Recharging alkaline cells

Recharging alkaline cells

Post by HWells.El_Segu.. » Fri, 23 Jul 1993 00:01:55

Sorry for the late contribution to this subject, but I'm about a week behind in
reading my E-mail.

Several years ago I performed several experiments with charging techniques for
alkaline PRIMARY CELLs.  All of the results were NEGATIVE when compared to
recharging cells such as NICAD.

In primary cells, one of two electrodes is consumed as energy is released and
the process can not be reversed by a charging technique.  What I was able to
determine was that a pulsing DC charge tended to remove or temporarily displace
gas bubbles exposing a greater electrode surface.  The result of the
"recharging" was an apparent rejuvenation of the cell.  But the life of the
cell, at a specific current drain as compared to an "uncharged" cell, ended up
being the same.  In plotting the discharge curves for each of the cells, the
"recharged" cell exhibited a small lift in the voltage curve at the point of
recharge, but the drop-off in the curve that followed was characteristic of a
NICAD at discharge - a sudden drop with the termination point of the recharged
cell being equivalent to the uncharged cell.

During the experiment, I also tried using a steady state/constant current
charge.  The results were very conclusive:  EVERY cell that was recharged began
leaking electrolyte within a matter of hours.  The charge current values were
varied, actually decreased as the experiment evolved in an attempt to find a
current value that would not cause the cell to weep.  Even a 1/2 ma of charge
current on a AA cell caused weeping after a time period.

The conclusion of my experiments was that there was NO ADVANTAGE in attempting
to recharge alkaline cells.  In fact, besides being a waste of time, the
leaking electrolyte caused severe damage to my "charger" and workbench.
Fortunately, I did not have a cell explode as was reported by others during
this discussion.

Hugh Wells,   W6WTU