Path: utzoo!attcan!uunet!bu.edu!husc6!unix!snmp.sri.com!larson
From: larson@snmp.sri.com (Alan Larson)
Newsgroups: sci.electronics
Subject: Re: Discharging NiCads safely
Message-ID: <16569@unix.SRI.COM>
Date: 25 Sep 90 19:08:59 GMT
References: <1990Sep13.123227.24228@ncsuvx.ncsu.edu>
Sender: news@unix.SRI.COM
Organization: SRI International, Menlo Park
Lines: 23

In article <1990Sep13.123227.24228@ncsuvx.ncsu.edu> kwf@ecersg.ncsu.edu (Ken Fernald) writes:
>
>I'm interested in designing and building a fast-rate nicad charger
>probably using a "dump-and-time" technique where you discharge
>the cells to place them in a known state, then charge at a high rate
>for a timed period.  I've been told that you must be careful about
>how you discharge cells in series because if some cells are weaker than
>others, they may be forced into a reverse current state and be damaged.
>
>Given this is true, is there a proven technique for the fast and safe
>discharging of nicad cells?  Should you discharge them individually?
>Discharging in series would certainly be simpler.

  You should discharge them individually.  This came from a lecture I
heard given by a battery company rep a few years back.  Otherwise, the
lowest cell will be reverse charged if you go to low.

  I would question the wisidom of discharging the cells first (especially
doing so quickly).  This is likely to increase their temperature, and to
cause shorter life (in number of cycles of service) from the greater amount
of chemical changes done.

	Alan