Solid [rigid] Aluminum 4" CPU Duct. Final Temps.
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Author:  Bluefront [ Sat Apr 05, 2003 3:53 pm ]
Post subject:  Solid [rigid] Aluminum 4" CPU Duct. Final Temps.

Here's my latest duct project. This duct , like my previous attempt, blows air directly on an Alpha heatsink. You can see a little fan mounted directly on the Alpha. This is a back-up fan, controlled by a Digital Doc 5, that only turns on when the temps get too high. Most of the time this duct, with it's 80mm variable speed fan, provides the only intake air to the whole case.

Other than the fan, I only used two parts. A Smart Choice Wall Offset Elbow....a drier vent part (BestBuy 7$). And a PlumbQwik Rubber Downspout Connector (Lowe's $2$). The vent is 4" in diameter, and I bent the fan end by hand .....an 80mm fan just fits and is held in place by crimping the aluminum. This holds it tight. Mounted in the case it is about 1/2" over the Alpha, and slightly offset to also blow on the ram.

The duct and the rubber sleeve were cut to fit with some small shears...very easily. The rubber sleeve is the only part that touches the case, so there are no vibrations. Right now there is a temporary mount...after the whole project is final, it'll be more secure.

There's a picture of the filter I'm using...same as before, a PowerCare lawn-mower filter. This duct could be polished and used in a case with a window...it looks good. But I'm going to cover it with some acoustic foam. Right now it's much quieter than my previous duct setup...Mostly because the fan is not in a direct line to the rear opening.

As far a temps are concerned, the cpu is about 1C less than before....but the ambient temps are up today...about 2C higher than my previous tests. The good part is the ram temps are down almost 4C, and the chipset temp is also down. So far, so good.


Author:  GamingGod [ Sat Apr 05, 2003 5:07 pm ]
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Does your power supply ever speed up, since its the only exhaust?

Author:  Bluefront [ Sat Apr 05, 2003 5:24 pm ]
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Well I have no way to monitor the rpm of the P/S. It's a smartpower 300w. If the RPMs raise I cannot tell. I do monitor the output temp of the P/S, using the DigitalDoc5. It remains fairly constant...29/30C.

I do have a slot fan under the Video card....running about 1/2 speed.

Right now there is a front case fan, controlled by the DD5.....only turns on at high cpu loads.

Author:  Gandalf [ Sun Apr 06, 2003 2:09 am ]
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So how do you get the air out? :/

Author:  Bluefront [ Sun Apr 06, 2003 4:36 am ]
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First-off the input volume is not that great....that 80mm fan runs at 2350rpm(about) at an idle. But it's output is directed at the hottest points of the board....cpu, ram, chipset.

There's the P/S output and the slot fan output. Both outputs combined are somewhat less than the input. So this is a positive pressure case. Now however tightly the case is sealed, the excessive positive pressure will escape easily...around the I/O ports for instance. So the positive pressure is not very great..just enough to prevent unfiltered air from entering.

Here's a sample of the temps at an idle: about 22C ambient.

psu output.27.5
video card.30.6

Two hours at 70% cpu usage (XP plus Sand Pendulum screensaver)

psu output....28.8
case ............21.8
video card....33.6

Torture test...One hour 100% cpu usage at 31.2C ambient

PSU output..35.5
Video Card...40.7

Hot day and I didn't turn on the AC. It passed the test. The duct fan ran up to about 4000rpm, the aux cpu fan turned on, and the aux front case fan turned on. These other two fans are running 1/2 speed and cannot be heard at all when they start. I usually have the central ac running at these ambient temps, so I imagine these are the highest temps I will ever record with this setup.

My hard drives are outside the case in a separate enclosure. All temps were taken with DigitalDoc5 sensors and verified with a non-contact infrared digital temp meter. So I'm certain they're correct.

Author:  Gandalf [ Sun Apr 06, 2003 7:14 am ]
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I probably do need a duct like that. sounds a very nice one and I guess it would help cool my SLK800 :)

Author:  Bluefront [ Sun Apr 06, 2003 4:57 pm ]
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If you were willing to endure higher cpu temps, the main duct fan could be much slower. Right now I have to get behind the computer to hear the thing....but it could be quieter.

I'd like to test this setup with a P4. This Celeron is drawing 53 watts which is on the low side....maybe I'll break down and get a P4. The 2.53 is down to about $175.

Author:  Bluefront [ Mon Apr 07, 2003 4:38 pm ]
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So who's going to be the first to duplicate this setup? It's got to be the easiest duct I ever made. The end that holds the fan is a perfect fit for an 80mm.....ablolutely. It can be bent by hand into a square. The fan then slips in. Hold it tight with some tape if you want. It could then be easily changed out.

Until you try a duct setup like this, you'll never know how cool you can run your computer with only one intake fan.....

I uploaded more pictures of the modification process.

Author:  Mark Larson [ Thu Apr 10, 2003 3:38 pm ]
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The 2.53Ghz is a hot mutha. Rather get an AthlonXP if you're looking for something that dissipates less heat.

Author:  Bluefront [ Sat Apr 12, 2003 6:39 am ]
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Well it's finished for now. The mount consists of one spring (had it laying around). I've seen these springs at Home Depot in the hardware dept. The new pictures show as best I could the mount setup. The one end hooks on the edge of the opening to the fan. The other end can be pulled by hand and hooked through a small hole drilled in the filter bracket.

It's a fairly stiff spring, so it only is stretched an inch or so. I suppose it's holding the duct with a 10 pound pull..about. The good points of this mount...you can remove the whole thing by hand, no tape, no screws. Comes off in a few seconds. Also when it's attached it can be adjusted, rotated slightly, moved up/down about 3/4".

The foam (compUSA) seems to have helped the noise slightly..hard to tell. It's also on the inside of the duct. Temps remain essentially the same as before the foam. Next time I have the board out, I'll clean up the edges of the case opening.

Overall I'm happy with the setup....haven't tried it with any other fans, just the PCToys Crystal Maxx. The sensor wire and the 3 pin power wire on this fan are long enough to remove the duct, leaving the fan attached to the duct, and the wires attached to the board.

So who else is going to make one of these? New photos here......


Author:  yaz [ Sun Apr 13, 2003 2:46 pm ]
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hmmm, I dont really understand the function of the spring... :O

Author:  Bluefront [ Sun Apr 13, 2003 3:08 pm ]
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Heh....I know it's hard to see. The spring holds the whole duct tightly against the inside of the case, and yet still allows you to reposition(aim) the fan to blow directly at the cpu.

I cut about 3" off the end of the stock duct, so the fan would be almost over the cpu. I couldn't cut it any shorter. Lucky for me it turned out to be about right. To make up for a cpu that's closer to the rear of the case, you can mount the fan in the duct with an offset....that will blow the air more drectly at the cpu. I didn't have to do that...but it would be possible.

Author:  Bluefront [ Mon Apr 14, 2003 1:13 pm ]
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Today I did a torture test on the setup.....ambient of almost 32C in this room. I did some video rendering which always maxes the cpu. Everything is working as designed, and the variable speed duct fan didn't get too loud, even though it speeded up to 4000rpm.

The final temp results are posted with the other temps in the above post.

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