How long can a AA battery power a LED?

Question

I have a brand new AA battery powering a single LED (with resistor). How long do you think I can keep this LED on before the battery runs out of juice? (no, i dont know what resistor or LED strength I have, but it ...does that matter?) The LED is of standard brightness if that does matter.

Answer 1

Well there's a whole bunch of different variables there.



First, an alkaline AA battery can hold from 1700mAh to almost 3000 mAh (Wikipedia). This is what governs how long it will last. An LED typically draws around 30mA (I assume you're not using a very bright one). So if you have a 3000 mAh AA battery and you're drawing 30mA, expect it to last 100 hours.



However, this is immensely complicated by the resistor and by the fact that most standard LEDs don't even light until you're running with over 1.7V. So yes, we do need to know what sort of LED you're using and what the value of the resistor is before we can give a more precise answer.



Rough guess - hope for 50 to 100 hours.

Answer 2

You ask a question assuming the variables don't matter, but they make all the difference. You can get an LED to emit light with just a few milliamps so you can barely see it, and in this state it means you have a very large resistor. Under these conditions you are running only 2000 uW or 2mw. Therefore, if, as someone mentioned, if you can run ~2000 milliwatthours on a cell you should be able to see light for about 1000 hours or 41 days continually (I assumed a 1K resistor, but it won't emit with such a high value and a single cell. You would need at least two to make calculations) but you can see it can work a long time under the right conditions.



Having said all this, you can't do it with a single 1.5v battery. the forward voltage drop of a standard LED is 1.5v, so your battery would have to be greater than that voltage to properly drive it. You are seeing the LED come on because you are at threshold and waaay under current to sustain light output. There is no way to tell what the current it without measuring it, as you are below the specs for the LED. I suspect it will last a long time and then fail catastrophically with the battery still having plenty of charge left for other things.

Answer 3

Single Led Lights Battery Powered

Answer 4

It will work until the battery runs out of power. The length of time is based on the resistor and LED strength to determine what power they are pulling from the battery.

Answer 5

"Malibu" lights with AA battery that recharges during the day will run the LED 4 - 8 hours at night.

Answer 6

Military Grade Tactical Flashlight : http://FlashLight.uzaev.com/?alpl

Answer 7

if its a dollar store battery disregard what the last guy said and go put in another one now