License Plate LED Load Resistors

[daveman]

I installed a 15 Ohm 25W Load resistor under my trunk lid today successfully inhibiting the Bulb Error, but DAMN that thing gets hot!

How have people managed to mount these under the trim without causing any problems? I'm not sure if I should be isolating it thermally from any other parts, or whether I should be looking for some thermally-conductive adhesive (Like this?) to attach it to the underside of the trunk lid to try to dissipate some of the heat..

Right now I have left the trunk trim off until I can come up with a solution.. Any takers? How have other people mounted them?

Cheers

[staticuxo]

i wrapped mine with header wrap and zip ties.. had both laying around in my garage.

[fly300kts]

Take a look at my DIY

http://www.audizine.com/forum/showth...ghlight=review

The inner side of the trunk is acting as heat sink

Phil

[theklug]

I just used zip ties in the same location as Fly....no problems for over a year now.

[daveman]

Thanks Phil,

Did you drill a hole? The wires on mine aren't very long so I am limited to how far away I can mount it. I'll have a look tonight and see if I can recognise where you have mounted yours..

I ordered that thermally-conductive adhesive pad, not sure how sticky it will be though! It needs to withstand the trunk being slammed closed.

[fly300kts]

Thanks Phil,

Did you drill a hole? The wires on mine aren't very long so I am limited to how far away I can mount it. I'll have a look tonight and see if I can recognise where you have mounted yours..

I ordered that thermally-conductive adhesive pad, not sure how sticky it will be though! It needs to withstand the trunk being slammed closed.

Yes, I drilled a hole and installed a Stainless machine screw. Works great. I have all the hardware available if needed

Phil

[shiro1745]

I just installed my leds and got no errors so no resistors for me

[blazeblunts4]

i used 100 ohms, which removed the CEL and will not get as hot as 25ohms, less current = less heat

[fly300kts]

i used 100 ohms, which removed the CEL and will not get as hot as 25ohms, less current = less heat

Oh boy!!

Phil

[daveman]

ok so..

I=V/R
12v/100Ohms is 0.12A..
12V/15Ohms = 0.8A..

P=V^2/R
144/100Ohms = 1.44W
144/15Ohms = 9.6W

100Ohm load uses 15% of the power of the 15Ohm load.

How much current has to be pulled before the ECU registers no bulb error? The 100 Ohm worked I'm guessing from the fact you have it installed..

[Inked]

I just installed my leds and got no errors so no resistors for me

which ones did you go with?color or red screen? and a link would be great! thanks

[shiro1745]

which ones did you go with?color or red screen? and a link would be great! thanks

http://www.tunerdomes.com/index.php?...d&productId=79

I have the red screen

[daveman]

http://www.tunerdomes.com/index.php?...d&productId=79

I have the red screen

I have the same LEDs and a red DIS, looks like it's a bit of a pot shot whether you get the error or not..

Just bought 50 and 100 Ohm 10W resistors from radioshack, going to experiment tonight..

[shiro1745]

I have the same LEDs and a red DIS, looks like it's a bit of a pot shot whether you get the error or not..

Just bought 50 and 100 Ohm 10W resistors from radioshack, going to experiment tonight..

K let us know how that works for you

[Inked]

http://www.tunerdomes.com/index.php?...d&productId=79

I have the red screen

thanks [cross fingers]

[daveman]

Did a little bit of experimenting,

The 100 Ohm resistor gave intermittent bulb warnings, the 50 Ohm resistor cleared them. I ended up using the 50 and 100 in parallel (~35 Ohms) and it's working ok. So I around-about halved the power being dissipated as heat..

The 50 Ohm is hot, but not like the 15 Ohm resistor before, and the 100 Ohm is cool enough to touch for a few seconds. I'm tempted to get 3 100 Ohm resistors in parallel to keep things cool, and mount them a bit better.

Anyway, here is how it is now, miles away from the inside-lid trim when it's in..

[blazeblunts4]

Oh boy!!

Phil

wow i get to explain something to phil >_<

I did a step further in my head. There are 2 resistors in parallel, the 25ohm , and the load resistor on the LED itself. Not to mention the voltage drop over the diode, but there is a load resistor in series with the LED too. So if you keep those constant, and increase the resistor from 25 to 100ohm, it will decrease the current through the 100ohm resistor, because voltage is directly proportional to current. I got to teach phil something !!!!

[blazeblunts4]

ok so..

I=V/R
12v/100Ohms is 0.12A..
12V/15Ohms = 0.8A..

P=V^2/R
144/100Ohms = 1.44W
144/15Ohms = 9.6W

100Ohm load uses 15% of the power of the 15Ohm load.

How much current has to be pulled before the ECU registers no bulb error? The 100 Ohm worked I'm guessing from the fact you have it installed..

