Jack.Winslade@f2.n285.z1.fidonet.org (Jack Winslade) (07/23/90)
I can assure you first-hand that zapping nicad cells does not fall in
the same category as the 'Mouse in the Soda Bottle' and the 'Kentucky
Fried Rat'.
Two people with whom I work (one a CBET, the other a PhD.) have made
nicad zapping devices. I have used both. They work.
I should qualify that by saying that in SOME cases, SOME shorted nicad
cells can be brought back to life by the careful application of energy
from a charged capacitor. Using this technique will not, however,
restore old, dead, cold-in-the-morgue nicads back to their original
virility.
The technique seems to work best on relatively new nicads that
seemingly will not take a charge. A good candidate would be a cell in
a 'stack' that shows zero volts, while the others in the stack show
normal or close to normal voltage.
Here's the tricky part. By trial, error, and experience, you must
gain a 'feel' for just how much energy it will take to burn out the
short without significantly damaging the rest of the cell. The zapper
will usually have a potentiometer to vary the charging voltage, and
maybe a switch to select a couple of different values of capacitors.
The idea is to let the shorted area dissipate almost all of the energy
stored in the capacitor -- that being in the form of the heat that
burns open the short. After the short is burned open, any additional
energy will be dissipated as heat by the good portions of the cell
itself. This can damage it.
A couple of caveats. Zap one and only one cell at a time. NEVER zap
across a battery ('stack') of more than one cell. If you do, most of
the energy will be dissipated in the form of heat in the good cell(s),
and it will have almost no effect on the bad one. If one zap burns
the short out, do not repeat it '... to see if it gets even better'.
Charge it and use it. If a zap does not burn out the short, raise the
energy a bit and try again. Stop after the first zap that
significantly raises the impedance of the cell.
In some cases, zapped nicad cells will appear to have close to their
rated capacity for close to their rated life. In other cases, they
will be weaker and fail prematurely. I would not recommend this
technique on cells used in critical applications, such as in
defibrillators, but for use in cellular phones, I don't see any major
problems. If it works, you've saved the cost of a new pack, if not,
well at least you've tried.
Good Day! JSW
[1:285/666@fidonet] DRBBS Technical BBS, Omaha (1:285/666)
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