# Interest in automotive LED conversions?



## NightShift (Jan 2, 2002)

I'm not sure how many of you are into automotive lighting conversions with LEDs, but does anyone else think these kinda conversions are really cool? 

http://www.rockcrawler.com/techreports/oyrcorners_led/page4.asp
http://people.ne.mediaone.net/katam25/tail%20light%20page.htm
http://people.ne.mediaone.net/katam25/bodyshop.htm

Being an LED junkie, I would love to do a conversion like this because I love the look of LEDs and want to show them off. But unfortunately I dont have a car that would neatly adapt to this type of conversion without hacking away at my existing taillights. I know about the 1157 LED bulb replacements, but the good ones are $60 per bulb, so scratch that for now.
I ordered and am currently awaiting a 60-LED amber truck light for my front turn signals. If I can adapt it well, I will order another and do the conversion...fun






So is anyone else into this type of stuff?

P.S.- I love getting stuck behind Cadillac DeVilles


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## BobSnow (Jan 6, 2002)

The 1157 LED replacement bulbs I tried were terrible. Not very bright and not very dirrectional - could only be seen straight back. Got them because my dual filament bulbs tend to burn out fairly quickly. Who makes the "better" ones?


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## NightShift (Jan 6, 2002)

LEDtronics makes the supposed "better" ones. I believe they are better than the ones i've seen and tried because they have 24 LEDs and multiple LEDs facing to the side to aid in lighting up the rest of the taillight. I've even e-mailed a person who tried them and they said they were much brighter and well worth the money. I think its kinda expensive though, so i might wait on it as much as i am tempted to try one. These links can describe them better than I can:

LEDtronics News Brief
LEDtronics Product Page
Customer's Review & Pictures <~~extreme closeup of the bulb here


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## Daniel Ramsey (Jan 6, 2002)

I hate to hog the boards but I just had a brainstorm about using one (yes just ONE!) red Luxeon with a dimmer resistor to use as a 1157 bulb replacement, you would have a dropping regulator from 14v to the voltage for full brightness for the brake or turn function and a resistor for a lower light output for the running or park function, it could be very compact and still fit through any size tailight even the sealed ones like on my wifes Subaru.


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## NightShift (Jan 7, 2002)

Daniel, my thoughts exactly about using the bulb on multiple cars, but until I can afford 4 LED bulbs costing me $200+ for my taillights, I think i'll stick with my incandescents and my money for now. Maybe the price of them will come down in a short time?

Concerning your luxeon idea, trust me - you won't need the dimmer and plan on using quite a few luxeons. Without the focusing lens, you will need a few luxeons to light up the taillight and i doubt it would be very bright at night, and hardly noticable during the daylight hours. With the focusing lens, it would create a small concentrated spot on the taillight lens. I shined my luxeon through the hole of my taillight once at night and it wasnt very bright at all. I can pretty much picture the scenario. Thats my opinion on it.


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## Daniel Ramsey (Jan 7, 2002)

A fresnel lense is whats needed basically thats what the ridges inside any tailight is. I just grabbed a 4" tailamp assembly common on all new tractors and trailers, it has 43 approx. 3mm SMD LEDs, these are very short with a square base, my guess is these are about 5000 mcd each.That comes out to 215,000 mcd and that may be a bit high. One Luxeon is about 80,000mcd so I would need about 3 for the average stop/run bulb (1157) so that would be about $45 for the Luxeons. For just a single filament bulb like an 1156 2 Luxeons or for a side maker lamp 1 in either red or amber. I do not have the price on the SMDs but my guess is about $1.25 each if bought in bulk. These lamps go retail for about $65-85 and I have most of my fleet of over 12 tractors or concrete mixers with these installed, like I said earlier I have yet to have a failure in the lamp itself after 3 years of 8+ hours a day of use, If I were to use Luxeons instead of multiples of LEDs it would be half of what I pay for the current product. Hopefully even the Luxeon's price will fall within the range of what the latest Nichias are going for ($5 or [email protected])


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## Bart (Jan 25, 2002)

