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From: crs@lanl.ARPA
Newsgroups: net.analog
Subject: Re: an observation, a new angle on batteries
Message-ID: <20522@lanl.ARPA>
Date: Tue, 29-Jan-85 11:37:24 EST
Article-I.D.: lanl.20522
Posted: Tue Jan 29 11:37:24 1985
Date-Received: Sat, 2-Feb-85 13:33:11 EST
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Organization: Los Alamos National Laboratory
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This is a reposting; the "f" key seems to have resulted in a
mangled posting.  Sorry about that.

References: <215@abnji.UUCP> <597@amdcad.UUCP>

> 
> O.K. maybe we can resurrect the nicad battery discussions, Remember
> all that talk about "memory" and nicads not fully charging if not
> fully discharged.
> 
> I just got a cordless drill, and the instructions seem contrary to
> my beliefs about nicads. They say that I should recharge the moment
> that I notice a reduction of torque from the drill, i.e. without
> completely discharging the batteries. Can you damage a DC motor
> by running it on a lower voltage than it is designed for? If not
> then why should I recharge so soon?
> 
> Mike @ AMDCAD

In reverse order:

Yes, you can damage a nicad *battery* by excessive discharge.
If the cells are not exactly matched, one may discharge before
the others so that continued discharge tries to *charge* the
discharged cell in the *reverse* direction, resulting, I believe,
in a shorted cell.

As I understand it, nicad memory has to do with discharge *rate*
(amps) rather than depth.  I believe the confusion arises from the
recommendation that a few *deep* discharge/charge cycles be 
to "erase" the cell's memory.  In other words, if a nicad that is
capable of supplying X amps is operated for a significant period
at a load of Y amps where Y is significantly less than X, the
nicad will, subsequently, be unable to supply X amps even though
it is "fully charged".

While it is often recommended that such a nicad be subjected to
several deep discharge/charge cycles to restore it to its original
discharge *rate* specification, care must be exercised in the
case of batteries for the reason mentioned in my first paragraph
(ie possible reverse charge of one or more of the cells).

Charlie Sorsby
...!lanl!crs
crs@lanl.arpa