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Old 3rd January 2015, 11:22 AM   #1
plasnu is offline plasnu  United States
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Default Heat Sink Rating

I'm trying to find heat sinks for Aleph J. Based on information on this forum, NP recommends 25 to 30 degree, and Aleph J dissipates roughly 100W par ch, so 0.25-0.30 c/w par ch is required for Aleph J. The heat sink of the 4U chassis sold at DIYAUDIO Store is rated 0.31 c/w at the size of 300x165x40, and I'm looking for the equivalent heat sinks for my own custom chassis.


I checked Aavid, and and the equivalent heat sink seems to be

Thermal Engineering and Heat Sink Manufacturing - Online Store

Although 80345 is made with 6000 Aluminum (best material) and it has about the same number of fins as 4U chassis, it has only 0.53 C/W at the length of 165mm (4U chassis), which is apparently inadequate for my purpose. Based on Aavid calculator, 500mm length is required for 0.3 C/W (3 times longer than 4U heat sink)


I'm wondering if I misunderstand something here...

Last edited by plasnu; 3rd January 2015 at 11:36 AM.
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Old 3rd January 2015, 12:51 PM   #2
evanc is offline evanc  United States
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10.080" Wide Extruded Aluminum Heatsink - HeatsinkUSA, LLC Store
Maybe a good choice? They claim .8c/w/3"
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Old 3rd January 2015, 01:02 PM   #3
plasnu is offline plasnu  United States
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Yes, I was looking at it actually, but based on the c/w/3 length correction chart below, I still need around 400mm for 0.4c/w.

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Old 3rd January 2015, 01:10 PM   #4
evanc is offline evanc  United States
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Putting theory aside. I built an f5 using 2 7" (about 178mm) pieces of the heatsink usa 10.08" extrusion and it was OK.
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Old 3rd January 2015, 01:12 PM   #5
plasnu is offline plasnu  United States
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Wow, your enclosure looks really nice!
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Old 3rd January 2015, 02:31 PM   #6
plasnu is offline plasnu  United States
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I measured my PASS LAB Aleph 5 (not DIY) dimensions.

A5 dissipates probably 250-300W, so the rating of A5 heat sink should be 0.4-0.5 c/w for each side (280w x 250h x 50d). The Aavid heat sink closest to A5's is 62185, which c/w is 0.65 for 250x250x50. 62185 is about 10% narrower than A5, and considering the distributed load of A5's FET (10% better performance expected, AAvid says), Aleph 5's heat sink real world performance should be around 0.52 c/w based on Aavid calculation method, which seems to be reasonable.

http://www.aavid.com/products/extrusion-heatsinks/62185

—————

Now I feel Aavid information is pretty reliable. then I recalculate Diyaudio chassis with the Aavid method.

I realized that the DIYAUDIO 4U heat sink has thicker bass plate than Aavid 80345 that I mentioned on my first post, so this time, I chose 70165 which has slightly more density and slightly longer fins than 4U heat sink. Considering the distributed loads of FET (10% better), I guess 4U heat sink should perform about 0.38 C/W in real world based on Aavid calculation, which is acceptable for AJ, although not perfect. I think DIYAUDIO heat sink calculated by different type of method. (I’m not criticizing about it, I’m just looking for universal calculation method that I can use to find adequate heat sink for AJ. Also, I feel that Aavid method is somewhat pessimistic, DIY is slightly optimistic, so the real world performance would be somewhere between them.)

http://www.aavid.com/products/extrusion-heatsinks/70165


In the other thread, someone was saying 0.3 c/w on paper is more like 0.4 c/w, so Aavid calculation matches to his comment as well.

Last edited by plasnu; 3rd January 2015 at 02:44 PM.
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Old 3rd January 2015, 05:08 PM   #7
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I believe I fondly remember a post where Papa suggests that you calculate what you need and then double it!

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Dan
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Old 4th January 2015, 02:55 PM   #8
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Quote:
Originally Posted by plasnu View Post
Yes, I was looking at it actually, but based on the c/w/3 length correction chart below, I still need around 400mm for 0.4c/w.

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i have this heatsinkUSA 10.080" profiles 6"long. and each of them can handle 65W without any problem. i run 250W dissipation on 4 of this sinks. they are running at about 25c above ambient.
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Old 4th January 2015, 07:06 PM   #9
plasnu is offline plasnu  United States
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10.080" profiles 6"long should be 0.584c/w according to AAVID, and 65W*0.584 = 37c above ambient is their estimate. They would say 10-12 inch is the correct size for 65W. They are just trying to sell more heat sink than what we actually need?, I don't know...
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Old 4th January 2015, 07:17 PM   #10
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cut out from FAQ at heatsinkUSA:
"Question: What are the C/W ratings for your heatsinks?

HeatsinkUSA does not offer specific advice regarding the thermal properties of our heatsinks. However, we have supplied Approximate C/W ratings for each profile for your reference."
in other words. C/W ratings from heatsinkUSA is nothing but guess work and not an exact science.
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