User 52121

Says he got them from superbrightleds.com, and used #74 and #194s.

eman930

Wait, Doenst the factory dimmer work? I have LED's in mine and I use the factory wiring/dimmer with no problems, I use the cool white leds

gruhsy

I'm doing the exact same thing and everything works.

Ryan_U

If you are using the dimmer in the car and not a pulse width modulation circuit what you are probably getting as a result is some minimal dimming and then the lights turn off when you no longer supply enough forward voltage to the series of leds. I have never seen anybody that has a fully functioning dimmer after a LED upgrade. If you do I would love a couple pics to see the range.

If your dimmer dims all the way then that means the leds are getting more power at full than the leds are rated for to compensate for the range of the rheostat. The LED will last only a short while if driven at more than the max rated 25 ma. Add to that the fact that the led components used are cheap to start with and you are looking at a MTBF in the 1000 of hours compared. While it may seem to work it is just bad for the whole system and the leds will fade quickly. Thankfully dash lights are on for relatively short periods of time but there is no way a resistor dimming solution is the proper way to do it. None, zip, zero, nilch, nada of the new cars that come with led lights in the dash use resistors for dimming. Why would car companies pay an extra 20$ for a dimming circuit if they could just use a 10¢ rheostat. These led compagnies that sell cheap stuff are just giving led lights a bad name.

Ryan_U

This kind of proves my point that just replacing with led lights is not the proper way to do it. LEDs need a CONSTANT CURRENT and a resistor setup is only good as a constant current if you have constant voltage.... which of course a car does not have. The voltage variations between alternator on or off (plus spikes that can go pretty high) mean that the LEDs are seeing variable current which = failed LEDs. 2 volts change represent about 25 ma of variance.... seeing as LEDs are rated at 25ma MAX and you can see a difference at dramatic life increase with 5 ma less, imagine what running them at 50 ma does to their MTBF. Trust me on this one guys. I have been researching this for months now and there is only one way to do this right and that is with a PWM constant current circuit.

Constent current circuits with PWM are about 7$-10$ from China and about 15$ from USA. If you want the LED driver's components to be automotive rated they cost about 25$ from a USA source.... That is just for the power source to run 3 led lights. Every series of three LEDs needs a seperate driver (can be used in parrallel but not recommended) Then you need to change the the signal from the dimmer from analog(volts) to digital(pulses) and that is where a micro-controller comes in because it takes an analog signal (0-5v) source and convert it to an on/off pulse signal. The problem with the micro-controller is that it needs 5v to operate and is also looking for a 0-5v signal. So you need a constant voltage circuit too (not the same as a constant current circuit) and need to convert the dimmer voltage from 12..x-14.x to a 0-5v. Then comes the programming of the micro-controller (yes, you have to write code).

This is how it should be done. Anything else is just a duct tape solution.

The good news is I'm working on such a system already. I have already tested out the circuit in a lab and I will soon be trying it out in my car.

I will make the information available to anybody for free. All you will have to do is buy the parts and wire it up.

Some guy on the 928 forum has already done something very similar and he has a nice write up but he doesn't explain the micro-controller, the led drivers, nor has he released the programming code he used. You will see he does hint at using an "Arduino".

An Arduino is an open source micro-controller. That is what I am using in my prototype. The fun thing about the Arduino is that it can also be used to do a ton of other things such as digital gauges, parking sensors, alarms ect.. .all on the same board.... An arduino is about 35$.

So yes, my solution will cost about 100$ but it will work perfectly, dim from 100% to 0% (or anything in between in as many steps as you want) in perfect linear fashion, supply up to 100 lumens, avaliable in Red, Deep red, Amber, Green, Blue, Royal blue, warm white, cool white, neutral white and last about 55000 hours with 98% lumen output (or 19 years at 8 hours on per day), generate little heat (~1 watt of heat per LED), use LEDS that have a wide viewing angle to maximize uniformity and look 100% stock.

DFASTEST951

I'm heavy into the diesel scene as I have a lifted Crew Cab F350 Ford with almost 600hp and 1,000lb tq. There's a company catering to the diesel community that sells replacement LED lights. They are pretty realiable as well. you can check them out at www.gorecon.com

Paulyy

All LEDs should last 20,000 hours.

