LED help (not automotive)

Back2Basics

Regular
Dec 30, 2005
317
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Milwaukee, WI
Alright, I need to hook up 12 LEDs. There are two ways I'm trying to decide how to do this......... Here is the first. What kind of battery(s) should I use? I need the small amount or smallest space possible to be used. Also, what resistor, if any, would be needed in this setup?

The second way is this........Forget the batteries and replace that with an electrical plug to an outlet. What would be needed for this setup?

Thank you!
 

Justin

Speakers?
Mar 31, 2005
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Spokane, Wa
Dark006 said:
Alright, I need to hook up 12 LEDs. There are two ways I'm trying to decide how to do this......... Here is the first. What kind of battery(s) should I use? I need the small amount or smallest space possible to be used. Also, what resistor, if any, would be needed in this setup?

The second way is this........Forget the batteries and replace that with an electrical plug to an outlet. What would be needed for this setup?

Thank you!

Google LED calculator for use with the battery... it'll tell you the optimal way to wire up 12 LEDs with a DC circuit.

An AC circuit would need a.... the word escapes me at the moment... but a circuit to drop down from 120 AC to (X) DC
 

annoyingrob

Boosted member
Jul 5, 2006
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Calgary, Alberta, Canada
To plug in a wall, all you would need is a bridge rectifier (4 diodes, and a small filter capacitor) to change 120VAC to 120VDC. Hell, you could run them off AC, but there would be a small flicker. to hook up 12, I would run all 12 in series. Assuming each LED will draw 20mA, and has a 3v drop (I use that for all of my LED calculations, and I do do a lot of them), you're looking at a string with a 36v drop, and 20mA current draw. plugging in (120-36)/0.02 = 4.2k ohm current limiting resistor.

For batteries, the smallest would be a 3V watch battery. Most LEDs will run off 3v drectly without the need for a curent limiting resistor. Off of a 3V battery, you would have to run all 12 in parallel, giving you a 240mA current draw. The battery wouldn't last very long. 2 AA batteries would also work. With a 240mA draw, a typical set of AA batteries should give you 5-6 hours of battery life. I once built a flashlight using 19 white LEDs. It ran off of 4 AA batteries. All of the LEDs were run in parallel with each other (Why I didn't just do a series-parallel configuration I don't know, it would have been more efficient.). Anyways, I built it years ago, and have taken it camping many times. I've never changed the batteries.
 

Back2Basics

Regular
Dec 30, 2005
317
0
0
Milwaukee, WI
I'm going to go with the wall setup. So.....I looked at the bridge rectifiers on Radioshack.com, but what one do I need? And there are 4 leads coming from them, where do the other two wires come from (besides the + and -)? A diagram of how this would be setup would really work if anyones got time. Thanks for the help so far.