Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!elroy.jpl.nasa.gov!decwrl!sgi!rpw3@rigden.wpd.sgi.com From: rpw3@rigden.wpd.sgi.com (Rob Warnock) Newsgroups: sci.electronics Subject: Re: Reply: NiCads in Smoke Detectors Message-ID: <88597@sgi.sgi.com> Date: 4 Mar 91 10:25:44 GMT References: <1991Mar1.145532.7118@lonex.radc.af.mil> <5170116@hplsla.HP.COM> Sender: news@sgi.sgi.com Reply-To: rpw3@sgi.com (Rob Warnock) Organization: Silicon Graphics, Inc., Mountain View, CA Lines: 38 In article <5170116@hplsla.HP.COM> tomb@hplsla.HP.COM (Tom Bruhns) writes: +--------------- | vanderwerkend@lonex.radc.af.mil (Dan Vanderwerken) writes: | >In article <233@pieta.gtephx.UUCP> you write: | >>Is it safe to use a NiCad rechargeable battery in my smoke detector? | >IMHO, putting a NiCad into a smoke detector is a waste of valuable resources. | You pay too much for 9V NiCd's. I find them for about $2.50. But a more | important point: NICADS LOOSE CHARGE RATHER QUICKLY. YOU WOULD HAVE TO | RECHARGE THEM ABOUT EVERY MONTH OR TWO IN THAT APPLICATION. ... | I use alkalines because I trust them. Cost in an application like that | should not be a consideration. +--------------- According to a nice little article I just read in the "MAXIM Engineering Journal" (note: they sell chips to make switching power supplies, not batteries), 9v lithium batteries offer the highest capacity (over twice the watt/hours of alkaline), only a modest price increment (they say $3.50 vs $2.50 retail), and a shelf life of five to ten years. Moreover, during discharge, a lithium battery delivers 90% of its available energy before the terminal voltage has dropped to 7v. (The "end-of-life" voltage for alkkalines is often considered to be 6v.) A sample brandname mentioned was Kodak "Ultralife" model U9VL. -Rob p.s. A 9v lithium cell's internal resistance is about 16 ohm, compared to an alkaline's 0.82 ohm. While this would not matter at all in the above fire-detector application, it does affect lithium's use in high-power pulse applications. In those, you may need a hefty electrolytic capacitor across the battery... ----- Rob Warnock, MS-1L/515 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311