NiCd memory theory
MartyW4500
I know of two explanations of how memory effect is formed in NiCd
batteries. My question is which one is the correct one? Both conditions
come about when a battery is partially drained then recharged on a regular
basis. One theory is that as a NiCd battery charges, crystals are formed
and then the crystals break down during discharge. When a battery is
partially drained the unused crystals become larger when the battery is
recharged, reducing the amount of cell surface area available to store a
charge rather than forming new smaller crystals. The other thoery says
memory effect is caused by gas bubbles building up on the cell plates when
a cell is partially drained then recharged. These bubbles reduce the
amount of cell surface area available to store a charge. Supporters of
this theory claim that a charger with a negative pulse will depolarise the
cell plate and strip the bubbles away thus eliminating the memory effect.
Could it be that the crystal theory is right and the pulse charger is
actually removing crystalline shorts growing thru holes in the insulation
between plates on older batteries?
Mark Fellhauer
Neither theory is correct. Both things you described happen in
NiCads, but memory effect doesn't exist. It was only noted several
years ago in certain satellites in certain orbits with extremely
regular duty cycles. Even then, it only affected performance of the
NiCads a few percent. This was a big deal to the people who
micro-manage satellites and are trying to eek out every drop of life
and performance from them.
NiCads today are formulated to charge normally without dendrite
formation or outgassing. Dendrites big enough to cut through
separators have ruined the NiCad. Zapping them is only a partial
temporary cure.
Chalk memory effect up as an urban legend and marketing ploy. A
marketing ploy that borders on criminal fraud. Face facts, NiCads
wear out. One should only expect maybe 300 charge/discharge cycles of
a NiCad before they need to be replaced, and that's if they're well
taken care of. Depth of discharge determines the life of a NiCad, and
all battery exercisers do is REDUCE the life of a NiCad. Don't buy
any device which automatically discharges NiCads before charging.
They only enrich one person, the guy that made it and sold it to you.
Now I've even seen claims that these devices will help you NiMH
batteries, too. Sheesh! And we we originally sold NiMH's because
they don't have "memory" effect.
I hope that helps,
Mark Fellhauer
KC7BXS
Eric Smith
spar...@primenet.com (Mark Fellhauer) wrote:
>taken care of. Depth of discharge determines the life of a NiCad, and
>all battery exercisers do is REDUCE the life of a NiCad. Don't buy
How does a deep discharge reduce the life of a NiCd cell,
and by how much?
One good reason to discharge it is that some chargers
charge at a constant current for a fixed amount of time.
-- Eric Smith e...@cinenet.net
Mark Fellhauer
On Fri, 20 Dec 1996 17:23:30 GMT, e...@cinenet.net.nospam (Eric Smith)
wrote:
>spar...@primenet.com (Mark Fellhauer) wrote:
>
>>taken care of. Depth of discharge determines the life of a NiCad, and
>>all battery exercisers do is REDUCE the life of a NiCad. Don't buy
>
>How does a deep discharge reduce the life of a NiCd cell,
>and by how much?
Depth of discharge is directly related to the amount of chemicals used
in the conversion process of chemical reaction to electricity.
Deeper discharges use up more of that potential. In most cases
upping depth of discharge from 10% to 20% on a regular basis can
reduce cell life by as much as 60%! So you can see why discharging a
battery before charging EVERY time can be so damaging.
>
>One good reason to discharge it is that some chargers
>charge at a constant current for a fixed amount of time.
Not a problem. Constant currant charging won't hurt a NiCad as long
as the battery isn't left on the charger too long or charged at too
high a rate. Remember, memory effect is only a scam perpetratred on a
technically feeble minded public.
Mark Fellhauer
KC7BXS
spar...@primenet.com