On Fri, 13 Jul 2007, Jim Lux wrote:
I have never seen a NiCd last that long. One is lucky to get a hundred
power cycles out of them.
Something is seriously wrong.
Typical Lead Acid should take 1000 cycles (where a cycle is full discharge)
NiCds, properly charged and used, should last for tens of thousands of cycles
(e.g. they use them in spacecraft orbiting the earth 14 times a day)
NiMH aren't even doing too well in my copious
supply of rechargable batteries at home. And of course a car battery
that makes it to seven or eight years is more the exception than the
rule.
That's more driven by exposure to high temperatures and vibration in the
under-hood environment.
Yeah, well, empirically the memory effect kills the NiCds way earlier
than that. And I don't think anything is "wrong" -- I think that's just
the way OTC NiCds work. Maybe the space program does it better, but
they probably spend a few thousand dollars each on those 10Kcycle
batteries... and their chargers.
Just as with UPSes, they carefully design the battery charger/life to not be
too long (hence too expensive). It's a sufficiently well understood
engineering exercise that they can draw a fairly accurate graph of charge
capacity vs time (with the variability of mfr and use factored in).
you get real long life in a spacecraft application because they carefully
hand select and match the cells, and very carefully manage the charge and
discharge profiles.
This I believe.
rgb
FWIW, the Mars Rovers use Lithium Ion batteries, with nominally 1000 cycles
life. (which they've exceeded by now)
--
Robert G. Brown http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567 Fax: 919-660-2525 email:[EMAIL PROTECTED]
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