How to identify VRM modules?

[JazzJackRabbit]

I have P4P800 motherboard that was manufactured long before all this fuss about VRM efficiency and cooling. Since I'm currently redoing my main system I thought about putting some heatsinks on VRM modules just in case, especially since I want to try to overclock my CPU even further. How can I identify VRM modules on P4P800?

Thanks.

[cmthomson]

In general, MOSFETs come in square black packages about 4mm square. The most effective way to identify overly hot components is with your finger. If you can't hold a finger on it, it's too hot. If you jump (YOW!) it's way too hot. If it raises a blister, it's about to fail.

[Tibors]

If you look at the mobo you can see next to each other:

1. heatsink mounting bracket
2. row of capacitors
3. row of three coils
4. row of flat things (these are MOSFETs)
5. row of capacitors
6. printer port

2, 3 & 4 (& maybe 5) together are the VRM. The only thing you can put heatsinks on are the MOSFETs.

[anaqer]

JazzJackRabbit -
judging by images of the board, applying heatsinks to the MOSFETs is going to be a huge pain in the ass due to space constraints - I wouldn't bother unless a) it already runs very hot, b) you are going to raise vcore significantly, or c) you are trying to OC a Prescott.

[JazzJackRabbit]

Thanks guys. Unfortunately as anaqer already have said, I took a look at mobo today and yes, it's next to impossible to attach heatsinks to mosfets because they are all positioned between coils or capacitors.

anaqer
I have no idea how hot they are running, I never bothered to check, partially because simply getting there is a pain in the @ss because of the tight space between exhaust fan and Ninja heatsink. I have an old school northwood core 3.0GHz 30-capper which already runs at 3.4GHz at stock 1.55V voltage. I hope to get it up to 3.8GHz with minor votage boost up to 1.6V. Shouldn't be that hard for 30-capper, but of course, it's always YMMV when it comes to overclocking.

[TomZ]

I have P4P800 motherboard that was manufactured long before all this fuss about VRM efficiency and cooling. Since I'm currently redoing my main system I thought about putting some heatsinks on VRM modules just in case, especially since I want to try to overclock my CPU even further. How can I identify VRM modules on P4P800?

Seems like you got some answers already, but I'll add this anyway. Adding heatsinks to the tops of surface-mount MOSFETs (DPAK and D2PAK) is pretty ineffective anyway, because MOSFETs like this are designed to dump their heat down into the PC board, and not up through the tops of the plastic packages. So the majority of the dissipated power (80-90%) would not at all benefit from a top-mounted heatsink.

[jaganath]

Adding heatsinks to the tops of surface-mount MOSFETs (DPAK and D2PAK) is pretty ineffective anyway, because MOSFETs like this are designed to dump their heat down into the PC board, and not up through the tops of the plastic packages. So the majority of the dissipated power (80-90%) would not at all benefit from a top-mounted heatsink.

Interesting, I would never have suspected that. BTW Tom, how come you know all this stuff? ISTR that you're always on the ball when it comes to really technical topics, do you work in the biz (PCB design/manufacture)?

Also, how come Abit and MSI, Asus etc put whacking great heatsinks on their MOSFET's on performance boards? Are they using a different kind of MOSFET there?

[TomZ]

Interesting, I would never have suspected that. BTW Tom, how come you know all this stuff? ISTR that you're always on the ball when it comes to really technical topics, do you work in the biz (PCB design/manufacture)?

Yes, I do some electrical engineering work, some of it with power circuits like power supplies and power drivers.

Also, how come Abit and MSI, Asus etc put whacking great heatsinks on their MOSFET's on performance boards? Are they using a different kind of MOSFET there?

I don't know specifics about those boards, but there are some different possibilities. There are some MOSFETs that are designed to be cooled from the top side, e.g., DirectFET from IRF: http://www.irf.com/package/pkhexfet.html. But most I've seen on motherboards are D2PAK. Putting heatsinks on the tops will help a little bit, especially if the design is otherwise marginal, but the bulk of the heat will flow down into the PCB.

I suspect that many of these heatsinks are actually meant to make the board look cool, rather than to be cool. Besides the above, the other thing I see a lot is that these heatsinks are anodized, which is a no-no if you are really concerned about heat heat transfer. Anodizing reduces the ability for aluminum to transfer heat to the surrounding air.

[jaganath]

the other thing I see a lot is that these heatsinks are anodized, which is a no-no if you are really concerned about heat transfer. Anodizing reduces the ability for aluminum to transfer heat to the surrounding air.

Yeah, we had a thread about that discussing the anodized heatsinks on Silentmaxx's rebadged Fortron Zen power supply; but anodizing increases the emissivity of the heatsink, so maybe it balances out?

PDF on ways of decreasing operating temps of electronic equipment, including increasing emissivity of heatsinks

SPCR thread on silentmaxx PSU