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Sources for 3 Vdc
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fixit7:
I have a laser beam alarm circuit.

The detector and piezo speaker uses less than 100 ma.

It will be going outside on my porch.

It currently runs from 2 aa batteries.

I could run a line from outside to supply the voltage but would prefer a battery source.

What are my options for the battery source. I would them to last around a year.

I already have some 18650s.

I would put the detector and laser in some kind of waterproof enclosure.

Thanks.
sokoloff:
The very first thing I'd do is try them with two D-cell alkaline batteries...
DDunfield:
How much less than 100ma?
What is the actual idle (or better yet average) current draw of the device?

100ma is a LOT of current to draw from a battery over a year.

Very basic calculation with no account for internal leakage, fall-off, self-discharage etc:

Year = 365.25  x 24 hours = 8766 hours

8766 x 100ma = 876600 mah (milliamp hours)

A good alkaline D cell might have 15000 mah.
Which means it would run a device drawing 100ma for about 150 hours, or just over 6 days.

Dave
fixit7:
I want to make sure I don't ruin my circuit.

To find the exact current, do I measure it by putting my meter in between the positive lead and the switch?
garethw:
Put the multimeter in a position so that all of the current passes through it. Right at the battery or in-line with V+ or V-.
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