I salvaged some components out of a cordless phone, including a nimh battery pack with what appears to be two AAA batteries in series... I'm curious as to whether I can use these in a circuit somehow with the abiility to recharge them while the circuit is powered via USB or perhaps a solar cell. I do know LiPo and LiIon batteries need special circuitry to manage the charging, but I'm not sure about the NiMH batteries... Anyone know if this is easily doable?
If you have a variable supply try charging (current limited) to 1.35V per cell,
then discharge through a load to 1.2V per cell (monitor both cells) and repeat
if capacity is poor.
Suggest a current limit of about 1/4 nominal capacity (4 hour charging
rate).
Otherwise you'll have to separate them and use a standalone NiMH charger
(these charge two or four AA or AAA cells, typically)
If they've been fully discharged to 0V they won't be too healthy (true of nearly
all rechargables).
I can get ahold of voltage regulators; so since it's two cells in series, should I apply a ~2.7v to charge them? How would I know when it's 'done'?
Best done by current regulation not voltage.this can be just a resistor.
You know when they are done by measuring the terminal voltage