Getting rid of 55W of heat???!- Mtbr.com
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  1. #1
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    Listen! Getting rid of 55W of heat???!

    I'm in need of a little assistance here.

    I have searched through all the threads looking for the best way to remove large amounts of heat from a small area but they havent realy answered my question.

    Basically, the light will be 50mm (w) x 37mm (h) x 70mm (d) and have 3mm (w) x 5mm (d) 'fins' milled into the top surface. It will be made from aluminium.
    I will be mounting the LEDs directly to the body of the light on the short end, ie. without the stars.

    So, will the aluminium be able to remove the heat quickly enough to protect the LEDs or should I have another materail in there, like copper. I see its always copper that is used for CPU heatsinks.

    I was thinking about a layer of copper sheet, between the LEDS and the ali body. The copper will continue through the top surface of the light, and bend back and sit inbetween the fins that will have been milled into the ali body.
    Sorry, I would post up a picture but I am currently in a tent in Helmand Province and there just isnt enough bandwidth!

    Or is all of this just far too much work and the aluminium will be fine?? The light will have an output of 55W, using MC-Es.

    I know it is alot but I have spoken to George and there are drivers that can do it!

    Thanks for any assistance. If I dont reply immediatly its only because I cant get online, reception aint that good in the desert!

  2. #2
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    Not knowing what you are making it's kind of hard to comment usefully.

    The short answer is you will need forced air cooling. Think something like a CPU heatsink and fan that is used in a computer. The CPU in a computer is usually at about that same heat level. You might consider using a CPU heatsink as a integral part of your light. Due to your location getting something from a local computer store might be a problem. If you have any broken computers that could be a source.

    The airflow is key. A heatsink with no forced air flow would have to be huge to dissipate 55 watts. Many times the size you quote.

    If the airflow is limited or intermittent a fan is almost a requirement. The small lights on this forum only work because they are normally moving. It might be a good idea to use a driver that turns down the power as the LEDs get hot.

  3. #3
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    It is a bike light for use on the handlebars.

    I will be using a hipFlex so will be able to use the dimming facility in the software. It will be 6 MC-Es in 2 rows of 3. However, I might put all 6 in one row, therefore increasing the surface area of the light.

    I live in the UK so have access to all the normal stuff, just doing my bit in Afghanistan at the mo.

    I will looking into forced cooling, only problem will be keeping the fan watertight.

    Thanks for you input, more ideas on the drawing board now!

  4. #4
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    Reputation: ocean breathes salty's Avatar
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    Quote Originally Posted by piesoup
    It is a bike light for use on the handlebars.

    I will be using a hipFlex so will be able to use the dimming facility in the software. It will be 6 MC-Es in 2 rows of 3. However, I might put all 6 in one row, therefore increasing the surface area of the light.

    I live in the UK so have access to all the normal stuff, just doing my bit in Afghanistan at the mo.

    I will looking into forced cooling, only problem will be keeping the fan watertight.

    Thanks for you input, more ideas on the drawing board now!
    How are you planning to attach the LED's to the heatsink? Soldering offers much better thermal efficiency than AA however it is very difficult to solder to Aluminium. Making a significant portion of the body out of copper may be a good idea as it is much easier to solder to and is a better thermal conductor. If you get the interface between the LED and the housing correct, you are half way there.

    Do you have alloy bars? If you do, you should investigate some of Trouties designs which use the bars as part of the heatsink.

    Stay safe in Afghanistan, I hope things are getting better.

  5. #5
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    Quote Originally Posted by ocean breathes salty
    Soldering offers much better thermal efficiency than AA
    I don't know the source of it, but I found it's very informative:


  6. #6
    aka RossC
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    Quote Originally Posted by Itess
    I don't know the source of it, but I found it's very informative:

    I stand corrected! Why the heck would you solder when AA does such a good job?

  7. #7
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    Quote Originally Posted by ocean breathes salty
    I stand corrected! Why the heck would you solder when AA does such a good job?
    Looks like soldering does a little bit better job. Yesterday I used Arctic Silver for mounting bare MC-E and it heats the case at 6.5W just in seconds. I am satisfied.

  8. #8
    aka RossC
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    Quote Originally Posted by Itess
    Looks like soldering does a little bit better job. Yesterday I used Arctic Silver for mounting bare MC-E and it heats the case at 6.5W just in seconds. I am satisfied.
    Certainly it is slightly better, but the magnitude of difference was much less than i was expecting. The star mount is the real surprise....

  9. #9
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    Quote Originally Posted by Itess
    I don't know the source of it...
    I found the source: Cree XR-E Thermal Concerns

    As you can see, the Arctic Alumina Thermal Epoxy to the copper plate nearly works as well as soldering directly to the plate. The ETGTech MCPCB doesn't work nearly as well as the other two options.

    The AA Thermal epoxy XR-E has a dome temperture of 42 degrees C.
    The direct solder XR-E has a dome temperature of 39 degrees C.
    The ETGTech MCPCB has a dome temperature of 54 degrees C.

  10. #10
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    Quote Originally Posted by Itess
    I found the source: Cree XR-E Thermal Concerns
    Good stuff in that post. Just remember the MC-E problem is worse since there are four emitters in the same small package.

  11. #11
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    I think that you will be better off without an extra layer of copper. Creating a perfect thermal junction between the copper layer and aluminum is almost impossible and you will probably end up with higher overall thermal resistance than if you just used aluminum. Keep it simple and direct mount the MC-Es to a well designed aluminum housing. With the HipFlex you can rely on the thermal protection capability to keep things from melting when you're stopped. I'm looking forward to seeing what you come up with!

  12. #12
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    Interesting reading with regards to the solder vs AA. I think I will use AA, soldering 6 LEDs in the correct position will be hard work!
    I have drawn up a CAD design using the copper and ali housing, and there is no way on gods earth I will be able to machine that without a CNC machine!

    So, I have got another idea, same front end with the LEDs mounted directly to the ali, but with a hollow back with some sort of multi finned CPU heatsink. That should draw the heat away from the back of the ali holding the LEDs. I have a temp sensor so can continually measure the LEDs to keep them safe.

    Also, the hipFlex will help too.

    Just bought 6 MC-Es and a hipFlex, should arrive just intime for when I get home!!
    As soon as I get back I will post up some designs.

    Thanks for the assistance

  13. #13
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    Quote Originally Posted by ocean breathes salty
    Certainly it is slightly better, but the magnitude of difference was much less than i was expecting. The star mount is the real surprise....
    Not really a surprice for me. The star adds extra thermal resistance and it looks like the led isnt soldered to the star. So there are 2 AA bonds (or something similar) instead of one.

    Maybe I'll do some experiments with other materials then aluminium and copper in the coming weeks when I can find some free spare time. I'll keep you informed.

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