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From: myers@hpfcrlm.HP.COM (Bob Myers)
Newsgroups: sci.electronics
Subject: Re: NiCd behavior
Message-ID: <17660174@hpfcrlm.HP.COM>
Date: 18 Jun 91 18:36:27 GMT
References: <1991Jun15.023737.2673@mccc.edu>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 32

>>I have a 10 ohm 10 watt resistor connected to the terminals of a 7.2V
>>1000maH camcorder battery and the terminal voltage refuses to go below
>>about 2.2V.  Is this sufficiently low to be considered a full-discharge?
>>If not, how can I drop the voltage even further.
>>

>Keep at it. Unless you COMPLETELY kill it it will still retain memory.

ABSOLUTELY NOT!  As previous posters have mentioned, 2.2V is already VERY
low on the curve for this battery; a 7.2V battery is six NiCd cells, each 
with a nominal voltage of 1.2V.  IF each cell were to discharge equally,
2.2V across the battery means each cell is only at a little over 0.3V -
which is definitely "deep discharge" for this technology!  But - as has
also been mentioned - it is very unlikely that the cells will discharge at
exactly the same rate, to exactly the same level; this sort of "very-deep-
discharge" is likely to wind up with one or more of the cells in the stack
being reverse-charged, which is a Bad Thing for NiCds.

The real lesson to be learned here, though, is that such intentional
discharging is completely unnecessary - there is NO reason to be concerned
about "memory" in NiCd cells/batteries.  For all practical purposes, it
doesn't exist.  It's a myth.  A phantom.  A falsehood.  A misconception.
(Get the point yet? :-))  What has been mistakenly labelled "memory" in
consumer electronic application is almost without exception actually a
phenomenon called "voltage depression" which results from improper or
excessive CHARGING, *not* from anything having to do with how the cell is
discharged.


Bob Myers            | "There is a law of inertia.  And I have found that of
myers@fc.hp.com      |  all the inert substances, the most inert is the       
                     |  human brain."         - Edward Teller