heatsink cooling required?

Building a fixture. Heatsink is going to be 36" long, 10" wide, with 1" fin height. So if my math is accurate:

10x36 = 360 (area on plate)
2x36 = 72 (area per fin) x 26 = 1872 (total area over 26 fins)
7x36 = 252 (area in valleys)

So total surface area for the heatsink is 2484 sq. in.

It's going to have a total of 42 leds. 2 banks of 21, because I have a center brace, so no point putting lights there.

Will I need fans? Or do you think passive cooling will be enough? Is there a formula to follow? Oh ya, they are 3w luxeon LED's, being driven at 900mA.

 

IMO, $25 bucks for fans to save X amount of $$ and time in the leds and your labor is worth it. They'll prob be ok, but that small investment may save ya years on the leds lifespan keeping them cooler.

 

Well said, better to cool than not to cool.

 

Yes, you will want a fan. A small computer fan would work, I like the arctic f12 pro, as it is thermostatically controlled and silent most of the time.

 

ok thanks for the replies. If I'm going to be cooling it regardless, then I'll get 2 shorter heatsinks instead to save some weight. Gonna put it all together into a nice custom acrylic fixture.

 

A good read on the subject.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CGIQFjAA&url=http%3A%2F%2Fwww.crydom.com%2Fen%2FTech%2FHS_WP_FA.pdf&ei=RhfsT97KHafE2gXhoLWhAQ&usg=AFQjCNFeac5TPo05E2iMWa5S5EhBPQwGSg

 

I would say it is a requirement. I ran without and regretted it. This is what I did to fix it.

http://www.3reef.com/forums/led-aquarium-lighting/72-watt-rapid-led-pendant-build-131386.html

 

second part to the question....

what do you think of the makersLED heatisnks? Do you think 2 x 12" heatsink, each with 21 leds on it (42 leds total) will be enough to cover the tank? Like I said, it's 36" long with a 2" center brace, and 18" front to back. 60* optics will be used, and light about 10" above the water.

My concern is that it's not going to be wide enough to cover the tank front to back.

thoughts?

 

you should be ok, 80 degree or 90 may be a good idea for the outside leds, but I'd guess you'd be ok!