zapping NiCAD Cells

Richard richard1941 at gmail.com
Sat Jul 19 23:20:47 MDT 2014


You reminded me of the old procedure for magnetizing an iron bar.   Wrap it
with heavy insulated wire, and wire it in series with a much finer wire that
acts as a fuze.   Then plug it in.   Current rises as rapidly as the AC
power waveform and the inductance will allow until the fine fuze wire blows.
The current gets very high, more than enough saturate the iron bar beyond
its magnetic capabilities.

The fuze wire must be fine enough to blow in a small fraction of one cycle
of the 60 Hz AC power.

I tried this method when I was about 15.   My dad smelled the burned wire
and came running in.   When he saw what I had done, he was really angry.
But the house circuit breaker did not blow.   I guess my fine fuze wire was
fine enough. 



-----Original Message-----
From: hhc-bounces at lists.brouhaha.com [mailto:hhc-bounces at lists.brouhaha.com]
On Behalf Of Roger Hill
Sent: Sunday, July 13, 2014 9:51 PM
To: Handheld Computing Conference discussion list
Subject: Re: zapping NiCAD Cells

Hi all,

The capacitor method would undoubtedly be better, though my model train
power supply did work every time for the cells in HP printer (or tape drive)
battery pack.  I didn't aim for any particular amount of power applied.

Actually, I do use a 3500-uf capacitor charged up to 30+ volts to operate
the electromagnets used to throw the track switches on my model railroad
layout.  The switch machines have coils designed to operate on 12-15 volts
AC/DC, but by giving them a good "wallop" from the capacitor they are much
more powerful, and because the pulse is very short, the coil is less likely
to burn out (which could happen if a steady voltage is applied for too
long).  I use relays and other capacitors to control the time (around 1
second) for charging the main capacitor so that it is ready to throw another
switch.

Looks like the recommended procedure (below) is similar to my
switch-throwing circuitry but with a bigger zap.  And agreed, the zapping
procedure can effective for cells that won't hold their charge (due to
shortage from internal conducting "whiskers" or filaments), but would
probably not be effective from a cell that is weak for other reasons (or has
too many whiskers).

-- Roger

------------ On Richard N's messages ------------

> The usual procedure is to charge a capacitor and discharge it into the 
> cell. This provides an energy controlled pulse.  Check the Internet 
> for UF values and voltages.

> "To zap a NiCd battery, a 47,000mF capacitor is charged to 90V, after 
> which the raw power is discharged directly across a single NiCd cell 
> of 1.2V. After the shock treatment, the cell is cycled and then zapped 
> once more. Experts say that once a cell is treated and used in 
> service, zapping will no longer improve performance, nor does it 
> regenerate a weak cell."
 

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