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Thread: Help wanted with constant current circuitry for automotive lighting!

  1. #1

    Default Help wanted with constant current circuitry for automotive lighting!

    Hey guys and gals,
    I am starting to make some LED conversion taillights for a couple cars that my friend has. The factory taillights have a 3w driving lamp and a 25w brake lamp, both incandescent tubes. They are extremely dim, and the light housings are rather small (3" round), so it makes seeing a very expensive car rather hard at night.

    I would like to have 1-3w of LED for the driving light and maybe up to 10w of LED for the brake light. I am machining new aluminum backplates for the conversions.

    I am new to the LED game, and heard that you want to run all high power LED's through a constant current regulator/driver, or else you will damage the LEDs.

    I am pretty proficient at soldering, so that wont be an issue. I will be buying LED's and reflowing them onto stars myself, or just finding pre-mounted LED's. I want to avoid the cheap ebay LED's, and will most likely go with something from Cree, as they are easy to get and easy to find stars/MCPCB's for.

    I am willing to make my own drivers, or use off the shelf drivers if they fit.

    Any help or suggestions is much appreciated!

  2. #2
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    Default Re: Help wanted with constant current circuitry for automotive lighting!

    Hello and welcome ( back ? ) to CPF

    Your post above has been approved, but the thread was moved to Automotive, as you are asking about transportation-associated safety equipment.

    I imagine that some of our local experts will be by shortly to assist you. Adding important and relevant details, such as specific makes / models / years and such, is of great help in this process.

    Cheers !
    ... is the archimedes peak

  3. #3
    Moderator Alaric Darconville's Avatar
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    Default Re: Help wanted with constant current circuitry for automotive lighting!



    Please reread this sticky, including:
    Quote Originally Posted by Alaric Darconville View Post
    [*]Homemade headlamps, taillamps, stop lamps, turn signals, fog lamps, etc, are not safe, effective, or legal. We will not help you build or troubleshoot them. We will not argue this point.
    Being a machinist and being proficient at soldering is a great thing, but there's also the science of optics and the complexity involved in making a light source that will result in a compliant beam pattern in the regulated motor vehicle safety equipment we're dealing with.

    There are some off-the-shelf LED "drop-ins" that can perform acceptably in many automotive turn, stop, and tail lamps. The "corn cob" and "spiderweb" styles are pretty much a no-go, but some from Philips and Sylvania can be decent. You can attempt to evaluate their safety to see if they're not an obvious no-go.
    Last edited by Alaric Darconville; 10-23-2020 at 10:13 AM.

  4. #4

    Default Re: Help wanted with constant current circuitry for automotive lighting!

    Hi, there, Alex.

    Alaric is right: homemade car lights really are (and really must be) a hard, flat no. Every lighting function on the outside of a vehicle is specified in very complex detail as to their design, construction, multiple aspects of their performance, durability, etc. Engineering, designing, and building an effective, safe, and legal car light requires specialty equipment and the knowledge to use it correctly; this is nowhere near just a matter of looking up lumen specs and driver outputs, and it's far more complicated than just "it's dim red for the tail light and brighter red for the brake light".

    It sounds like you're working with the lights on a very old car, if we're talking about tubular bulbs and 3w tail lights. That's going to mean there are no workable "LED bulbs" for an application like this. But your mention of a 3" round size suggests good help for the situation available on an off-the-shelf basis. For example, these (also in clear) are just under 3" diameter, and these (also in red) are just over 2" diameter. Look at "hiding" one of these within the car's existing housing, behind its original lens, or if that won't be possible, machine a new mount to mate the new lamps to the old car, and preserve the originals for reinstallation during car shows if necessary.

    If this car flashes the brake light to provide the turn signal function, you will have to use an appropriate flasher to provide the correct flash rate (60 to 120 flashes per minute, that is 1 to 2 per second) with the LEDs.

  5. #5

    Default Re: Help wanted with constant current circuitry for automotive lighting!

    Thank you for the advice and info. I have tried many of the drop-ins, and they are are pretty much just as bad or worse. The taillight is for a 1960's Porsche 911 R, and it is an inherently bad design. It was a VERY limited production lightweight car that didn't give much in the lines of safety and basically only cared about weight. Like many European lights of the day, the housing had no reflector on the back, which drastically decreased the useable output of the lamp. For the purpose of this, I really only need help making a couple constant current regulators or whatever would be needed to drive my lamps of choice. I wont ask anyone to break any rules by helping me make a tail light lamp.

    Here are the taillights that need major internal improvement.



    Last edited by Alaric Darconville; 10-23-2020 at 01:54 PM. Reason: Removed wholesale quote

  6. #6

    Default Re: Help wanted with constant current circuitry for automotive lighting!

    Quote Originally Posted by -Virgil- View Post
    Hi, there, Alex.

    Alaric is right: homemade car lights really are (and really must be) a hard, flat no.
    As I put in my last reply (which may have not been approved yet), I am not interested in housing design, lamp design or anything like that, just interested in how to make the proper circuitry to drive an LED/LEDs of my choice.
    Last edited by Alaric Darconville; 10-23-2020 at 02:03 PM. Reason: Pared down quote

  7. #7
    Moderator Alaric Darconville's Avatar
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    Default Re: Help wanted with constant current circuitry for automotive lighting!

    Quote Originally Posted by AlexTheMachinist View Post
    As I put in my last reply (which may have not been approved yet), I am not interested in housing design, lamp design or anything like that, just interested in how to make the proper circuitry to drive an LED/LEDs of my choice.
    Yet, strangely, you included pictures of taillamps you wanted to make light modules for.

    I wont ask anyone to break any rules by helping me make a tail light lamp.
    Essentially, that's what you're doing. You want us to help you make internals for a taillamp that may reduce road safety.

    Quote Originally Posted by AlexTheMachinist View Post
    As I put in my last reply (which may have not been approved yet), I am not interested in housing design, lamp design or anything like that, just interested in how to make the proper circuitry to drive an LED/LEDs of my choice.
    Then this is where we stop. We know you want to try to upgrade the existing lamps in a particular car by designing driver circuitry for the LEDs of your choice, and you've had it explained that what you are attempting to do is unwise and unsafe. You plan to tamper with life-critical safety equipment and the electrical issues are not the problem, the photometric issues are the problem.

    You didn't get the answer you wanted because you got the answer you needed. Your question was based on not understanding automotive lighting, and so that's why you got the answer that you did, even if it wasn't the handhold you wanted to go down a path of endangering road users' safety.
    Last edited by Alaric Darconville; 10-23-2020 at 09:25 PM.

  8. #8

    Default Re: Help wanted with constant current circuitry for automotive lighting!

    Yup, this is really very simple: you're right, those lamps are not even close to adequate. There is nothing you can do to them, with LEDs or anything else, that will make them adequate. If the goal is to keep this very expensive car from getting hit in traffic (are we really driving these cars in traffic?), then mount a pair of these and a pair of these. They should fit the existing mount locations without much difficulty, without preventing you from reinstalling the useless lights as necessary for judged shows.

    (Either that, or install a set of standard Porsche 911 taillights for driving on the street)

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