what type and size resistor?

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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=96018
Printed Date: May 16, 2024 at 12:36 AM

Topic: what type and size resistor?

Posted By: bazza2468
Subject: what type and size resistor?
Date Posted: July 29, 2007 at 11:39 AM

Have a problem, I need to fool a truck into thinking the side marker lights are connected. Its a 2007 Mercedes Sprinter the side markers are 12v 3w and there are two per side. Can anyone give me some help or the formula to work out what size ballast resistor I will need to use as Iits starting to drive me crazy :errr: or is it a case of use the V=IR and work it from that in which case I think I know the answer. Thanks in advance for any help.

Replies:

Posted By: Mad Scientists
Date Posted: July 29, 2007 at 12:30 PM

Based strictly on your numbers, you'd use W=V*I, then V=I*R

3 watts = 12v * 0.25 amps (you could also measure this to verify)

12v = 0.25a * 48 ohms per bulb.

I'm guessing 4 bulbs total, for a total draw of 1 amp.. so your resistor size would have to be around 12 ohms.

12 volts = 1 amp * 12 ohms.

Now, the wattage rating of the resistor would be calculated as follows..

12 watts = 12 volts * 1 amp

So.. you'd need either (1) 12 ohm, 12 watt resistor, or (4) 48 ohm 3 watt resistors.

Pretty big resistors.

Jim

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