I think I posted this link before... long time ago... can't remember. Anyways, I converted my tail lights to LED's and also converted my cluster, dash and window/door lock switches on my doors to blue LEDs. http://aol8mydog.freeservers.com for a directory listing of some pictures. I used 92 normal 5mm superbright LEDs for each tail-light and 27 snapLED LEDs for each brake light. My third brake light has 20 snapLEDs. For my side marker lights I am using one luxeon star LED in each one using my steel quarter panel as the heat-sink (works perfectly)... which is a little brighter than a 5watt incondescent normally used for side markers (Luxeon running at ~300mA). One of these days I will redo my tail lights with the super-flux LEDs from Lumileds.com which are available at www.futureelectronics.com. Either that or I'll use luxeon LEDs, but I want to be able to design a specific shape rather than rely on one light source that has to be diffused or reflected to illuminate a larger area. The SnapLEDs I am using now aren't sold anywhere and basically I sweet talked my way into getting some samples. They're used in the cadillac deville. They don't sell them because they have to be mounted by their "clinch" technology and cannot be soldered. I soldered them but with a fan blowing constantly on them while soldering. Messy job, but it worked... barely. A few LEDs weren't as bright as the others because they got too hot. They've been working for about a year now, through rain, snow, and 90 degree heat with the sun shining on the (black) tail light housings. Anyways, even though I always check to make sure my tail lights and brake lights are working, I feel better knowing that they won't burn out like incondescents. If you have the patience and don't mind cutting away the backside of your tail lights, a do-it-yourself LED conversion is worth it... just the unique look of my tail-lights compared to others is worth it.


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## Darell (Jan 25, 2002)

Well done Bart. I'm very impressed.

Next time I have a car that is NOT under warranty any more, I'm right there with you. This is absolutely the wave of the future...


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## Bright Scouter (Jan 25, 2002)

I like the idea of using leds for a totally different reason. I want them in my rv. If I run lights in my motorhome for two nights, my battery is running down to the point where I can't start the generator. The leds would help extend that a LOT longer. There are many times where I don't want to run the generator and the extended quiet time would be nice.


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## Darell (Jan 25, 2002)

Del -

After you install the LED lighting, next consider photo voltaics to keep the batteries charged up. A relatively small array up on the roof will don wonders for you in the summer. You may start leaving the generator at home! Then the only sound you'll hear is the blender right before the margaritas are served!


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## Bart (Jan 25, 2002)

darrel, thanx



not exactly the best looking on the inside, but no one sees the insides of the tail-lights anyway





del rockwell, that would probably be one of the best applications for LEDs. One of the reasons I would like to make my whole car LEDs (except for the headlights of course) is because of their efficiency. I'm always paranoid about my car breaking down some day, and I would like to be able to have my hazards on for a prolonged period of time if needed. with LED turn signals, they'd last a lot longer. Also, less strain on the alternator while the engine is running. I may never need my hazards, or may never put that much strain on my alternator, but it's always nice to be sure. On top of it all, I just like to create my own lighting designs for my car.


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## NightShift (Jan 26, 2002)

Hey Bart, nice work! Cool to see some of the electronic (lighting) guts of an Intrepid since my dad just recently got his 2002 intrepid. I dont think he'd let me take it apart though like you did 

A question for ya....when I sat in his drivers seat, I noticed the door ajar light to be bright when viewed directly...im pretty sure that was an LED, right? Did Dodge use (all) LEDs in the instrument cluster? - the holes look small for incandescents.

How is the brigtness of the tail/brake lights?
Did you blackout your taillights?


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## Bart (Jan 26, 2002)

NightShift, most of the dash lights are LEDs. The ones that aren't are the illumination lights, turn signals, highbeam indicator, and cruise control indicator. For the door ajar, I just switched the red LED for a white one just for fun.





yeah, my tail lights are blacked out... in the pictures I used window tint film and then glazed it over with a clearcoat. I took that off and now I have that tail light tint spray. ~$8 at a local autoparts store and it works pretty good. I masked off the areas that light up and tinted the rest pretty dark... I then took off the tape and tinted the whole thing a little bit more. Then I put clearcoat on to make it more glossy since the tint spray had a flat luster to it. The areas that light up are tinted a little bit, but look more tinted since there isn't much outside light getting into the housing. This way the brake and tail lights don't lose that much brightness. The tail lights are brighter than standard tail lights when viewed straight on (from the corner of the car at an angle), but just as bright straight back from the car. My brake lights are a little bit dimmer than standard brake lights mostly because I have them diffused quite a bit with an extra freznel lens and the pillow lens of the tail light housing.


