Want to convert to HID - PeachParts Mercedes-Benz Forum

need2speed · #1 08-03-2002, 12:17 PM

So I want to convert to HID technology with one of those kits like HID4Less or Belloff....

Apparently they draw only 35 watts versus 55 watts for a standard H4 halogen bulb. This has caused the "bulb out" warning light to go on in other Mercedes vehicles that have posted the modification here.

Any electrical wizards out there? Can you splice a resistor into the wiring to create a 55 watt draw and would that avoid triggering the bulb warning lamp?

Advice is appreciated,

JCE · #2 08-03-2002, 01:24 PM

The only alternatives I have seen involve either removing the warning bulb, or tracing the warning bulb circuit and taking the headlight bulbs out of the loop. This approach might be difficult as I believe the circuit looks at total lighting resistance rather than on a bulb specific circuit (?)

You would need a fairly hefty resistor circuit to make up 40 watts (20 watts per bulb), a little under 2 amps draw. Or you could add a 20 watt load in series with each headlight, but what to use? Hella makes some miniaturized HID driving and fog lamps - If they are rated at 20 watts a pair might. But it might not as the warning lamp circuit seems pretty unforgiving to slight variations in bulb type.

20 watts is not much draw for a useful driving light or auxiliary fan, and too much draw for a resistor to waste as heat. I would just pull the warning bulb and save my alternator the 2 amps draw.

need2speed · #3 08-03-2002, 01:30 PM

Thanks John, excellent advice as usual

#4 08-03-2002, 06:45 PM

I am about to upgrade to a relay kit with 100w bulbs on my 126 and have the same issue with the lamp out feature. www.bergwerks.com have a modded lamp out controller that they sell to remove the headlights from this circuit.

Matt.

JCE · #5 08-03-2002, 08:07 PM

Mattman:

That is nice to know! I have been planning on ordering one of their relay kits as well, but never knew they had a modified warning light module, and couldn't find it on their web page - is there a part number or do you have to ask about it when ordering the relay kit? Thanks for any info.

#6 08-03-2002, 08:10 PM

I know they have the modded controller for my W126, Carl Genberg from Berwerks mentioned it when I was looking at ordering the relay upgrade kit. It is a core swapout option where they send you the modded controller and you return your controller to them. My kit should be here in a few days time so I will let you know more then.

Matt.

JCE · #7 08-03-2002, 10:07 PM

Thanks! I would also be interested in your impressions of the relay/wire kit. They are about 2x the avg price of other relay kits claiming to use 12/14 g wire and Hella relays, but I thought they might be worth it if everything was pre sized to my w124 and had all the proper connectors, etc. Reading their site again led to the disclaimer that their kits were 'not model specific'. I am not quite ready to do this project, (doing speakers on the C230) so I haven't called them with questions. Your feedback would be welcome!

#8 08-03-2002, 10:10 PM

Yes I agree they are certainly priced at the higher end of the market. They do have the advantages of experience with product so if they recommend this kit I know it will work, plus they had the modded controller for lamp out which is not available anywhere else.

Matt.

#9 08-04-2002, 10:44 AM

Okay, this one requires some application of Ohms law. Adding a resistance in series will not increase current flow it will decrease. To increase current flow the resistance must be put in parallel, and will have to be a large power resistor.

Each headlight drawing 55 Watts at 12 Volts is about 4.5 Amps. This means that the effective resistance of this bulb at 12 volts is 2.66 ohms. Therefore 2.66 Ohms is what the bulb out circuit wishes to see.

The HID resistance of the 35 Watt load is 4.1 Ohms. To make this look like 2.66 ohms to the bulb out circuit, we will need a 7.5 Ohm resistor in parallel with the 35 Watt load to present a 2.66 Ohm load to the bulb out circuit. This will need to be a 20 Watt resistor.

Seeing as how I have been on the software side of the world for about 15 years, I no longer have catalogs to see what the standard available values are. You will need to look it up and get as close as possible.

My calculations were based on 12 volts, when in reality the system will apply about 13.5 volts most of the time, but these calculations should be close enough.

Mount this high power resistor where it can get a little cooling air. It would be better to get a power rating greater than 20 Watts, as long as the resistance is pretty close to 7.5 Ohms.

You realize that this means that there will be one of these resistors wired in parallel at the point that originally saw the 55 Watt bulb. This means you will need two of these resistors, one for each bulb.

Good luck,

JCE · #10 08-04-2002, 12:23 PM

What, me use Physics?

That will teach me to type faster than I think, especially on topics I haven't used in 35 years!! Larry is, as usual, correct: parallel, not series! Screwed the pooch on that one.

Larry: If Michael decides to go with the resistor instead of the modified warning light module, do you think the control lamp circuit will be tolerant enough of any minor variation in load to work properly? I had problems with the 'lamp out' light when I used a generic tail light bulb, solved by going with a quality bulb.

#11 08-04-2002, 03:43 PM

JCE,

I have no idea how tolerant the system will be. What you could do is use an adjustable power resistor and tweak it. There are some large ugly brown power resistors with a lug that you move by loosening a clamp with a screwdriver and moving the lug. That would allow you to adjust it to 7.5 Ohms or whatever it was I calculated, then if that doesn't work with all lamps burning, do a little trial and error.

Much engineering is done through trial and error. The first real job I ever had in 1974 was as an Associate Electrical Engineer. I worked with a very experienced engineer on an extensive high speed (for then) digital logic card for a nuclear medical system. Once we had the logic right he said: "well I think we've got it, all we have to do is start hanging capacitors on it, until it works." The application of decoupling capacitors was difficult to engineer and had to be done by trial and error. Science only goes so far sometimes.

Good luck,

need2speed · #12 08-04-2002, 04:50 PM

Hmmm, seems the easiest thing to do would be remove the headlamp warning bulb??

Would this be recorded as fault codes in the diagnostic system?

Curiously,

#13 08-04-2002, 06:45 PM

I doubt that removing the warning bulb would set a code, but that gadget is pretty handy. It's no big deal to go to Radio Shack and get a couple of power resistors. If you can't get them at Radio Shack, there many electronics supply houses that cater to the TV/Radio shops. This is a simple fix, four pieces of wire and two resistors.

Good luck,

omegabenz · #14 08-04-2002, 11:05 PM

Dean, go to benzsport.com and look at the front page, there is an article written about the conversion vs oem. I know that you have the H4 bulb, but the reflectors arent really made for the xenon bulbs and so what it does is makes a lot of glare for other drivers. I know because my friend put S class bulbs and ballasts in his 190E headlights and they blind you. The article on benzsport makes a comment that OEM xenons dont hurt the eye.

need2speed · #15 08-06-2002, 07:24 PM

Austin, that was a good test by benzsport.com on HID conversions versus factory HID lights.

I guess the moral of the storey is to stick with stock!?!?