Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: More questions on NiCads...
Message-ID: <1991Feb23.231737.1413@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <233@pieta.gtephx.UUCP>
Date: Sat, 23 Feb 1991 23:17:37 GMT

In article <233@pieta.gtephx.UUCP> schiefferr@gtephx.UUCP (Ron Schieffer) writes:
>Is it safe to use a NiCad rechargeable battery in my 
>smoke detector?  What about the "low battery" sensor
>which automatically returns short beeps when the battery
>gets low??

Hmm.  First question is whether the somewhat-lower output of the NiCd
would trip the low-battery sensor immediately, but that can be resolved
by experiment. :-)  Given that, there should not be much trouble with
false trips, since NiCd output voltage is quite stable until they are
just about dead.  The one concern I can see is that the voltage might
not get low enough to trip the sensor until the battery is so close to
extinction that it couldn't support the "replace my battery!" beeps
for very long.

A more fundamental problem is whether you will gain by the substitution.
NiCds are ill-suited to this sort of low-drain long-duration standby
application:  they discharge themselves over time, and not a terribly
long time at that.  You might end up having to charge the thing every
couple of weeks.
-- 
"Read the OSI protocol specifications?  | Henry Spencer @ U of Toronto Zoology
I can't even *lift* them!"              |  henry@zoo.toronto.edu  utzoo!henry


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