Question for all you LED gurus

[H@rry]

I have a DIY LED setup using 3/4 U channel from Lowe's for heat sinks. If I measure the temp on the back side of the U channel directly opposite the LED, how can I compute the "junction tempature" as noted in the datasheet. I'm using XT-Es and I'm reading 115.8.

 

[Pete H.]

How thick is the 3/4 u channel aluminum? 1/8 inch?

 

[TJ's Reef]

Harry, are you just using passive cooling ? I mostly am on my DIY array and to help with temp added cooling fins made of aluminum angle and attached to U channel with thermal adhesive. My outside two circuits are cutout from back hinged area to access overflow boxes which does not allow for adequate passive cooling. After cooling fins were added temp came way down. Pics below showing application process.



Pieces I fabricated to use.


I've since added them to both sides of channel on both end circuits like below pic.


Cheers, Todd

 

[H@rry]

How thick is the 3/4 u channel aluminum? 1/8 inch?

More like 1/16 inch.

Harry, are you just using passive cooling ? I mostly am on my DIY array and to help with temp added cooling fins made of aluminum angle and attached to U channel with thermal adhesive. My outside two circuits are cutout from back hinged area to access overflow boxes which does not allow for adequate passive cooling. After cooling fins were added temp came way down. Pics below showing application process.

Cheers, Todd

Todd - that looks very effective (although pretty labor intensive to cut all those). My LEDs are on 19 x 19 racks. I put 5 temp sensors on one rack; one in each corner and the other one in the center. The center is the warmest with the outsides about 4 - 6 degrees cooler. I have fans in the ends of the canopy left over from MH days but they mostly blow under the splash guard with a little air going over the LEDs. I unplugged the fans and the temp went up about 7 or 8 degrees. I have some smaller 12v fans coming that I plan to put in the middle of each rack blowing down through it. That should get it.

I looked at the temp a few minutes later and it showed 115.5. Converted to celsius that is 46.4. The datasheet lists temps in the range of over 100 celcius so it might be fine as it is.

What is your temp and what current are you running?

 

[TJ's Reef]

Harry, they were not to difficult to do just cut to length with chop saw and sanded a bit on belt sander before gluing in place. The temp had originally gotten to over 130* and burnt out a few Epistar and BridgeLux emitters with the old acrylic lens's currently peak at around 92* in middle of end channels. Since just recently built a canopy facade to block light pollution and still plan on light plywood top I have a couple of 200mm fans I will be using to draw air up through the aluminum grid work. They run a very low rpm with just 3-4.5 volts powering them, so dead quiet.

Cheers, Todd

 

[ReefLEDLights]

I like to keep my fixtures under 90 Degrees.

Our latest measured 85 Degrees in a 79 degree room.

The cooler the LEDs are the longer they last and the more light they produce. As they heat up they start putting out less light. I've seen PAR start at 525 and after a few minutes drop to 520. I would hate to see the drop on a fixture with poor thermal properties.

I would do everything you can to keep the temp a cool as possible.

Aluminum is a good conductor the more mass and surface area the better.

Bill