LED Headlight Shunt Resistor Heat Experiment

[SatchelHopkins]

Background
So, as we mostly all know, when we replace a headlight lamp with an aftermarket LED one, the LED draws much less current than is expected by the computer which can cause it to throw warnings unless the unit incorporates a shunt resistor to draw additional "sacrificial" current, thereby tricking the computer into thinking everything is normal.

Here is the unit that I replaced my headlights with, which have a shunt resistor and work fine without throwing warnings.


With this unit, the lamp part mounts where the halogen bulb would have been. It has fan built in to help cool the lamp unit. The resistor disc then basically just has to be crammed inside the housing behind the dust cover.

The question in my mind is what kind of power does this resistor have to dissipate and how hot does it get.

Setup
So I wired a spare lamp up to some wire and plugged it into a bench supply and taped a thermocouple to the disc to monitor the temperature.



While I was not sure what voltage is applied to the lamps in the bike, I made the assumption that it is the full system voltage. So I set the power supply to 13.7VDC which caused a current draw of about 4 amps. So between the light, the fan, and the excess heat, we are sinking about 55 watts per bulb.



The results

So, I turned the thing on and just it hang in space while I monitored the temperature.



Initial and "Final" Temps



So, I turned the thing off at 177 degrees F. It was still climbing, though more much more slowly. I got tired of waiting at this point. At this temp, it will very much burn you.

This is in free space, so it really makes me wonder what is happening inside the light housing inside the dust cover. Also, keep in mind that the LED fan does not blow onto this part. I hope that there is some level of airflow through this housing, but I don't know if there is or not.

What are your thoughts? Is this level of heat a possible problem? By the way, I didn't measure it, but I can tell you that the lamp housing with the built in fan also get quite hot but not nearly as hot as the resistor disc.

 

[PGlaves]

My thoughts: Others will disagree. But what a kludge! In my house I have replaced all of the bulbs with LEDs. What were 60 watt bulbs are now 7 watt bulbs and my electrical consumption is reduced accordingly. But with a marvelous German engineered motorcycle we have several computers which monitor and control things. So we get an aftermarket LED headlight that draws a few watts but then add a resister to boost consumption up to 55 watts like the original bulb so as to fool the computer gizmo to ascertain we still have a 55 watt bulb in the system. With all due respect - this is STUPID!

 

[omega man]

LED’s don’t dissipate heat the way a filament style bulb does. In order to get the LED’s to generate even more and more visible light output, the heat generated needs to be dealt with.
Incandescent bulbs (filament) get hot but really don’t care. Throw in a CANBUS style operation and the bulbs will need a resistor circuit to adjust what the computer “sees”.
All of this confusion generally occurs when an LED is tried to be integrated into a fixture that wasn’t really designed for an LED and came factory equipped with a conventional (filament) bulb.

Some light reading here-

Why Do LED Headlights Have Fans? Exploring Cooling Systems

Discover the ins and outs of LED headlight bulb heat management, learn effective cooling methods so you can make informative decisions when choosing the best LED headlight bulbs.

sealight-led.com

OM

 

[oldcamper]

Non shunt leds are working well in my airhead and dirt bike to save watts for heated gear, but it appears it’s better to just leave incandescent bulbs in the newer BMWs.

I am reminded of the old Lucas electric motto “A proper gentleman does not motor about after dark” and the “off, dim, flicker” light switch label t-shirts that were popular back then … ah, progress!

 

[SatchelHopkins]

I think there are a number of points that could be made.

1. The bulb mount for the bikes was designed to handle 55 watts of power dissipation so no problem there. The issue is that we are now shifting a lot of that heat from the bulb mount into the cavity behind the bulb mount, which may not be able to deal with it as well.

2. When the bikes were designed, there was no such thing as a readily available LED replacement bulb, so no allowances were made for them. In their minds a lamp would always draw 4 amps, so if that current ever dropped below 2 amps, or whatever it is, then that would indicate a burned out bulb. I don't know that I can really fault them on the design other than as mentioned in #3 below.