Read post above

[daveman]

Disregarding the constant loads (LEDs etc..) you can calculate the current and power across the additional "load" resistor using ohms law. A 100 Ohm resistor with 12V across it will always pull 0.12A/1.44W. A 15 Ohm resistor will always draw 0.8A/9.6W.

Each "lamp" (LED and series resistor) is wired parallel to each other and the "load". Obviously there is some current being drawn by them.. but we don't need to worry about it. Basically you want as large resistance as possible to stop the bulb warning to come on as this will draw less current and therefore dissipate less power as heat.. You are absolutely right that a 100Ohm resistor will consume less power (only 1.4W!), it will also run cooler. 100 Ohm didn't work in my case, or 50 Ohm :( I'm defo going to put 3 100 Ohm resistors in there though as the 100 is noticeably cooler and combined they will have a larger surface area to dissipate the heat. Just need to find a nice way to mount them..

[blazeblunts4]

Disregarding the constant loads (LEDs etc..) you can calculate the current and power across the additional "load" resistor using ohms law. A 100 Ohm resistor with 12V across it will always pull 0.12A/1.44W. A 15 Ohm resistor will always draw 0.8A/9.6W.

Each "lamp" (LED and series resistor) is wired parallel to each other and the "load". Obviously there is some current being drawn by them.. but we don't need to worry about it. Basically you want as large resistance as possible to stop the bulb warning to come on as this will draw less current and therefore dissipate less power as heat.. You are absolutely right that a 100Ohm resistor will consume less power (only 1.4W!), it will also run cooler. 100 Ohm didn't work in my case, or 50 Ohm :( I'm defo going to put 3 100 Ohm resistors in there though as the 100 is noticeably cooler and combined they will have a larger surface area to dissipate the heat. Just need to find a nice way to mount them..

Yeah, that's all I was really saying, the Voltage will change though when you have the resistance in series....I probably just should have said that from the start.

[fly300kts]

wow i get to explain something to phil >_< I got to teach phil something !!!!

Yes you did...Naaaaaaaat

Phil

[blazeblunts4]

Yes you did...Naaaaaaaat

Phil

hehe

just as a follow up though, I put 2, 100Ohm 2W resistors on my Sonic tuning LED's and they were warm, but not hot. Only had a couple volts over them

[rogue]

hehe

just as a follow up though, I put 2, 100Ohm 2W resistors on my Sonic tuning LED's and they were warm, but not hot. Only had a couple volts over them

I researched this a bit further.. trying to get the highest resistance possible. What I discovered may be interesting to anyone looking at doing this mod.
I tried a few high resistors, 220, 470, 1K8. but only the 100 Ohm resistor worked, when touched to the terminals of the number plate light socket as a replacement for the globe.

At one stage in my testing though, I had a normal globe connected at the same time as the 'error-free' LED that I have and the warning didnt come up.. but it did if I removed the error free LED.

Given that my "error-free" LEDs raise the warning on their own.. this made me realise a few things..
1) The resistance is being measured for the whole circuit - both globes at the same time rather than each individually. (Because one error-free LED was enough combined with the normal globe to not raise the warning, but won't work when both of them are installed).
2) My error free LEDs have some current drain on their own, but not enough to fool the B7 circuitry.

Given point 1, you can draw the conclusion that adding resistor(s) in parralel with the LEDs will decrease the total resistance and consequently increase the total current drain in the number plate circuit..

So based on that, I took a guess that the 2 220 Ohm resistors wired in parralel and in addition to the two error-free LEDs would be enough to fool the circuitry and it was.
Of course the error-free LEDs are simply LEDs that have had some resistors wired in.. so it is really a case of getting the resistance right, adding enough resistance (in parralel) so that the total current drain is enough.

The benefit of all of this extra effort meant that the resistors are not the big bulky ones.. so all I needed to do was wire in my 2 220 Ohm resistors in parralel with the LEDs.. but they are small enough to fit in the housing - which is nice. :)

[leftovers]

^ I did this tonight. I used a 68 OHM 3 Watt resistor that I purchased on ebay along on each of the $10 ebay "error free" lights bulbs. It's working just fine on my color display.

[Audi_509]

How about the heat?

[leftovers]

How about the heat?

After 20 minutes of driving with the lights on last night, I didn't notice any heat.

[Audi_509]

After 20 minutes of driving with the lights on last night, I didn't notice any heat.

Thanks for the information. Do you remember the wattage on the resistor?

[Samsonite]

Do you remember the wattage on the resistor?

3 watt looks like..

I used a 68 OHM 3 Watt resistor that I purchased on ebay along on each of the $10 ebay "error free" lights bulbs.

