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  1. #1
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    Idea! driving XPGs with high currents

    A few months I posted here the test report of driving an XP-G at 1.5A on a MCPCB (metal core board). The results were discouraging. The initial increase in output (which could be measured during the first second) was diminished almost to nothing in a minute of run. I tried different board types with enhanced heat conductivity, even copper clad ones, but the results were very humble, nothing similar to what I expected to have.

    This ensured me in the belief that metal-core PCB is a mere compromise. This technology is relatively cheap and provides much better heat sinking in contrast to classic FR4 laminates. It works fine in the most cases but the recent generation of power LED-lamps raises the requirements which cannot be fully satisfied with it. The main problem with MCPCB that in this technology there’s a thin insulator layer between the metal core and the LED heat terminal. Although its thickness can be very small (about 0.1mm), the thermal conductivity of best insulators hardly ever exceeds 5W/Km (the best which we could try and which cost us a lot of money was rated at 2.5-5W/Km). Just for comparison, copper conducts heat 100times better (up to 500W/Km). Almost all metals have this property rated in range 150-400. The thermal gradient on the insulator can be easily calculated. For example in case of an XP-G (the thermal pad size is 3.5mm x 1.5mm) which runs @1.5 amps dT = 40K which is added to the core temperature and it makes the LED to run at t>100C where its efficiency is 20%-30% less.

    A few months we were experimenting in creating new production technology which should become a breakthrough in this area. The release on new CREE XM-L lamp confirmed that we’re on the right way, the LED’s power is increasing year by year while there’s no progress in the insulator materials. The main idea is very simple – just to get rid of the insulator and solder the LEDs directly on the metal core. The preliminary results are very promising, it seems it’s possible to mix classic PCB board technology with CNC which will let to print circuits on metal parts machined or stamped with an open mound. Precision CNC also provides much better finish quality which reduces the heat conductivity losses between the board and the heat-sink.

    I update my progress in the blog here (a new photo posted today):
    http://www.lux-rc.com/view.php?p=con...ab/1400_lumens
    Last edited by quazzle; 01-28-2011 at 07:03 AM. Reason: grammar fixes

  2. #2
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    so the thermal pad on the LED sits on a small mound, but the terminals are slightly raised and isolated? Is the idea to have the circuitry sit on top of the copper base, with the LED mounds poking through? Just trying to visualise the idea

  3. #3
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    exactly, Mat, you explained the idea in 2 sentences better than I in 2 kilobytes :-)
    As I said, the idea is very basic. But implementation is difficult. I'm trying to keep the costs in acceptable limits so had to go though many prototyping cycles.

  4. #4
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    Have you done tests at 1.2 and 1.4 amp as well? Slightly off topic but I'm curious why you don't offer a 35mm/MR11 version of your products.

  5. #5
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    Quote Originally Posted by quazzle
    exactly, Mat, you explained the idea in 2 sentences better than I in 2 kilobytes :-)
    As I said, the idea is very basic. But implementation is difficult. I'm trying to keep the costs in acceptable limits so had to go though many prototyping cycles.
    I guess your tolerances will have to be very close in all 3 planes for everything to fit together. It'll be very interesting to see what you come up with!

  6. #6
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    This isn't really new and is even used in some lights already. Niterider uses this approach in some of their lights to get better thermal conduction. Too bad the lights have so many other problems..... I've used a similar approach in past projects where I machined out the slug area in the PCB and created a matching area machined into the case. It does create a better thermal path than an MCPCB.

  7. #7
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    35mm is too big for a triple. :-) but we have 36mm 7UP in the 2011 pipeline

  8. #8
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    Quote Originally Posted by quazzle
    35mm is too big for a triple. :-)
    Honestly, I think there are plenty of people who don't buy your products simply because they don't like the beam that 3up 20mm optics provide. The proliferation of 2up products that end up costing more than your 3up board with integrated driver speaks towards that. At least with 35mm optics there is much less of a compromise. Perhaps even less need to push so hard towards the maximum output in a setup that just doesn't use the lumens well to begin with.

  9. #9
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    Quote Originally Posted by kan3
    Honestly, I think there are plenty of people who don't buy your products simply because they don't like the beam that 3up 20mm optics provide. The proliferation of 2up products that end up costing more than your 3up board with integrated driver speaks towards that. At least with 35mm optics there is much less of a compromise. Perhaps even less need to push so hard towards the maximum output in a setup that just doesn't use the lumens well to begin with.
    +1
    The 20mm triple is of little use on the road.
    An oval 2up board with mounting holes for the regina optic would do very very well, option of XPE or XPG and a mix too.
    DIY LED Bike Lights:
    A few Dynamo builds and some Small battery lights

  10. #10
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    Quote Originally Posted by kan3
    Honestly, I think there are plenty of people who don't buy your products simply because they don't like the beam that 3up 20mm optics provide. The proliferation of 2up products that end up costing more than your 3up board with integrated driver speaks towards that. At least with 35mm optics there is much less of a compromise. Perhaps even less need to push so hard towards the maximum output in a setup that just doesn't use the lumens well to begin with.
    Me for one. I've done the tiny Carclo optic thing and it just is not my idea of a useful beam. Lots of light going places I just don't care about lighting up. Integrated triple for the Cute SS now we're going to talk!( especially if you keep enough room around the LED for the base of a Regina and drill holes for the Regina pins to fit).

  11. #11
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    I think the bottom line comes down to cost.
    Other than frontal area of the body, why would I want to run 1x XPG at the absolute max current, when I could run 2x XPG at significantly lower power and produce the same amount of light with the same amount or less heat.

    Don't get me wrong, I love innovation. It's projects like this one that push technology progression. But, all I'm seeing is $$$$ signs for this application.

  12. #12
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    Quote Originally Posted by quazzle
    The main problem with MCPCB that in this technology there’s a thin insulator layer between the metal core and the LED heat terminal.
    Not entirely true. One MCPCB manufacturer suggested that it is possible to grind this thin insulator layer and solder the thermal pad directly to bare metal. But this is expensive.

    I saw Niterider housings - they are die-cast, so the LED "mound" is not very flat.
    CNC LED light housing for DIY projects

  13. #13
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    A guy on here with the name of cloggyabroad did a 3 up MCE board that is one of the best innovations I have ever seen on here, the mce sit flush with the bottom of the board meaning they are mounted directly to the housing. Ah here is the thread on the light and the custom board. -
    Another Triple MC-E Light

  14. #14
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    Troutie did an MCE light with bare emitters AA,d directly to the housing. Don't recall the outcome, but it looked tough to build.

  15. #15
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    Quote Originally Posted by Vancbiker
    Troutie did an MCE light with bare emitters AA,d directly to the housing. Don't recall the outcome, but it looked tough to build.
    MC-Es are easy to AA... I did it also without much trouble. XP-E/G, XM-L are trickier.

  16. #16
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    Quote Originally Posted by bikerjay
    A guy on here with the name of cloggyabroad did a 3 up MCE board that is one of the best innovations I have ever seen on here, the mce sit flush with the bottom of the board meaning they are mounted directly to the housing. Ah here is the thread on the light and the custom board. -
    Another Triple MC-E Light
    of course I saw this project and we tried a similar design in our L30 project, the LED is installed on the sink via a through hole in the PCB:


    But what we're doing now is not exactly the same. Instead of using standard MCPCB laminates with a flat clad, we're experimenting with profiled machined cores on which the PCB layers are printed directly. This also should let us create many assy layers on it while as you know standard MCPCB allows just one layer.

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