Andrew said...
> Charging in series is fine, with one proviso -they must all be matched
> cells. Generally this means brand new, identical cells permanently
> wired before even the first charge. Difficulties arise when series
> charging different cells, or identical cells that have had different
> amounts of use.
Joel answered...
> Unfortunately they don't remain matched for very long. Every charge/
> discharge cycle affects each cell slightly differently and the
> differences are amplified each time, with some cells getting
> overcharged and losing a tiny bit of capacity and others discharging
> before the others and getting pushed too deep.
Allow me to disagree with all due respect with both of you. For a start,
there isn't anything like "brand new, identical cells". The fact that
they
are brand new doesn't mean at all that they are identical. The 2100mA
cells
I'm currently using for rebuilds show a tolerance of about +- 50mAh, i.
e.
their capacity varies from about 2050mAh to about 2150mAh. If you'd put
a 2050mAh cell and a 2150mAh cell into the same pack, you might or might
not be right with your assumption that the weaker cell will eventually
be
harmed. This depends on how "cautious" the discharge monitoring system
is. If it switches the device off early enough, no cell will be
deep-discharged.
The only decent thing to do (which hardly anybody does) is measuring
each
and every cell before using it. That's how I do it. I buy them in
batches
of about 20-30, measure each cell's capacity and match them as closely
as
possible. Cells that don't fit my definition of "closely" are kept back
until I have four that are in the same capacity range. That way the
effect
you are descibing is reduced to almost zero. Cells that are as closely
matched as those you'll find in the packs rebuilt by yours truly will
almost
certainly age in an identical way if they are kept in the same pack
and if you don't harm them during the rebuild by heating them up too
much by
soldering too long a time.
> NiCds suffer a lot more in a battery than NiMHs do - but they are
> history.
I'd like to disagree humbly again. NiCad batteries are still the cells
that almost every power tool uses these days. Only very recently has
some company begun to put LiIon batteries into these tools.
Frank
-- Newton software and hardware at http://www.pda-soft.de
-- This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries Official Newton FAQ: http://www.chuma.org/newton/faq/ WikiWikiNewt for all kinds of articles: http://tools.unna.org/wikiwikinewt/Received on Mon Jun 19 15:56:42 2006
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