I have a device that needs a constant power supply and can only use batteries as an energy source. Using multiple batteries, I can swap a drained one for a fully charged one. Since I have to have a constant power supply, I want to install a smaller (lower mah) battery that will supply power during the swap. After I put in the larger (higher mah) fully charged battery, both batteries will contribute power in parallel.
All batteries are Lithium ion 3.7V (only different mah) . The problem arises when I swap batteries. If the difference in voltage between two batteries connected in parallel is greater than 0.2V a huge rush in current is transferred until the batteries equalize. This could be a problem…
The larger battery will need to recharge the smaller one. Would putting in a resistor between the small and large battery do the trick? Or do I need a more complex protection circuit?
Thanks in advanced!
Best Answer
A simple diode-or circuit will handle this. Connect a diode from each battery's positive terminal to VCC; when you plug two in, only one will supply load if it's at a higher voltage. If the voltages are close or identical, they will load-share. When you unplug a battery, the other one will take over.
Charging lithium ion batteries is a complex task, best handled by a dedicated charge controller. Instead, why not use two identical size batteries, and simply swap them over by plugging one in before unplugging the other?