LED DRL mod - need advice on resistors

[gtiller]

Hi all,

I am just in the process of finishing the S6 LED DRL mod, and currently, I am getting the bulb failure warning - so I need a resistor.

As my LEDs replace a H7 55 watt lamp, I am trying to determine what size resistor I need, and whether i need to install in series or parallel.

It's been a while since I went to school, put I do remember V=IR and P=VI

That means I am looking for a 2.62 ohm resistor?

I have a couple of 2R7 50W resistors in the garage, and as they are set in a nice big heat sink, I would like to use them if possible... however, I think they might not be heavy enough, although the resistance is almost spot on.

Any advice would be appreciated!

Thanks.

[craigyb]

Basically they are just emulating current draw.

As you have two of them, you could try them in series first 2.7 + 2.7 = 5.4 ohms and see if one of the light failures goes away.

I personaly think trying to emulate a 55W current draw is too much and you would probably be better with a 10 ohm 50W resistor on both sides.

[gtiller]

Thanks Craig - i'll give that a try.

Do you know if this needs to be wired in parallel to the LEDs?

The other option is VAG-COM - is it possible to disable the bulb failure warning?

Edited December 28, 2008 by gtiller

[craigyb]

They would go in paralled with the LEDS, the LEDS draw a small amount of current so the resistor draws the rest of it.

AFAIK you cannot disable the bulb failure warning.

[gtiller]

Cheers Craig!

I have ordered a pair of 10 ohm resistors (50 watt)

The 2.7's put out the bulb failure warning lamp, but got much too hot - I guess they don't offer enough resistance?

Hopefully the 10 ohms ones will be better suited.

Thanks!

[A8_Tony]

You'll have to post up a bit of a 'how-to' when you're done fella. I'm sure there are plenty of '6 owners out there who're interested in doing this

[craigyb]

Yep, those 2.7 ohm resistors will be drawing 4.4 Amps which is 53 Watts approx, so just over their limits of there wattage.

A 10 ohm resistor will draw 1.2 amps or consume 15 Watts approx which should be plenty enough to fool the circuit that the original lamps are in place.

[gtiller]

Nightmare...

I have a pair of 10 ohm 50 watt resistors, and the bulb failure warning goes off :mad:

However, I also got some 5 ohms 50 watt resistors at the same time. These stop the bulb failure warning, however burn really hot

So on the grounds that the 2.7's also put out the warning, but even hotter than the 10's - it looks like there is an absolute maximum of 5 ohms before the warning sounds.

I didn't realise the system would be as sensitive as this.

Obviously, when I put the multimeter across the H7 55 watt lamp, it reads as a dead short circuit (zero).

I am thinking this, order a pair of 100 watt resisotrs with an impedance of 2.7 ohms.

This would draw 4.44 amps

Which means it will burn at 53.33 watts - half the rating of the resistor

Whilst they make even lower resistance models (as low as 0.22 ohms) I think 2.7 is a low as I dare go.

What do you reckon?

Is my maths right?

Thanks

Edited December 30, 2008 by gtiller

[craigyb]

The higher the resistance you can use the less power they will draw and the less heat they will generate.

A bulb shows dead short as it's when it heats up that the resistance builds.

As you now have 2.7, 5 and 10 ohm resistors you can have a little play

2.7 + 5 in series will give you 7.7 ohms, try that to see if the bulb failure goes out.

These resistors are designed to be bolted down to a metal surface to help dissipate the heat

[artinmoTTion]

Thanks for all of your thoughts on this. Trying to do the same thing with the same bulb out warning despite different resistors. Last one was a 10ohn 50 watt resistor. Any resolutions here yet? Should I go for the 100 watt 2.7 ohm resistor? Hard to tell, I suppose, what the S6 LEDs are drawing since it's not listed anywhere.

FWIW, I've also replaced my stock A4 DRL (in the headlamp assembly) with a very bright 5W luxeon LED (that matches the S6 LEDs very well), but I get a "main beam headlight out" error now also since it must check the current / resistance from the whole headlight unit. Any thoughts on that one are much appreciated as well, as a resistor will likely be needed there also, but I don't want one inside the headlamp assembly, thanks.

[gtiller]

There is another post on this forum that may be of help to you?

Have a look here: http://www.tyresmoke.net/forum/audi-rs/100461-how-fit-leds-rs4-b7-drls.html