At 12:14 PM 5/27/2004 -0400, you wrote:
>Fred,
>
>The voltage you measure from a 9 Volt alkaline battery near the end of its
>life
>depends upon the load placed on the battery at the time you are measuring it.
>You can take an alkaline battery that is near the end of it's life and
>allow it
>to sit on a shelf for a while and measure it's voltage.  The voltage will read
>pretty high.  Draw some current from the battery and the voltage will drop
>rapidly.  The more you draw, the sharper the drop.  Let the battery rest again
>and the voltage will pop back up.
>
>With that said, I think you will need to experiment with different usage
>scenarios for your product.  If you're lucky you can determine voltage
>readings
>that give you the warning duration you want to provide under each of the
>scenarios.

There are good discharge curves available for alkaline cells, but they
tend to assume constant resistance load. If your load is pulsed you may
have to experiment a bit. Note that a sizeable (in proportion to the energy
in the pulses) capacitor across the battery can significantly extend the
usable battery life. Batteries don't tend to decrease in actual open-
circuit cell voltage much during their life, it's the voltage with a
load that changes as the internal resistance increases.

Check the battery manufacturer sites first for the discharge curves, that
may be all you need if your load can be considered to be steady. I've found
Panasonic Industrial's data to be useful.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics