Are the MOSFET heatsinks too big??

marc999 · Feb 24, 2004

I found some awesome OCZ pure copper MOSFET heatsinks here but they're way too big for my MOSFETS (I have an ASUS A7N8X-X and I'm thinking the MOSFETS are like 10mm square). So if it overhangs my MOSFETS (like 8mm on each side) is there a risk of electrical arcing? Will electrical tape underneath the excess heatsink applied directly to my MOBO help? If two of my MOSFETS are close enough, is it a good idea to use one of these coolers on two MOSFETS, or am I better off with two smaller ones on each?

I could always get these instead, but even they are a bit too big I think.

Advice/feedback/suggestions .....

Yuriman · Feb 24, 2004

Copper is way overkill for mosfet sinks. Cut up an old socket7 sink you have laying around, make your own. I think electrical tape would work, but just to be safe, buy the ones in your 2nd link, and cut them down if necessary.

Silversinksam · Feb 24, 2004

marc999 said:
I found some awesome OCZ pure copper MOSFET heatsinks here but they're way too big for my MOSFETS (I have an ASUS A7N8X-X and I'm thinking the MOSFETS are like 10mm square). So if it overhangs my MOSFETS (like 8mm on each side) is there a risk of electrical arcing? Will electrical tape underneath the excess heatsink applied directly to my MOBO help? If two of my MOSFETS are close enough, is it a good idea to use one of these coolers on two MOSFETS, or am I better off with two smaller ones on each?

I could always get these instead, but even they are a bit too big I think.

Advice/feedback/suggestions .....

Both those you linked to are to large for mosfet cooling, ideally they should be 10mm x 10mm

I wish I bought more of those BGA 10mm sqr heatsinks from Allied as I bought them for a dime each and sold them for a dime each. All told I sold 1300 of them to members here and at Xtremesystems.

Theres a Mod selling them at [h] for $.55 cents each, but I wasnt greedy. I wish i had bought all 13,000 they had as those were the perfect size for Mosfets and BGA memory modules.

tio · Feb 24, 2004

Yuriman said:
Copper is way overkill for mosfet sinks.

Not always. If you're running at a very high FSB, I would say copper is the way to go. Mosfets can get extremely hot. Just take a look at some of the results Prescot users are seeing right now. Overclocking a Prescott will make your board's mosfets sizzle, in some cases, literally. Just take a look at some of the more recent posts in this thread: http://www.ocforums.com/showthread.php?s=&postid=2540927#post2540927

I like those first ones you linked two, but the second ones would let you cut them up to whatever size you need a bit easier...

As for the one heatsink for two mosfets deal, that's generally better than having two individual sinks cut for each one, since you'll end up with more surface area for better heat dissipation. You won't end up with electrical arcing inside a computer; there's not enough of a potential difference to cause that. As long as the copper sinks aren't actually in contact with your board's components, there shouldn't be a problem. Just to be on the safe side though, you could use the electrical tape.

fhanderson · Feb 24, 2004

I cut up one of these to make my mosfet heatsinks:

http://www.allelectronics.com/cgi-bin/category.cgi?category=270&item=HS-70&type=store

Agent_Mull · Feb 24, 2004

But i have heard that copper isnt that good w/o a fan on top of it. Aluminium is better for passive stuff.

Chixofnix · Feb 24, 2004

Agent_Mull said:
But i have heard that copper isnt that good w/o a fan on top of it. Aluminium is better for passive stuff.

really?

squeakygeek · Feb 24, 2004

Agent_Mull said:
But i have heard that copper isnt that good w/o a fan on top of it. Aluminium is better for passive stuff.

I don't know where people come up with this stuff...

Copper conducts heat better than aluminum. Period. End of story.

dreadlord79 · Feb 24, 2004

If I am remembering correctly, aluminum gets rid of heat quicker but copper absorbs more. I think that is why some HS have been rather successful with slower fans when the core is copper and the fins are aluminum. Of course I might be wrong since this is info that I have picked up here and there while on the boards.

*edit* The best though is silver, gold or platinum but WAY to expensive!!!*edit*

Cyberwiz01 · Feb 25, 2004

actually, gold and platinum are not better than silver or even copper for that matter. In eletrical conductivity gold is better, I don't know about platinum. But for our purposes copper is the best performing for the money.

tio · Feb 25, 2004

^ Yes, that's correct. You can check out the thermal conductivity of various metals of interest here: http://www.overclockers.com/tips188/

As for aluminum being better for passive applications, I think you're refering to the fact (at least I think it's a fact, if I remember correctly...) that aluminum radiates heat better than copper. While you would think that this would mean it is better for passive cooling, from what I've read, copper still proves to be the better metal for this application because of its higher thermal conductivity.

marc999 · Feb 25, 2004

Thanks to all for your help.

One thing that just occured to me, if you used one heatsink for two MOSFETS, would you create an electrical short (between the two MOSFETS)?

PatrickBateman · Feb 25, 2004

I'm not sure, but I doubt that you'd create a short. If anything, you might link grounds, but that's "common" already. It would be precarious to have a live heatsink no matter where it is.

mccoyn · Feb 25, 2004

I doubt that all the mosfets have their heatsinks at ground. I don't think anything in the mosfet is connected to ground in fact, and to have the most effecient heat transfer, they connect the heatsink to one of the pins.

squeakygeek · Feb 25, 2004

marc999 said:
Thanks to all for your help.

One thing that just occured to me, if you used one heatsink for two MOSFETS, would you create an electrical short (between the two MOSFETS)?

You are going to be putting the heatsinks onto the plastic package of the MOSFET, not the metal back. So no, you won't have a short or live heatsink.

ZachM · Feb 25, 2004

I have seen boards come from factory with all of the mosfets covered with one large heatsink. I think that would be the best way because you would only have to epoxy the heatsink down on either ends of the heatsink. On the mosfets in between the end ones you could just use thermal paste. The heatsink and residue would be much easier to remove than having a bunch of individule heatsinks if you need to take the heatsink off for any reason. That's my opinion at least.

larrymoencurly · Feb 26, 2004

Even Radio Shack sells a small multifin aluminum heatsink, but their price is high, $1.99. I have some like it on the MOSFETs and diodes of a 300 MHz mobo that for some reason runs them at 90C outside the case (capacitors are not faulty), and heatsinks drop this to 70C.

karsten · Feb 27, 2004

i just installed those aluminum heatsinks from radioshack, cut to size, and my cpu temp went up a whopping 5deg C. Any ideas why this happened?

thanks
karsten

mccoyn · Feb 27, 2004

Did the voltage change? Are the heatsinks blocking airflow out of the CPU heatsink?

larrymoencurly · Feb 28, 2004

Are the Radio Shack heatsinks blocking any air flow? If not, I can't think of any reason why the CPU temperature would increase 5C. I found that temperatures can be influenced by even tiny air currents, and it's also necessary to let the equipment run for at least 30-60 minutes and measure the room temperature.

Are the MOSFET heatsinks too big??

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