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batteries and milliamps and mah

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xanadu vector

New Member
I built a pushbutton timer circuit to run a LED using a 556 IC. It runs the LED at 20ma for 8 minutes. When the LED is off the circuit draws 2ma. The entire thing runs on a 9v battery. All of the dry cell 9v batteries don't have a mah rating... Is there a way to figure out how long the 9v battery will last at a 2ma drain or what a batteries mah is? I mean without actually finding out by running it down...

And, does anyone know of a schematic I can use that will enable me to accomplish the same thing with less or no standby power?

Thanks!
 

audioguru

Well-Known Member
Most Helpful Member
Go to the site of a battery manufacturer like Energizer to see the spec's of their many different types and sizes. Their mA/hr ratings are for different ending voltages.

Use a Cmos 555 like an LMC555 or TLC555 for low operating current.
 

DirtyLude

Well-Known Member
I'm just taging on to this post, but say my project uses 3.5mA at idle; the battery is a 225mAh coin cell batery. That means the poject will wun for 225 / 3.5 = 64 hours?

Is that correct?
 

audioguru

Well-Known Member
Most Helpful Member
DirtyLude said:
I'm just taging on to this post, but say my project uses 3.5mA at idle; the battery is a 225mAh coin cell batery. That means the poject will wun for 225 / 3.5 = 64 hours?

Is that correct?
Just look at the battery cell's datasheet.
Energizer's CR2032 lithium coin cell is rated for 225mA/hrs at a current of only 0.29mA and a finished voltage of 2.0V (2.9V to start).
It is shown to have a 188mA/hrs capacity when it has a pulsed 6.8mA load.
 
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