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  #1  
Old 09-29-2002, 05:47 PM
actofgod actofgod is offline
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Unhappy need help w/ LEDs plz...

I'm trying to do a tail/headlight mod w/ 4 LEDs. I have two 3mm red ones and two 3mm high output white ones, but I noticed that the white ones are really dim when wired with the red ones. I tried swapping in some yellow ones and the problem went away (all 4 LEDs bright).

I thought this might be due to higher voltage requirements of the white ones so I used two lithium batteries instead of one; the red ones got brighter but the white ones still didn't come on much at all unless I was using them separately from the red ones (at which time they were just fine). Could the white ones have more resistance or something so that the extra current just goes to the reds?

All other LEDs I have (yellow, green..) work just fine w/ the reds. Does anyone know where I can get some white LEDs that will work on lower voltage? (I found that two lithium cells wouldn't fit in the car so it's got to be 3.0v for all 4 LEDs) Maybe it was just b/c they were "high output" ones or something. Links to places I could find these or other info would be much appreciated!

Thanks for helping a newbie. Great site here.

Last edited by actofgod; 09-29-2002 at 08:56 PM.
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  #2  
Old 09-29-2002, 11:43 PM
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tinyrc tinyrc is offline
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Wedginator, any ideas?
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  #3  
Old 09-30-2002, 02:11 PM
JaMeZzZ122 JaMeZzZ122 is offline
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i dont wanna buy a set to do the headlights and taillights mod...i wanna do the one that is on thes site but i dont know where to get the leds from...what do u guys use and would christmas lights work?
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  #4  
Old 09-30-2002, 03:30 PM
Shacky Shacky is offline
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Wedginator, I hope you don't mind me answering their questions.

actofgod, it sounds like you have different voltages/current for the whites and the reds. Use Ohm's Law (V=IR) to setup a resistor in line with the reds to even out the power. Wedginator has a good description on how to handle this on his website. Do a search on these forums to pull a thread he's responded to and use his link. The led info is under the miniZ section.

JaMeZzZ122, you can find leds at your local Radio Shack. I picked up mine from Fry's, which is a little less expensive and they sell the super brites in packs of 10. Depending on your location, there may be another place you can pick them up.

Wedginator is really the resident expert on leds. I've just been dabling a bit.
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  #5  
Old 10-01-2002, 05:45 PM
Wedginator Wedginator is offline
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Hey, Sorry for the late reply. Been busy lately. Anyways, That happened to my too: when I put whites up front and reds rear.

For some strange reason the reds are brighter. Experimenting with different combinations of colors, I figured out that the voltage likes to go to the lower voltage rating LED.

For example, a Red LED is rated 1.85V and the white is 3.6V. Since it requires less voltage to power the Reds, the voltage likes to go there.

In conclusion, it's due to the voltage resistance of the lights. I tried putting a 10 ohm resistor on the reds and that seems to help out the voltage go to the whites.

I'm a bit lazy, er... busy to calculate the exact resistor value so use trial and error (I know it's more work, but it sure beats using my noggin )

So here's how I would calculate this resistor voltage. I'd take the red voltage use the battery voltage and subtract it (3V-1.85V=1.15V) then use the 1.15 volts to calculate the resistance to limit the voltage from the battery to 1.15V to the red light.

It's just your basic resistance calulations. Won't go into too much detail. For more info on resistance calculations, go to my website (http://www.geocities.com/mini_zracer/main) and click on the LED light section.


[edit]: I guess Shacky summarized this already

OHH one more important thing. Don't overload the battery with LEDs. The poor battery only supplies little amperage. So if you somehow load it up with like 4 superbrights, they will be all dim due to the massive pulling of all the lights. Better off using more batteries.

Last edited by Wedginator; 10-01-2002 at 05:50 PM.
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