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I sent the previous message from MS Exchange operating under a web
browser. It apparently mangled it. Here it is again sent a differen=
t
way.
* * * *
My knowledge of this comes partly from personal experience and partly
=66rom lots of reading of various sources. Nonetheless, there seems =
to be
considerable confusion, and I do not claim to have perfect answers. =20
It seems clear it is better to discharge NiCad batteries nearly
completely before recharging. Otherwise they suffer what is referred=
to
as a "memory effect" that reduces their ability to deliver a full
charge. Some NiCad rechargers can be set to further discharge a
partially discharged battery before charging it. This is generally
known as "conditioning" the battery.
=20
It seems clear it is not good (indeed very destructive) to completely
discharge the lead-acid battery in your car. A single case of comple=
te
discharge can ruin the battery.
=20
It is not clear that the degree of discharge before recharge has much
affect on the lifetime of NiMH batteries or Li-ion batteries. Most
sources say these batteries do not suffer a "memory effect" and can b=
e
deeply cycled or shallow cycled without long term consequences.
Nonetheless, the batteries do have a finite number of cycles before t=
hey
need to be replaced. The point is that this number of cycles does no=
t
seem to relate nearly as much to the depth of discharge for these
batteries as it does for NiCad or lead-acid batteries.
=20
I have a fairly large number of NiMH batteries I use in a digital
camera. CD player. GPS, Celestron Telescope, etc. I have run
charge/discharge cycles on these in which I have plotted (with a char=
t
recorder) many charge discharge cycles under various depths of
discharge. I have not been able to discern any pattern that seems to=
be
better or worse for these batteries, so I am inclined to believe the
advertisements that claim you don't have to follow any particular
regimen for these batteries.=20
=20
I am using a recharger specifically designed to recharge NiMH batteri=
es
(Maha is the manufacturer). Rechargers specifically designed to
recharge NiMH batteries recharge at a high current, then switch to a
type of trickle current when the battery is nearly charged. But it i=
s
more complicated than that. The microprocessor initially charges the
battery with a high current that is pulsating. Then it switches into=
a
steady mode and monitors the voltage over time. When it detects a
voltage peak it goes into a "trickle mode" in which it alternates no
charging with low charging (rather than a continuous low-level
charging). It is something in the neighborhood of 10 minutes of no
charging cycled with 2 minutes of trickle charging.
=20
This shows that battery manufactures are playing with recharge method=
s
in an attempt to squeeze out more recharge/discharge cycles before th=
e
batteries needs to be replaced. In my experience they are having som=
e
degree of success with NiMH batteries. I do not have much experience
with Li-ion batteries.
=20
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu