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 2nd July 2002, 07:43 AM #11 diyAudio Member     Join Date: May 2002 Location: The great city of Turnhout, BE Blog Entries: 7 heatsink question Yes, mostly bigger is better. But how much bigger do you need to be better? So, even if you don't wont any stinkin calculation, you need at least some intelligent reasonning to get to the ballpark, right? Treat heatsinks as resistors for heat current, and dissipation as heat voltage. Example: Your output stage dissipates 100 watts, and you want to limit the max temp to 90 degrees at 40 degrees ambient, this is a temp rise of 50 degrees, right? You need a heatsing that has at most 0.5 degrees per watt "resistance". Using a larger heatsink of say 0.25 degrees per watt resistance, multiply by the dissipation gives 0.25 times 100 is 25 degrees temp rise above ambient. If you use a bracket between the output transistors and the heatsing, that add "heat resistance" in series to the heatsink. There is also the "heat resistance" of transistor junction to case, say 0.15 degrees per watt (don't know how realistic this is, look at the data sheet). Example: use the 0.25 degrees per watt heatsink with a bracket that adds say 0.1 degrees per watt, and a transistor with a 0.15 degrees per watt juntion to case heat resistance, total 0.5 plus 0.1 plus 0.15 = 0.5 degrees per watt. With your 100 watt dissipation that gives 100 times 0.5 equals 50 degrees temp rise. With 40 degrees ambient that gives a max temp of the output transistor junction of 90 degrees. Easy. It's surprising how far you can yet in amplifier design with just some secondary school math.... Cheers, Jan Didden
diyAudio Member

Join Date: Aug 2001
Hi Circlotron,

Quote:
 Originally posted by Circlotron If you have the choice between a tall skinny heatsink and a short broad one with a same area, the short broad one will win every time. Only the first couple of inches seems to do anything much, after that the rising air has been warmed enough as it rises through the fins that it cannot cool any further fins higher up. GP.
to reduce this effect you must mount the transistors as high as possible so the temperature difference between air and sink keeps as high as possible. In most amps I see people mount the transistors as low as possible for some mysterious reason.

love fans too! I can get away with 4x0.65°K/W for an Aleph5 (250 watts dissipation) and a bit over 50°C heatsink temp.

Apogee,

it´s not so difficult to calculate for paralleled heatsinks. If you use 4 x 0.65°K/W you get 0.16..°K/W. You must just add the thermal resistance for the connection from aluminium to heatsink wich is quite low (measured almost <1°C difference between them)

william
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 2nd July 2002, 04:44 PM #13 diyAudio Member     Join Date: Apr 2002 Location: Athens I don't calculate either. I always use Fischerelektronik LA1-10A with Papst 4184NXH and i never bother about noise because there is no noise. Nick
 3rd July 2002, 01:47 AM #14 diyAudio Member     Join Date: Feb 2002 Location: Tacoma, WA Thanks all for the help!!! I appreciate it!!!! __________________ "If I had my life to live over again, I would have made a rule to read some poetry and listen to some music at least once a week." - Charles Darwin
 3rd July 2002, 01:50 AM #15 Banned   Join Date: Apr 2002 What was the link to the heat sink store i got ther catoouge but i cant find it in my mess ..
 3rd July 2002, 02:38 AM #16 diyAudio Member     Join Date: Feb 2002 Location: Tacoma, WA JasonL: Go here: http://www.diyaudio.com/forums/showt...tals#post22723 Good luck! __________________ "If I had my life to live over again, I would have made a rule to read some poetry and listen to some music at least once a week." - Charles Darwin
diyAudio Member

Join Date: Mar 2001
Location: Quebec City
Quote:
 Originally posted by Nelson Pass Calculations? We don't need no stinkin calculations! We just make them really big!
I love this philosophy too...
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FrankDIY's Audio Corner

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Join Date: Apr 2002
HUmm

Im thinking about using these for my aleph 5 amps.. any one comment on this..
Attached Images
 pair thick base.jpg (83.9 KB, 1325 views)

Banned

Join Date: Apr 2002
or i could use 2 of these witch are verry heavy and thick and came off come old radio equipment from my dads work..
Attached Images
 single thick base.jpg (86.7 KB, 1258 views)

diyAudio Member

Join Date: Jan 2002
Location: Lisbon,Portugal
Heatsink fashion '02

Check this drawing of my future SOZ

There you can see a cross section of the profile I'll use.

It has 0.30m of heigth.

(all the measures are in meters).

the weigth of each one is 12kg.

Later i'll post a real picture
!
Attached Images
 soz2.jpg (70.1 KB, 1228 views)
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