Hein (fub) wrote,
Hein
fub

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Minicomputer, day 9: Airflow engineering

After a long hiatus, it was once again time to get cracking on the minicomputer. Recall that, in a previous post on the subject, I had mentioned I was concerned about the high temperatures within the case. With no airflow in the case, there was little the CPU cooler could do but recycle the air inside the case, that had already been warmed up by the northbridge.
And so, I decided I should construct something to replicate the airflow generated by the original PSU -- but of course, with a less noisy fan. And with the little heat-production of the C3 CPU, I could get away with much less airflow too. I still had that northbridge cooler-fan, and so I set to work...


From plywood, I made a 'backplate' of sorts, with holes for the fan and for connecting the power-supply to the stabilisation PCB. On the left is the plate to place between the motherboard and the PSU PCB, to emulate the airflow generated by the original PSU. Recall that the intake fan of the PSU was right next to the CPU. This plate closes off the side of the mobo upto the CPU. Both plates have been grounded and painted black on both sides.


Backplate with the fan installed (actually, glued on). The round hole is the same size of the rotor, and there's no fanguard, so the air can flow unimpeded (and less noisy!). The minicomputer will have its back against the wall anyway, so there's little chance of fingers or cat's tails being stuck in it when it's running.


I sawed a new plate to screw the PSU stabilisation PCB on, glued the backplate in place, aligned the PSU PCB and glued that in place too.


My excuses for the unclear picture. This shows that the plug for connecting the power brick to the PCB is aligned with the square hole in the backplate. That's no coincidence. ;)


From the back. Note the connector through the square hole.


The side-plate glued into place. It ends just before the ATX power plug of the PCB, which sits just next to the CPU. The cool air is attracted through the holes in the back (above the backplate of the motherboard), travels over the northbridge and the CPU, and is then blown to the outside by the fan.
If I hadn't installed the side-plate, the fan would have attacted air directly from the outside of the case as well, which wouldn't do us any good.
Note that there's also another path for air to travel: from the holes underneath the harddisk enclosure, towards the back of the case. I hope that this will also cool the harddisk a bit better.


A shot of the completed assembly, in use. Taken with a flash.


This is what it looks like without a flash. Yes, the blue LEDs are still on that fan...

I had connected the fan to a Zalman Fanmate fan-controller to control the RPM (and hence the noise) the fan makes. However, even with the fancontroller switched to the maximum speed, there is very little noise -- probably because of the absence of a fanguard. This means I can simply disconnect the fancontroller, because it serves no purpose.

So, you ask: what are the results? Actually, the results are quite good. When idle, the CPU is at a temperature of 32 degrees with a case temperature of 19 degrees. Harddisk runs at 31 degrees. Yes, it's cooler now than when I did the previous measurements -- if you estimate a drop of 10 degrees in temperature, the temps are pretty much the same as back then.
When playing a DVD, the CPU runs at 46 degrees with a case temp of 23 degrees, and the harddisk is stable at 32 degrees. And when stressed (playing DivX'es fullscreen), the CPU runs at 49 degrees, case at 25 degrees and harddisk at 32.

It's mostly the case temperatures that are much lower -- and a lower case-temperature (actually that means lower northbridge temperature) means that all components run cooler. At a minimal gain in noise (I had to close the windows to block out the sounds from outside to hear the machine), I'm pretty pleased. Also, the air that's expelled by the fan is rather warm -- another indication that the cooling issue is now much improved.
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