In article <ke%sq.55358$
034...@en-nntp-06.dc1.easynews.com>,
Wild_Bill <wb_wi...@XSPAMyahoo.com> wrote:
>I don't know about the newer chemistry types, but I spotted a comment a
>couple of days ago that claimed one type can't be recharged if discharged
>below a specific level (don't recall if it was lithium or poly-something).
>
>NICD and NIMH types shouldn't be used when discharged to a point below
>approximately 80% of full charge, some manufacturers claim the limit should
>be about 0.8V per cell.
My own preference is to stop when the battery hits 1.0 volts per
cell... this is usually soon enough to keep the weakest cell in the
battery from being over-discharged into a state of voltage reversal,
and since there's usually only 5-10% of the battery charge left at
that point it isn't really wasteful.
Part of the problem here - and I suspect what Phil was alluding to -
is that some types of batteries have a voltage-discharge curve which
makes it difficult to measure their charge state accurately over much
of their charge range.
Alkaline battery output voltage tends to "droop" quite a bit over the
battery's useful discharge lifetime, and the "voltage droop vs.
percentage of charge used" curve is fairly flat over much of this
range. The voltage per cell (under load) can drop by half a volt or
more, between the "10% used" and "90% used" points.
A standard "battery level indicator" intended for use with alkaline
batteries will probably use this phenomenon - put a load on the
battery, measure the voltage, and show a rough indication of lifetime
remaining based on the voltage.
This isn't as easy to do with NiCd and NiMH cells. These chemistries
have a much flatter voltage-discharge curve... a bit of droop at the
beginning, a nearly constant output voltage over most of the remaining
time, and then the voltage "drops off a cliff" when there's only a few
percent of the charge remaining.
So, with these batteries, you can probably distinguish "fully
charged", "almost entirely dead", and "somewhere in the middle"
without too much trouble, but it's difficult to get a more accurate
estimate of just *where* in the middle the battery might be. "10%
left" and "90% left" don't look very much different, voltage-wise.
A battery measurement tool calibrated for alkaline batteries is likely
to give misleading readings when used with NiCd/NiMH batteries.
Take a look at
http://www.powerstream.com/AA-tests.htm to see one
example of some of the data.
--
Dave Platt <
dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page:
http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!