NiMH batteries discharge

Discussion in 'General Electronics Chat' started by CVMichael, Jan 9, 2012.

  1. CVMichael

    Thread Starter Senior Member

    Aug 3, 2007
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    17
    I have 8 NiMH AA batteries in series, and they have a different discharge rate (even though they are new batteries), therefore having some batteries going on the negative side, while others are still 1.2 Volts.

    What can I do to protect each battery to discharge below a certain voltage, like 0.9 Volts (edit, 1 Volt) ?
     
    Last edited: Jan 9, 2012
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    718
    Never discharge below 1V/cell unless you know what you are doing, such as in a battery analyzer, where you can go to 0.7V/cell individually to revive them.

    If they've gone negative, revival is usually not possible.

    I'd add a cutoff circuit for 0.9V/cell in the electronics, and a low battery warning at 1V/cell
     
  3. CVMichael

    Thread Starter Senior Member

    Aug 3, 2007
    416
    17
    OK, 1 volt then... I edited my first post.

    The question remains... what to do (schematic ?) to prevent from over discharging?
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Often a Zener diode to turn on a MOSFET transistor to allow current. When the Zener hits the cutoff point, a high value (1M-ish) resistor in parallel with the Zener will discharge the MOSFET gate and turn the MOSFET (which allows all current to the rest of the circuit) off.

    Do a search for low voltage cutoff circuits and you'll find many.
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    A controller that monitors each cell voltage and disconnects the load when any of the cells is depleted.
     
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