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NiCad rejuvenation

Discussion in 'Electronic Design' started by Jerry Girard, Apr 20, 2004.

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  1. Jerry Girard

    Jerry Girard Guest

    Does anyone know how to rejuvenate a NiCad battery? I have several 1.2V
    cells in an old cordless drill that I want to bring back to life. I
    remember something about 20 years ago that you can zap it with about 70
    volts reverse polarity. I can't seem to find anything on the internet about
    it. Anyone know? Thanks.
     

  2. The best way is to take them out and throw them away and replace the
    cells with new ones of the exactly correct type (or buy a new battery
    pack).

    Yes, there is a way to blow off metallic spikes (that apparently short
    NiCd cells) with a brief high-current pulse, but it generally doesn't
    last very long and it just might blow your face right off your skull
    if the cell explodes, so I'm not going to suggest it.

    Best regards,
    Spehro Pefhany
     
  3. Tam/WB2TT

    Tam/WB2TT Guest

    You may be thinking of gel cells. But it is not reverse polarity. Also, more
    like 20 -30 V.If you try this, remember, they do sometimes explode.

    Tam
     
  4. Ross Mac

    Ross Mac Guest

    http://www.speff.com

    This reminds me of the old picture tube rejuvenators...
    Zap the tube with thousands of volts and it will look better....but not
    much....like you say...buy a new one!
    Have a great one.........Ross
     
  5. The standard rumor is to put each cell across a 12V car battery for a
    few seconds. The idea is to blast away any zinc dendrite (crystalline
    fingers) that are shorting the cell. I've done this a few times with
    lousy success.
    http://www.slams.freeserve.co.uk/Q&A/NiCad FAQ.htm#NICDBATTERY_022
    Do *NOT* do it reverse polarity or more than one cell at a time. It's
    positive to positive and negative to negative, one cell at a time. If
    it explodes in your face, please let me know and I'll apologize.

    Another method that only works with if you're really desperate. I've
    noticed that some NiCd's die an early death due to electrolyte loss.
    The cells are overcharged for various reasons, outgas when
    overheated[1], and KOH (potassium hydroxide) electrolyte is lost. So,
    my bright idea was to notch the edge of the cell with a triangular
    file, and use a syringe to refill the cell with KOH. Batting average
    was about 30% which basically made it a wasted exercise.

    Cordless drills are not known for using the best quality NiCad cells.
    Methinks you're not going to have much luck. If it happens to be a
    Makita battery, there are plenty of online vendors with rebuilds and
    clones for reasonable prices.

    Also, be sure to recycle your old NiCad batteries. Cadmium is a
    rather nasty pollutant.

    [1] Nicads only get hot when overcharged. You can charge a nicad at
    almost any rate you can deliver, without any overheating, as long as
    the cell does not overcharge. I've charged 625ma-hr AA nicads at
    about 12C rate (7Amps) and gotten a 90% full charge in about 5 minutes
    with zero temperature rise. However, I've also exploded cells that
    were even slightly overcharged at this rate. Be careful.
     
  6. If you have, in a string of multiple cells in series, one or two
    cells that seem to be shorted, you can take those out and put
    them on a power supply set at 1.2V and a 10K resistor in series.
    Leave it for 12 hours. After that, if they measure 1V or something,
    you can charge them in a normal way.

    Better is to buy new batteries, but if it's a rather cheap drill,
    throw away all of it, and get something new.
     
  7. Barry Lennox

    Barry Lennox Guest

    I used to have a regular and free source of "D" size Nicads that were
    dodgy, but worth recovering when D Nicads cost real money (25 yrs ago)
    I could recover more than 1/3 of them by momentarily flashing them
    across a 12v car battery. I used to place them on the floor with a
    lump of 4x2 on top of them, and stood on the 4x2 (wearing safety
    goggles and riggers gloves) Never destroyed one, but it was a bit
    tough on the nerves.

    A softer approach I have read of, but never tried, is to charge up a
    big cap, 5000uF? to several volts and let it discharge through the
    Nicad.

    All these tricks are done with the correct polarity!! ( + to +.) Don't
    even think about reverse polarity.


    Barry Lennox
     
  8. JeffM

    JeffM Guest

    I [recall] you can zap it with about 70 volts reverse polarity.


    Liebermann has it mostly right.
    You want something that can deliver a high current for a very short time.
    I've had better luck than he has with zapping,
    with some cells being restored to near-normal service.
    In many cases it *IS* just a stop-gap measure.

    I have poked holes thru the plastic casing of multi-cell packs
    to access individual cells.
    These weren't mine and had been badly abused before I saw them,
    so the efforts were for naught.

    I use a technique closer to the one described by Barry Lennox.
    Make a very good connection to the cell;
    in the jaws of a vise with an insulating layer against 1 jaw works.

    Charge a multi-milliFarad bank to ~40V and dump it into the cell.
    Sometimes it takes multiple attempts.
    Long-term success is inversely proportional
    to the number of trys required.

    I've never seen one explode. Never heard of it either.
     
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