tomb@hplsla.HP.COM (Tom Bruhns) (03/03/91)
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? What about the "low battery" sensor >>which automatically returns short beeps when the battery >>gets low?? > >IMHO, putting a NiCad into a smoke detector is a waste of valuable resources. >Radio Shack sells a 9 volt NiCad for about $10. You can get a cheap Ever- >Ready from the local grocery store for under $1.00 which will easily (in >my experience--and I have three smoke detectors at home) last a year or >longer. This means you'll need to use the NiCad for at least 10 years to >even break even--not to mention the hassles of recharging (what will you >do with the detector while the NiCad recharges for 14 hours?) and the fact >that the NiCad may not last 10 years. 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. YOU WOULD BE MORE INCLINED TO FORGET ABOUT THEM AND BE WITHOUT PROTECTION!! (imho.) I use alkalines because I trust them. Cost in an application like that should not be a consideration.
rpw3@rigden.wpd.sgi.com (Rob Warnock) (03/04/91)
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
paul@x.co.uk (Paul Davey) (03/06/91)
I own two smoke detectors. Both had manuals which specified Alkaline batteries. I don't use zinc/carbon or nicads. I agree that lithium should be OK though. -- Regards, pd@x.co.uk IXI Limited Paul Davey pd@ixi.uucp 62-74 Burleigh St. ...!uunet!ixi!pd Cambridge U.K. "These are interesting times" +44 223 462 131 CB1 1OJ
schumach@convex.com (Richard A. Schumacher) (03/07/91)
OK, now two folks have opined that lithium batteries will probably work in a smoke detector, even though one pointed out that the Li battery has ~16 ohms internal resistance versus ~.8 ohms for the alkaline. It would seem safer to contact the detector manufacturer to ask whether it's OK rather than assuming it is, given that they all do specify using certain batteries.
tomb@hplsla.HP.COM (Tom Bruhns) (03/08/91)
rpw3@rigden.wpd.sgi.com (Rob Warnock) writes: (Good notes about lithium batteries deleted...) >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... Hmmm. This worries me a little. The smoke detector must idle along at very low current for (hopefully ;-) a very long time, but when it must do what it was put there for, will the lithium battery hack it? I confess I don't know how much current the alarm part draws, but assume it must be in the hundred milliamp range. Perhaps I can check this out, but I don't think it's safe to assume that the higher resistance would be inconsequential in a smoke alarm! (One alarm I have has two batteries, one for the alarm and one for a rather bright light.)
ijk@cbnewsh.att.com (ihor.j.kinal) (03/08/91)
Most brands of smoke detectors I've purchased recently SPECIFICALLY state to use only the REGULAR type of 9V - thereby excluding alkaline or lithium [or ni-cad] cells. Since these regular 9volts typically come in a 2 pack, which costs almost as much as an inexpensive alkaline, and since the storage life of these regular batteries is minimal, the second battery usually goes to waste [or could I freeze it to extend the storage life??]. The question I really have, is assuming that the smoke detector people know what they're talking about, is why??? Are the internal resistances that different, that it makes a difference??? [I remember that power transfer is greatest when the internal resistance is equal to the external, but a smoke detector is not a car starter equivalent, is it???] Just curious [hey I'm basically a software person] and include standard disclaimers: from Ihor Kinal att!cbnewsh!ijk
tgg@otter.hpl.hp.com (Tom Gardner) (03/10/91)
Many fire alarms specify that zinc-carbon batteries should be used, not alkaline, not nicad. What follows is informed speculation. For nicads and, to a lesser extent, alkaline cells the voltage remains more-or-less constant until the cell is exhausted. Then it falls very rapidly. The voltage of zinc carbon batteries falls constantly during the cell's life and the voltagecan be used as a crude indicator of the remaining life. In many fire alarms the battery voltage is monitored and as the voltage falls below a certain level the alarm emits a plused shriek to indicate that the battery need replacing. Thie shrieking draws more current and thus the battery is drained faster, but hopefully not before the battery is completely discharged. It can be seen that the zinc carbon battery will thus shriek for a longer period before it is completely useless, thus increasing the chances that someone will notice it. It would be a great shame if the (nicad) battery took 1 day to die completely, and the owner was away for that day. ZnC cells will continue to shriek for more than a week.
rpw3@rigden.wpd.sgi.com (Rob Warnock) (03/11/91)
In article <schumach.668308126@convex.convex.com> schumach@convex.com (Richard A. Schumacher) writes: +--------------- | OK, now two folks have opined that lithium batteries will probably | work in a smoke detector, even though one pointed out that the | Li battery has ~16 ohms internal resistance versus ~.8 ohms for | the alkaline. It would seem safer to contact the detector manufacturer | to ask whether it's OK rather than assuming it is, given that they | all do specify using certain batteries. +--------------- As the one who said that lithium batteries have higher internal resistance, let me reassure you that this only makes a difference *during an alarm*. That is, a lithium battery will dissipate a little more of its power internally under *heavy* loads. (I.e., when the alarm is squalling and bouncing you out of bed!) If you are concerned about it, test one in your detector, with a cigarette or some other source of smoke to set off the alarm. Compare the volume with the lithium to that with an alkaline, and make your decision based on that. The increased internal resistance matters not a bit to the service life of the battery, as the standby current of the alarm is in microamps (or less). There, the lithium wins. [While it can't hurt to ask the alarm manufacturer, the difficulty is finding the right person to ask. It's all too easy to find a marketing dweeb who'll tell you anything just to get rid of you. And if that causes you to incorrectly choose a less reliable battery...] -Rob ----- 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
smithj@hpsad.HP.COM (Jim Smith) (03/11/91)
Or you could stuff a lithium battery in a smoke detector and blow some smoke at it to make sure it triggers... (Of course, this wouldn't assure that it will trigger on an OLD lithium battery...)