If there are no stampings on it as you describe then the easiest way to determine the resistance of the coil is to measure it with an Ohm meter. These are cheap and readily available at Radio Shack as an analog multimeter.
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www.radioshack.com]
or a digital version.
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www.radioshack.com]
These meters will also allow you to verify battery voltage and current draw on your system. So I'd recommend getting one.
Following on eTrump's electronics 101 discussion you can also make a low voltage power supply using a "wall wart" plug in supply like those used by all kinds of consumer electronics devices. Like a telephone answering machine et.al. Add a simple resisitor dividing network to drop the voltage to what is needed and you'll never need to replace batteries.
I'm an electrical engineer so I could design one for you that will be bullet proof if you need help.
Dan
Edited 1 time(s). Last edit at 12/28/2009 07:30AM by bookemdanno.