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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:

enter image description here

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

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  • \$\begingroup\$ No, this won't work, because the "Cell 2 charger" is charging one cell, but the "Cell 1 charger" is charging both cells. \$\endgroup\$
    – uint128_t
    Commented May 14, 2016 at 19:16
  • \$\begingroup\$ @uint128_t, I've corrected the circuit. \$\endgroup\$
    – Cerin
    Commented May 14, 2016 at 20:03
  • \$\begingroup\$ the two USB ports would have to be floating (i.e. unconnected) to each other.. which seems more of a hassle than a solution \$\endgroup\$
    – Wesley Lee
    Commented May 14, 2016 at 20:11
  • \$\begingroup\$ @WesleyLee, Why would they have to be unconnected? \$\endgroup\$
    – Cerin
    Commented May 14, 2016 at 21:09
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    \$\begingroup\$ 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. \$\endgroup\$
    – Sam
    Commented May 14, 2016 at 23:49

1 Answer 1

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Yes potentially it will work, but it will not work if both USB power inputs are connected together

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.

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  • \$\begingroup\$ I see your point. If I want to use a common input supply for both chargers, such as the external 8.4V, what's the solution? Is there any way to isolate them? \$\endgroup\$
    – Cerin
    Commented May 15, 2016 at 0:21
  • \$\begingroup\$ I think it would be simpler to use a two cell charger. \$\endgroup\$
    – Jasen Слава Україні
    Commented May 15, 2016 at 3:04

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