🚀 go-pugleaf

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