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Old 12th November 2002, 03:23 AM   #1
cowanrg is offline cowanrg  United States
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Default heat issues

hey all.

im getting along quite nicely with the aleph2's and im at the part where i need to start putting them together. im wondering exactly how you calculate heat transfer properties of a heatsink. i found some i would like to use on aavid.com, but they only have a C/W rating of 0.54 (for a 3 inch section). from my calculations, with a monoblock, 1 heatsink per side, using 3 8" sections of this heatsink, i would get a 11.4 C temperature increase per heatsink... is this ok? is this calculation even right?

in trying to figure out which heatsink would be needed for the 3 2-channel aleph2's, i am unable to calculate any reasonable values... basically, the aleph2 generates 300 watts of heat PER side, so there needs to be a heatsink that can get rid of 300 watts... what is an appropriate temperature gain? could 100F increase in temp be fine? what would be a nice SINGLE heatsink that could tolerate 300 watts of heat?
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Old 12th November 2002, 03:54 AM   #2
BrianGT is offline BrianGT  United States
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Default Re: heat issues

Quote:
Originally posted by cowanrg
what would be a nice SINGLE heatsink that could tolerate 300 watts of heat?
Are you insane? One heatsink? That would have the be a very large heatsink, unless you are considering active cooling.

What is your desired chassis size? You could use multiple extrusions to make the sides of the case, like:
http://www.passdiy.com/images/gallery/a2-p1-f2.jpg
but taller and deeper, giving you 600W total dissipation.

I am using 4 of these per channel:
http://www.aavidthermalloy.com/bin/e...8&airflow=57.2

I picked them up surplus for $25 each

If you do in for a large order of heatsinks, I wouldn't mind joining in on the order to get a set for myself if the prices are reasonable. Let me know if you are interested in doing this.

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Brian
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Old 12th November 2002, 03:58 AM   #3
cowanrg is offline cowanrg  United States
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well, when i say one heatsink, i mean that there is one block of heatsinks.

the chassis dimensions depend on the heatsinks

ill first have to figure out what will cool the amp, then see where i could find it, and how much. could anyone answer my questions above? that would help me out a LOT.
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Old 12th November 2002, 04:01 AM   #4
halojoy is offline halojoy  Sweden
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What i have read somewhere an increase
of max 40 degrees Celsius (C/W) is desirable.
I would guess you can accept up to 60 degrees Celsius. But I refuse to count it in Farenheit. To much trouble for me.

Look at each section.
How much Watt will this section dissipate?
Watt x C/W-value= degrees Celsius (temp increase)

If you have 8 sections and 300 watt.
Each section takes care of 300/8= ? (help me please) watt

By the way, Anders Celsius was a Swedish scientist.
Hurray for Sweden! Buuh, for Fahrenheit. Sounds German
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Old 12th November 2002, 04:10 AM   #5
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I use the 250mm(H) x 230mm(W) x 65mm(D) 18-fin heat sink for 40W dissipation at 15C temp increase. If I want to keep the 15C temp increase with 300W, I might need 7 or 8 of this size for one side.

JH
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Old 12th November 2002, 04:14 AM   #6
BrianGT is offline BrianGT  United States
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I would go with three tall ones of these per channel/side:
http://www.aavidthermalloy.com/bin/e...2&airflow=57.2

They go together nicely and are heavy:
http://brian.darg.net/ax-chassis

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Old 12th November 2002, 04:24 AM   #7
halojoy is offline halojoy  Sweden
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The essential temperature is inside the transistor.
Not on the case of the transistor, not on the heatzink.

Between the inner of a T and the case, there is a t-resistance.
It is also in C/W. Can be like 0.7-1.0 C/W
The mounting-isolation also have C/W. Usually like 0.2-0.4
Then heatzink. Which is in contact with the air.

So temp inside the transistor is= temp of air + total resistance x Watt

Total temp resistance is:
Rth of heatzink
Rth of Isolation
Rth of Transistor (case to inner)

All this added is the total temp-resistance
between air and inside the transistor
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Old 12th November 2002, 05:35 AM   #8
cowanrg is offline cowanrg  United States
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if i have read you correctly, after calculation, less than 40 C overall change in heatsink temp is acceptable?

if this is the case, i was looking at around 20 C, therefore it should work out FINE.
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Old 12th November 2002, 05:40 AM   #9
halojoy is offline halojoy  Sweden
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Default Yes, I think you are safe, cowangr

Let's wait for Nelson.
99% sure he will have a comment for us
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Old 12th November 2002, 05:51 AM   #10
cowanrg is offline cowanrg  United States
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i hope, because im really worried about this! if you say 40 is ok, and im sticking around 20, that should be MORE than fine... but we will wait for the great one to have his say...

i still need to FIND these things after i figure out what i need. i think im gonna start a heatsink/capacitor company. just make huge power supply caps and heatsinks. it seems like its the two things no one can ever find!
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