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Overheating mosfets

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  • CPUs
  • Motherboards
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February 10, 2013 4:17:58 AM

Motherboard:Asrock 970 Extreme 3
Cpu:AMD FX-6100 oc @4.2

If the mosfets overheat can they cause my cpu clocks to go way off.
I have airflow through that area, but they are still getting hot :fou: 
Any better ways of cooling them for this motherboard

More about : overheating mosfets

February 10, 2013 4:30:09 AM

how hot is hot (some boards let you monitor this I believe) ?

That board looks like a 4+1 vrm
Having active airflow over the area would be a definite plus
Hard to say if you'll fry a mostfet/driver or if your overclocks will be limited.

Some boards let you chage the frequency of the vrm with lower generating less heat. I'm partial to doing this, disabling llc, disabling spread spectrum, and keep the voltage at a reasonable level. You might have to raise the vcore an extra .01v or so with all this disabled to maintain stability, but it'll put less stress on the vrm.
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February 10, 2013 4:45:36 AM

They are too hot to keep my hand on it for more than a couple seconds. Speedfan isn't giving any temp that looks like it is coming from there. I have all that stuff disabled and my voltage is as low as it can go while staying stable.
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February 10, 2013 4:49:15 AM

ASrock's OC tuner should give you the heat readings under system health.
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February 10, 2013 5:01:56 AM

Asrock utility is less usefull than speedfan. And why would I put heat-sinks on the caps
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February 10, 2013 5:15:35 AM

If you can't keep your finger on them, then they are too hot.
I believe they only spec many mosfets at 30c or lower.
So efficiency and max amps per phase will go down a lot if they are as hot as you say.

4+1 vrm really aren't designed for overclockers even tho they often get marketed as such.
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February 10, 2013 5:19:09 AM

Heat sinks will only help a little, since you'll just be cooling the casing of the component and a significant amount of the heat is actually dissipated through the leads into the motherboard. Your best bet is to get more air flow in that area.

Keep in mind that this board is designed to work with a cooler that's blowing air over the CPU and onto the surrounding components. If you have a large heatpipe cooler that's offset from the board these components will get hotter than intended. Good full case airflow is critical here.

As for monitoring the temp, there probably isn't a sensor on the FETs. There might be one nearby, but unless you can see exactly where it is trust your fingers over the readout (or get an IR heat sensor).

Don't be too afraid of heat. FETs get hot; they shouldn't be too hot to touch, but being uncomfortably warm isn't the end of the world.
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February 10, 2013 5:19:37 AM

What are those little Gray box things next to the mosfet heatsink? I think burnt my finger on them. Also if I stress test long enough my cpu will throttle, even though it didn't get hot enough to. Are there any better coolers for the mosfets or should i back down on overclocking a little bit.
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February 10, 2013 6:23:05 AM

knuckleonAMD said:
What are those little Gray box things next to the mosfet heatsink? I think burnt my finger on them. Also if I stress test long enough my cpu will throttle, even though it didn't get hot enough to. Are there any better coolers for the mosfets or should i back down on overclocking a little bit.

those are the caps that I said put a heatsink on. Technically speaking they are covered (capped) inductors.
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February 10, 2013 6:30:15 AM

A small fan and some zipties.
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February 10, 2013 8:47:31 AM

Soul_keeper said:
If you can't keep your finger on them, then they are too hot.
I believe they only spec many mosfets at 30c or lower.

30C is often below the temperature of the computer interior, and I've never seen a MOSFET rated for less than 125C. Even the CPU is rated for at least 65C and the DRAM for at least 70-85C.

Do not install heatsinks over the capacitors since the thin metal and lack of good contact will result in little heat conduction, and the heatsinks will block the vents of conventional electrolytics, possibly creating an explosion hazard.. It's much more reasonable to install heatsinks over the MOSFETs.

The inductors are not capped. Those are their cores. I don't know if heatsinking will help, but I've never seen heatsinks used on inductors.
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February 10, 2013 3:36:36 PM

I am going to back down my overclock to 4ghz. I don't want to kill the board. I read a bunch of reviews say with the 8 cores are overheating the mosfets at stock. when i upgrade this computer i am probably going to get a new motherboard.
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February 11, 2013 10:04:55 AM

bryanl said:
30C is often below the temperature of the computer interior, and I've never seen a MOSFET rated for less than 125C. Even the CPU is rated for at least 65C and the DRAM for at least 70-85C.

Do not install heatsinks over the capacitors since the thin metal and lack of good contact will result in little heat conduction, and the heatsinks will block the vents of conventional electrolytics, possibly creating an explosion hazard.. It's much more reasonable to install heatsinks over the MOSFETs.

The inductors are not capped. Those are their cores. I don't know if heatsinking will help, but I've never seen heatsinks used on inductors.



Sorry for the confusion
I'm not talking about the maximum temp rating, i'm talking about the spec.
IE: 30A at 30c 25A at 40c 20A at 50c etc. (random example)

efficiency has a negative correlation to temp, even if within maximum rated temp.
These must be considered when pushing things to the max.
You'd need to consult the datasheet for all the components involved in the phases for the exact numbers.

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February 11, 2013 10:38:33 AM

knuckleonAMD said:
I am going to back down my overclock to 4ghz. I don't want to kill the board. I read a bunch of reviews say with the 8 cores are overheating the mosfets at stock. when i upgrade this computer i am probably going to get a new motherboard.


Wise choice.
I recently backed down my overclock as well. Sometimes it's just not worth the extra 200MHz or so if you plan longterm use.
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February 11, 2013 3:21:43 PM

bryanl said:
30C is often below the temperature of the computer interior, and I've never seen a MOSFET rated for less than 125C. Even the CPU is rated for at least 65C and the DRAM for at least 70-85C.

Do not install heatsinks over the capacitors since the thin metal and lack of good contact will result in little heat conduction, and the heatsinks will block the vents of conventional electrolytics, possibly creating an explosion hazard.. It's much more reasonable to install heatsinks over the MOSFETs.

The inductors are not capped. Those are their cores. I don't know if heatsinking will help, but I've never seen heatsinks used on inductors.

Really? Might want to look at some 990 fx boards, almost all of them are heatsinked, pretty much any high end board for that matter.



The thing is if you looked at the extreme3, you can't heatsink the capacitors without heatsinking the covered inductors.

This is what they look like if you removed the cap on the inductors.



Here is the underside with the copper coil installed in the cap, packaging varies, but they are near identical on the inside.

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February 11, 2013 5:23:50 PM

AFAIK low end mosfets are only rated to carry their max power when in the 30c ish range and are less effective as they heat up while quality ones will have higher temp ratings arround 65-125c and will output max power at much higher temps

Ironic in that mosfets that are quality are on quality boards are likey to have good cooling that they don't really need while cheap mosfets are on cheaper boards that lack mosfet cooling when they are the ones that need it the most
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February 17, 2013 11:24:23 PM

Best answer selected by knuckleonamd.
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