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Old 02-16-2004, 03:26 PM   #1
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Default LED powering question

If I tapped into the cigarette lighter in the dash, would i be able to power 4 or 8 LEDs?

I've done this before on my PC, i have two blue LEDs in parallel off the power supply, with a 285ohm (or so) resistor on each. Just do the same thing in the car?

/twiddles thumbs
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Old 02-16-2004, 03:40 PM   #2
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Set up your array with a rheostat in between. Dial it high, then turn on the juice. Adjust the rheostat until it looks right, then remove it and measure it
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Old 02-16-2004, 06:02 PM   #3
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You mean like a PC rheo bus? Damnit you know i don't have a voltmeter lying around. I'd just wire them up in parallel, some resistors, and flip my switch.
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Old 02-17-2004, 04:05 AM   #4
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Oh, for chrissake, go buy a Volt/Ohm meter!!! $10 for a cheapy at WalMart, Radio Shack, etc. And Rheostate is a fancy word for variable resistor, like the volume control **** on an (old) radio. You can use it to manually adjust the brightness of your neons, or like will said, determine the correct resistance for the amount of light you want.
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Old 02-17-2004, 10:31 AM   #5
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SO i could run one rheostate as a brightness **** (oo a **** for my switches) and such? I'm sure the lighter has enough juice for 4 or 8 LEDs....
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Old 02-17-2004, 10:45 AM   #6
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Potentially, yes....
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Old 02-17-2004, 11:45 AM   #7
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Generic LED have 30 milliamp rating so for a 14.5volt system (your car) you need 470 ohms. 390 ohms will make them burn brighter but have a shorter life.
Solder the resistor is series with positive lead and cover with heat shrink tape.
To tell the diff between the positive lead and negative lead on an LED, the negative lead is on the flat side of the LED (the led only looks round, its actually a 'D' shape).

Heres a site to show you the color code for the resistors.
http://www.dannyg.com/examples/res2/resistor.htm
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Old 02-17-2004, 12:27 PM   #8
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don't use a volume control for this. Volume controls have a non-linear 'Audio' Taper. Use a standard rheostat, or get a potentiometer instead, and run a jumper to turn it into a rheostat. Radio Shaq for both. Very inexpensive.

When you start running arrays of LEDs, you have to stop and think. Do you want to bias each one seperately with a resistor on each, or one resistor for the whole array?
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Old 02-17-2004, 03:05 PM   #9
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So if i want to do them all in parallel, i'll need around 400ohm resistance for each one? So if i'm doing 4 LEDS find a rheostat around 1.6k resistance? or for 8 do two of those, or one that does around 3.2k ohm resistance?

I'd rather use one adjustable rheostat for the whole array.
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Old 02-17-2004, 11:37 PM   #10
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The cig lighter has a 10 amp fuse so you could hook up 500 standard led'* to it. average led'* need 20ma not 30ma like I stated above.
This site has what your looking for in a variable brightness led.
http://members.shaw.ca/roma/thirty-one.html
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