# Quad MC-E Heat Management Question



## zinetti (Dec 7, 2008)

- 4 MC-E K Bin LEDs running at 2.8A - Internally wired in P, 4 wired in Series


Hey guys, i have been trying to determine what size heat sink i will need to have behind these to keep them at a safe temperature. I have run across a crude calculation of
- Rise in temp C per watt = 50 / sqrt(surface area in sq cm)
- I have a 50 sq in heat sink which shows to be around 2.7C/watt

At an ambient of 10c and an LED efficiency of 15% (guessing) the heat sink would be at around 219F, this sounds way too high but here's my math using the crude results from above of 2.7c/w.
- 10c ambient + 2.7 * 40w * 85% inefficiency ) = 102c

Can someone let me know
- What is a safe upper temperature for the heat sink nearest the LED - LED to Star board soldered - Arctic alumina star to heat sink
- What is efficiency of MC-E - How much of the ~40 watts will be turned into heat?
- How large of a heat sink will it take?
- What is the formula to determine heat sink size?
- For both static air and if you use a fan to move air across it - is the a formula taking into account cubic foot per minute?
​Thank you for your help,
Jason


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## yellow (Dec 8, 2008)

*THERMAL PASTE between Star and sink, no Arctic* 
(this Arctic is really something that must have been glued into the ppls heads)

Arctic is "just" a very expensive Epoxy glue, mixed with metal particles for more heat transfer, 
(possibly a very small layer of Epoxy instead of the Arctic has the same capabilities)
thermal paste easily moves way more heat away

then, as one uses stars and a large sink: use screws to attach the Star
--> removable
--> more force, so hopefully a slimmer layer of paste/Expoxy 


the proper way of mounting a Star/Led:
* place with thermal paste on back
* move it around to make layer thinner, get air out, come to an almost-glued (but removable) position of Star/Led
* when Star: use screws into sink to fix them
* if Led (if screws not possible with star): now - after the _paste placing _- glue the thing in with Epoxy applied around it


no help with the size of Your sink, but an advise: *massive* 
I have an Osram 6-die emitter, mounted on a Pentium II heatsink (14*9*3 cm). 
When the led is run at only 500 mA, it gets too hot to handle within a few mins! 
I think, with moving air, 1 Pii sink for every MC-E might be enough - if You want them mounted "in the open".
... no scientific explanation, sorry.


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## zinetti (Dec 9, 2008)

Thanks Yellow for the mounting advice. I used the stove and some solder paste to mount them to the boards, worked great.

Jason


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