4S+2S=6S?

[rgp1942]

I'm know that creating a 6S battery pack with 2 X 3S in series works fine. But is there any downsize to creating a 6S with 4S + 2S in series? All batteries would be of the same capacity of course. I charge the individual packs separately. By downside I mean safety, capacity, heat, etc. Thanks!

[Twowingtj]

Welcome to Hobby Squawk rgp1942! Short answer to your question is yes. You can run a 4S and a 2S to get a 6S. And you are right with using the same capacity. Ideally you "should" also have them be the same age, C rating, and brand. The reason being, to have the output roughly equal to each other. If they are a bit mismatched, base your flight time and draw on the lowest rated pack.

I fly several birds on 9S using a 4s and a 5S in series and have never had an issue. I buy them together and keep them as a pair.

[fhhuber]

When I put packs in series I make sure they were in the same order from the supplier. Same age, very similar use history (if not always used in series) Identical brand/type, capacity and C rating.

Its like the devices that call for a few AA cells in series. You want the cells to match. Replace just one and the device might work again, but not for long and all you really accomplished is ruining the new cell.

If they do not match you get diverging voltage between cells as they discharge. Since cells never perfectly match, this is why we have to use a balance charger to bring the cells back to all having the same voltage at full charge.

I usually put packs of the same cell count in series because its convenient.

You can also put packs in parallel as long as voltage (cell count) matches. C rating and capacity are not really important. You just go by the lowest C rating (multiplied by total capacity).

Series match capacity and add voltage.

Parallel match voltage and add capacity.