Charging 7S with 8S Charger

Hey guys,

I have just recently removed a dead cell from my 8S pack, as described in this thread..

New problem is that I need to trick my 8S charger into charging my 7S pack. I have made my own charging port using a D-Sub15 pin plug (essentially a big VGA plug) and now I just cant figure out how to re-wire it to make it work.

This here is my charger:

If someone could draw me a quick sketch, basically explaining how a 8S to 7S JST adapter would look like, id be forever greatful :slight_smile:

Thanks guys!

um is the busted cell still wired in series? if it is not, you just need to make a 7s balance plug…

Hey @Cobber, no I cut it out and re-wired it to be a 3S pack. So I have a 7S battery that is made of a 4S and a 3S Lipo.

Thats exactly what I dont know how to do :slight_smile:

You have 9 pin connector and 9 cables. Remove first or last cable. Use 8 pin connectors. Done. Seriously, not sure what’s bugging you, it’s the simplest thing :slight_smile:

putting un-balanced cells together in a single battery aside… the cells would all need to be in series with the 7 balance wires in a single balance lead… be careful. you will need to watch charge and discharge voltage constantly. you don’t want a fire

The cells were all balanced to ±0.02 difference in voltage :slight_smile:

For sake of simplicity, lets just assume i had a 7S battery with a single 7S balance lead. How do I connect that to my 8S balance lead on the charger? Thats ultimately my question

plug the 7s plug in to the 1-7 cells on your chargers balance port?

Remove the extra wire that’s not connected to any cells…

Does your charger have setting for charging 7s pack, is it configurable in any way?

Well on the manual it says its capable of charging 2-8S batteries and it also originally came with a balance board (its long gone), so i am assuming it can

And do you have 9pin JST coming out of your pack?

along the lines of what sceppy said, what does your balance lead look like? 7 cell balance wires?

No i am hooking up the balance leads into my vga port, so that i have a plug’n’play solution without bms, so i am not actually using the jst plugs on my lipo

Alright, but you do have pin 0 (gnd) - pin 8 (v+) and getting around 29,4V across them?

I have 8 balance leads:

1st pack is 3S:

  • and + first cell,
  • second cell,
  • third cell = 4 balance wires

2nd pack is 4S:

  • first cell (leaving - disconnected as its redundant),
  • second cell,
  • third cell,
  • fourth cell, = 4 balance wires

= 8 balance wires in total

yeah i do, voltages seem ok

Alright, yo need to make a cable that will connect (-) from the charger to the pin 0 on the VGA, following through pin 1 (4,2V), 2 (8,4V)… up to 8 (29,4V). Pin 8 will finish at marking 7 on the charger. 8 on the charger will be free.

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Thank you, i think i got it, i will try in a few hours when i am at home!! :slight_smile:

No problem. If your charger doesn’t have auto detection and selection of number of cells, make sure you switch to the 7S mode. BTW, where did you get the charger? :slight_smile:

I got it from but now its also available on amazon