Cooling CPU & PSU with single 80mm nexus, is this wise?

The Gangrel · Post by **The Gangrel** » Sun Feb 24, 2008 9:21 am

I have a large server case, PSU mid mounted as is convention. CPU heatsink is just underneath PSU, so I thought "why not use a single 80mm Nexus to cool the lot".

Nexus fan blows up into the PSU, taking hot air from CPU heatsink pushing it out of PSU fan hole(grille has been snipped out), all other escape routes for hot air to come back inside the case from PSU have been filled(white-tack, nonetheless).
Anyhow, I like the Nexus to run really slowly, i.e just above 5 volts(use a zalman twisty thing to control voltage), now this setup is certainly quiet but doesn't move much air.

At the moment the cpu/heatsink combo I'm using is an ML-37 turion and a Zalman flower cooler, under prime 95 the CPU is approaching 73C, which may be because the Zalman doesn't seem to be able to screw particularly tightly onto the CPU, hence bad transferal of heat.

I'm thinking of trying a Ninja Rev B in this setup instead, is this the best heatsink to use to for such low airflow?.
Secondly, is one nexus 80mm fan going to be enough to cool the PSU sufficiently given the low airflow, should I add another where the old PSU fan used to be and use that aswell as the one removing heat from CPU heatsink(kinda worried this might be too noisy, now I've got used to just the one).
How hot is too hot when it comes to air coming out of the PSU(it certainly gets warm rather fast!).

FlorisNielssen · Post by **FlorisNielssen** » Sun Feb 24, 2008 11:33 am

I wouldn't recommend it. I also would not recommend removing the fan from your PSU. It would probably run too hot.

With good PSU's, the fan is thermal controlled. With low power, the fan runs at minimum speed. Except if the air that gets into the PSU is hot. Then it'll run faster to keep the PSU cool. Makes sense.

With your setup, I can imagine the PSU to get too hot. As for this Seasonic PSU (scroll down for results), the exhaust temp (at maximum load) doesn't exceed 46 degrees. If your cpu's getting as hot as 70 degrees and you blow the air inside the PSU, I can imagine that being not too good. Of course, as you point out, the heat transfer might not be too good (put some pressere on it yourself and try if the temperature drops), so the air won't be as hot as 70 degrees.

What I would do:
First: add a fan to the PSU. If you add a quiet one it won't run fast and cool the PSU sufficiently without too much noise. (Don't add a Nexus. Although quiet, they don't start too good at a low voltage.)
About your cpu-heatsink:
A Ninja is very good at low airflow. Indeed on of the best. But a 9500 (or 9700, I presume you mean on of those) is a good heatsink too. (Not the fan though.) If you can somehow add more presure and hereby solve the problem I wouldn't buy a Ninja.

How's your current setup exactly? The Nexus directly on the heatsink? If so, you might want to set the fan a little faster. Nexus fans don't move much air. Certainly not a 5V. If you put it a 7V. It'll probably not get much louder.

Good luck with it!

Post by **NeilBlanchard** » Sun Feb 24, 2008 7:09 pm

Hello,

If the one fan was a 120mm, you have a chance of making it work; quietly even. But I doubt that one quiet 80mm fan will be enough.

nutball · Post by **nutball** » Mon Feb 25, 2008 12:16 am

I've cooled and PSU + CPU with a single fan in the past, but that fan was a 120mm Nexus. I doubt that an 80mm would cut it. I also had a duct to ensure that the air which cooled both came from outside the case (hence was cool) rather than having been pre-heated by other components in the case.

The Gangrel · Post by **The Gangrel** » Mon Feb 25, 2008 5:02 am

FlorisNielssen wrote:I wouldn't recommend it. I also would not recommend removing the fan from your PSU. It would probably run too hot.

With good PSU's, the fan is thermal controlled. With low power, the fan runs at minimum speed. Except if the air that gets into the PSU is hot. Then it'll run faster to keep the PSU cool. Makes sense.

Just to clarify, the nexus fan is mounted to the bottom of the PSU, blowing air up into it and out through where the old fan was(grill has been removed, now just a hole). The PSU is circa "the first Pentium 4's" model, cheap as chips with no variable fan setting to speak of.

Neil: Would a single 120mm fan be as quiet as the single 80mm. I don't think it's running at quite 5v, probably a little more, but the fact that I've had a fan running below the noise floor means it won't be coming back above it.

The other problem being now I notice the whine my LCD screen makes. You never catch the dragon, you just keep chasing it...

Nutball: I've love some pictures or just if you could elaborate.

All this is leading me to thinking: thin client that remote desktop's into the server, which I'll stick in the kitchen cupboard or something with the door ajar. Even then, I don't want a noisy kitchen....and so it continues...