Battery Pack Fundamentals
Mark Willis email (remove spam text)
Graeme Smith wrote:
> Hi Guys....
> <snipped a bit>
> The battery pack is supposedly a NI-MH type, rated at 12V and 2.2A for
> 10hrs. it has 10 "Sanyo TWICELLS" rated at 1.2V each.
> But a similar phone pack, using the same Ni-MH technology, has cells rated
> at .6v each.... Am I right in assuming they are hiding two cells in the
> TWICELL cylinders? and that the base voltage of a Ni-MH cell is .6V?
> Or are the phone cells simply under-charged?
> GRAEME SMITH email: freenet.edmonton.ab.cagrysmith
> YMCA Edmonton
(Tired so I'll partially reply, need to go sleep here <G>)
I'd expect 3.6V not .6V (1/3A cells - 3 in series - would come out at
3.6V, they make a wide variety of "sub" and fractional sized cells.)
NiMH cells are definitely 1.25V (or so) apiece, normally. You want to
charge NiMH cells a little differently than Ni-Cad's, read up on it
before trying to just dump power in there <G>
Usually the cells are rated in milli Amp Hours (mAH), that's the least
confusing terminology to share.
http://www.nicdlady.com (among many others) has NiCad and NiMH cells for
pretty reasonable pricing.
It's quite common in Ni-Cad packs as well as NiMH packs to find
thermistors (or other temperature measuring items), so you don't
overheat the pack during charging (REALLY hard on the pack.) Circuit
breakers aren't a bad idea in there either, to prevent shorting problems
from hurting the packs. (Look at what they do for Li-Ion packs, some
I've seen a NiCad pack discharged to as low as nearly 0V per cell (NOT
a good idea. It happens when some twit leaves screws loose inside a
laptop, though. And blows up traces on the motherboard. Wirewrap wire
does wonders for repair, here <G>) You may need to gently & fully
charge & mostly discharge a couple times to get full power from the
batteries (I've found it best not to discharge Ni-Cads too deeply, but
don't just barely use them & then fully charge them again - overcharging
isn't good for Ni-CADs. Especially hot overcharging. Hot batteries are
NOT good... NiMH is more forgiving about some things, less of being run
hot IIRC. But it's late & I'm decked...)
See also: www.piclist.com/techref/power/batterys.htm?key=battery
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