On Aug 24, 1:50*pm, Brian Lawson wrote:
Hey an,

Explain a bit more please. *Be specific for a dummy like me. *Is that
just to charge them, or "shock" the ones that don't want to re-charge,
or what????

Brian Lawson,
Bothwell, Ontario.
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On Sun, 24 Aug 2008 12:42:40 -0700 (PDT),
wrote:



On Aug 24, 9:43 am, "Stupendous Man" wrote:
My in-law knows a lot more than most about electical things. He buys old
devices with bad ni-cads, then charges up a huge capacitor with something
about twice the battery's voltage and zaps it. he says half of them come
back as it toasts the sulfate short-circuits.

* * * * I use a DC mig welder, set at around 25 volts, to zap my 12V
cordless batts for about three seconds. Works OK.

* * * Dan- Hide quoted text -

- Show quoted text -

Old nicads grow whiskers inside that short out the various layers.
The cell is then shorted and won't take a charge. By burning out the
whiskers, you can then get some extra life out of the cell. I've done
this, success rate was about 50%, second time around sucess rate was
nil. Note that you don't do this on the WHOLE pack, just the one
shorted cell. There've have been various circuits to do this over the
years, usually a capacitor is charged up to 25-100 volts, then
discharged through the cell. Charge the pack and check the voltage
across the cell. Repeat until fixed or until you are bored. This
does NOTHING for good cells and will damage them. Also, if the cell
has been shorted any length of time, there are probably one or more
reverse charged cells in the pack, which tends to overheat them and
they then vent electrolyte, the souce of the white grunge you see
inside a dead pack. Some cell designs have a valve which closes after
the pressure vents, some have a puncture diaphragm, once it goes, the
cell dries out. No way of knowing ahead of time which type you've
got. Best bet is to re-cell the whole pack.

Stan