Electrical – MOSFET to connect two batteries in series


I am designing a small bidirectional circuit consisting of two batteries in series as a power source. Part of the circuit will be a charger, to charge the batteries when they are not in use, which is triggered by external circuitry.

The problem I am having is that each battery has its own charging circuit, therefore I think that the must be disconnected from each other in order to facilitate charging.

I had the idea of using a MOSFET which joins the positive of one battery to the negative of the other battery when the circuit is discharging, and then disconnect the two when it is charging. But I am having difficulty implementing this. I have tried simple simulation with PSPICE using only voltage sources however I could not get it to work. Is this possible? If so how can I do it?

Best Answer

While thinking that could be used relays the desired operation, I provided an outline of a possible circuit using MOSFETs. Be especially careful that the control signals must be complementary. The intrinsic diode of M1 does not impose a problem for charger 2, since M3 is conducting in this case. I leave to you the determination of resistors and proper part-numbers.

Series battery -connect/disconnect