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Old 18th November 2009, 02:13 PM   #1
DQ is offline DQ  Romania
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Default diy heatsinks - please give some advices

Hello. I hope this is the right forum to post in, and please bear with me since I'm a diy beginner. I need a couple of serious heatsinks, each capable of dissipating 70W heat continuously, so I'd like to have a thermal resistance of about 0.25, certainly no more than 0.3 degrees C / W. Since they are quite expensive, I'd like to try the diy route.

Based on the materials locally available I am considering the following components (for 1 heatsink):
- 1 main aluminum sheet, 22.5 / 50cm (that's amplifier's height / depth front to bottom), 3mm thickness;
- 22 "teeth" 22.5cm in length (that's their height when mounted vertically), L shaped in section (4cm / 2cm), 1.5-2mm thickness. They will be cut from some (sorry for my English, it's too technical for me) stair grip like this - linked only for a better visual representation, mine are made of black anodized aluminum. They will be mounted with the smaller side (2cm) against the main aluminum sheet, using
- Arctic Silver Ceramique for better thermal transfer (that's a very big surface, more than 1000 square cm / heatsink, so I can only hope 1 syringe with 22 grams / heatsink will suffice) and
- many many rivets (I was thinking about 5-6 rivets / "tooth")

Now please advise me:
1. Do you think my attempt is realistic?
2. Do you have any particular recommendation to make?
3. Is Arctic Silver Ceramique a good idea on the long term or it might just dry in several years and force me to disassemble everything?
4. Do I need to fine sand or polish somehow the main aluminum sheet and the corresponding side of the "teeth"? (and if this is a must, although I'd very much like to avoid this, please tell me how to do it correctly as I have no clue how to do it other than by hand and then I don't know how make it smooth enough and how to avoid creating small surface irregularities, pits and dips...)

Thanks in advance for your support.
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Old 18th November 2009, 03:08 PM   #2
pilli is offline pilli  France
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I'm really no expert on the subject.
I just remember reading somewhere that rivets could be inferior to screws, because they may be not as tight in keeping the two surfaces in perfect contact. I have seen this in small TO-220 things "fixed" to their small heatsink with a rivet, that ends up losening.

Apart from that, you seem to have your ideas quite clear...

But still, just in case:
DIY Heatsink

HEATSINKS by SM0VPO
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Old 18th November 2009, 03:43 PM   #3
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Default I have found that a square piece of aluminium... 2 milimeters thick, 10 centimeters

side, is able to dissipate 16 watts...enougth to a 10 watt RMS amplifier.

So....10 pieces of that will be enougth to a 100 watt amplifier..playing full power, continuous and undistorted (unclipped)..and the heatsink will not increase the temperature above 52 degrées celsius when your environment average temperature is 29 degrees celsius.

I have discovered, tested and found it perfect..since that (1969) i am using this method...even to evaluate heatsinks people send me as gift or parts from dismounted amplifiers or junk that i use to buy to use into some prototypes.

When evaluating heatsinks that have complex shape, i use to dismount them in my mind, and to calculate area exposed to the air...i use only one face to do that..each 100 square centimeters is good to 10 watts rms or good to dissipate 16 watts of heat.

regards,

Carlos
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Old 18th November 2009, 04:11 PM   #4
Magz is offline Magz  United States
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If you have any old computer monitors lying around, they all contain some pretty massive heat sinks you can cannibalize. Just a thought.
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Old 18th November 2009, 05:06 PM   #5
Bigun is offline Bigun  Canada
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I've used superglue in the past to assemble heatsink pieces - if the joint is large so there is a good surface area for heat conduction and if you can clamp the pieces to ensure a thin and even coverage of glue...
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Old 18th November 2009, 08:02 PM   #6
lgreen is offline lgreen  United States
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You can mix the arctic silver ceramique with epoxy to make a thermally conductive adhesive. I have done this before with success. If you clamp the stairs to the big metal and let it dry you should not have to sand. Try it with one or two and see how well it holds.

Why do you want to use arctic silver ceramique (not electrically conductive) vs. arctic silver (potentially electrically conductive under high pressures?). The regular artic silver has better thermal properties and I assume you don't care about electrical conduction for this application.

Assuming everything holds together it may work. It would be kind of funny if the fins started falling off though. Ok, that would not be funny. Maybe epoxy and a couple of screws or bolts.
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Old 18th November 2009, 08:07 PM   #7
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Making your own heatsinks can be cheaper, especially if you get the material for nothing:

Picture 209.jpg

But must be weighed against your time and safety. Working with aluminum, especially with power tools, can be dangerous and it is hard to justify the savings after you have been sitting in the emergency room at the nearest hospital for five hours.
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Old 18th November 2009, 08:38 PM   #8
defect9 is offline defect9  Ireland
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arctic silver makes an epoxy (for attatching ramsinks to vid cards and such), no need to mix arctic and some other kind of epoxy
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Old 18th November 2009, 10:05 PM   #9
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by MJL21193 View Post
Working with aluminum, especially with power tools, can be dangerous and it is hard to justify the savings after you have been sitting in the emergency room at the nearest hospital for five hours.
Yikes - what happened ?
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Old 18th November 2009, 10:14 PM   #10
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IT hasn't happened to me (knock wood) because I have a lot of experience, I'm very careful and I have the luck of the Irish...
It needs to be said whenever someone talks about working with metal, especially a metal that many of the members here think that it machines like wood. That is NOT the case. Wood can funk you up pretty good if it binds in the tablesaw and flicks back at you - aluminum becomes shrapnel in that situation, a potentially lethal projectile.

Be safe, it might be well worth buying that "expensive" heatsink.
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