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Awesome, I've been looking at these headlights for when I can afford them.
Since the small bulbs will eventually be subject to burn out as well, maybe these load resistors
(https://www.superbrightleds.com/more...ion/2175/5075/) could be used instead? I'm sure the connectors aren't correct, but they could be soldered in per these instructions.
I measured a 194 bulb I had and it showed 4.7 ohms, so 6 on the load resistors should be close to the 168 bulb.
Great post and write up!
I was wondering why the resistor was in the kit. Now I know...
My car has the fog lights grounded directly so it's not a problem for me.
Awesome, I've been looking at these headlights for when I can afford them.
Since the small bulbs will eventually be subject to burn out as well, maybe these load resistors
(https://www.superbrightleds.com/more...ion/2175/5075/) could be used instead? I'm sure the connectors aren't correct, but they could be soldered in per these instructions.
I measured a 194 bulb I had and it showed 4.7 ohms, so 6 on the load resistors should be close to the 168 bulb.
Great post and write up!
You asked a great question, and I will answer it in detail below!
You wouldn't want to use these in a C4, while they would work, there would be no benefit over my solution, not even a cost savings.
Also, you brought up an interesting point when you said you measured the resistance of a 194 bulb. Unfortunately, the measurement you made yielded deceptive results. Many are not aware of the dynamic properties of an incandescent lightbulb, and that's completely fine. For this reason, I will elaborate on that a little later on.
Before I begin explaining things, I will turn your attention to two useful and basic formulas which are necessary to substantiate my point:
Ohm's law: Voltage is equal to current multiplied by resistance, or, V = I*R
Power equation: Power is equal to the square of the voltage potential divided by resistance, or, P = V^2/R.
Using the formula above, we can easily calculate the power dissipated by one load resistor:
P[ower] = (14v*14v)/6ohm, or 32.7w. While this might not seem like much, this amount of power in a small area equates to a very substantial rise in temperature. In fact, if you were to touch one of these resistors when 14v is applied to it, you'd burn your fingers pretty nicely. I would not be at all surprised if the temperature of the resistor exceeded 175F.
As an irrelevant aside, in my line of work, two of the most important characteristics to electrical engineers are cost of materials and thermal characteristics of a design.
I return now to the measurement you took of a 194 bulb:
The resistance you measured of a 194 bulb is not representative of the true resistance of the bulb while it is operating. What is not in any way intuitive is, the resistance of a bulb when it is off, especially when cold, is nearly a short. As the temperature of the bulb rises, so does its resistance. Complicating matters further is, the relationship of the bulb's resistance with respect to its operating current is not exactly linear. I won't bore anybody with the physics behind this.
In order to ascertain the true resistance of a 194 bulb when it is operating at 14v, we need to use the power formula above, and some algebra. I won't go into the algebra necessary to perform the calculation, so trust me on the accuracy of the calculation.
Since a 194 bulb has a power rating of 3.78w in a 14v circuit, the true resistance while it is operating is equal to 51.9ohms. At this point, you're probably saying "Then why does my meter read so different? Is there something wrong with it?" The answer to that is, no, there isn't anything wrong with your meter. The way a meter measures resistance is by applying a constant current to the resistor being measured, and calculating the resistance by measuring the voltage created across this resistor. The typical meter has a measurement current of about .001 amps, not nearly enough to turn the bulb on, or anywhere near the amount of current present when the bulb is in a 14v circuit.
Just as a reminder, I recommend against using a 194 bulb, and using a 168 bulb.
Lastly, I'm going to address an interesting point you made about longevity of the incandescent lightbulb used in the modification.
In my modification, I specified a 168 longlife bulb. In practice, a longlife bulb lasts several years when used properly, I've seen as long as 5-10 years. As a reminder, the purpose of the 168 bulb is pull the foglight relay coil to ground, and prevent the highbeam input to the LED headlight from being "tickled on". In this state, the coil of the foglight relay greatly limits the amount of current through the bulb, so much so, that it doesn't even light up at all. Under this condition, it is not unreasonable to expect the 168 to last nearly forever. The only time the 168 bulb will illuminate at full intensity is when the highbeams are switched on; for most people, they don't drive with their highbeams on continuously anyway. Even under this circumstance, the bulb would last a very long time since I've recommended a longlife bulb.
I hope this information is useful for you
Last edited by Circuit Doctor; 04-08-2015 at 09:54 PM.
Well, you've convinced me, for one. Even though the 194 bulb seems to work fine on mine currently I'm going to go ahead and swap it out for a 168 just for the peace of mind.
Well, you've convinced me, for one. Even though the 194 bulb seems to work fine on mine currently I'm going to go ahead and swap it out for a 168 just for the peace of mind.
