led's, 12 volts the right voltage to stop?

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compudude86

Member - Posts: 36

Joined: March 29, 2006

Location: United States

Posted: October 15, 2008 at 8:02 PM / IP Logged

hello,

I am doing an LED project, and I have a question. I've wired LEDs into my instrument panel twice, and both times they burned out, flickering before they quit. I'm guessing this is because the voltage isn't exactly 12 volts and the ebay sellers give you 12V resistors, when it should be somewhere around 13-15 volts?, to be safe, im guessing. I think I've observed this when I replaced the dummy lights in the dash and some were dimly lit, im guessing from slight residual voltage even though they were off. also, should I add some regular diodes to the beginning of the circuit to prevent any kind of reverse voltage from possibly damaging the chip on the LED?

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KPierson

Platinum - Posts: 3,527

This member consistently provides reliable information

Joined: April 14, 2005

Location: Ohio, United States

Posted: October 15, 2008 at 8:56 PM / IP Logged

I've had the best luck with finding the forward current of the LED and using Ohm's Law. If you have an LED with a If of 25mA and you want to make it "safe" calculate a resistor value based on 15vdc.

R=V/I

R=15/.025

R= 600 ohms

Of course you need to use the If from your specific LED.

Kevin Pierson

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disker

Member - Posts: 33

Joined: August 04, 2006

Location: United States

Posted: November 04, 2008 at 7:43 PM / IP Logged

So, if I was to run an LED off a 12v battery (14.4 while chargin, 15 for safety) and the LED is rated with a current of 20 mA, then I would use:

15/.02 or 750 OHM.

Did I get that right?

Disker

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led's, 12 volts the right voltage to stop?

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