Re: Non-exploding NiMH batteries

In article <J1r9vF.MA3@xxxxxxxxxxx>, Wilson Heydt <whheydt@xxxxxxxxxxx> wrote:
In article <e865pk$6f7$1@xxxxxxxxxxxxxxxxx>,
D. Glenn Arthur Jr. <dglenn@xxxxxxxxx> wrote:
In article <J1pK0y.6tD@xxxxxxxxxxx>, Wilson Heydt <whheydt@xxxxxxxxxxx> wrote:
In article <e84na6$ql9$1@xxxxxxxxxxxxxxxxx>,
D. Glenn Arthur Jr. <dglenn@xxxxxxxxx> wrote:
In article <ddfr-81C81B.12301128062006@xxxxxxxxxxxxxxxxxxxxx>,
[...] A lead-acid automobile battery
_is_ a battery, as it comprises multiple cells (eight, I think,
but I'd have to go pop the hood of my car and peek to be sure).

6...the nominal voltage for Lead-Acid is 2v per cell. If you had
a NiCad, it'd be 10 cells.

Of course, if it were NiCd, I probably wouldn't be able to tell
just by looking at it, because it wouldn't have those holes for
topping up the water. ;-) (OTOH, I already knew that NiCd
cells are 1.25V, so I wouldn't have had to look.)

You still use a car battery that you have to add water to?

Sort of. I'm not supposed to have to add water. I'm probably
not supposed to be able to add water. I don't expect to ever
need to add water until sometime after the warranty expires,
in that short window between realizing the warranty has expired
and coughing up the money for a new battery[*], and even then
it's a 'maybe'. But IIRC, with a little effort I'll be able to
open it up at that time if I need to. (I know I could on my last
one, which was also never supposed to need it; I'd have to go
look to see whether I'm remembering corectly about the current
one. If it's one of those seamless-flat-top beasties, then no.
But I think it's got vent covers.)

Hmm. Since I know that lead-acid cells can be charged to slightly
more than their nominal voltage, and alkaline and ... uh, whatever
chemistry is in "regular" and "heavy duty" AA cells start out
higher than their nominal voltage (I don't happen to know whether
NiCd and NiMH do this as well, though I've got a wild-ass guess),
how do they decide what the _nominal_ voltage _is_? I'm guessing tha
t it's not just an arbitrary "nearest round number" thing (is it?).
Is it something like, uh, what it puts out under a particular load
(different from the load of a normal voltmeter), or the middle of
the voltage range observed during a particular portion of the
discharge curve, or what?

I dunno. I do know, though, that if you measured a Lead Acid under
heavy load, you'd conclude that the voltage per cell was a bit over
1 volt...and it's a worse drop for Ni-Fe (Edison) cells.

Yah, if you leave the meter hooked up when you crank the starter,
it drops way down. Helluva a load, that starter motor. First
time I saw that I thought it meant the battery was hosed, then I
found out it was the expected normal behaviour.

Where might I have encountered an Edison cell? Is that what
old fashioned AA/C/D cells (i.e. regular or "heavy duty" but
not alkaline) are? And lantern batteries?

Hmm. I wonder how many battery technologies I've used. I know
I've used Li-ion, NiCd, Hg[**], Zn-air, Ag, NiMH, and of course
alkaline and Pb-acid. I wonder whether there are any others in
devices I never peeked inside.

Are NiCd cells still around, or have they been superceded by
Li-ion and NiMH? (Alternate form of the question: are there
applications for which NiCd is still the best solution?)



[*] There's an aspect of lead-acid batteries being a "mature
technology": the manufacturers know really well just how long
most of 'em are going to last, and set the warranty period
right before that point. You seldom have one go bad early and
collect on the warranty, and having a battery need to be replaced
within three months of its warranty expiring is pretty common.
(And once in a while you might get an extra eight months or a '
year out of one ... but in general you can look at the warranty
when you're shopping and know approximately when you'll be buying
the next one.) Except that I never remember that long, so my
usual clue is that the battery starts going south and then I look
and see that the warranty expired the previous month. I imagine
folks who baby them or abuse them see different results, but
for typical driving patterns using a battery big enough for your
car and climate, they seem to last pretty much as long as the
manufacturers promise and not much more.

[**] The Hg cell was replaced with a Zn-air cell when it died,
of course. (Anyone wanna play guess-which-camera?)
--
D. Glenn Arthur Jr./The Human Vibrator, dglenn@xxxxxxxxx
Due to hand/wrist problems my newsreading time varies so I may miss followups.
"Being a _man_ means knowing that one has a choice not to act like a 'man'."
http://www.radix.net/~dglenn/ http://dglenn.livejournal.com
.

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