battery life, and indicator meters? two questions:

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battyboy
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Last seen: 12 years 2 months ago
Joined: Thursday, November 20, 2008 - 15:38
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battery life, and indicator meters? two questions:

I need to power a small circuit that needs 7-12v 250mah.
I guess my choices are using 6 AA's in series, or a 9v.

If I use 6AAs, I'll get about 7.2 to 8.4 volts. I think that the best AA's are about 2500mah. Does that mean I should get *10 hrs* if my circuit needs 250mah???

If I used a single 9v, which is 180mah, I'll just get under an hour?

Question two is about battery life indicators.
I need a small easy circuit that shows some idea of how much power I have, or just that the battery is still good. Maybe just an LED that comes on as the batteries are getting low?

Any pointers to a simple circuit for this?

Thanks!!

Dave-s
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Last seen: 9 years 7 months ago
Joined: Monday, March 10, 2008 - 03:22
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Re: battery life, and indicator meters? two questions:

If you open up the casing of a 9v bat. you will find 6 AAA batteries in series, so either 6AAs or 1 9v will give you the same voltage.
If your circuit needs 250mA, then the 9v is not a good idea.
Any circuit you add to measure the voltage will drain the battery. You can add a LED, 6v Zenner diode and 100 ohm resistor all in series to give an indication if the battery is good (once the voltage drops under 7v the LED will go out). I'd also add a push button so that the LED doesn't drain the bat.

battyboy
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Last seen: 12 years 2 months ago
Joined: Thursday, November 20, 2008 - 15:38
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Re: battery life, and indicator meters? two questions:

thanks
Why does the led go out at 7v if it s a 6v zener?

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