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Nicad battery rejuvenating

Discussion in 'Electronic Repair' started by Lenny, Nov 21, 2004.

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  1. Lenny

    Lenny Guest

    I found a number of Dewalt 18V cordless tool battery packs of the same
    rating at the dump and was able to use good cells from one to repair
    some of the others. Afterwards, I decided to see if I could bring any
    of the dead ones back. I charged up a 1500MFD cap to 60V and
    discharged it across each dead cell and then attempted to charge them
    at a rate equal to 10 percent of their rating. While some would not
    budge others seemed to come up and so one by one I charged them for
    almost 20 hours at this rate. They all reached over 1.30 V at what
    appeared to be full charge. I marked each one after I finished with it
    so that I wouldn't inadvertently try to charge it again. After I
    finished with the last cell, I went back to look at the ones
    previously charged and to my surprise only one or two were at 1.25V.
    Some were reading below 1.0 V but almost all of them had gone dead
    again. It seems to me that I had employed a similar technique
    mentioned above in the past to revive dead nicads with some success
    but this time it was different. Can anyone comment on my experience
    here? Did I over blast these things or perhaps were they just really
    dead horses to begin with? Or perhaps others have used a different
    procedure in the past with more success. Thanks. Lenny Stein, Barlen
    Electronics.
     
  2. Harvey

    Harvey Guest

    I've managed to get some life into dead nicads before now by blasting a few
    amps through them (5A or so) for a few seconds to get them working, then
    cycle them up and down half a dozen times on a fast charge/discharge cycle.
    It works about 50% of the time - the ones that work get about 50-80%
    capacity, the ones that don't get about 2% capacity and end up in the trash
    (err.. I mean 'they are recycled'.)
     
  3. NSM

    NSM Guest

    | I found a number of Dewalt 18V cordless tool battery packs of the same
    | rating at the dump and was able to use good cells from one to repair
    | some of the others. Afterwards, I decided to see if I could bring any
    | of the dead ones back. ...

    Sometimes you can burn out internal shorts. Sometimes they're just plain
    dead.

    N
     
  4. mike

    mike Guest

    Cells grow pointy things on the plates that punctures the separator
    causing the short. Your mission is to blow out the short without
    hurting the insulator further. You may have overkilled it.

    BUT
    Problem is that the hole is still there in the separator and it will
    leak. And probably short again eventually.

    I've had mixed results zapping nicads. Self discharge rate is often
    high, but if you use 'em right away, you can sometimes get some use out
    of 'em.

    Most of the failures of drill batteries has been heat due to seriously
    overcharging them. Don't think I've ever successfully recovered one of
    those.
    mike

    --
    Return address is VALID.
    500MHz Tek DSOscilloscope TDS540 $2200
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    Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
    Bunch of stuff For Sale and Wanted at the link below.
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