I have a great idea to bolster you swapping this out:
You raised a concern about the temperature of the bulb compromising the insulation of the wires it may touch. Although there is nothing to be worried about, you can put a piece of black heatshrink tubing over the bulb when you change it out, for even more piece of mind. That'll provide an extra layer of insulation between the bulb and the wires near it.
I have a great idea to bolster you swapping this out:
You raised a concern about the temperature of the bulb compromising the insulation of the wires it may touch. Although there is nothing to be worried about, you can put a piece of black heatshrink tubing over the bulb when you change it out, for even more piece of mind. That'll provide an extra layer of insulation between the bulb and the wires near it.
That is an excellent idea, I'm ashamed I didn't think of it.
You asked a great question, and I will answer it in detail below!
Before I begin explaining things, I will turn your attention to two useful and basic formulas...
Using the formula above, we can easily calculate...
....{Not kidding about detail!!!!!! }....
But thanks, the underlying theory and thought process are always helpful. I used to work in the engineering department of an utility company, so basically familiar, but on the AC side - at hundreds of amps and thousands of volts. And very few direct measurements
Originally Posted by Circuit Doctor
Unfortunately, the measurement you made yielded deceptive results.
...
The answer to that is, no, there isn't anything wrong with your meter.
I dunno, tried again after reading your reply and got this reading...
Originally Posted by Circuit Doctor
Just as a reminder, I recommend against using a 194 bulb, and using a 168 bulb.
I didn't clarify, but I had a 194 in the garage, but not a 168, so measured what I had and guesstimated a value for the 168...
Originally Posted by Circuit Doctor
...You wouldn't want to use these in a C4, while they would work, there would be no benefit over my solution, not even a cost savings.
The bottom line, as most of us have at least some of the parts already laying around to build your design at no cost.
But again, thanks for your detailed explanation! Very instructive.
You asked a great question, and I will answer it in detail below!
You wouldn't want to use these in a C4, while they would work, there would be no benefit over my solution, not even a cost savings.
Also, you brought up an interesting point when you said you measured the resistance of a 194 bulb. Unfortunately, the measurement you made yielded deceptive results. Many are not aware of the dynamic properties of an incandescent lightbulb, and that's completely fine. For this reason, I will elaborate on that a little later on.
Before I begin explaining things, I will turn your attention to two useful and basic formulas which are necessary to substantiate my point:
Ohm's law: Voltage is equal to current multiplied by resistance, or, V = I*R
Power equation: Power is equal to the square of the voltage potential divided by resistance, or, P = V^2/R.
Using the formula above, we can easily calculate the power dissipated by one load resistor:
P[ower] = (14v*14v)/6ohm, or 32.7w. While this might not seem like much, this amount of power in a small area equates to a very substantial rise in temperature. In fact, if you were to touch one of these resistors when 14v is applied to it, you'd burn your fingers pretty nicely. I would not be at all surprised if the temperature of the resistor exceeded 175F.
As an irrelevant aside, in my line of work, two of the most important characteristics to electrical engineers are cost of materials and thermal characteristics of a design.
I return now to the measurement you took of a 194 bulb:
The resistance you measured of a 194 bulb is not representative of the true resistance of the bulb while it is operating. What is not in any way intuitive is, the resistance of a bulb when it is off, especially when cold, is nearly a short. As the temperature of the bulb rises, so does its resistance. Complicating matters further is, the relationship of the bulb's resistance with respect to its operating current is not exactly linear. I won't bore anybody with the physics behind this.
In order to ascertain the true resistance of a 194 bulb when it is operating at 14v, we need to use the power formula above, and some algebra. I won't go into the algebra necessary to perform the calculation, so trust me on the accuracy of the calculation.
Since a 194 bulb has a power rating of 3.78w in a 14v circuit, the true resistance while it is operating is equal to 51.9ohms. At this point, you're probably saying "Then why does my meter read so different? Is there something wrong with it?" The answer to that is, no, there isn't anything wrong with your meter. The way a meter measures resistance is by applying a constant current to the resistor being measured, and calculating the resistance by measuring the voltage created across this resistor. The typical meter has a measurement current of about .001 amps, not nearly enough to turn the bulb on, or anywhere near the amount of current present when the bulb is in a 14v circuit.
Just as a reminder, I recommend against using a 194 bulb, and using a 168 bulb.
Lastly, I'm going to address an interesting point you made about longevity of the incandescent lightbulb used in the modification.
