Charging two 3S Li-Po packs at the same time

3689443330?profile=originalSimulated charging arrangement. Always use fireproof container for the batteries when charging!

I updated my charged to balancing one a while ago, but for some reason I didn’t buy one of those new multichargers, which pack a number of separate chargers in to one device. I use two 3S battery packs in parallel configuration on my plane and I have three sets of those. After a day of flying, charging six 3S packs separately is a long and laborious task. Since my charger can handle 6S packs, I thought why not to make an adapter cable to charge two packs at once. Since all the cells are rated the same capacity, charging 2x3S packs in essentially same than charging one 6S pack.

The following cables were build:


3689443456?profile=originalFirst adapter combines balancing leads from two packs to one connector. If you look closely, you can see that the ground wire is a little wriggly. When soldering the cable I did not think it all the way through and connected ground wires from both connectors together. When I connected the batteries, one of the ground wires vaporized with a loud pop. So be sure to leave second ground wire unconnected (pin 1 of the 2nd connector).

Second adapter is more obvious, it just connects the two packs in series. I suggest to number the battery connector which ground wire goes straight to the charger with number one and also the balancing connector which has ground wire connected as number one. These numbered connectors should be connected to same battery.

After connecting the batteries, set your charger to double voltage that the rated pack voltage (22.2v in this case) and charging current to the same as the rated charging current of the pack. It does not matter whether the packs are as empty or not, since the individual cells get balanced (although if there are big differences, balancing seems to take time at least on my charger). All that matters is that both packs have the same capacity and can handle the same charging current.

You can also make the same kind of adapters for 2S batteries, or even for the batteries more than 3S. The only limiting factor is that how many cells your charger can support at one time.

You can find schematics to adapters from my blog:

E-mail me when people leave their comments –

You need to be a member of diydrones to add comments!

Join diydrones


  • 100KM

    @Ellison - I have this as well, but it's not the same as Janne's creation. Besides mine being soldered incorrectly, it does not allow the charger to see all 6 cells, only the merged 3 cells. Unless I'm not using it right?

    @Janne - I remember seeing your post a while ago and was thinking the same thing, and made the same mistake re. the second ground pin, both my batteries ground vaporised, but I could save the one battery! Wish I properly read your post before... ;(

  • Distributor

    @Ellison  yeah, using the same thing but with different connectors! this is the way to go! 

  • I also run two 3s packs in parallel, but I didn't want to make the cables.

    Got this instead.  If you got a charger that can support it, you can charge 6 packs at once.  It's only $9.


  • Moderator

    There is a real risk of creating a direct short if not careful, plug the two packs' balance plugs in one way all is fine ("A" plug into "A" socket) but get it wrong ("A" plug into "B" socket) and you create a direct short over 22+V. If I charge 2 x 3S packs then I charge without the balance taps, imbalance is negligible and the next charge will be with balance.

    There's a video here about something similar which explains how the short is created:

    and some more diagrams here:
  • Developer

    i use to do this, but chargers are cheap enough to just have 2 or 5 chargers....

This reply was deleted.