22 Oct
2004
22 Oct
'04
4:01 a.m.
From: "Dave Dunfield"
<dave04a(a)dunfield.com>
I won't charge them in the calculator, they are regular AA cells so I
can remove them and put them in a proper charger. :^)
Here's a question for battery guru's ... I have a gadget I built for
preventing "memory effect" in various nicad powered devices - mainly
ones like my Digicams which only discharge the battery 1/2 way (or
less) before complaining that the battery is low.
It is basically two springy metal bars which lets me put up to 10 AA or
C cells in parallel to discharge (I've got portable @M and 70CM rigs powered
by a C cell pack), an Ammeter, a low resistance, and a stud rectifier diode.
Basically, it draws about an amp from the cell when they are near fully
changed, and trickles down to nothing as they approach .7ish volts, and
never lets them go to zero.
Hi
Actually, NiCad's can be discharged to zero without problems. It
is tha back charging in stack, as batteries, that causes the problems.
In fact, NiCad's are often shipped with shorting bars across the
terminals.
-- I took apart the 25's battery pack and replaced
the nicads with
nickel metal hydride cells (the same ones I use in my camera)
Not a good idea. Nickle metal hydrides need different types of
charging. The won't last long with a NiCad charging circuit. I works REALLY well with nicads - I've got cells
that I've been using in
my radios for many years and they still work very well (Prior to using
this, they would noticably lose capacity after a while)...
But: It doesn't seem to be quite as effective with NMIH cells ... they
still seem to be losing capacity ...
These cells shouldn't be discharged to zero. Just different technology.
One thing you might try ( as an experiment ). Hit them with a momentary
high current load. This is done on NiCad's to improve their performance
and may have a similar effect on nickle metal hydrides. It does need
to be controlled because like NiCad's, once the burst seal is broken,
expect them to be worthless in a few months.
Dwight
Any explaination, comments etc.?
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Vintage computing equipment collector.
http://www.parse.com/~ddunfield/museum/index.html