# Combining single cell LIPO chargers into a multi-cell charger

I have a 2S lipo battery that I want to charge. Normally, I'd charge it with a balanced 2S lipo charger like this, but for my application, I want to embed the charger in the device, and consumer chargers are too big.

I also don't want to design my own balanced 2S charger from scratch.

I have several super cheap tiny single-cell lipo chargers like this. Is it possible to combine two of these to make a 2S balanced charger?

The circuit I'm thinking of would look something like this:

Would this work? Is there anything I'm missing? Should I put schottky diodes between the charger output and the positive cell terminal?

• No, this won't work, because the "Cell 2 charger" is charging one cell, but the "Cell 1 charger" is charging both cells. – uint128_t May 14 '16 at 19:16
• @uint128_t, I've corrected the circuit. – Cerin May 14 '16 at 20:03
• the two USB ports would have to be floating (i.e. unconnected) to each other.. which seems more of a hassle than a solution – Wesley Lee May 14 '16 at 20:11
• @WesleyLee, Why would they have to be unconnected? – Cerin May 14 '16 at 21:09
• Because the input grounds and the output grounds of the charger would most likely be connected and if they went to non-isolated USB ports (which also have their grounds connected) the Cell 2 would get shorted out as the ground of Cell charger 1 would be connected to the main ground. – Sam May 14 '16 at 23:49

if you use individual AC to USB adapters ("phone chargers" or similar) it will work, but if you try to connect both Li-poly chargers to the same USB supply you'll have gnd on both Li-poly chargers connected together. if you follow the lines you'll see that that would short-circuit cell2.