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Re: [OM] NiMH vs. NiCd cells

Subject: Re: [OM] NiMH vs. NiCd cells
From: Jim Couch <spknsprkt@xxxxxxxxxxxxx>
Date: Thu, 26 Oct 2000 08:02:30 -0700
In my experience (20+ years of photgraphy and 20+ years of selling bicycle
lighting systems) the one thing that really kills both NiMH and NiCD batteries 
is
overcharging! Most chargers for these batteries are like the energizer bunnie,
they keep going and going and going... dumping a charge into the battery wether
it needs it or not. A simple way to avoid this is to find out (from your owners
manual) what the max charge time is for your pack, and then plug the charger 
into
one of those lamp timer units you can get at hardware stores, ect. Set the timer
so that it automatically shuts off after X hours. BTW the time for the 15v NiCD
or NImh MD pack is about 4 hours.

Jim Couch

Eric Pederson wrote:

> I'm a big fan of NiMH batteries (use a home made 5 cell 4.5AmpH pack for my
> bike lighting commute). Your mileage may vary, but there are a few ways in
> which NiMH seem to be more vulnerable that NiCd cells and which may give NiMH
> an undeserved poor reputation. The main problem is that NiMH seem even more
> sensitive to overcharging damage than NiCD. With both battery types, such
> damage is permanent, though apparent partial recoveries are reported.
> That means you want a "smart" charger with a very low (or no) trickle charge
> after full voltage is reached. Most NiCD units are sold with cheap chargers
> which just charge and charge, which is marginally acceptable with NiCD, but
> less acceptable with NiMH cells.
>
> Another point is the self-discharge rate of NiMH is higher than NiCds. So if
> you let the cells sit around after charging, you may not experience higher
> capacity. With both types of cells, you are best off storing the cells after
> use without charging and then recharging the night before use.
> Better for capacity and battery life.
>
> Last point: please dispose of all cells (even alkaline) properly. Most US
> residents just dump this toxic waste in the regular trash. Your community
> probably has a place to dump these and you can store up a shoebox of drained
> cells and drop it off there every few years...
>
> Just charging along,
> Eric Pederson
> epederso@xxxxxxxxxxxxxxxxxxxx (no "n" in "epederso")
> Professional home page:
>         http://logos.uoregon.edu/uoling/faculty/pederson/pederson.html
> Personal home page:
>         http://darkwing.uoregon.edu/~epederso/
>
> > Many ads I've seen state that "you can just keep using your nicad charger
> > with NiMH batteries".  The consensus on the list was to not charge the pack
> > for more than 5 hours (after a big discharge) when using NiMH.
> > I've accidentally left my NiMH test pack on the charger overnight.  In the
> > morning the test light  won't go on and the pack doesn't work.  After a
> > while, the pack recovers by itself and everything seems to be back to
> > normal.   I don't know the affect of repeated overcharging though.
> >
> > John  Hermanson
>
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