3. As mentioned by Paul, the whole thing blows. Intentionally wasting energy is not my favorite thing. I guess the marketing crowd could spin it as a positive. "It has heated grips, heated seats, and a heated dash."

4. Personally, I hate that it is even an issue to contend with. It doesn't have to be. I could stick with the halogens. However, the LEDS are SO much brighter that I am willing to try and deal with the negatives. Add on driving lights might convince me to go back though.

 

[GTRider]

My thoughts: Others will disagree. But what a kludge! In my house I have replaced all of the bulbs with LEDs. What were 60 watt bulbs are now 7 watt bulbs and my electrical consumption is reduced accordingly. But with a marvelous German engineered motorcycle we have several computers which monitor and control things. So we get an aftermarket LED headlight that draws a few watts but then add a resister to boost consumption up to 55 watts like the original bulb so as to fool the computer gizmo to ascertain we still have a 55 watt bulb in the system. With all due respect - this is STUPID!

I’m in agreement with Paul on this one. IMHO if one wants more light on these bikes the most workable solution is the addition of aftermarket LED auxiliary lights. That resolves both issues with fitting LED “bulbs” into fixtures designed for incandescents: heat management, and proper beam control and focus. Both the reflector bucket and the lens in an incandescent light are designed for the specific placement and orientation of an incandescent filament. Try as they might, LEDs can’t exactly match that. Time to suss out the many aftermarket providers of high-quality LED auxiliary lights lighting. My current fav is Ruby Lighting but there are many others.

Best,
DeVern

 

[omega man]

My thoughts: Others will disagree. But what a kludge! In my house I have replaced all of the bulbs with LEDs. What were 60 watt bulbs are now 7 watt bulbs and my electrical consumption is reduced accordingly. But with a marvelous German engineered motorcycle we have several computers which monitor and control things. So we get an aftermarket LED headlight that draws a few watts but then add a resister to boost consumption up to 55 watts like the original bulb so as to fool the computer gizmo to ascertain we still have a 55 watt bulb in the system. With all due respect - this is STUPID!

It’s kinda tough to remember that the filament in a good old incandescent bulb is the resistance (resistor) and as long as the rated voltage is not exceeded (by very much) the bulb will work. The incandescent bulbs can be illuminated by voltage from a usually 0 to 120 volts and as the voltage climbs from 0 on its way to 120 volts, the bulb will glow brighter to the rating of the filament which is held in a vacuum to keep it from its own destruction.
This LED business has (generally) none of this flexibility. When shopping for an LED bulb, one has probably noticed that bulbs are specifically marked as “dimmable” which needs to be considered electronically.
Any time there is more voltage available to a device than the device needs, the excess has to be absorbed- somewhere.
OM

 

[r0ckrat]

I tried a set of Sealight bulbs that were advertised to fit and work, and I haven't had an error on the dash yet - they've been on the bike since February.

Sealight for 2016 R1200R

 

[omega man]

I tried a set of Sealight bulbs that were advertised to fit and work, and I haven't had an error on the dash yet - they've been on the bike since February.

Sealight for 2016 R1200R

Great!
There is definitely a difference in quality control in the way the LED lights are constructed.
OM

 

[pauls1150]

Feel free to refer to my "Speedmetal Conversion", in the Similar Threads below.
I've mounted their "driver" in some airflow, and also relieved the rear of my headlight cover.
Still seems to work pretty well.

 

[bhodges]

My thoughts: Others will disagree. But what a kludge! In my house I have replaced all of the bulbs with LEDs. What were 60 watt bulbs are now 7 watt bulbs and my electrical consumption is reduced accordingly. But with a marvelous German engineered motorcycle we have several computers which monitor and control things. So we get an aftermarket LED headlight that draws a few watts but then add a resister to boost consumption up to 55 watts like the original bulb so as to fool the computer gizmo to ascertain we still have a 55 watt bulb in the system. With all due respect - this is STUPID!

Paul, the flaw in your argument is that we replace our halogens with LEDs not to save wattage but to have a brighter, whiter light. Tricking the canbus to see 55 watts still uses the same wattage as the original halogen. We get better light and bulbs that have much longer life.
I don't call that stupid, I call it brilliant!...pun intended.