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Old 05-17-2005, 04:09 PM   #1
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Default LED'* and resistors, how does it all work?

i had an electronics class when i wa slike 10 but i cant rmemeber enough, ok so the standard LED is 3.5-3.8 volts, so which resistor would i need for that, and if i were to add more led'* onto that would i need a different resistor?
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Old 05-17-2005, 04:13 PM   #2
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I think you mean a standard LED is 3.5 to 3.8 Ohms?? Basically, you need tro make sure the LED you are wanting to use is rated for the correct voltage (this will vary, depending upon the LEDs intended use), and add resistance to match the bulb you are replacing (making sure the resistor is also rated for the proper voltage)

OR, if you're just after light output, and not worried if it'* brighter or setting off a Bad Bulb alert, just wire them straight. No extra resistors. NOTE: Without resistance, don't try using LEDs in your turn signals....
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Old 05-17-2005, 04:16 PM   #3
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i wanna do the interior lights, i was at radioshack looking at LEDs and they were labled in volts not ohms
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Old 05-17-2005, 04:45 PM   #4
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Not sure exactly what you need, but yes...led'* are usually about the voltage you mentioned. For me testing on a pinball circiut board with +5V I use a 180 ohm resistor (cause that'* what the book said)

I would google something like resistor for led 12V and ...guess what?

http://www.kpsec.freeuk.com/components/led.htm
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Old 05-17-2005, 04:52 PM   #5
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Wow. I was wrong, huh??
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Old 05-17-2005, 04:56 PM   #6
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Originally Posted by MOS95B
Wow. I was wrong, huh??
Happens to all of us occasionally. Specially when shooting from the hip as I usually do. Recently I was at Rat Shack picking up some LED'* for the pinballs....that'* why I remembered.
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Old 05-17-2005, 06:07 PM   #7
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Ok, I'd like to add to this. Why does an LED "bulb" that is rated as a 194 (our corner light bulbs) not work correctly in our cars? Same with the rear turn signals. I REALLY like the way they light up and work but I can't seem to get them to work correctly in the bonne.....
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Old 05-17-2005, 06:14 PM   #8
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Quote:
Originally Posted by driverjohn2005
Ok, I'd like to add to this. Why does an LED "bulb" that is rated as a 194 (our corner light bulbs) not work correctly in our cars? Same with the rear turn signals. I REALLY like the way they light up and work but I can't seem to get them to work correctly in the bonne.....
May not have proper resistance. The resistance of the bulb works along with the flasher unit to make the signals work. Compare the resistance of the LED replacement and the real bulb and see what the difference is, if any...
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Old 05-17-2005, 06:14 PM   #9
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Quote:
Originally Posted by driverjohn2005
Ok, I'd like to add to this. Why does an LED "bulb" that is rated as a 194 (our corner light bulbs) not work correctly in our cars? Same with the rear turn signals. I REALLY like the way they light up and work but I can't seem to get them to work correctly in the bonne.....
Dunno but when you figure it out I'm puttin one on my atv also.
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Old 05-20-2005, 01:30 PM   #10
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You cannot measure LEDs with an ohmmeter, they do not have a resistance, rather a reverse voltage potantial, that must be overcome by the source voltage to make the LED work. Since there is technically no resistance, if your source voltage is higher than the rated LED voltage, you must use a resistor in series with the LED to limit the current. The voltage and current ratings are listed by the manufacturer. The correct resistor value can be calculated using Ohms Law V x I = R (v- voltage, I- Current, R- resstance)
just rearrange the equation to find whatever value you are looking for.

What resistance does the turn signal circuit require to work properly? You could put a resistor of this value in parallel with the LEDs and it should work the same way.
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