Need an Electrical Engineer's help

mcali17 · September 15, 2002

If there are any electrical engineers out there that could help me with a problem I am having with a Philips 9006 HID headlight conversion, in my 2002 Envoy, I would really appreciate it. And also if you can explain to me how a relay works that would be great.

Here is the story as brief as possible. First the background:

The GMC Envoy uses the Low Beam Headlight bulbs as the DRL (Daytime Running Lights). These headlights also illuminate when it is dark and you use the keyless entry (perimeter entry lighting). Of course in these two modes the headlights are on at a reduced amount of power. I checked with two different HID distributors that carry this kit. They both assured me that since these kits (see links to wiring diagrams)

http://community.webshots.com/photo/50163506/50163819LHzsVR

http://community.webshots.com/photo/50163506/50163724WDtgbi

are directly connected to the battery it did not matter. "The relay only requires a trickly current" from the stock headlight connector, once it received this current it would switch the relay on, which in turn would draw full power from the battery, power the ballasts and ignite the HID's. So in instances where my DRL's should be on at a reduced power, my HID's would be on at full power. Which is fine by me.

Yesterday my brother and I installed the system. They are awesome. However, when the DRL's are on, the relays make a loud buzzing sound and the HID's flicker almost like strobe lights. The other problem is when it is dark, and I use my keyless entry the same thing happens.

My guess is that either (now help me out here) the voltage or amperage is not high enough to switch the relay and draw full power from the battery to ignite the HID's. They actually do light, but have a flicker to them.

What I am thinking is that if I can find a relay that will switch at a lower voltage? or amperage? and still be able to handle the 12-14 volts from the battery to the ballast, I will be in good shape. Can anyone help me on if this is right? Or where I could even find such a relay or have one made that would work? The last thing I want to do is damage the ballasts or bulbs and I am sure that when the truck goes into DRL mode, that is what's happening. Thank you for your help in advance.

I have emailed the company I purchased them from but they are not open on the weekends, so I am waiting to hear from them but I wanted an experts opnion in the meantime. ???

carguru · September 16, 2002

The relay in the system just acts as a remote switch. Since the the stock system cannot output the voltage required for the Xenons, they have to be controlled by a remote switch that powers the ballasts. Inside the relay is a spring that is normally in one position. Normally a voltage is connected to the spring (battery voltage, 13v). When a signal voltage is applied, (your stock light switch turning on, for example) it pulls the spring and contact to a second position (headlight ballast power). This completes the circuit. When the signal voltage is turned off, the spring drives the contact back to position 1, thus breaking the circuit. In a nutshell, that is how a relay works.

Getting to your problem. There may be one of 2 things happening here. First, the relay may be too large. This means that when the drls kick in, the voltage is not enough to keep the relay engaged, but it is fine when the normal headlights come on. This could be solved by going to a smaller relay. However, the drawback to going to a smaller relay is that the contacts in the relay might not handle the voltage at normal voltage. With this, you will have problems with relay life.

The second thing that could be happening is that the reduced voltage for the drl is not truly reduced voltage. It might be modulated. This means that the voltage is being switched on and off. Directly connected to the light, you would not notice the swtiching. Standard filament lights are very forgiving of short term power flickers. Power flickers to a relay, can cause some problems. It can cause the relay to chatter. I am not certain whether or not the Trailblazer has a modulated system. I have heard of this method being used on drls and twilight sentinel features for some cost savings in the design.

As for problems this may cause, first off, the lights will flicker with the drls and perimeter entry lighting. This is just an annoyance. This can cause premature wear of the relay and bulbs. It should not hurt the ballasts. Good luck.

mcali17 · September 16, 2002

carguru- Thanks for that great explanation. My guess would be the modulated theory as the relays make a very lound buzzing noise when the DRL's are on. If this is the case, can I hook a multi-meter up to the stock 9006 bulb connection and look for this voltage modulation while in DRL mode? Will it just kind of increase or decrease or does it actually go from 13V to 0V very fast? Can it be seen on a multimeter? At least that way I would know what I am dealing with. Do you know of anyway I could make this work, like a relay that has a delay? Don't they make electronic and not mechanical relays? The company's technical service person is supposed to contact me tomorrow. I will let you know what they tell me.

