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Old 1st April 2003, 05:32 AM   #1
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Default heatsinking and thermal resistance

is lower thermal resistance better or worse. i'm building a dorm audio project with the lm3875 and lm1875 chips. i will likely use fans to cool the heatsinks. like i said, this is a dorm room, and next semester there will be 3 computer in the room, my computer having 5 80mm fans and 1 annoying 60mm. my roomate will have 2 computers, which should be at least equal to my computer in terms of noise. so i don't see any harm in adding a few more fans that will not be noticable.

in any case, how big are these heatsinks supposed to be?
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Old 1st April 2003, 05:50 AM   #2
sangram is offline sangram  India
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Lower thermal resistance means better conduction of heat, so cooler running devices - yes, lower thermal resistance is better.

Ask your roomie to use a 60 to 80 mm adapter so his computer can make less noise. Those CPU fans can be very irritating. Three less 60 mm fans is three times less noise - those 60 mm fans are about 40 dBa, a well made 80 mm fan is about 23 dBa.

Vantec makes some very quiet 80 mm fans, lower than 20 dBa. Check those out for a quiet and pleasant environment.

Depending on the number of devices you use, the heatsink's overall thermal reistance should be about 0.5 c/w. Sounds very low, but the average computer cooler with a fan is about 0.6-0.8 c/w, and I'm not talking top dollar CPU fans which are about 0.4 or better. Now get this - without that noisy whining fan, the thermal resistance goes up to about 5 c/w, so a reduction of about 10 times is possible with a powerful fan.

Bottom line, if you're aiming for a 0.5 c/w total thermal resistance, a 2 c/w heatsink and some nice quiet vantec fans will get you there no problem. I dunno what size it is you're gonna be looking for, but with fans it won't be too big. about half a rack width (9/10inches) and 2 units high would be a rough guess for an okay heatsink though you'd be better served by having a heatsink spec in front of you. Most suppliers will give it to you anyway.
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Old 2nd April 2003, 04:43 AM   #3
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oh, i assure you my case will be the dominant producer of noise. i was looking at the Thermalright AX7 or SK7 or SLK800 ect.

I had found an all copper HSF unit for PCs and was just thinking of building a really dirt simple power supply that would just run fans in the case with a driving voltage of like 8 or 9V. (7V won't turn on some 12V fans).

actually my roomie's HSFs aren't gonna be all too bad, he already has a thermaltake volcano 7 (with the thermal senseing 80mm fan), and the other comp has the stock 60mm x 15mm fan which isn't all that loud. my case has the 60mm x 25mm coolermaster fan on the HCC001 HSF (which is the easiest HSF to install by far!)

BTW, i need something that will switch grounds on my fans from 0v to 5v. the 80mm case fans will not spin up when driven from 7v (12v to 5v), however they will spin at that setting if given an intital push... i need basically a cicut that detects the lack of spin and switches to 12v to kick the fan into moving. great another new project!
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Old 2nd April 2003, 07:30 AM   #4
sangram is offline sangram  India
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One good thing about the SLK 800 is you can add an 80 mm fan of your choice.

A single 6V 1A transformer will run your fans just fine, full load DC voltage will be about 8.2 volts...

Or you can use the 12V rail and a zener multiplier...

What is your config anyway that you need so much cooling - and what will you be doing? SETI?
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Old 2nd April 2003, 08:57 AM   #5
karma is offline karma  Canada
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Default fans

have a look at this link. u could allways go with a fan with a thermister on board that way u can a the full 12v and let the fan do the stepping. i of course went with thermaltake water cooler
works great

http://www.bigfootcomputers.com

copper is better

stay away from orb coolers thay crack athlon core's

or go with a nexus fan controller by vantec
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Old 2nd April 2003, 09:04 AM   #6
karma is offline karma  Canada
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Old 2nd April 2003, 09:05 AM   #7
karma is offline karma  Canada
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Old 2nd April 2003, 06:35 PM   #8
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got plexi?

actually you can fit an 80mm fan on the sk6... it has to be turned a bit, but the clips will hold it just fine. sadly i don't have a sk6. (the sk6 was my first choice but was 2x as expensive!)

the ax7 also takes 80mm fans.

my computer is just an athlonXP, i guess i could cut back on the fans, use the software cooling mod and all. i find it wrong when the CPU temp drops below the case temp though... especially with air cooling.
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