Turbo17

You've answered all the questions here, and explained why I'm thinking of PWM. Anything you want to post would be appreciated. I've played with all sorts of LEDs - from Chinese ebay junk to high performance stuff. I was hoping to go for a middle approach.

There are some dedicated LED controller chips designed for automotive use that should be less expensive than an Arduino and a full roll-your-own design. All you need to worry about is the heatsink and supplying regulated power, but you don't have to write any code as yo do with the Arduino. There are also some complete LED PWM dimmer circuits I've seen intended for automotive use. They've got a dimmer pot, voltage regulator, heat sinks, etc already. You're supposed to mount them in a hole in the dash. I hoped I could buy one of those and modify it to use the factory dimmer on the dash instead of drilling a hole.

I do appreciate all the posts here. I was delayed in responding due to a computer crash.

I think I'll pull the odometer gear and check the tooth count, then play with some LEDs I have already to see what color I like.

Turbo17

If you run them within specs, they'll last a long time, but it's very easy to kill them if you just use a resistor to limit current. The voltage in a 12V vehicle swings widely and there are lots of spikes. With a resistor, half the time you're either too dim or so bright you're burning out the LED.

You'd be amazed at the complex circuits used for LED lighting in well-designed automobiles.

Ryan_U

The problem with the Porsche rheostat is that it has a very low resistance value so you need a controller that will map the values. Also, since the resistance value of the dimmer is small, any tiny movement of the dimmer will make the dash lights flicker. That is why I choose an Arduino for this application because I can code in a buffer or a "debounce" as it is called, to avoid a jittery/sensitive dimmer. For the LED I have settled on the CREE XP-E (sorry I confused it with an XR-E in an other post). Since the LED puts out over 100 lumens at 350 ma you will only need one per housing = 3 LEDs. With a forward voltage of 3.1 volts, you can then drive 3 leds on a driver. They Cree XP-E is nice and small on a 14mm PCB and has 130° viewing angle. Since I use an older generation bin, they are fairly cheap at about 3$ a LED. So I think you can get a kit together for about 50$ including the arduino, driver, leds, voltage reg and all. Not too bad a price I find. I'm also hoping to use the Arduino to control daytime LED running lights I am also designing so the 30$ for the controller is shared between projects. I'm happy somebody understands that LED are more complicated than they seem.

User 52121

Seems like an awful lot of work when you can just steal a chunk of tin foil from the box in the kitchen drawer and get the same bright light in the cluster. If you want different colors just get some bulb condoms...

Not knocking your solution, it's definitely neat - and me being an engineer, I love engineering just for engineering's sake. Just seems like a lot of work if all the OP wants to do is brighten up his dash lights.

Turbo17

As an engineer - I also like engineering, but actually, I just figured I'd rejuvenate and upgrade to LEDs as long as I was in there working on the odometer gear.

I'm still not convinced I can't use the factory pot that's already in the dash (to control a dimmer circuit - not directly). It might be possible to replace the pot with whatever resistance is needed. Or, if that won't work, it should be possible to "map" the output using basic analog techniques. If I buy an LED dimmer designed for automotive use, pull the pot that comes with it, figure out what voltage range I need to emulate, I should be able to come up with a simple circuit that uses the factory low resistance pot to provide whatever voltage is needed to the new dimmer circuit. It's amazing what a few resistors, transistors and zeners can do. I'm not particularly worried about smooth operation and a few spikes, but if I go with LEDs, I wouild like it to have a decent dimming range from very dim to very bright.

Of course, if I get lazy, I can always grab the tin foil. I just figured I'd see what others were doing with LEDs before I had the cluster out of the dash.

Turbo17

I was thinking of using something like this
It's in a bulky box, and it causes some power supplies to buzz, but it's got a separate pot that I could substitute. You could take the circuitry out of the box, or just mount the box under the dash. I suspect automotive power won't buzz, or if it does, you won't hear it, and if you do, adding a large cap would fix it according to one review. For $8.00 it's worth playing around with.

86 951 Driver

You could search, but it is below.

http://www.superbrightleds.com/morei...edge-base/199/

F18Rep

It doesn't get any better than that. ...Bruce