How to balance charge a 12s battery pack

I’m about to start building on a few battery packs for my new build and I have one issue that I haven’t quite figured out yet, so I’m hoping you guys can provide the answers. So, these packs are going to be 12s4p, and what I am having trouble with is in regards to balance charging these. From what I understand, the highest number of series that can be balanced is 10. I’ve seen they used to offer some chargers that would go above, but they didn’t work well, and are no longer offered. On a YouTube video I saw, a man solved this by simply making the connection in the center no longer connected, thus giving 2 separate batteries now 6s4p. One thing I want with my setup is to basically never need to open it again, so any port or connector, all be wired to the enclosure so I can plug everything I need to it. So is there a way to say, make 2 6s4p packs (or whatever size, mainly anything over 10s) and have 2 charging ports, one for each, yet use only 1 BMS for them? Or is this something that I’d need 2 BMS’s, and to go inside the board each time to deal with balancing…?

Why not use a 12s BMS? You’d have just one charging port.

Well yes I will most likely do that, but sometimes they aren’t very reliable, and balance charging specifically from that type of charger is best.

You may get better balancing from a balance charger but then the cells aren’t protected while discharging.

@mmaner has some coming that would would great with a 4p pack

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Oh? I just looked at that post a few min ago. Those are bestech right? Is that the best brand for BMS’s?

if you make paralle 6s charging lines in addition to 12s line, you can use cheap rc charger.

which im doing. now u have 4 charging port to deal with

I didn’t really understand what you said… Could you rephrase that please, lol.

Yes those are bestech, best brand for bms? I can’t say, but I know a lot of people use them and I haven’t seen any issues. That specific model has an e-switch so there’s no need for an anti-spark switch or loop key.


Oh well I really love that, I was reading that thread where all the anti spark units were all failing…

There’s a few approaches, but BMS will be more convenient.

  1. 12s balance charger. there are a small handful.

  2. break connection at middle, charge as 6s

  3. put 12s bms on charger side

  4. find a separate battery balancer

For #1, you can do tricks, like breaking the series connection with a loop key that’s panel mounted.

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Stand alone E-switches are notorious for failure but the Bestech built in E-switch is dependable

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Yep, BesTech BMS’s. The best BMS’s in my opinion.

So you can make 12s battery and outputs 48v and if you hi jek between the 6s cell make additional line of balancing cable and charging port, now u have 1+4= 5 power port

it is a bit complex system hard to describe in words. I think I can build a switch btween 12s and 2*6s for additional safety

but u can charge quick safe and cheap. and you dont have to open the box ever.

drawback is now you have 4 ports outside instead of 1. and if you dont have cover ports can damage and corrode from water.

I should mention, you don’t have to break the connection if you charge 6s at a time. If you try to series or parallel charge two 6s packs that are still connected 12s, you’ll probably see fireworks, from the common ground somewhere.

here’s a picture of a really well done split 6s trick (might not be 6s) with ebike. Follow the link in the link for more detail

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So basically, I shouldn’t worry about it as long as I have a proper BMS then?

I guess I could build 2 packs each with its own BMS and then connect them with one of those 3 sided series connectors, and each charging port would be able to balance, I’d just need to connect an extra set of sensor wires for each pack to also be hooked up when balancing. So there should be a set going to the BMS and another could be mounted to the enclosure for balance charging.

BMS is not magic – you should always worry. There are many failure modes BMS won’t help you with.

And I’ll caution once more (I couldn’t understand what you were saying). If you try to charge 2 subpacks that are still series at the same time (with 2 chargers, or with parallel charging), it’ll most likely blow up due to shared ground.

Well yeah, that’s why I’m asking about balance charging, without the BMS. If I thought that then I wouldn’t concern myself with this stuff.

If I was to have 2 separate packs with 2 separate chargers, I would connect them with a series connector, but disconnect them when charging. (to avoid the shared grounding)

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Do any of you guys run a 12s, and if so, how do you charge… or rather, do you charge it any differently than normal?