[Audi_509]

^ Thanks but the other poster used 220 ohm resistors.

[rogue]

^ Thanks but the other poster used 220 ohm resistors.

Yes I did, but I have actually been having some problems with my method - they indeed must be getting hot.

I am using 220 Ohm resistors, which sounds like they shouldn't be drawing a lot of current.. but my "error free" LEDs must be creating a fair bit of heat on their own and have a smaller resistance value than that. The sum total is enough that my installation actually failed - there was enough heat to soften the solder and the resistors lost contact, so I got the warning back about the trunk light being out.

So - I am now advising to tread carefully with the approach I have suggested here and perhaps it is indeed better to use a large resistor and mount it against the trunk lid where it will dissipate the heat to a large surface area. The resistors in the light compartment dont really have anywhere to dissipate the heat to .. so maybe this 'shortcut' isnt totally perfect.

[drewgold]

I gave the soldered load resistor method a try tonight and so far, so good on my colour DIS. No more error! First time I have been without an error with an LED bulb, and I have tried a number of different "error free" bulbs.



Ended up using the same as the poster above, 68 ohm 3w resistors. (62 ohm resistors are pictured which I also tried) I bought a variety but the bulb out sensor seems to be very sensitive. With 82 ohm resistors, I got intermittent bulb out warnings. My bulbs are 6x 5630 LED chips which is 3w power usage. Not sure what sort of resistor they have on board but it can't be very much being as 82 ohm resistors would use about 1.7 watts for a total of 4.7w. The system expects 5w bulbs and 4.7w wasn't enough to trick it.

We'll see what the longevity is like for the 68 ohm resistors.

EDIT:
Also forgot to mention that one of the biggest challenges is that the voltage fluctuates quite substantially at the license plate lights. With the car off and the coming home feature on (accessory lights on) there's 12v exactly at the light terminals. However when the engine is started, there's 13.9v at the lights. This means that any resistor that is installed will have to deal with quite a bit more power. A 68 ohm resistor uses 2.12w at 12v and climbs to 2.84w at 13.9v
I expect that this will be too much for a 3w load resistor. Good chance it will burn out sooner rather than later.

[rogue]

Wouldn't this all be so much easier if there was a soft coding for the instruments!

[drewgold]

So far my bulbs/resistors are still working. Only small issue is that right when I start the car I get a bulb out warning then it goes away immediately. Once the resistors have warmed up I don't get the warning when starting the car.

Anyone else have this issue? Those with the larger wired resistors, have you had this problem?

Can't believe how sensitive the bulb out warning system is, haha.

[rongeur]

I have the USP bulbs with built in resistors and they have worked flawlessly. Once in a blue moon if I only turn my key to on but not start, it will give bulb out but then disappear immediately on start.

[drewgold]

I have the USP bulbs with built in resistors and they have worked flawlessly. Once in a blue moon if I only turn my key to on but not start, it will give bulb out but then disappear immediately on start.

I tried the USP LEDs and had intermittent bulb out warnings. All of the sudden I'd just get a warning for no apparent reason. Got really annoying. Ended up selling them. Think it depends a lot on the vehicle, options, etc.

[BenMTL]

I took off my trunk liner, and used silicone glue and zip tied my resistors to bare metal for better heat dissipation.

For the guys that used the "solder-resistors-directly-to canbus LED" method, after driving for 30 minutes for example, and you put your hand to the trunk light plastic enclosures, are they hot to the touch? Like burning or only slightly warm?

[drewgold]

I took off my trunk liner, and used silicone glue and zip tied my resistors to bare metal for better heat dissipation.

For the guys that used the "solder-resistors-directly-to canbus LED" method, after driving for 30 minutes for example, and you put your hand to the trunk light plastic enclosures, are they hot to the touch? Like burning or only slightly warm?

The enclosure never got hot but my soldered connection for the resistor just failed. Thinking there's too much heat and heat/cooling.
Going to go with Phil's style of resistors and not have to worry about messing with things anymore.

[waiapasi2006]

I'm lucky to not be dealing with this. I had my leds on here for more then one and a half year.
Still running strong.

[leftovers]

I'm lucky to not be dealing with this. I had my leds on here for more then one and a half year.
Still running strong.

That's only helpful if you tell the rest of us what you're using.

So, for my setup, the LED lights starting flickering and working inconsistently. I have two more of the same lights and two more resistors. I may build another set and see if my results are any different.

[waiapasi2006]

That's only helpful if you tell the rest of us what you're using.

So, for my setup, the LED lights starting flickering and working inconsistently. I have two more of the same lights and two more resistors. I may build another set and see if my results are any different.

I have some fixing to do in my trunk, so I'll see what I got in there for you.
Don't mind sharing at all.