Power FETS - Should I bother cooling?

dadi_oh · May 15, 2008

I have an ASUS P5K-E motherboard that I recently added watercooling to the Northbridge (P35). Because of ASUS' use of heatpipes when removing the heatsink from the NB I am also, by default removing the radiator over 8 power FETs. This radiator serves a dual role, taking heat from the NB and placing it in the airflow from the CPU heatsink fan, as well as being attached by a thermal pad to the power FETs. I believe that the NB cooling is the major purpose of this radiator evidenced by the fact that, on this board anyways, they do not even bother cooling the FETs located at the top of the board (even though there is provision for heatsink attachment).

So my theory is that this radiator is not actually that important for the FETs. If I take an IR thermometer I am only reading temps of these devices in the mid 40's C with the CPU running Prime 95. Most FETs are rated for Tj in the range of 150C + so I am thinking they are fine as is.

See attached pic as reference. The FETs circled in yellow have no heatsink installed from the factory. The area circled in green has now exposed the 8 FETs when I removed the heatsink.

I could consider gluing on heatsinks to the FETs but now I am thinking I won't bother. If I ever have to sell the board I will want to restore it to factory heatsink anyways.

The board seems to be overclocking fine as is. Any thoughts?

Darknova · May 15, 2008

I would, I've seen many reports of bare CPU fets burning out without sufficient cooling.

Although there seems to be a mixed opinion and you will find people who disagree with me completely. I've even had one guy say I'm making things worse by cooling them.

But IMO, buying a set of Enzotech Fet sinks and sticking them on is a good idea, and better safe than sorry, what happens if they do burn out?

newconroer · May 15, 2008

Use simple and small individual copper heat sinks, passive.

FETS aren't a huge deal until you start really cranking or topping out your board.

And as you say, the temperatures at the moment seem fine, so, if it's a hassle, don't bother.

FatForester · May 15, 2008

I have the P5K-e Wifi, and have been wondering the same thing. If you're going to be watercooling, I assume you'll be overclocking quite a bit which means those MOSFETS will probably get pretty hot. I'm looking to get some coolers to slip on mine just in case.

JUDAS3 · May 15, 2008

get these, ive got the same board and they fit a treat:

http://www.chilledpc.co.uk/shop/product_info.php?cPath=117&products_id=578

make a nice addition.

Silverel · May 15, 2008

+1 to cooling em. MSI had to revise the K9A2 CF board with a heatsink on em, and it's not even rated for 125w processors...

dadi_oh · May 15, 2008

Silverel said:
+1 to cooling em. MSI had to revise the K9A2 CF board with a heatsink on em, and it's not even rated for 125w processors...

Concensus seems to be to cool them so i guess I will slap some on there with thermal tape. That way I can always get back to stock and thermal tape should be good enough since the FETs are rated for high temp anyways.

Since all the ASUS boards (at least 3 of the ones I have owned... P5N32-SLI, P5N32E-SLI, P5K-E) seem to use the same layout for a heatsink on these FETs it would be nice if someone made one that used the pre-existing mounting holes. I saw some watercooled blocks somewhere once that were the ASUS standard but they were expensive and also overkill for this application.

JUDAS3 · May 15, 2008

dadi_oh said:
Concensus seems to be to cool them so i guess I will slap some on there with thermal tape. That way I can always get back to stock and thermal tape should be good enough since the FETs are rated for high temp anyways.

Since all the ASUS boards (at least 3 of the ones I have owned... P5N32-SLI, P5N32E-SLI, P5K-E) seem to use the same layout for a heatsink on these FETs it would be nice if someone made one that used the pre-existing mounting holes. I saw some watercooled blocks somewhere once that were the ASUS standard but they were expensive and also overkill for this application.

READ MY POST - I HAVE THE SOLUTION - SEE ABOVE - ACKNOWLEDGE PLEASE

Arctucas · May 15, 2008

Passive heatsinks:

http://www.thermalright.com/new_a_page/product_page/chipset/hr05_ifx/05-09-mcl.htm#asusP35

I did not see the P5K-E listed, but I believe the P5K Premium/WiFi-AP has the same MOSFET layout?

dadi_oh · May 15, 2008

JUDAS3 said:
READ MY POST - I HAVE THE SOLUTION - SEE ABOVE - ACKNOWLEDGE PLEASE

Sorry. I did see your post and clicked on the link. The main concern that I would have is applying 16 heatsinks (there are 8 FETs X 2). The surface area of the FET is very small and thermal tape is typically not all that strong so my main concern was having these falling off if I were to just bump them. A solution that covers multiple FETs is easier to apply and has the added bonus of applying sticking power to more surface area.

At least that is what I went through my brain when I looked at it

Thanks though. Good info.

JUDAS3 · May 15, 2008

i know what your saying but the grip really well, i will look again though.

dadi_oh · May 15, 2008

Arctucas said:
Passive heatsinks:

http://www.thermalright.com/new_a_page/product_page/chipset/hr05_ifx/05-09-mcl.htm#asusP35

I did not see the P5K-E listed, but I believe the P5K Premium/WiFi-AP has the same MOSFET layout?

That's the ticket. HR09 type 2 is listed for P5K-E Wifi which is my mobo. Looks expensive though but very polished. If I had a windowed case I might consider it :laugh:

Thanks.

Darknova · May 15, 2008

dadi_oh said:
Sorry. I did see your post and clicked on the link. The main concern that I would have is applying 16 heatsinks (there are 8 FETs X 2). The surface area of the FET is very small and thermal tape is typically not all that strong so my main concern was having these falling off if I were to just bump them. A solution that covers multiple FETs is easier to apply and has the added bonus of applying sticking power to more surface area.

At least that is what I went through my brain when I looked at it

Thanks though. Good info.

Thermal tape is designed to strengthen when heated. I found that I could knock them off quite easy first time I applied them, but now they are pretty damn solid. Would take a bit of force to get the blighters off.

dadi_oh · May 15, 2008

dadi_oh said:
That's the ticket. HR09 type 2 is listed for P5K-E Wifi which is my mobo. Looks expensive though but very polished. If I had a windowed case I might consider it

Thanks.

$20 bucks apiece at NCIX :eek:

I'll just stick on some VGA RAM heatsinks methinks.

largon · May 16, 2008

Find some old Slot-A/1 heatsinks, saw 'em to pieces and use the original mounting holes on the board to mount the buggers.

dadi_oh · May 16, 2008

largon said:
Find some old Slot-A/1 heatsinks, saw 'em to pieces and use the original mounting holes on the board to mount the buggers.

Now that is a good idea. Make sure it is wide enough to reach the mounting holes and then just drill and tap some holes in the heatsink from below. Very creative. And best of all... cheap :laugh:

Thanks. I just might pull my motherboard out... again... millionth time.... why does EVERYONE exaggerate....

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Power FETS - Should I bother cooling?

dadi_oh

Attachments

Darknova

newconroer

FatForester

New Member

JUDAS3

Silverel

dadi_oh

JUDAS3

Arctucas

dadi_oh

JUDAS3

dadi_oh

Darknova

dadi_oh

largon

dadi_oh

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