I'm having a hard time grasping the concept of using a mosfet as a relay. I don't have a schematic yet because I can't figure out what the circuit needs to be.

Here's what I'm trying to do:

I have (3) 18650 Li-Ion Batteries and (1) TP4056 charging module. I need the batteries to be connected in series when they're actively powering the load. Then I need to disconnect the load from the batteries and charge them via the TP4056 which they need to be in parallel for. Or I can use 3 individual chargers for each individual battery. Would the Mosfet go between each battery and the TP4056?

Any help, ideas or suggestions would be appreciated!

  • \$\begingroup\$ Alternatively I can charge the (3) cells if I could find the right IC which I haven't been able to. \$\endgroup\$ – Cadmium685 Apr 17 '18 at 1:44
  • \$\begingroup\$ There are chargers that will charge cells in series while also helping to balance them. \$\endgroup\$ – Wesley Lee Apr 17 '18 at 1:56
  • \$\begingroup\$ Buy a 3S BMS board and connect the batteries in series with it. You can charge the batteries via the BMS by supplying 12V to the board. They are not that costly. Implementing the type of connections you want using MOSFETs will probably cost more than the BMS. \$\endgroup\$ – Rupesh Routray Apr 18 '18 at 12:14
  • \$\begingroup\$ Also, TP4056 module will not be able to provide enough current to charge all the batteries at once. \$\endgroup\$ – Rupesh Routray Apr 18 '18 at 12:18

Put a search in DigiKey and filter to see ICs specifically for 3S cell configurations. You can further refine your search for the pack voltage and battery chemistry you are desiring. Then you can do another search for Battery Balancing ICs and again specify for 3 cells.

It wouldn't be prudent to charge them in parallel because it would require more current and the batteries may be at different SoCs (see my newbie question here for more info).

DigiKey Li-Ion Charger Search

  • \$\begingroup\$ Thanks for trying to help the OP. Note that the question is actually from April, though. Most likely the OP is gone for good never to be heard from again. It may be better to focus on newer questions, although I recognize that it is a matter of choice. Your answer may help other people who come along and find this question via search engine. \$\endgroup\$ – mkeith Dec 31 '18 at 1:54

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