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.

"Lenny" wrote in message
om...
[...]

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'.)

"Lenny" wrote in message
om...
| 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

Lenny wrote:
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.

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

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