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'[OT] Battery Pack Fundamentals'
1999\05\24@040229 by Graeme Smith

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Hi Guys....

As part of my current project recycling old computers.... for charity, I
have come accross a few old battery packs, left over from lap tops...

Thinking about what someone had said about there usually only being a few
bad cells in a pack, I cracked one open, to take a look inside.

Sure enough, there were a few bad cells, and a few extra components I
hadn't expected to find.

Taking apart a second, different type of battery pack, has added to my
confusion, and just increased the number of questions I have....

I figure one old 10 hour laptop battery should have more than enough power
for  a PIC for quite a while, so I was looking at the design, in order to
figure out how to borrow parts of it for my PIC'N.

Anyways, I figure the radial lead unit that looks like a cap, with a
pointed cap, is some sort of temperature cut-out element that breaks the
circuit if it overheats, its labeled micro-temp, so this seems likely. and
I figure the square cross-section but long can, with the Isuzu label on
it, is probably an auto-rated breaker to cut the circuit if it goes
over-amps....

But what I can't figure out, is why the only two cells that have anything
wrong with them are the ones these two circuit elements are connected to?

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?

                               GREY

GRAEME SMITH                         email: spam_OUTgrysmithTakeThisOuTspamfreenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.

1999\05\24@044658 by Mark Willis

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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?
>
>                                 GREY
>
> GRAEME SMITH                         email: .....grysmithKILLspamspam@spam@freenet.edmonton.ab.ca
> 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
day!)

 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...)

 Mark

1999\05\24@070214 by Neven Skender

picon face
Graeme Smith <grysmithspamKILLspamFREENET.EDMONTON.AB.CA> wrote:
Hi Guys....

As part of my current project recycling old computers.... for charity, I
have come accross a few old battery packs, left over from lap tops...

Thinking about what someone had said about there usually only being a few
bad cells in a pack, I cracked one open, to take a look inside.

Sure enough, there were a few bad cells, and a few extra components I
hadn't expected to find.

Taking apart a second, different type of battery pack, has added to my
confusion, and just increased the number of questions I have....

I figure one old 10 hour laptop battery should have more than enough power
for  a PIC for quite a while, so I was looking at the design, in order to
figure out how to borrow parts of it for my PIC'N.

Anyways, I figure the radial lead unit that looks like a cap, with a
pointed cap, is some sort of temperature cut-out element that breaks the
circuit if it overheats, its labeled micro-temp, so this seems likely. and
I figure the square cross-section but long can, with the Isuzu label on
it, is probably an auto-rated breaker to cut the circuit if it goes
over-amps....

But what I can't figure out, is why the only two cells that have anything
wrong with them are the ones these two circuit elements are connected to?

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?

                               GREY

Hi!

All accus (NICd, NiMH or LiOH) have cell rated at 1.2V. You have an
undercharged accu. When you try to charge that cell use source of constant
current with aprox. 1/3 of nominal capacity (1/3 of 2200mA is ~700mA) for
about 4-6 hours. You should discharge cells first with same current.

                                     Neven Skender

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