LED Circuit - Power Requirements

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Old 04-04-11, 08:37 PM
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LED Circuit - Power Requirements

Hey all. This is my first post, but I'm running into a snag and I hope you can help.

I'm trying to create an LED array that contains 2 white LEDs that are powered by a 3v supply (2 AAs.) These arrays will be installed into costume heads that are primarily craft foam.

As it stands I am looking to install a set of white LEDs that have a forward voltage of 3.2v - I understand that my source voltage is lower than the forward voltage but at this point I can't find any LEDs that have a forward voltage lower than that.

What I want to find out is the type of resistor I need to keep the circuit working, if it will at all.

Thanks guys, I hope that info helps.
 
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Old 04-05-11, 04:06 AM
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Welcome to the forums.

A voltage drop of 3.2 volts won't work with a 3-volt power supply. You'll need to double-up on the batteries. Four AA's in series will get you to six volts.

Have a look at this LED resistor calculator.
 
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Old 04-05-11, 06:32 AM
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Radio Shack and online electronics parts supplies usually have resistor multi packs that are great if you will be doing a number of projects. It just seems crazy when you are looking at the bag of 500 resistors you just bought. If you are just doing this one installation then I'd calculate the value you need and just buy that one. They are so cheap they are usually sold in packs of 4 or 5.
 
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Old 04-05-11, 11:39 AM
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I appreciate the answers so far, guys. The deal is I want to power LEDs with the smallest, most easily-replaceable power supply available - 4 AAs seems to be the best I've heard so far but I'm afraid it will add to the bulk. These battery packs would be stored (theoretically) somewhere on the costume head, but can be extended elsewhere. Otherwise I was considering using 9v battery cases of the same style but have had no luck finding any.
 
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Old 04-05-11, 12:06 PM
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Do you just want lights for the eyes? I have used these balloon lights before. They are really tiny and will run continuously for a week on their little watch battery. I think the source I linked only sells them in bulk (packs of 25) but you might be able to find something similar at a local dollar or discount store.
 
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