

The 30v 10amp is even less and should get the job done faster. Or save more on the 30v 5a

You may eventually find it has more uses.