* "BurninSidy" <[EMAIL PROTECTED]> on Sun, 10 Jun 2001
| I 've just read some kind of statement about NI-CD and Ni-MH rechargeable
| batteries.
| Is it true that Ni-Mh has no memory effect?
It is more accurate to state that modern rechargeable batteries of any sort
have no memory effect, including NiCd and NiMH.
"Memory" occours in sintered plate NiCd cells used in old communications
satellites, and only under laboratory conditions. It just doesn't happen
in the paste type cells you get at the local Best Buy.
NiCd and NiMH cells are basically the same thing, a paste rolled between
thin layers of nickel. As the cells age, crystals form and grow in the
paste. Charge capacity is inversely proportional to the number and size of
the crystals. This is normal. This is not "memory", though some
mistakenly call it that. NiCD cells have a life of approximately 1000 full
cycles, NiMH about 500. Deep discharging of NiCD (which requires some
specialized hardware) cells can break up these crystals somewhat, restoring
some charge capacity. Deep discharging of NiMH and Li-Ion cells will
render them useless.
NiCD and NiMH cells get very hot when overcharged, and the paste dries
out. Dry paste means no chemical reaction between the nickel sheet and the
metallic paste. That means no current. This is what is colloquially
called "memory", but it is not memory, it is physical damage due to misuse
or abuse, and it is irreparable. NiMH cells are a little more tolerant of
overcharging than NiCD, but it is still a bad thing to do.
Li-Ion cells are impervious to overcharging due to their built-in charging
circuitry, and they have very high charge densitites. But they are good
for only about 300 cycles.
--
Rat <[EMAIL PROTECTED]> \ Ingredients of Happy Fun Ball include an
Minion of Nathan - Nathan says Hi! \ unknown glowing substance which fell to
PGP Key: at a key server near you! \ Earth, presumably from outer space.
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