On Sun, 28 May 2006 19:57:15 +0100, Andy Hall
wrote:


Voltage depletion is probably a more accurate term,

Voltage depression if you really want to be accurate. It is caused
by overcharging - nothing whatsoever to do with the mythical "memory
effect".

but most people haven't
heard of that, so "memory effect" has become used to refer to a number of
phenomena that cause problems where poor quality NiCds are charged
inappropriately with poor quality chargers.

Which of course affects NiMH far more severely than NiCd.

Of all the rerchargables I have had so far the Nicads have shown to be
the most durable ..

Provided that they are good quality ones, properly charged with a decent
charger then that may well be true.

NiCd is always more durable than NiMH with an equivalent quality (or
lack of) charger. The ones to avoid are the "5 hr" chargers. NiCd
can be happily charged at a 10 hour rate with almost anything, and
will tolerate 36 hours at this rate quite happily. NiMH won't.
Either, with an appropriately designed charger, can charge in
anything from 30 mins to an hour - but it reduces cell life, more so
for NiMH than NiCd. In any situation NiMH is good for about half the
number of recharge cycles of a similar NiCd battery.

The problem with the 5hr (or thereabouts) chargers is that they are
essentially uncontrolled and a 5 hour rate cannot be sustained for
any length of time without damaging the battery. Used with a time
switch they are adequate but no more. The safest way of charging
batteries, and the one which gives best battery life, is to charge at
one tenth of the cell capacity for about 11 hours.







--
Peter Parry.
http://www.wpp.ltd.uk/