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

Discussion in 'The Projects Forum' started by Supernerd Sven, Feb 16, 2015.

  1. Supernerd Sven

    Thread Starter New Member

    Feb 16, 2015
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    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!
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    The stepper is intrinsically current limited, so crank away.

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

    Thread Starter New Member

    Feb 16, 2015
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    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!
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    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.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    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.
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Unless you're planning on trekking in the desert or jungle using it as a hand charger, i wouldn't bother!
     
  7. Supernerd Sven

    Thread Starter New Member

    Feb 16, 2015
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    0
    Thanks for your input, everyone!
     
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