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## Daniel Ramsey (Jan 26, 2002)

Do you have a third brake light? Thats the best place to put extra bright red LEDs and its better for those to see behind you.If I was younger and still showing off I would have the LEDs set up to spell a message, If you have any problem with the turn signals or 4 ways not flashing fast or at all then check your flasher(s)and see if its the old style resistance type,some cars use two, the LED draws so little power it wont make these work properly. Get the electronic version, plus it always has the same flash speed. How about adding some strobes to your emergency lights? Some new vehicles have these and its an eye catcher, just like the Indy pace cars and firetrucks. You can buy it complete but its pricey.I'm not trying to tell an experianced electrical person what he already knows but passing on info for those that want to do the same, after all thats how most of us learn the tricks of the LED trade here.i was totally green on LEDs not long ago (still am)


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## Bart (Jan 26, 2002)

The third brake light was the first thing I ever switched to LEDs since it was the easiest. Actually, I was so intent on having an LED third brake light I made one for my first car that didn't have one at all. I tested the wires on my brake pedal switch for a + signal and ran a wire from that. I hated the logic circuits they sold because on my particular car, the brake lights were also the blinker. If you had your brakes on, the third brake light would come on but if you turned your blinker on, the third brake light would blink as well. I've seen that on some pickup trucks that had a third brake light on their canopy and it was pretty annoying to look at when they braked and turned at the same time.

The message thing would be pretty interesting... Would be quite a project though. As far as the strobes, that would be a good idea. They don't take too much energy and are really noticable like you said. I know they make those aftermarket "just for looks" add-ons for those typical honda and acura boys... I wonder if they make amber colored strobes.


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## sike (Nov 29, 2002)

Bart, nice conversion on your car. I have a 94 intrepid and trying to do some projects on it with LEDs too.

I have this question on a different section of this forum but I guess it wasn't for that place.

Is there a way to make an LED act like a dual filament? Let's say connect it to the parking lights and it's dim (half potential power) and hit the brake and you have the full power (bright)?

I have yet to design a new third brake light for mine because I drill a hole in there for a blue LED with my alarm. nobody really notice it though

I also have a strobe light from good ol pep boys and wire the positive with my reverse light. I ran a wire for the ground all the way by the shifter side through a on-off switch. Just in case there's a cop behind me when backing up.

I want to know if anybody knows a site with a chart (for people with very little electrical knowledge) for wiring LED. let's say led that's 2 volts 20ma. how many of them do I need to make 12 volts and what kind of resistor (if needed)

thanx in advance
sike


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## NightShift (Nov 30, 2002)

Hi sike.



> Originally posted by sike:
> *Is there a way to make an LED act like a dual filament? Let's say connect it to the parking lights and it's dim (half potential power) and hit the brake and you have the full power (bright)?*


<font size="2" face="Verdana, Arial">Yes, but not on a third brake light. You need two wires (park - turn/brake) to distinguish the functions. You can use a higher value resistor on the park wire to the LED (less current), and a lower value on the park/turn (more current).



> Originally posted by sike:
> *I want to know if anybody knows a site with a chart (for people with very little electrical knowledge) for wiring LED. let's say led that's 2 volts 20ma. how many of them do I need to make 12 volts and what kind of resistor (if needed)
> *


<font size="2" face="Verdana, Arial">If the LEDs are 2 volts, then you can use 6 in series without any resistor (6x2=12volts) and will be safe. You can also use a 1 ohm just in case.
Here are some LED resistor calculator sites:

http://www.csgnetwork.com/ledresistancecalc.html
http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm

There are many more - you can search on the web "LED resistor calculator" or on the board.


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## Jonathan (Nov 30, 2002)

> Originally posted by NightShift:
> *
> If the LEDs are 2 volts, then you can use 6 in series without any resistor (6x2=12volts) and will be safe. You can also use a 1 ohm just in case.
> *


<font size="2" face="Verdana, Arial">This is _very_ bad advice, especially for automotive applications. The setup _might_ work, but it will not be safe, and chances are the LEDs will either be very dim, or be severely overdriven.

You are entirely correct that the forward voltage of the LEDs will add when connected in series, and you are further correct that when you connect a LED string of voltage Vf to a supply of V, that the proper current will flow if Vf=V.

However, this is only useful if the voltages are almost _exactly_ the same. The issue is the voltage versus current relation of an LED. At low voltage, very little current flows, almost none. Then you hit the threshold voltage and the current starts climbing like crazy. This means that a _very_ small change in supply voltage will cause a very _large_ change in current flowing through the LED.

