# LED Questions



## chrisb (Jan 3, 2008)

How many LED's can I power with a 2 AA battery holder and have the lights work for at least a few days.
I would like to run about 4 or 5 LED's to light a building. Brighter is better. I was thinking of using 
5mm high intensity 3.3 v from radio shack.

Should I run more or different batteries?

Would the LED's be in series or parallel?

I have some 1K ohm, 1/2 watt resistors, would one of those work?

Thanks.


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## George Schreyer (Jan 16, 2009)

I assume that you mean a white LED. Most white LEDs will work to some extent wired directly across a 3 volt battery. You don't get good current control but they run fairly bright at about 10 mA each.


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## Bill Swindell (Jan 2, 2008)

And the LED's should be in parallel.


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## George Schreyer (Jan 16, 2009)

if you want to do it right, each LED wants a constant current source, or reasonable facsimile, driving it. 

see link 

http://www.girr.org/girr/tips/tips7/white_led_tips.html


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## Greg Elmassian (Jan 3, 2008)

You might want to google the amp hour capacity of AA cells... that will give you the piece of data to allow you to calculate the time. 

Greg


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## Dan Pierce (Jan 2, 2008)

If you use rechargable batteries, you may get much longer time depending on the amp hour ratings. There are 4000ma units available. 

1000 ohms with LEDs are for dropping 20 volts at 20 ma. 

Use a 10 ohm resistor to limit led current (DEPT 56 does this in there battery units).


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## chrisb (Jan 3, 2008)

Thanks.The 1000 Ohm are left overs from doing the shay headlights 
Just bought a pair of 5mm white, bright, 3.3v LEDs from Radio Shack. 
Maybe I can get by with just 2 LEDs. Would I just use one of the 10 Ohm resistors on the positive battery terminal or does each LED get one? 
Also bought a 10mm white LED to see what it looks like when lit.


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## Greg Elmassian (Jan 3, 2008)

Hey Dan! I want some of those 4000 mah AA cells







(he specifies AA cells in the first post)


Greg


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## Dan Pierce (Jan 2, 2008)

I saw this one, a little fatter than a AA, but 3.7 volts, and up to 10 amps discharge. 

http://www.batteryspace.com/limnnirechargeable26650cell37v4000mah10arated148wh.aspx 


Looks like the 4000mah was 2 2000 mah in parallel that I saw.


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## Trains West (Oct 4, 2008)

stanard AA is 2000 mah

the 3.3 volt led draws 25 ma each 

so 2 will draw 50 ma 
at 50 ma amps the batterys will be dead at 40 hours but the voltage will have droped low enough that I would guess at 24 hours they would be getting dim


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## Greg Elmassian (Jan 3, 2008)

That's better! 

The batteries you had were not only not AA, but super high tech Lithium Metal batteries, in this case Manganese Nickel. 

Greg


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