I’m working on a project that I want to charge via USB
Right now I have it working with a 1-cell lithium ion battery charging with an MCP73831
I would really like to upgrade to 2 separate 1-cell lithium ion batteries in series
To charge them I was thinking of making a balance charger using 2 mcp73831 IC’s. The issue is if i just connect them directly they will have different ground levels. My idea to get around this is to use a P-channel logic mosfet to separate the two batteries when 5v is applied to USB and an N-channel logic mosfet to connect the unconnected “-” terminal on the battery to ground. (see attached schematic)
A.) Am I nuts? or is this a plausible idea
B.) My concern is in the event that the P channel mosfet fails and the N channel works it will be basically shorting one of the batteries (also if the n channel switches prior to the P channel there will be a short is there a way I can protect from this
C.) if the mcp73831’s fire up prior to this switching occuring it might freak them out if they sense the voltage of the packs in series rather than individually
D.) if there is an easier way to do this and still be able to charge via USB I’d be ok with this, I don’t need to be able to charge them separately so I could have just a single 2s pack.