Even worse, the Vf of the LED will change with things like temperature and age, so you can never pin down the exact voltage to run the LED string at to get the proper current to flow.

Finally, what is the supply voltage in a car? I can tell you now that it is _not_ exactly 12V. The battery nominal voltage is 12V, but when the car is running the charging system is on, and the entire electrical system is held at the 'float' voltage of the battery, which is more like 13.8V. When the car is running of the battery only (say parked with hazard lights on) then the voltage could be as low as 10V. If a 'load dump' occurs, then the voltage could momentarily spike up to 60V.

What all this says is that you _don't_ want to connect a '12V' string of LEDs to a car electrical system. You want to use resistors, and they need to be appropriately sized for the current requirements of the LEDs.

The tradeoff is that the more LEDs in series and the smaller the resistor, the more efficient the LED string is, but the more sensitive it is to slight voltage changes. The fewer LEDs and the larger the resistor, the more robust the system is, but the less efficient it is. If you go with a 'zero' resistance system, then you will fry your LEDs the first time you start your car. For a car, I would put no more than 7-9V of LEDs in series, and then I would calculate resistor values based upon a 13.8V supply voltage. If the results weren't good enough, then I would use a switching power supply.

-Jon


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## NightShift (Nov 30, 2002)

> Originally posted by Jonathan:
> *This is _very_ bad advice, especially for automotive applications. The setup _might_ work, but it will not be safe, and chances are the LEDs will either be very dim, or be severely overdriven.*


<font size="2" face="Verdana, Arial">This was how my LED brake light worked that came with my spoiler. Each LED was 2 volts and 6 of them were run in series, with a small resistor.

If you are talking about the "no resistor" as bad advice, then I might have been mixing ideas with my computer's lighting mod which I have 6 LEDs in series with no resistor, and was told I should be safe in doing so. They have been running 24/7 for almost 5 months perfectly.


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## Jonathan (Nov 30, 2002)

I claim that "no resistor" with a voltage source to run LEDs is bad advice. The voltage source and the LED have to match just right, or the LED will be driven out of spec.

The case of the computer mod is somewhat special, in that you have a well regulated 12V supply, something that you don't have in the automobile. The LEDs do have _some_ incremental resistance, so if the voltage is in the proper (very narrow) range, then the device will function. I do not doubt that you have a functioning light with 6 LEDs and no resistor, but I bet that the product shows wide variation in performance from copy to copy.

In the car, the operating voltage range is quite large, and a no resistor system would show significant changes in brightness between engine off and engine running, and would IMHO not be acceptable.

-Jon


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## highlandsun (Nov 30, 2002)

Even with a resistor you'll see huge variation in brightness, this is why I researched the constant-current circuit described in this thread
http://www.candlepowerforums.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=15;t=000090

The normal range quoted for automotive electrical systems is something like 10-16V. If you're putting a bunch of LEDs in series you should design a circuit that will operate at the desired brightness level, at 10V. The circuit I use will drive 4 Luxeon Stars at the correct brightness, with 9.6V across the LEDs, and the transistor can withstand up to 60V on its input. So it will deliver the exact same brightness level no matter what the car's electrical system is doing.


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## INRETECH (Dec 1, 2002)

I can not overstress the following details:

In an automobile system, there is a 12-14v power supply from the battery, but at starting time when you put 400-600A into the starter to "turn over" the engine, there are INCREDIBLY high voltage spikes that are returning from the starter EMF field as the brushes lose contact with the armature of the starter

These very high voltage spikes, although very small will easily DESTROY any sensitive electronics such as LEDs/etc

Make sure your electronic devices that you insert into the automobile system have a small inductor/cap. on the power input and a voltage clamp device such as a Tranzorb or Zener (not GeMovs) to keep these high voltage spikes from damaging your expensive LEDs


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## NightShift (Dec 1, 2002)

I remember pointing out to someone that when you turn the ignition to start the car, it cuts the power to everything while it starts, then everything returns. This is a protection measure due to that high voltage spike you are talking about Inretech, right? So in assuming that you know this already, im guessing that is not enough protection?


