Help with a hand-powered AA (probably NiMH, right?) charging circuit

Thread Starter

Supernerd Sven

Joined Feb 16, 2015
6
Hello everyone, I've salvaged a stepper motor that puts out a couple of volts when being turned at a reasonable rate and would like to use it in a battery charger. I have a varying voltage and current depending on how quickly I'm cranking the motor, so I'm thinking I need to construct a voltage regulator to keep it at 1.2V per battery and a circuit to cut off charging when the battery is full.

The trouble is that I'm new to working with batteries and I don't know the details. For example, I'm not even sure whether or not it's a problem to be using a voltage a little higher than 1.2V per battery, and I don't know current I should try to maintain, or how I should determine when to stop charging. Any help would be greatly appreciated!
 

MikeML

Joined Oct 2, 2009
5,444
The stepper is intrinsically current limited, so crank away.

Your are going to get tired before the battery is full...
 

Thread Starter

Supernerd Sven

Joined Feb 16, 2015
6
The stepper is intrinsically current limited, so crank away.

Your are going to get tired before the battery is full...
Are you saying that I can just crank away without worrying about overcharging it or causing any other sort of damage?
Also, I just checked its current output and it's capping at a few hundred milliamps. That seems like a fair amount to me... are you sure it's fine?
Thanks for replying!
 

Bernard

Joined Aug 7, 2008
5,657
You might add gears or pulleys to boost RPM, & use one shottky diode to rectify the AC output. Can add a V detector with LED indicatoe to show when single cell reaches 1.46 V.
 

Kermit2

Joined Feb 5, 2010
4,162
even if it puts out 500 mA you will have trouble 'cranking' that handle for the whole 120-150 minutes required to charge a single 1000 mAh battery.
 
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