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Heatsinks and wearable LEDs
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Heatsinks and wearable LEDs

by tomchaps on Wed Dec 05, 2012 5:57 pm

My 7-year-old son and I are planning to create a "Lightning Man" superhero costume for him, using conductive thread and some superbright LEDs. Eventually I'll probably get a FLORA or other wearable Arduino to control the lights, but for now, I just want to sew a simple circuit with a 9V battery and a single 3W to 5W LED. (The "switch" will be him clapping his hands, since the palms of the gloves will be conductive...)

My question is an obvious one--what should I do for a wearable heatsink? Those bigger LEDs can get quite hot, and I don't exactly want to have to explain to my wife why our son has been branded with a little star...

If you're wondering, the LEDs do need to be VERY BRIGHT (according to my son). He wants to be able to surprise and blind people with his superpowers, and the little ones we've been playing with don't cut it. But don't worry, he promises to use his powers only for good. Chaotic Good or Neutral Good, maybe, but still Good.

Does anyone here have experience with heat issues on wearable LEDs?
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Re: Heatsinks and wearable LEDs

by adafruit_support_bill on Thu Dec 06, 2012 6:29 am

I just want to sew a simple circuit with a 9V battery and a single 3W to 5W LED.

You will want a current limiting resistor in there too to protect the LED. Are these bare LEDs or pre-mounted on a 'star' as in the photo below? The aluminum star would probably be a sufficient heatsink for a short duration flash. If you need to dissipate more heat, you can make a larger aluminum backing plate. A thermal adhesive (such as Arctic Aluminum) will assure good heat transfer to the backing plate.

Image
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Re: Heatsinks and wearable LEDs

by tomchaps on Thu Dec 06, 2012 3:14 pm

Yep, I was planning to use one of the star-shaped mounted LEDs, with a resistor. (We've burned out an impressive number of small LEDs over the past few years...)

What would you make an aluminum backing plate out of? (My concern would be if/when he decided break character and keep the sucker on for a long time.) I presume any thin bit of aluminum would work--say, some flashing from the hardware store. Is surface area or mass more important for a heatsink?

Thanks for the help!
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Re: Heatsinks and wearable LEDs

by adafruit_support_bill on Thu Dec 06, 2012 3:39 pm

Is surface area or mass more important for a heatsink?

You need some mass to effectively conduct the heat away from the led and surface area to dissipate the heat. Flashing is probably on the thin side if you are expecting much heat buildup. My local hardware store carries 4" x 10" plates, 1/16" (0.064") thick. If you can't find it locally, there are plenty of on-line suppliers that carry K&S metals. Or go to KSMetals.com.

Another approach - a little more sophisticated - is to put the flash under microprocessor control. You can still have the "thunder-clap" activation switch, but have the processor meter out the pulses to drive the flash at the brightest possible level while still preventing it from overheating. This example uses the Flora sewable LED modules. But you could drive a higher power emitter with the addition of a transistor.
http://www.adafruit.com/blog/2012/12/05 ... wednesday/
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