John Henderson writes:

"ASAAR" wrote:

But adding negative pulses (slightly discharging between positive
charging pulses) supposedly leaves the chemical structure of the
battery in a better state. i.e., the batteries retain their
fullest capacity for a greater number of charge cycles.

As I understand it, PCR (periodic current reversal) has a beneficial
effect on the physical structure of a metallic cathode as it's
formed, rather than a chemical effect.

There are at least 2 effects.

In fact, I believe PCR is required in electroplating, otherwise the
plated material is too spongy to be useful. In a battery, this can
mean dendrite formation.

My own electroplating experiments (without PCR) when I was young
produced very soft deposits.

This has been knowm by electroplates since the year dot. Almost all EP
is done by ofset AC current so as the get a sound solid plate. If the
metal is prone to growing dendrite of crystals, the current reversal
is concentrated at the dendrite and quickly removes it.

The other effect is stopping an `overvoltage' layer forming and the
resultant gassing off. This is also known as surface charge, and can be
quite significant.

Sealed NiCd and NiMH cells generate a lot more heat once they are fully
charged, and this temp rise reduces the series resistance of the cell
*LOTS*. It is this that causes the drop in voltage rise rate on charge
and discharge that can be used to signal end of charge.

Note that with NiCds, charging at low tempps is VERY bad news. Keep
them above 20C at the start. I don't know if this is a problem with
NiMH cells.

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