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I was wondering what the recommendations are for creating a charging circuit for 2 LiPos when they are connected in series, but as a split rail, shown below.

2 LiPos connected in series, as split rail

Currently I am just disconnecting them and charging them using the sparkfun charger PRT-10217. Previously I have implemented a charging circuit around the MCP73831 for a single LiPo, so I was wondering if it were possible to use two of those in this type of configuration: Two MCP73831

This is of course assuming that I disconnect the batteries from the rest of the circuit first!

Is there anything else I need to be careful of? Thanks

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Since lipos can be very dangerous, and 'assuming that I disconnect the batteries from the rest of the circuit first' doesn't lend much confidence, I advise you make it as fool-proof as possible.

Adafruit has a decent article on multi-cell charging, of which I'll reproduce here. Basically, you'll want a 3PDT switch (not abundant, but available) to switch between connecting the batteries to the load and to the chargers.

Fast charging two lipos

Otherwise, you could just remove the batteries from the circuit and charge them. Whichever method you choose, again, I advise not to assume that the operator (you or another user) remembers to hit a switch in order to avoid a potentially unsafe state of the batteries.

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  • \$\begingroup\$ I'd recommend against paralleling them as in your second circuit: if they're not equally charged, dangerous current could flow. \$\endgroup\$ – Abe Karplus Oct 23 '17 at 20:06
  • \$\begingroup\$ @AbeKarplus Good call -- I removed it from my answer. \$\endgroup\$ – calcium3000 Oct 24 '17 at 1:50
  • \$\begingroup\$ Ah yes, I was a bit more blasé about that then I meant to be. That seems a good way to go. Its probably a good idea to also add some logic to the LED indicators so they only show when both cells are fully charged. Thanks \$\endgroup\$ – Jimbles Oct 24 '17 at 10:15
  • \$\begingroup\$ @Jimbles You never can tell what someone's thought of on the Interwebs :) And yes, I'd take full advantage of that STAT pin: you could put one LED on there (VDD to STAT) for charging and one (STAT to GND) for complete. Or just one for charging with the MCP73832. \$\endgroup\$ – calcium3000 Oct 24 '17 at 12:34
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Connect the balance wires together. Both wires have to be the same type of lithium polymer battery with the same mA-Hours. They use two 2200 mA-H or 2s lithium polymer batteries and connect the balance wires

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