Rating battery for intermittent drain

Mar 03, 2012 7 Replies

I am designing a compact signal generator to be powered by a 9V alkaline battery. It consists of a transistor (not op amp) phase shift oscillator and emitter follower. The output is a square or sinewave at



60Hz. Draws 12mA.

Given that the drain is not continuous, due to the waveform's duty cycle, how do I estimate the total operating time in hours, assuming the battery will provide 500mAH?



The circuit will function fine down to 6V, with corresponding loss in amplitude.



Mike Stern


If you use the math for power in alternating circuits you can get close to your figure. In sine wave stuff, it would be P = IV*Cos(angle), you do a bunch of samples and sum them up.

for a square wave, it would be 50% of what it would be when on, that is is the square wave is 50% duty cycle.

Watts being a 1J/Sec, so I guess you can accumulate a second of that times the duration of your test.

More on it later I am sure. :)

Jamie

"Mike Stern"

** Completely irrelevant.

If your meter shows 12mA - that * IS * the battery drain.

From the data for the Energiser 522 that equates to about 45 hours.

BTW:

This kit from Altronics does what you describe and uses only 2mA from a 9V battery.

Output level is constant with frequency and battery voltage down to 6V.

formatting link

Designed by me and published in EA magazine in 1996.

It will fit in a much smaller box than the one shown in the pic.

... Phil

"Jamie = Maynard A. Philbrook F****it Radio Ham KA1LPA "

** Maynard never has the right answer.

The know nothing code scribbler is never even close.

.... Phil

Not to rant, but have you ever compared the capacity of a 9V battery compared to 2AA cells and a boost? Basically I hate designs with 9V batteries. AA cells are more cost effective. [In any country, you can find chickens, AK47 ammo, and AA cells.]

Basically people snicker at designs that use 9V batteries these days. It is not good engineering.

So is 12ma with no load?

Phil, you surprise boy, I gave the correct answer. I gave him something to work with. You on the other hand just want to blow smoke because you most likely don't know how to break it down.

Doing power usage with loads of that type requires you to decompose the time frame with the signals you are using and load levels they are exerting. Those summed together can be used as an average energy use to properly calculate the battery life.

Go blow smoke else where, I don't don't smoke and I don't like smokers around me.

Jamie

"Jamie = Maynard A. Philbrook

F****it Pycho Radio Ham KA1LPA "

** Exactly what I wrote - you f****it, septic criminal s*****ad.

.... Phil

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