I've got a robot that I use two batteries on. One of the batteries power the servos and engines and the other is for the digital boards.

  • The servos need 5 V.
  • The control board and LCD run on 5 V.
  • The engines use 12 V.

Both batteries are identical 12 V packs (3x 18650) each with their own BMS.

The robot is using DC-DC 12 V to 5 V step down converters to get appropriate voltages to the different parts.

I want to be able to charge both batteries from one 12 V source but also keep them isolated so the motors battery cant take juice of the digital battery and vice versa.

Can I use diodes on the 4 lines (2+, 2 Ground) coming from the single charger two for each battery to accomplish this separation?

Should I put a diode on each side of each battery or for example only on the ground or volt?

Is there a better way?

The lines between the Arduino and the controller don't link the batteries in any way. But the common charged does which is the problem I want to solve.


  • \$\begingroup\$ What kind of circuit do you have in mind? I really can't envision a case where this power flow problem can be solved with a diode, but I also don't know everything nor have in my head what you have in yours – please draw a schematic explaining what you have in mind!! \$\endgroup\$ – Marcus Müller Nov 4 '18 at 12:52
  • \$\begingroup\$ thanks for the schematic, but where do you want to fit in the diodes? \$\endgroup\$ – Marcus Müller Nov 4 '18 at 14:08

Essentially you are asking how to charge a 3s2p pack. The better answers will involve battery balancing. A process which, in the most rigorous examples, involves extra wires to every battery terminal and a processor controlled charger.

Likely, the simplicity of using 2 independent chargers on 2 independent 3s1p packs outweighs the complexity of balancing a single 3s2p pack. Even more so as the 2 independent 3s1p packs will have different power demands and therefor different charging histories.

  • \$\begingroup\$ each 3s1p battery pack has BMS and so have to barrel jacks coming from them for input and output. the BMS lets me charge them together but the cables also makes it behave like a 3s2p pack which is bad as the engines introduce noise and also can reset the digital board if they stall. \$\endgroup\$ – Ekim Nov 4 '18 at 13:49

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