How To: Make a Y Balancer Harness

[BrianG]

Yes, these diagrams are for charging in series, which is the same voltage as how they are run in the vehicle. Charging in parallel is possible, but not recommended. Differences between end-of-run pack voltages can vary depending on the setup. So, if you parallel connect two packs with slightly different voltages, there will be current flow as the higher voltage pack will "charge" the lower voltage pack in the attempt to equalize. This will cause sparking, and if the voltage difference is too great, can exceed the recommended charge current rating.

Pack voltage difference becomes more of an issue with packs greater than 2s. To get a total pack difference of say, 0.5v, between two 2s packs, each cell would have to be off by ~0.13v. But, for two 3s packs, that same 0.13v difference on each cell would create a 0.8v difference, which could cause problems when connected together in parallel.

If using an Hv ESC, the voltage between two 2s packs will be different because one pack runs the BEC, so it will be drained further.

I'm not saying each pack will be different, but they could be.

The only way I'd parallel charge is 1) if the packs were always hooked in parallel when run and charged since they were new, or 2) balance offline (not hooked to a charger) in series first. Once all cells are balanced, then hook them in parallel to charge. Kind of a PITA IMO.

If your charger is not capable of 6s charge, the above method (2) would be the only way to charge two 3s packs without getting another charger.