Aluminum Square Tube heatsink

[cocojakes]

What do people figure is the most dense I could put LEDs on 1 inch square aluminum extrusion? I plan on going quantity over power, in an attempt to make a sot of, LED powered, actinic T5 bulb look.

 

Ideally I'd like to squeeze two groupings of 25 LEDs, onto each 42" piece. I only plan on using 500ma drivers, and most likely won't be driving them past 200ma due to the high volume of Diodes. Am I gonna have huge heat issues here, or do you think I'll be okay?

[evilc66]

Forced air flow down the tube, or passive?

[cocojakes]

I'd like it to be passive, but could cut slots in the top and install fans to force air through the tube if nessisary

[gulfsurfer101]

Following as I'll be doing something similar with a much lower led count running passive but with fan in canopy to cool my t5's!

[evilc66]

If you want passive, then use c-channel with the legs pointing up. That will allow heat to rise naturally. With the tube heatsink, airflow will be critical, as the center cavity will just trap heat, meaning you effectively lose half your surface area, and have a larger thermal hotspot that you won't be able to cool effectively.

 

I've personally tried the square tube heatsink idea in the past, and while it works, I just don't like it due to it's reliance on airflow through the cavity. What is nice though is that if you size the tube and the fan correctly, you can fit the fan inside the tube so you won't ever see it. Unfortunately, you are relying on very small fans (40mm will fit inside a 2" tube with 1/8" wall IIRC) that will have a higher failure rate.

[Beer]

Even if you maxed out the drivers, you'd be looking at something around 65W of LEDs. As long as you have a decent finned heat sink instead of the square tube as evil stated, you shouldn't have an issue. If the web of the c-channel has a decent thickness, you should probably be fine. Fins would be better. Surface area is as important as mass. I've been meaning to find equations for sizing heatsinks and how to determine heat dissipation.

 

You mentioned two clusters of LEDs. Are they going to be two separate, densely packed clusters? That would make a significant difference in the cooling requirements. In that case, the area that is covered by one cluster would need the capability to dissipate the heat from half of the dies. If you sized it based off of typical recommendations, which typically assumes a more evenly distributed layout, you could end up with localized hot spots behind the dies due to the limited capacity for heat dissipation, even if you are running the dies at reduced power.

[cocojakes]

The Idea is to basically have the 20mm stars touching. Of a 42 inch long C channel heatsink (so far, all I can find is 1 inch wide, with two 3/4 inch fins) there would be 48 LEDs on it (24 in the first 20 inches, then a 2 inch break, then 24 in the next 20 inches). Like I said, currently They would only be maxing out at 350mA and I doubt I would need to drive them that hard, because they're just intended as supplemental lighting for the pair of Kessil A160s

[evilc66]

Just order this as long as you need it

 

http://www.heatsinkusa.com/1-813/

 

It will have way more surface area than c-channel, and really doesn't cost all that much more. ($7.92/ft vs $7.21/ft at Online Metals for 2"x1.25" c-channel in 6061-T6)