zapping NiCAD Cells

Roger Hill rhill at
Sun Jul 13 22:50:41 MDT 2014

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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