What resistor to protect 12v LED?

Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=81200
Printed Date: May 12, 2025 at 3:49 PM

Topic: What resistor to protect 12v LED?

Posted By: agentk98
Subject: What resistor to protect 12v LED?
Date Posted: August 04, 2006 at 12:54 PM

Hi guys. New here to the forum and loving the site. Good thing someone suggested this. :)

Anyway, i just installed an aftermarket side-lamp or fender light. I plan to place my 12v Blue LED in it. As i'm sure you know, automotive voltage jumps up to 14v. I would like to protect the LEDs in some way. What resistor can i put to keep the voltage at a steady 11v-12v?

Replies:

Posted By: placebo-pete
Date Posted: August 04, 2006 at 4:00 PM

Hi There

If its just a single Blue LED a 10K resistor should do nicely

Placebo-Pete

Posted By: agentk98
Date Posted: August 04, 2006 at 9:12 PM

Thanks Placebo-Pete! Is the 10K resistor this one?
5W, 0.1Ω (TFNF12NR10KU)

P.S. i tried the calculator. This was the result:
1.2K Ohm, 1/4 Watt. Which then? :)

Posted By: placebo-pete
Date Posted: August 05, 2006 at 5:47 AM

Hi agentk98

Didn't answer the qustion properly there did I posted_image

Would you have the manufacturers specification of the LED you see to choose a resistor you would need to know what current the LED draws,power output etc.etc.

So if you can post those I'll be able to help out

Placebo-Pete

Posted By: agentk98
Date Posted: August 05, 2006 at 12:34 PM

no pete.

i didn't have the manufacturers specs. I just used the default values from the calculator. The LED i'm using is a super bright Blue one. I got it at an automotive accessories shop and is supposedly just "plug and play". Though i know i would prolong the life of the LED by adding a resistor. :)

Posted By: placebo-pete
Date Posted: August 05, 2006 at 1:58 PM

Hi no worries

I'm guessing if its a super bright LED the manufacturers specs will be about 450 to 500 milliamps output power with a 1.4 volt drop across the diode

I would recommend a
22 Ohm Resistor
with a Calculated Resistor Wattage of about
5.3 Watts

That should do the trick

Take Care

Placebo-Pete

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