In message <752ad56e1f1562d1b771c13325940bf4@mac.com>
          William "Chops" Westfield <westfw@mac.com> wrote:

> It's only so-so at detecting end-of-charge on the cells I normally
> use with it :-(  While dV/dT might be usable in theory, it looks
> like in practice the values you're looking for can vary quite a bit,
> depending on battery make, age, initial charge state, and so on.

That's one of the (relatively few) reasons that's making me look into Li-Ion
technology. Easy to charge - just feed the pack 4.2V/cell at 0.5C current
limited, wait a few hours for the current to drop to about 0.01C then kill
the power. The problems start arising when you foul up the charge procedure
and end up feeding them (say) 4.5V or 0.75C. Can you say "lithium
firecracker"?

I've got a pair of Compaq Evo laptop packs here that I've been gutting for
cells. A quick call to the local TI and DalSemi distributors got me the
safety management chips, and now I've got a pair of 4AH 3.6V packs and a load
of spare cells. Of course, cellphone battery packs are also a good option if
you don't feel like playing with lithium firecrackers :)

It is relatively easy to test the cell monitors though - feed the cell side
from a 5A PSU, then deadshort the output. If the PSU's ammeter reads current,
the cell protector is fried. Do the same the other way to check the cell
voltage and charge overcurrent protection. DalSemi produced a checklist that
goes over all the tests for Li+ cell protectors - it covers most of the
checks that should be done before wiring a protector up to a Li+ cell/pack.

I really do need to look into building a GPIB-enabled
multimeter/voltmeter/data-logger so I can watch what the charger IC gets up
to. I've been using a Solartron 7150plus (need to get a service manual for
that thing) but I can only monitor voltage or current with it, not both.
Which is rather annoying when you need to keep an eye on both of them.

Later.
-- 
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
philpem@philpem.me.uk              | Athlon64 3200+ A8VDeluxe R2 512MB+100GB
http://www.philpem.me.uk/          | Panasonic CF-25 Mk.2 Toughbook
... The Eternal Triangle is usually right tangled.
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