HID resistor
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 911
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From: Southern IL
HID resistor
How do I select a resistor wattage to correct my headlight doors?
I've got 9005 HB3 100W bulbs - no idea on the ballasts.
Will any 35w or 55w resistor restore order and peace to my headlight system? Or does it have to match my bulb wattage?
I've got 9005 HB3 100W bulbs - no idea on the ballasts.
Will any 35w or 55w resistor restore order and peace to my headlight system? Or does it have to match my bulb wattage?
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 911
Likes: 27
From: Southern IL
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 911
Likes: 27
From: Southern IL
I can't accurately tell without pulling off my headlights. All I can see is the ballast and the backside of the bulbs. I don't have any fancy projectors or anything like that. The hi-beams look stock and the resistors in the fusebox are 10A.
I have to turn on the hi-beam switch to close the buckets. I think it's really tacky leaving it like this, and I spent hours last week chasing a weird electrical issue, while the whole time it was just the buckets wanting to come up for no reason.
I like the look of the light though...big improvement from stock. I ordered the 35W resistor from a vendor.
Last edited by Vicarious.; Oct 19, 2011 at 10:25 PM.
Instructor
Joined: Feb 2011
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From: eustis FL Saved and blessed; what else matter?
Resistors are rated in ohms and watts. The ohm rating tells you how much load you are adding to the circuit, The watt rating tells you how much current the resistor can handle without burning out. You need HIGH watts to make the resistor last. You need enough ohms to mimic the incandescent light amp draw. If you go LOWER than 55 watts, your resistor will burn out quickly. The reason a marker lamp works is because the lamp dissipates a lot of heat easily. Even a 55 watt resistor will get VERY hot. A 5 watt resistor in parallel with a headlight circuit could get hot enough to start a fire if it lasted long enough. Go with what;s proven to work instead of risking your car by trying to reinvent the wheel.
Race Director
Joined: Apr 2007
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From: South Western Ontario
Huh? A 5W resistor will dissipate 2W of power no problem. A resistor that provides a couple of watt of load is all you need. A 5W resistor providing a couple of watts of load is not the same as trying to provide 55W of load with a 5W resistor.
The 35W or 55W resistors are oversized and unnecessary. But, the vendors sell them so everyone thinks that's what's needed. To be honest, I look at those 55W prepackaged load resistors and find it extremely hard to believe that size of resistor can provide 55W of load. They look good for providing maybe 10W of load.
The 35W or 55W resistors are oversized and unnecessary. But, the vendors sell them so everyone thinks that's what's needed. To be honest, I look at those 55W prepackaged load resistors and find it extremely hard to believe that size of resistor can provide 55W of load. They look good for providing maybe 10W of load.
Instructor
Joined: Feb 2011
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From: eustis FL Saved and blessed; what else matter?
Huh? A 5W resistor will dissipate 2W of power no problem. A resistor that provides a couple of watt of load is all you need. A 5W resistor providing a couple of watts of load is not the same as trying to provide 55W of load with a 5W resistor.
The 35W or 55W resistors are oversized and unnecessary. But, the vendors sell them so everyone thinks that's what's needed. To be honest, I look at those 55W prepackaged load resistors and find it extremely hard to believe that size of resistor can provide 55W of load. They look good for providing maybe 10W of load.
The 35W or 55W resistors are oversized and unnecessary. But, the vendors sell them so everyone thinks that's what's needed. To be honest, I look at those 55W prepackaged load resistors and find it extremely hard to believe that size of resistor can provide 55W of load. They look good for providing maybe 10W of load.
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Le Mans Master
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From: Hilton NY
You don't specify the most inportant parameter which is resistance in ohms, this along with the maximum car voltage will determine the power used by the resistor. I used a 150 ohm resistor, at 15 volts that would be 1.5 watts used by the resistor. A 5 watt resistor at this value would provide a cooler running resistor than a 2 watt but you need to check whatever one you pick to make sure it doesn't get too hot in the environment it's mounted. To determine the value for my car I wired a small 10 turn wirewound potentiometer in parallel with the HID ballast and adjusted it until the headlight doors just started to work, about 220 ohms, then I replaced it with a 150 ohm resistor to ensure operation. There is no reason to add a low ohmic value resistor when the car computer thinks 150 ohms is the same as the old headlights. A ten ohm resistor for example will consume 22.5 watts at 15 volts. I used a 25 watt resistor only because I had one already and it runs cool.
Race Director
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From: South Western Ontario
LOL, a 50 ohm resistor will be dissipating about 4W maximum connected to the 14.2V maximum electrical system in the car. Why do you need a 50W resistor? A 5W resistor would be too small to ensure reliable operation, but a 10W resistor would be more than enough and it certainly would not quickly burn out. Maybe you forgot the basics during your 50 years of being an electronics technician?
A 100ohm, 5W resistor will work fine for this purpose.
A 100ohm, 5W resistor will work fine for this purpose.
Instructor
Joined: Feb 2011
Posts: 228
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From: eustis FL Saved and blessed; what else matter?
You don't specify the most inportant parameter which is resistance in ohms, this along with the maximum car voltage will determine the power used by the resistor. I used a 150 ohm resistor, at 15 volts that would be 1.5 watts used by the resistor. A 5 watt resistor at this value would provide a cooler running resistor than a 2 watt but you need to check whatever one you pick to make sure it doesn't get too hot in the environment it's mounted. To determine the value for my car I wired a small 10 turn wirewound potentiometer in parallel with the HID ballast and adjusted it until the headlight doors just started to work, about 220 ohms, then I replaced it with a 150 ohm resistor to ensure operation. There is no reason to add a low ohmic value resistor when the car computer thinks 150 ohms is the same as the old headlights. A ten ohm resistor for example will consume 22.5 watts at 15 volts. I used a 25 watt resistor only because I had one already and it runs cool.
Instructor
Joined: Feb 2011
Posts: 228
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From: eustis FL Saved and blessed; what else matter?
LOL, a 50 ohm resistor will be dissipating about 4W maximum connected to the 14.2V maximum electrical system in the car. Why do you need a 50W resistor? A 5W resistor would be too small to ensure reliable operation, but a 10W resistor would be more than enough and it certainly would not quickly burn out. Maybe you forgot the basics during your 50 years of being an electronics technician?
A 100ohm, 5W resistor will work fine for this purpose.
A 100ohm, 5W resistor will work fine for this purpose.
Instructor
Joined: Feb 2011
Posts: 228
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From: eustis FL Saved and blessed; what else matter?
THANKS FOR THE CLARIFICATION! I offered the post as a help to those who have been trying to get their headlight actuators to work right and have been confused by previous posts. I've said all I need to say on the subject and I'll leave it up to you guys to work out the details on resistor ohmage. I intend to try the 150 ohm resistor myself. Thanks for the tips guys!
Race Director
Joined: Apr 2007
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From: South Western Ontario
I have never confused ohms with watts. But apparently, me posting that you need to install a resistor to dissipate 2W of power is confusing to you.
Lets see, I have 14.2V and want to apply a 2W load. 14.2^2/2 = 100 ohms. So, I am recommending 100 ohms. I wouldn't recommend using a 2W resistor for 2W of power, so use a 5W resistor to be safe.
Simple, right?
Also, for the record. your only mention of 6 ohms was this which really says nothing about the resistor you actually used or that this is the ohms needed.
Last edited by lionelhutz; Aug 13, 2012 at 09:25 PM.
