Balance charging on the cheap

[kavic5150]

I just tried balance charging with a 5A battery active balancer that I bought from feebay and wanted to share the results. If this works it will be cheaper than sourcing a balance charger that handles up to 12s. I’ve only found 2 of those and both are in the $200 range. The 5A active balancer was around $60 or so.

So I used the charge (not balance) function and left the 5A active balancer plugged in to the balance lead. It stayed cool at a 2A charging rate and the cells remained balanced within .03v

The new version of this already has a jst-xh connector so you wont have to solder and shrink 15 wires then solder 15 connector pins like I did.

You might have to charge your pack slower than 2A when you go to higher cell counts. Keep in mind that the 5A rating is this active balancers maximum and it doesnt balance as fast when the cells are closer together.

Will experiment with this further and see if the cells remain in balance all the way to the finish. As you can see from the pics I stopped at 4v just to check the progress so none of the cells would go over 4.2v and overcharge.

[kavic5150]

Paused again at the 4.10v mark. Voltage delta has hit .04v so 2A is a bit too fast for this balancer to keep up. The pack is only 6s 4,000mah btw. So maybe 2 or 3A charging can be done until you hit 4.1v then slow things down so the balance charger can keep up.

I should put another 12s jst-xh male connector on this balancer so I can keep the battery checker plugged in while charging.

[kavic5150]

Aaaaand I’ve overshot by .03v. Even at 1.2A charging current the 5A active balancer couldnt keep up.

This is still doable but you’ll have to slow your charging current to a trickle for the last mile. Or maybe charge to 4.1v, then let your pack rest and balance for a bit before finishing the charge.

[JoeyZ5]

What about using a 12s BMS? A smart one is only around $40 and has Bluetooth monitoring and balancing. Just feed in 50.4v and it charges and balances. I’ve used them for my boards running Lipo and Lion.

[kavic5150]

How does its charging methodology work? The concern I have are the BMSs that wait until cells hit 4.21 or 4.22v then bleed off extra current thru resistors as heat. Doesnt that damage cells by keeping them overcharged?

[Andy87]

@JoeyZ5 suggestion is way better in my opinion. I did that for my travel charger and it workday well. With the smart bms you can between active balancing (balancing after the pack was fully charged) or balancing while charging (balancing starts at what ever voltage you plug the charger in). You can also set the bms to cut off at 4.15V for example. No worries that the cells will be slightly overcharged before they get balanced.

I would have a look into smart bms. It’s a cheap alternative to a good balance charger and there are many parameter you can change so that all works how you want. Plus you can check each p-group voltage at every time with your phone.

[kavic5150]

Sounds good for that one BMS in particular. But how many people are using a more primitive BMS? One that waits until one cell hits its maximum to bleed off current thru a few resistors?

[skatebored]

First off, they transfer charge to lower cells. Second, you dont need to limit use to charging. It works full time, and shuts down when they get close enough. So you could leave it plugged in full time. I think it is close to zero drain when balanced.

If they started out balanced when you start charging, then unit could keep up. This would allow charging to 80 or 90 percent full time, and double or triple longevity of pack.

If the connector was mounted on enclosure, then it could be hooked up periodically.

[kavic5150]

Which ones do that? Surely not all BMS have active balancing. Many of them engage resistors when one cell voltage goes too high.

[skatebored]

You could go sans BMS if you had the active balancer.

[kavic5150]

I have the active balancer. Those are my pics.

But a BMS is good for riding around. If one cell happens to go under voltage it can prevent damage.