bring nicads back to life

Discussion in 'General Electronics Chat' started by lokeycmos, Feb 3, 2012.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    7
    i have a 9.6v nicad battery pack for my cordless drill. it only holds a charge for a couple minutes. i have to constantly keep it on the charger so its ready when i need it. i read that these can be shocked back to life. could someone please explain how this works and will i be able to get it to hold a charge for a lot longer? thank you
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,692
    2,756
    The theory is that, after multiple charge/discharge cycles, metal whiskers grow between the electrodes inside the battery.

    Supposedly, charging a cap to a high voltage and then discharging it quickly into the battery melts the whiskers and restores capacity.

    I don't know how much energy is required to do this, and whether it actually works or not, and, if so, how much capacity is restored. I usually just throw for a new battery...
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You could try to build a "reflex charger" line the NC2000.
    See the attached PDF for more info.

    Bertus
     
  4. K7GUH

    Member

    Jan 28, 2011
    191
    23
    It does work, but you won't get 100% capacity from the pack. Try the zap technique. You have nothing to lose --- either your existing pack is now a paper weight, or you can restore it to some reasonable level of charge. Be careful of the capacitor, as you want 150 volts or so for the discharge time of the cap. It may take more than one zap to restore the pack. You'll know it worked if the pack will then hold a charge for more than a few minutes. Good luck.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    I've restored them with a large capacitor charged to 30V and then discharged across the battery. You probably want a cap of at least 1000μF for that voltage. The larger, the better.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    NO. The insulator has been compromised.
     
  7. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    I've also heard that the zap technique only works for a short time since the electrolyte is left with open tracks for the metal whiskers to quickly regrow into.
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    The reason the cell gets shorted is because the insulator is compromised which lets the shorting bridges grow. The high current zap blows them away but they come back.
     
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