Thanks again for the great information, I really appreciate it.

mcali17 · September 16, 2002

Carguru- I have one other question that you may be able to help me with. I don't know if you looked at my wiring diagram, but what if instead of connecting the stock 9006 connection, which provides power to the bulbs in regular and DRL mode, to the relay (which turns on the HID's when it gets power) I instead ran this wire from the relay to the healight switch directly. Then, when either I turned on the headlights or they came on automatically this would provide the constant 13V to switch the relay on. If the truck sends voltage to the stock headlight connectors they won't be attached to anything, or I could always splice these into some other type of bulb or something? Do you think that would work???

carguru · September 16, 2002

Yes, they do make a semiconductor type relay. Operates on similar principle except no moving parts. The one I described was a mechanical relay. The semiconductor type just operates with transistors instead of springs and coils. You may be able to get a voltage reading using the AC voltage reading. It might not be a very accurate reading. Typically the modulated waveform is a square wave. This means that the voltage will go from 0-13v and vice versa very fast. The best way to measure this is with an oscilloscope. You can measure the duty cycle (on/off time) of the signal. Typically the voltage on the DRL is roughly 7-9 volts. A modulated voltage of 13 volts to give the 7-9 volts is roughly 70-80% duty cycle.

You may be able to just connect the relay to the headlight switch. This will enable the HID, but you will lose the DRL and the entry lighting. I'm not 100% sure, but it may also set a code in the body control module also. One way around this might be to put a large enough capacitor to filter the modulation and keep the connection the way it is now. This would give enough power to keep the relay from chattering during the modulated off time. I'll look into this further this evening.

mcali17 · September 16, 2002

carguru- Thank you so much for all of this great information. The capacitor idea sounds like a good one. The HID's look and perform awsome and if I could just keep the current setup as is, because there are no splices or anything with the facotry wiring, and just add a capacitor to each wire lead to each relay that would be perfect. Then I would retain all functions DRL's, Perimeter Lighting, and Headlight flash when the alarm is tripped. This would be the ideal way to go. I will look for your reply tomorrow morning, if you have the time to look at this tonight. If not, whenever you can get to it that would be great. One other question. So the capacitor would be able to handle either the modulated voltage or the regular 13 volts coming in? I guess that makes sense since the modulated voltage would be between 0-13V and normal voltage would be 13 volts. So as long as the output voltage is 13 volts I should be all set.

Let me know when you find out and thanks again.

carguru · September 16, 2002

Probably will use a 25V capacitor. Have to take into account jump start voltage. Do you have the part number for the relay that is used? This will probably help to determine whether or not the relay is correct for the system.

GnatGoSplat · September 16, 2002

It sounds like your DRL is definitely PWM (pulse width modulated). Try a 1000uF 16V or higher voltage electrolytic capacitor across the #85 and #86 coil terminals of the relay. Make sure to hook up the capacitor's polarity correctly. That ought to do the trick. I've done the same thing myself with PWM DRL's.

mcali17 · September 17, 2002

OK I really appreciate both of you guys helping me out.

I have confirmed that the DRL's are in fact Pulse Modulated.

The Bulbs and Ballasts are made by Philips, I can't see a part number on the relay, I would have to take apart too much right now, but I will email technical service and ask what the part number is. The relay was supplied with the kit.

carguru-What do you mean by confirming the relay is correct for the system? I don't know if I ever mentioned it, but with the headlights on, the HID's work perfectly.

GnatGoSplat-What do you mean by 1000 uF, (1000 micro Farads), across the #85 and #86 coil? The relay has 4 wires coming off of it (see diagram below). Two wires are connected to the harness that plugs into my factory 9006 headlight bulb connector, one wire goes to a 30 amp fuse and then to the positive terminal of the battery, the other wire connects to the ballast, which in turn connects to the negative side of the battery. Would the capacitor just go in line so that the two wires that connect to the factory harness go through the capacitor and then pass from the capacitor to the two terminals on the relay?

