Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!mit-eddie!media-lab!adam
From: adam@media-lab.MEDIA.MIT.EDU (Adam Glass)
Newsgroups: sci.electronics
Subject: Re: rechargable battery "memory"
Summary: From an RC'er's standpoint...
Message-ID: <3132@media-lab.MEDIA.MIT.EDU>
Date: 10 Aug 90 01:03:28 GMT
References: <105@javelina.cs.arizona.edu>
Reply-To: adam@media-lab.media.mit.edu (Adam Glass)
Distribution: na
Organization: Carnegie Institute of Technology
Lines: 38

cliff@cs.arizona.edu (Cliff Hathaway) writes:
>3) Is it possible to overly drain rechargable batteries so that they will
>   no longer take or hold a charge?

Yes.  When batteries go into this state, they're called "deep
discharged."  It has not happened to me, but my RC battery charger
has lots of caveats about over- and undercharging your NiCds.

>4) What is the lifespan of a typical rechargable battery?

The batteries I have are rated for about 500 charge cycles.  Keep in
mind, however, that they are built to handle rapid charging and
discharging (i.e., being charged at 6A for 15 minutes, or discharged
at 10A.)

I believe that you're supposed to slow-charge the batteries every once
in a while to help cancel the adverse effects of the rapid-charging.
This rejuvination I have personally witnessed; every Thursday night,
before the Friday races, I set the battery packs on "trickle" charge...

I have heard some talk about zapping the "whiskers" that develop in
NiCds after a while.  Come to think of it, I may have seen these
so-called "whiskers" -- whenever I go out on a remote shoot, I have to
take about 5 camera batteries because they're so old, and each one
holds it charge for about 25 minutes, whereas two years ago, the same
batteries would last an hour or more.

On a related topic: NiCds will drop a few tenths of a volt when
they're "peak" charged.  In the RC business, we use "delta peak
chargers" to stop charging the batteries when the voltage drops by the
characteristic .1 or .2 volts.  How would one go about making one of
these peak detector chargers?  I've seen one which only uses one 8 pin
chip (presumably some sort of comparator) and various secondary
components: resistors, capacitors, maybe a transistor or two, and a
relay to cut off power.

Adam
--
"I'll post more when I know more." -- George William Herbert