In my modification, I specified a 168 longlife bulb. In practice, a longlife bulb lasts several years when used properly, I've seen as long as 5-10 years. As a reminder, the purpose of the 168 bulb is pull the foglight relay coil to ground, and prevent the highbeam input to the LED headlight from being "tickled on". In this state, the coil of the foglight relay greatly limits the amount of current through the bulb, so much so, that it doesn't even light up at all. Under this condition, it is not unreasonable to expect the 168 to last nearly forever. The only time the 168 bulb will illuminate at full intensity is when the highbeams are switched on; for most people, they don't drive with their highbeams on continuously anyway. Even under this circumstance, the bulb would last a very long time since I've recommended a longlife bulb.
I believe these would be the correct plug and play LED headlight/foglight "load resistor" wiring solution for a C4 with OEM H4 headlight plugs. You agree that these would work @ $17.95 for the pair with no soldering, cutting, or any other parts required. I think this may be the easiest plug and play solution for C4 1990~1995 owners with this LED issue out there. Yes those resistors may get hot but if you look at this H4 wiring pair you'll see the load resistors are much larger than the ones on the 9006 kit linked to above, they pretty much look like large heat sinks that can be hard mounted or zip tied out of the way very easily. Correct me if I'm wrong but these appear to be a commercially available wiring solution that mimics your well though out and executed home made solution with the ease of simple plug and play installation.
No bulbs to worry about or have to replace, simple plug and play solution that doesn't require cutting and soldering your OEM wiring harness, made to work specifically with our OEM H4 headlight terminal plugs, @ the correct current draw, and only $17.95 for the pair!
Im curious... with the nighthawk leds.. Will the fogs function normally with the headlight switch in parking (headlamps off) ? And am assuming the headlights will work fine when on with fog lamps off? I don't use them together ever. I use the fogs as driving lights but am planning a few trips and cruises and I cant be blinding all my friends with the HID fogs because the light goes everywhere.
But thanks, the underlying theory and thought process are always helpful. I used to work in the engineering department of an utility company, so basically familiar, but on the AC side - at hundreds of amps and thousands of volts. And very few direct measurements
I dunno, tried again after reading your reply and got this reading...
I didn't clarify, but I had a 194 in the garage, but not a 168, so measured what I had and guesstimated a value for the 168...
The bottom line, as most of us have at least some of the parts already laying around to build your design at no cost.
But again, thanks for your detailed explanation! Very instructive.
Jay
Jay -
Glad to hear your positive feedback on my post, nice to know you have a decent amount of electrical knowledge, it certainly goes a long way! I tried to be succinct, but also detailed. I'm pleased to hear it was not received as condescending.
To your point, I tried very hard to conjure up a solution using materials which are cheap, and likely already in people's junk drawers.
High power distribution is no joke! You're certainly right about voltage measurements being made without contact. Even still, you have almost no room for error.
In my discipline, I deal with aircraft electrical systems and products; primarily, DC. I always tell people DC stands for "dangerous current". Unlike AC, DC never crosses zero. Making body contact with a high enough DC voltage can make one get stuck to it, and then you're basically screwed. In the aircraft world, 270v DC is common, and is potentially lethal. AC, on the other hand, tries to almost "push you off" as it changes its polarity back and forth. Of course, at the AC voltages you've dealt with (which makes 270v DC look like a joke), you're as good as dead if a mistake is made.
I believe these would be the correct plug and play LED headlight/foglight "load resistor" wiring solution for a C4 with OEM H4 headlight plugs. You agree that these would work @ $17.95 for the pair with no soldering, cutting, or any other parts required. I think this may be the easiest plug and play solution for C4 owners with this LED issue out there. Yes those resistors may get hot but if you look at this H4 wiring pair you'll see the load resistors are much larger than the ones on the 9006 kit linked to above, they pretty much look like large heat sinks that can be hard mounted or zip tied out of the way very easily. Correct me if I'm wrong but these appear to be a commercially available wiring solution that mimics your well though out and executed home made solution with the ease of simple plug and play installation.
No bulbs to worry about or have to replace, simple plug and play solution that doesn't require cutting and soldering your OEM wiring harness, made to work specifically with our OEM H4 headlight terminal plugs, @ the correct current draw, and only $17.95 for the pair!
Mako,
The issue I have with these resistors, aside from thermal (even in spite of a slightly larger form factor), is that I don't know what's "in the box". While they appear to be well made (as is pretty much everything superbrightleds sells), I have no way of knowing (without purchasing one) what the resistors are physically connected to. My suspicion is that the resistor is wired between low beam and ground only, presumably to preclude false triggering of a load-sensing circuit which warns the vehicle operator that one of their headlamps are burnt out - a feature of some modern vehicles. In a C4, no such circuitry exists, so there would be no benefit, nor solution to the foglight/highbeam conundrum, in this configuration. In order to make this do what you want, you would have to open the box up, and physically alter it so that the resistor is wired between high beam and ground instead. Additionally, I'd be concerned the resistor in the box is "potted", or submerged in regular RTV (silicone), or a thermally conductive RTV, in which case, it'd probably be more trouble that it's worth since you'd have to dig all of that material out of there, and re-fill it. Because of all this, I personally wouldn't recommend those, even though the price really can't be beat.
