On Thu, Jul 29, 1999 at 02:30:33PM +0000, Declan Moriarty wrote:
> I thought Ni-Cd always had memory effect. The one that hasn't
> is Ni-MH, which drains away instead - like a slow puncture ;-).
> The memory effect can be dealt with when it occurs by fully discharging
> the battery (i.e. to bleed power until the voltage halves), and then to
> charge it fully at the fastest rate you can.
The memory effect is a bit controversial as to whether it exists or not
and what effects it has. Ask different people and you will get different
opinions.
Here is what I am given to understand about the memory effect. This is
second-hand evidence, but it sounded credible at the time.
It happens to NiCd batteries when they are overcharged. Overcharging causes
the battery to drop its voltage by several millivolts, but this effect is
reversable. If you drain a charge C from the battery and then recharge it
then the effect will be partially reversed. This means that the battery now
has its full voltage again and will function normally until the charge C has
again been drained. At that time you start using the "old" stored charge
which is still suffering from the memory effect, and the battery voltage
drops by several millivolts. Now, if the equipment is well designed then
it shouldn't mind this small voltage drop and should continue functioning
normally. However, it is possible that the equipment will see the voltage
drop as a sign that the battery has run out, and the remaining charge in the
battery will be unusable.
The fix for this is of course to drain the battery completely and then
recharge it normally, taking care not to overcharge it.
imc