Also some questions for both of you: Where can I even get the capacitors you are talking about? Can I order them online or just go to Radio Shack? How expensive are they? I need two, one for each side. And since you guys differ on the voltage, which voltage? And why is the voltage of the capacitor more than 13V. I only need a constant 9 to 13V to switch the relay on and keep it on. But I guess I have to take into account that at sometimes the capacitor will be receiving the full 13Volts, like when the headlights are actually on and not in DRL mode. If you could provide me with part numbers of the capacitors, or brand names or anything that would help me get the right ones, that would be awsome.

I cannot tell you how much I appreciate your help with this. I know quite a bit about DNA and mechanics, but don't know too much when it comes to electricity. Thank you both so much. If I can ever help you out I would be glad to return the favor.

Looking forward to your answers,

Mike

carguru · September 17, 2002

Mike,

I was looking for the part number for the relay to make sure that the kit speced the right relay for the job, but it doesn't matter that much. Based on a couple of rough calculations, 680 uf should do, but 1000 uf as Gnat recommended will work also. I would recommend going with the 25v version (not much of a price difference between 16 and 25 v) because of jump start issues and potential surges in the electrical system as the vehicle ages. I would also recommned going with a high temperature version since it is going under the hood. The ones at Radio Shack are good to +85C. This is good enough for testing, but I would not rely on them for long life. Go to Digikey. They will carry the 125C part. The part numbers for the 25v are as follows:

Value Digikey P/N BC P/N

1000 uf 4132PHBK-ND 2222 118 160102

680 uf 4131PHBK-ND 2222 118 16681

You will need 2 of these. They are less than $1.50 each.

Make sure the polarity is correct. The capacitors are polarized. Negative terminal should be clearly marked on the capacitor. As for the #85 and #86 terminals mentioned by Gnat, I believe what he meant was to connect the capacitor closer to the relay terminals instead of by headlamp connector. Trace the wires that connect to the relay leading from the original headlamp connection for the correct terminals. The reason for putting the capacitors here would be because the capacitor would be more effective at the relay terminals (less losses, etc). Good luck. Let us know how it comes out.

mcali17 · September 17, 2002

Carguru-Thanks again. I know I must sound like an idiot for asking so many questions and you have been great with your answers.

So here is one more. Do I need two capacitors, one for each HID headlight setup, since I have two relays. Or, do I need four capacitors, two for each HID headlight setup i.e. one for each wire from the factory headlight housing to the relay? I just want to make sure I do this correctly and not fry anything.

carguru · September 17, 2002

There are no stupid questions. Definitely helps to make sure you have all the info you need. :thumb:

You just need to have 2 capacitors--one for each relay. As for the size of the capacitors, the diameter of the body is 12.5 mm by 30 mm length according to the Digikey/BC catalogs.

mcali17 · September 17, 2002

carguru-

Well, since there are no stupid questions? Since there are two wires going from the headlight to the relay, and each wire connects to a different terminal on the relay, which wire gets the capacitor?? I take it one wire is + one is -, so which one do I attach to the capacitor, Or do I attach both?

Thanks again.

Mike

carguru · September 17, 2002

Attach the capacitor to both. One wire is a + and the other is a negative. To determine which one is which, swtich the headlamp switch to on, and probe with the voltmeter. Connect the ground of the voltmeter to any part of the body/frame for chassis ground. Use the other lead to probe the 2 wires. The one that reads 0 volts (or something real close will be connected to the negative lead of the capacitor. The one that reads close to 13v, will be connected to the positive lead of the capacitor.

mcali17 · September 17, 2002

So then, for arguments sake, lets say that the "top" of the capacitor is positive and the "bottom" negative. Take the positive wire from the headlight, attach it to the positive on the capacitor and then run a wire from the positive on the capacitor to the positive side of the relay?

Then take the negative wire from the headlight, attach it to the negative side of the capacitor, then run a wire from the negative side of the capacitor to the negative side of the relay?

Is that correct, so basically the + and - wire come together at the capacitor and then split off back to the relay?

I think I got it.

Thanks, and I will let you all know what happens.

Mike