For clarity sake, this would be of no value, irrespective of configuration of the resistor, to your 1989, since the foglight circuitry is different from 1990-up. I infer that you're aware of this, and are merely proposing a turnkey (or, "plug and play") alternative to my modification for 1990-up C4s, which is appreciated!
Last edited by Circuit Doctor; 04-09-2015 at 06:55 PM.
Im curious... with the nighthawk leds.. Will the fogs function normally with the headlight switch in parking (headlamps off) ? And am assuming the headlights will work fine when on with fog lamps off? I don't use them together ever. I use the fogs as driving lights but am planning a few trips and cruises and I cant be blinding all my friends with the HID fogs because the light goes everywhere.
I'll answer your question in two ways since it is not clear to me.
If you were to install nighthawk LED headlights without performing this modification (assuming your C4 is 1990-up), this is what would happen:
- Your foglights would not turn on at all, no matter what.
- When your lowbeams are on, and you switch on your foglight switch, your highbeams will illuminate as well.
- When your headlights are off, and you switch on your foglight switch, your headlights will flicker (assuming they are rotated up and you can see them).
- When you hit your highbeam switch, your highbeams and lowbeams will be on at the same time.
If you were to install nighthawk LED headlights and perform the modification, your C4's lighting system would operate exactly as it did originally:
- Your foglights would turn on when your parking lights are on, and so is your foglight switch as well.
- When your lowbeams are on, and you switch your foglight switch, your lowbeams and foglights will be on at the same time.
- When you hit your highbeam switch, your highbeams and lowbeams will be on at the same time, and your foglights will switch off - just as they were originally designed to do by GM before LED headlights ever existed.
The issue I have with these resistors, aside from thermal (even in spite of a slightly larger form factor), is that I don't know what's "in the box". While they appear to be well made (as is pretty much everything superbrightleds sells), I have no way of knowing (without purchasing one) what the resistors are physically connected to. My suspicion is that the resistor is wired between low beam and ground only, presumably to preclude false triggering of a load-sensing circuit which warns the vehicle operator that one of their headlamps are burnt out - a feature of some modern vehicles. In a C4, no such circuitry exists, so there would be no benefit, nor solution to the foglight/highbeam conundrum, in this configuration. In order to make this do what you want, you would have to open the box up, and physically alter it so that the resistor is wired between high beam and ground instead. Additionally, I'd be concerned the resistor in the box is "potted", or submerged in regular RTV (silicone), or a thermally conductive RTV, in which case, it'd probably be more trouble that it's worth since you'd have to dig all of that material out of there, and re-fill it. Because of all this, I personally wouldn't recommend those, even though the price really can't be beat.
For clarity sake, this would be of no value, irrespective of configuration of the resistor, to your 1989, since the foglight circuitry is different from 1990-up. I infer that you're aware of this, and are merely proposing a turnkey (or, "plug and play") alternative to my modification for 1990-up C4s, which is appreciated!
Again thanks for your response, and excellent incite!
Yes I'm aware this "solution" of course wouldn't work for my '89 with different grounding fogs but it might work for '90~'96 C4's. The fact that these could be plug and play, & cheap, makes them intriguing.
If your correct and those load resistors are wired between low beam and ground only that's not going to help. I didn't even think about that, as I assumed the resistors the would be wired between high beam and ground instead. Not sure why I assumed that, probably wishful thinking. But you are probably right on the money about that. Either way someone should try these out and find out for sure, they are certainly cheap enough to give it a shot.
I'm pleased to hear it was not received as condescending.
No worries, you'd have to try pretty hard for me to take something as condescending - after a beer or three I can sometimes be convinced to relate my experiences with a truly condescending former supervisor...
I am wanting to buy either the Nighthawks or the JW Speaker 8900 Evolutions. Just want to find where to get a good price on them since they seem to be sold separate at like $300 apiece, plus I want to figure out this wiring before the purchase.
I am wanting to buy either the Nighthawks or the JW Speaker 8900 Evolutions. Just want to find where to get a good price on them since they seem to be sold separate at like $300 apiece, plus I want to figure out this wiring before the purchase.
What did Daniel Stearn do, build a harness or something? By the way I either want the JW Speaker or GE LEDs, so will Daniel Stearns item work with these?
What did Daniel Stearn do, build a harness or something? By the way I either want the JW Speaker or GE LEDs, so will Daniel Stearns item work with these?
He will build a harness for you but has a lot of info and deals with cibies. They were better for my needs.
04-08-2015, 01:08 AM
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