PC Hacks 100 Industrial-Strength Tips and Tools

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Hack 29 Check the Vents

Add it all up—a screaming 7,200 or 10,000 RPM hard drive, a lightning fast CPU, stunning RAM throughput, blinding video performance, and a modest few watts of sound power—and you realize that puny little fan inside the power supply is not going to be able to suck out the extra BTUs of heat generated by all these hopped-up devices.

The operative words here are "suck out." For some reason, PC chassis and power-supply engineers think that one little 2" fan stuffed into the corner of the power supply box is going to unload hundreds of BTUs of electronically induced heat and pick that heat out of all corners of the chassis. It's just not so. Even a newer PC with a fan and duct work placed above the CPU to remove significant amounts of heat from the PC chassis is not cooling the system as effectively as possible.

Generic PC design recommendations tell us we should evacuate or use a vacuum to pull hot air off the CPU and out of the PC chassis, but they do not tell us that to do so requires construction of air deflectors and ducting to create a maximum vacuum or negative pressure near the CPU heat sink. This is not practical for those of us who are building our own systems. (As well stocked and equipped as my shop is, I know I do not have plastic molding or sheet metal fabrication capabilities!) Those of us hacking prebuilt systems that have fancy ducting can benefit from this hack as well.

The basic physics of vacuum theory are pretty clear in that the pressure, or negative pressure in a vessel, especially a leaky one like a PC case, will not be even throughout. You can prove this quite easily at home with an average cardboard box, a pile of dust (sawdust works well) in one corner, and your typical household vacuum cleaner. Apply the nozzle end of the hose of the vacuum cleaner in any other corner but the one the dust is piled in, close up the box as best you can by folding over the flaps, and without moving the nozzle or the pile of dust around, see if you collect any, much less all of the dust from the other corner. It won't happen.

Leaving everything as it is, reverse the function of the hose: connect it to the outlet/pressure side of the vacuum cleaner and watch the sawdust spew out from every crack and crevice. Pressure wins over vacuum every time. The material leaves the holes in the chassis pretty much evenly and this is how pressurized air cooling works: one inlet and even distribution of the airflow all around. (Have you ever been in a building that vacuums air around to distribute cool or warm air for ventilation?) I have no idea what you're going to do with the mess you've just made, but the point should be obvious—pressurize your PC case!

You will find that most server and network equipment chassis and enclosed rack systems use pressurization rather than convection and vacuum techniques to force-cool the contents. Assuming most server and network equipment rooms, and where you operate your PC, are relatively free of dust and debris, you should not have to worry about your PC filling up with every dust bunny, feather, and bug that happens to get near your chassis.

The little fan in the power supply is arranged to avoid blowing a lot of dust all over the components inside the supply, which happens anyway if all the air inside the PC leaves through the power supply: it heats up and fails faster. By luck and placement at the top of the chassis, a little convection flow will happen and some heat from the PC chassis will be drawn out, but not nearly enough. It's like trying to suck the air out of a balloon; as soon as one part of the balloon collapses you will never get all the air out.

Unfortunately, because of case design and all the cards and cables inside the PC, there are few places to mount a fan, inside or out, to be able to draw air in and blow it throughout the case. One of best places I've found is in between the plastic facia and the metal chassis, near where the PC speaker is typically mounted, or a grille area at the back of the chassis. I may rescue a 3-4" fan out of a failed power supply [Hack #19] (suitably disconnected from any power source and left to sit for a few minutes after removing power so there is no charge left on internal components) or buy a new 12v DC fan from a local electronics supplier, then attach male connector pins suitable to fit into an extra disk drive power connector, as shown in Figure 3-25.

Figure 3-25. Fans with Amp pins attached for connection to disk drive power connectors

Figure 3-26. Additional fan installed to move air into PC chassis from grille work and empty slots at the rear

Once the fan is ready to plug in, I find a suitable screw hole or two in the front or rear of the chassis (Figure 3-26), blowing inward through the copious holes that were supposed to draw air in for the power supply, mount the fan, and there it is—a cheap chassis pressurization system.

Just like the old "suction" method, pressurizing the chassis does have the effect of "inhaling" the dirt and dust bunnies that happen to float by your fan intake and pushing them around every component in the system. Adding a piece of thin foam-rubber padding as a filter to the intake side of the fan helps, but you have to remember to clean or change it occasionally to ensure ample airflow. While you're changing the filter, you can clean the dust off the components inside the case with a can of compressed air or a small vacuum-cleaner nozzle to avoid building up an unwanted layer of insulation. PC components do not like being snuggled into a blanket of dust bunnies because the layer of dust holds in the heat we are trying to get rid of.

My experience has been that so much air moves so fast with a new fan that the dust bunnies do not have a chance to take up residence and instead get blown out with the warm exhausted air. Besides that, what are you doing operating your PC in a dusty location anyway?

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