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Thread: Building LED light bar advice

  1. #1
    Unenlightened
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    Default Building LED light bar advice

    Hello all,

    I'm new to this forum so if there is any that can help me on this that would be much appreciated. Im trying to make an led light bar for my jeep using cree xhp70.2 leds.

    I need to wire 20 xhp70.2 together in parallel a need to know if there is a single driver that can control the current as I plan to use my 12v car battery to power the light bar.

    Thanks in advance for any info you might have for me! Link to Image on Dropbox I tried to insert an image with a link to a picture for reference but not sure if it worked.
    Last edited by Alaric Darconville; 07-30-2018 at 03:55 PM.

  2. #2
    *Flashaholic* idleprocess's Avatar
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    Default Re: Building LED light bar advice

    The simplest way to do this is probably going to be with resistors. Note the plural - you're going to want one resistor per LED. I suggest setting up the LEDs for 6V operation and using the remaining voltage overhead for current control. This will probably double the resistor count. You'll want to fuse the entire thing and likely want to use a relay to power it on so your control switch doesn't need to handle the full amperage.

    When it comes to drive currents I'd go conservative since htis device will run for long periods of time, dissipate a lot of power, and be subject to varying voltages due to the realities of automotive 12V. I'd plan on 14.4V as the true nominal design voltage, myself.

    Automotive electrical is a harsh environment and I've heard some tales of XHP LEDs being a tad sensitive, so you might also look into automotive-specific LED drivers. Still plural since odds are you'll need more than one, but I expect there are some that run in boost mode thus you won't need twenty either.

    If all of this is sounding complicated then you have two choices: read up on how power LEDs and driver circuits work, or turn to the markets that can surely deliver a turnkey product for less than it's going to cost you to make one.
    I apologize that this letter is so long; I did not have time to write a short letter

  3. #3
    Moderator Alaric Darconville's Avatar
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    Default Re: Building LED light bar advice

    Quote Originally Posted by idleprocess View Post
    Automotive electrical is a harsh environment and I've heard some tales of XHP LEDs being a tad sensitive, so you might also look into automotive-specific LED drivers.
    It's also a mechanically and thermally harsh environment. Protecting against mechanical shock, thermal shock (sudden cooling while hot), and just excessive heat will be a challenge. Finally, sealing in such a way to prevent water ingress, yet *venting* such that water can leave, is another challenge. There are some things best left to off-the-shelf solutions.

  4. #4
    *Flashaholic* idleprocess's Avatar
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    Default Re: Building LED light bar advice

    Quote Originally Posted by Alaric Darconville View Post
    It's also a mechanically and thermally harsh environment. Protecting against mechanical shock, thermal shock (sudden cooling while hot), and just excessive heat will be a challenge. Finally, sealing in such a way to prevent water ingress, yet *venting* such that water can leave, is another challenge. There are some things best left to off-the-shelf solutions.
    The aftermarket has a solution for the water ingress/egress problem ala the gore-tex patch. But otherwise I'm not sure that the hobbyist is going to beat the market when it comes to the kind of price/performance ratios that most are looking for.
    I apologize that this letter is so long; I did not have time to write a short letter

  5. #5
    Moderator Alaric Darconville's Avatar
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    Default Re: Building LED light bar advice

    Quote Originally Posted by idleprocess View Post
    The aftermarket has a solution for the water ingress/egress problem ala the gore-tex patch.
    The same vent that lets water vapor out can let it in. Proper vent design and placement is important. Another advantage to getting something that's already built!

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