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Can a 3.3v LED be used with 2 AAA batteries without a resistor? Answered

I want to make a torch with a 3.3v super-bright LED (used for case modding) with a 25mA forward current. The power source will be 2 AAA batteries (~1.5v alkaline) connected in series to make ~3v. Is a resistor required, and if so, what is the colour code/value?

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PocketBrain

10 years ago

Yes, but light intensity will drop off rather quickly as your cell expends energy and the voltage (and current capacity) drops. Search for the Joule Thief, a dead-simple, easy-to-build circuit that can boost the output of a 1.5V battery to drive a 3.3V LED. Also, you can get standard-size (20-30mA) LEDs for a quarter nowadays. I get them locally at Marlin P. Jones (10 for .25 each, or .43 each for the big ones).

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awang8

10 years ago

Actually, the min/max is 3.1/3.4 but with 3.0/3.1 theres not much difference, and I find it works fine (finished building torch).

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awang8

10 years ago

Thanks for the answer. That's exactly what I thought, but I had to made sure first (LEDs are like $4 each from local electronics store now.)

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steveastroukawang8

Answer 10 years ago

Thing is, they won't reach full brightness either on a 3V supply. You really NEED to drive them a little harder, from a bigger supply to reach rated current and brighteness.