passive led heatsink? good idea?

[rwb500]

I would love to design my LED canopy to have the bare fins of the heatsink sticking out of the top, and have no fans. This would allow the canopy to be very slim. How many people use no fans on their heatsinks? I am thinking of using 48.5" of the heatsinkusa 5.886" wide heatsink. I will have 48 led's. According to the heat dissipation data provided by the heatsink manufacturer, the heatsink will be less than 30 degrees fahrenheit warmer than the ambient temperature. So in an 80 degree room it would be 110 degrees.

Is this an acceptable temperature? Is this a good idea?

can i color the fins black to increase radiation while not hampering conduction? I read that a thin coat of automotive laquer might work for this? will that look nice? tall people will be able to see the top of the canopy. I dont want to do anodizing or powder coating.

 

[faisal629]

I have 36 leds' on 2 sinks (18 on each) of 60"x1.813" and they are on like a frame with bottom, top, sides open without fans, when i touch it is a little hot but i never measured the temp (maybe i should) with no fans.

 

[kcress]

I have no fan on my weird heatsink.

 

[mgargiullo]

I don't use fans on mine... Its a rack of 10w LEDs. If you can touch the heatsink, it's fine. If you want to paint the heat sinks, look for radiator (automotive) paint. It's designed to not effect the heat exchange. If your local shop doesn't carry it, check Eastwood... They carry automotive restoration materials and they have it.

 

[rwb500]

thanks everyone. i'll definitely look for eastwood radiator paint. looks like a good product. i guess i'll just go for it with no fans and have a backup plan in case i need some.

 

[djkms]

Interesting. I am in the middle of my build and rather hate the fans to be honest.

I have 2 Drilled/tapped 6" x 9" Black Anodized Aluminum Heat Sinks from RapidLED each with 24 3w LEDs capped at 65% intensity.

I wonder if I can get away with the same thing, no fans? It just hangs in the air, no canopy.

 

[ghellin]

I used heatsink USA's 10" by 1' heatsinks and built a frame to hold them half the weight of the massive one piece heatsinks and absolutely no heat you can touch the base of the LEDs running at 80% and its room temp. My tank is in my living room so no noise allowed (wifey's rule)

 

[ghellin]

Ahh behold the double post!

 

[Landsailor]

Don't paint the heatsink! You're just adding another barrier to radiating the heat to the environment so you're working against yourself. If you must have it black, get it anodized.

This sage advice (slightly modified to fit this situation) was given to me many years ago when I got my first VW Beetle where heat is also the mortal enemy.

Also, "chrome won't get you home" might fit, as well.

 

[mshaq]

Don't paint the heatsink! You're just adding another barrier to radiating the heat to the environment so you're working against yourself. If you must have it black, get it anodized.

This sage advice (slightly modified to fit this situation) was given to me many years ago when I got my first VW Beetle where heat is also the mortal enemy.

Also, "chrome won't get you home" might fit, as well.

The engineers at Cree would disagree, "Heat sink thermal radiation is a function of surface finish, especially when the heat sink is at higher temperatures.A painted surface will have a greater emissivity than a bright, unpainted one. The effect is most remarkable with flat-plate heat sinks, where about one-third of the heat is dissipated by radiation. The color of the paint used is relatively unimportant."

http://www.cree.com/products/pdf/XLampThermalManagement.pdf

 

[rwb500]

yes i think landsailor meant "conducting" where he said radiating. on a finned heatsink, the vast majority of heat is removed by conduction, so hampering conduction while boosting radiation might not be worth it. thanks for the pics ghellin! looks great!