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## Jonathan (Dec 1, 2002)

> Originally posted by highlandsun:
> *Even with a resistor you'll see huge variation in brightness, this is why I researched the constant-current circuit described in this thread...*


<font size="2" face="Verdana, Arial">_Very_ nicely done. I've been looking at switching power supplies, since I use LEDs for battery powered applications, where the losses in a linear regulator are too costly. But for automotive applications, simplicity is _king_, and your circuit will drive an array of LEDs at constant current with only a couple of bucks in parts, and I suspect that your circuit will be _very_ robust in an automotive environment. I might have to design a PCB






-Jon


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## highlandsun (Dec 1, 2002)

Let me know if you do, Jonathan! Otherwise it's all just gonna get soldered onto perfboard and then covered in epoxy...

Yes, absolutely, simplicity rules. And when you're talking about replacing a 27W bulb with 4W of LED, electrical efficiency is somewhat irrelevant - you're already way ahead on that score.

By the way, I measured a total of 116mA going through this circuit, ~103 thru the LS string and ~16mA thru the other leg. Reasonably efficient, really.


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## Jonathan (Dec 2, 2002)

Okay,

I spent some time with the circuit, and decided to use it as the basis of a slightly different, using the voltage across the current sense resistor to turn on a small PNP transistor, rather than to turn off the main power PNP. The small PNP transistor than steals base current from the main transistor, reducing the drive to the main transistor.

The voltage across the sense resistor is now only 0.6V, and it doesn't depend upon the diode drop matching the Vbe of the main PNP. This lets you use a darlington for the main PNP, and reduces the side current path to a couple of mA. 

I also added _two_ current sense resistors (with the corresponding small PNP transistor for each) so that you can have two _different_ regulated current values.

I've designed the PCB, and will need to stare at it some more to be certain that it makes sense



If you can use Eagle files, I could send the schematic to you.

I will 'piggyback' a couple of these PCBs onto a job that I've got to run this month, so if anyone is interested in copies, they'll be pretty cheap (like a buck or two each).

-Jon


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## sike (Dec 2, 2002)

this thread has been really interesting. Although most of them doesn't register up there yet (no offence), I'm trying to figure all these lingo out. I feel smarter everything I finally understand something. hehe





nightshift, on the two wires having it dual filament. If I use those as tail light abd brake light (not third brake), splice the positive so I can have two leads? I just run a higher resistor from the positive to the tail light and low or no resistor for the brake light, right? I want to have an equevalent of 12 volts. if there is two leads (one from tail and one brake) is the LED getting too much power when the taillight and brake light are on?

On this spike. Everytime I use the remote start for my car, parking lights light up and then gets dim from the starter cranking up, is this where the sudden "pulse" of voltage hits? If so, shouldn't the parking lights be brighter if there is a sudden increase in voltage? why would this affect the too much power for the LED?

Also, I don't know if there is an answer above for the regulated voltage yet. Having a stable 12 volts with or without the engine running.

I apologize for this newbie question guys. I do appreciate the help for this not every technical person learning the curves of electrical knowledge. Hoping other people who is too shy to post are also learning from this.

thanx in advance


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## highlandsun (Dec 3, 2002)

> Originally posted by Jonathan:
> *
> I've designed the PCB, and will need to stare at it some more to be certain that it makes sense
> 
> ...


<font size="2" face="Verdana, Arial">Sorry, I don't know what program "Eagle" is. Perhaps just a screen capture or something, or print to a PDF, etc.

I'm pretty sure the 2907 is operating in a safe region, but you may want to double check the transistor specs. With 14.4V coming from the alternator, and only 9.6V needed across 4 LS's in series, there's 1/2W being dissipated in the transistor.

I think I've seen a simple example of what you're talking about. Sounds good, but I'd still like to see it exactly.

re: stable 12V - I measured 12.2V with the engine off, 14.6V with engine running. This was actually for my headlights, going thru my homemade heavy-guage harness and Bosch mechanical relays. As for power surges during startup - I never turn on my lights until after I start the engine anyway, and I always turn them off before shutting off the engine. Just a longtime habit, not sure when/why I picked it up. But it certainly saves strain on the battery to wait till the alternator is running before powering up accessories and such.


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## Christoph (Dec 3, 2002)

Jon
I am very interested in this circuit. Keep us informed please. 
Chris


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## Jonathan (Dec 4, 2002)

Please see my post in the thread that highlandsun started:
http://www.candlepowerforums.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=15;t=000090


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