Custom "Blowhole" Case Cooling

From back around 2000...

The best processor I can afford right now is an AMD K6-2 rated at 400 MHz. Even without overclocking, in my system the K6-2 runs at about 140F on a good day. On a bad day, it gets high enough that the temperature alarm on the mainboard goes off. I don't know how high that is, but I assume it falls into the range of "too darn hot." And, more importantly, this was after I'd filled the case full of fans. I had a "slot" fan pulling air out the back, a "bay" fan pulling air out the front, and "regular" cooling fans blowing air across both my DirecPC satellite modem card and my Voodoo 3 3500TV card. Trying various combinations and rearrangements, I got the cards cool enough to touch without burning fingertips, and the overall case temperature within 10F of ambient, but the CPU was still running hot. I didn't want to start my overclocking experiments with the system in this condition. I did get some relief by wiring in an old PC/AT power supply fan blowing directly across the CPU heatsink. However, that single fan made an occasional ugly grinding noise louder than all the rest of the fans put together. I took this to mean impending bearing failure and discarded it (besides, it was waking me up at night). Wiring in one, and later two, "regular" cooling fans blowing across the CPU heatsink didn't cut it. I was running out of room to add fans, and all the wires were getting in the way. I took to running the computer with the cover off to keep it cool.

As luck would have it, I had a couple of 4.5" ~115V AC muffin fans laying around, rated at 10W and 14W. These used to be part of a cooling unit made by Northern Telecom but were tossed during an upgrade. I grabbed the unit out of the trash and, after splicing it into the AC power, used it as a room fan for many years. The fans moved serious CFM and even so were quieter than the old PC/AT power supply fan. After I removed the computer's cover and propped the fans so that they blew over the CPU and mainboard, I found that they brought the CPU temperature down by over 20F! However, they were way too big to fit anywhere inside the mid-tower case of my system. I didn't want to make any major modifications to the case or cover due to impacting future resale value. I didn't want to run the system without a cover due to cats and kids in the house. Realizing that my Dad has a complete woodworking shop and that I know which end of a hammer to hold, I finally got an idea.

My original plan was fairly simple: using scrap lumber, I'd throw together a custom replacement cover. Since I use the top of my case as a shelf for my keyboard, I decided to make the top of my custom cover oversized (as shown in red here). This (in theory) left room for one or both fans, the keyboard, and the mousepad. I didn't mark the fan location(s) yet, because I wasn't sure about exact placement or whether I would use one or both fans. I figured to put it/them a few inches in from the upper left corner of the top, more or less directly over the CPU and 256 MB of RAM. Though shown in red and black here for clarity, I intended the top to be one piece. I planned to run the fans from external AC power, seperate from the computer's. I also planned to keep the external on/off switch so I could turn the fans off when not needed. Well, I ended up keeping some of those plans...

I was still a little worried about noise, but once nailed into place, the fan was actually fairly quiet. Running it for just a few minutes made a major difference in case and CPU temperature. Problem was that I was still essentially running caseless, and I could just see me trying to clean cat fur out of my fans after Buddy came in to check out the new noise. Hey, forget the cat; I was afraid I'd get careless and touch something I shouldn't.

Speaking of getting careless, I discovered that the cute little inline switch I was using to control the fans only cut off one line of the AC. But, as we say in the south, it's only 120!

If I didn't mention it before, I decided to go with a single AC fan blowing down. Yes, I know that heat rises and the top of the case would make a good place to vent that heat, but I tried it both ways and this really does give me lower temperature readings. I guess this is because I'm blowing "cool" outside air over the CPU, memory, and the back half of my Voodoo3 3500 TV. I say "cool" because I don't have air conditioning and the "cool" air is about 95F today. I advise anyone reading this who is considering a custom cooling solution for his computer, but doesn't have one for his house, needs to re-arrange his priorities. Me, I'm just crazy.

I constructed a second frame to put above the first. This was a support for the old shelf I used to hold my keyboard and mousepad. This also left plenty of room between the two frames for the fan to suck in fresh air. I needed a way to connect these two frames, and I was still drawing a blank on how to cover the sides. I decided on a couple of old pieces of paneling.

The paneling was old and thin, but I figured it didn't have to be too strong since it was just going to hang there. On the other hand, it did have to be strong enough to hold a nail, which I found out it wasn't. I put together the first side and tried to turn it over to get the other, and the paneling just ripped right off. (Just as well, since I'd managed to attach one of the frames crooked.) If I'd had some scap plywood of the proper size laying around, I'd have gone with that.

For attempt two I decided to use a liberal amount of wood glue. I figured that and the half-inch brads would hold it together.

As you can see, with the new cover on and 115V fan going, there's a 20F drop. Even without the big fan running, I've found the CPU temperature rarely gets over 140F most days. I'd say mission accomplished!

Update July 12, 2000: I read somewhere that the amount of air coming into your case should be matched by the amount going out. Otherwise, the heat just kind of piles up in odd corners of the case. I didn't think I'd have that problem with the smaller fans I had blowing air out of the case. But I checked the big fan and, sure enough, it did seem to be bogging down after a few seconds. I decided to drill some vent holes down at the bottom of the cover. They are in that particular place and pattern because I was going to put the other 115V fan there. I figured I would have one blowing in and one blowing out; get a real hurricane going. However, when I tried running both fans together, I actually got CPU temperatures a few degrees higher than running them individually. Must have changed the pattern of air flow or something. Anyway, the new vent holes put out a steady stream of air, and the big fan is running with less noise now, so I'm leaving them there.

Here's a link to $link:http://www.hardocp.com/$ which provided a lot of info. Though I came up with the idea of a "blowhole" on my own, it was the articles and pictures available on that website that convinced me that it could be done. Keep up the good work, guys!