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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
PocketBrain

11 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
awang8

11 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
awang8

11 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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steveastrouk
steveastrouk

Answer 11 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.