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Water-Cooling Experiment |
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Putting it in, Firing it up, Results and Conclusions
anyone else nervous?
I ran the CPU at 2.2v because that was what it needed with the peltier by itself. As I've already said, it would boot 98 at 616MHz but would crash pretty soon thereafter. Also, due to my dodgy Maxtor hard drive, I had to turn off UDMA because it didn't like the overclocked PCI bus at 616MHz. So, I filled the bucket with water, let the pump run for a minute or so (to make sure the water-jacket was nice and cold) then cranked it up at 616MHz. It booted as expected, and cruised happily along for about 30 minutes of Unreal flyby+SETI before crashing, by which time the mobo temp sensor was reporting 37C. I put my hand into the bucket of water and it was quite warm.
Never satisfied with what I have, I put some fresh cold tapwater into the bucket and tried for 117MHz FSB, which is 643MHz core speed. The great thing about this speed is that the AOpen AX6BC-Pro has 2 options for your PCI speed at that FSB speed - one of which is 29.75MHz! This means the PCI is actually underclocked, which let me turn the UDMA back on for my hard disk. To my surprise it booted, loaded Unreal, ran fine for about 20 minutes until crashing with a bucket of very warm water as before. Here's some pics I took at 643:
Needless to say, I liked the taste of this speed. To prove it was really the heat and not the CPU just failing to cope with the speed, I got another bucket of fresh water and put 2 trays of ice-cubes into it. This ran at 643 for almost an hour, until the ice-cubes melted, the water heated way up and bang - you get the picture. :) During that hour I unzipped files, ran Prime95, SETI@Home, the Unreal flyby, played some Sports Car GT, copied a 288mb file from one directory to another and did a File Compare on them.. all fine. No errors. No crashes. Woo!
119MHz FSB, or 670MHz core, was a no-go. Locked up at the Win98 login screen, even at 2.4v with UDMA turned off.
In all the excitement I had forgotten about condensation. I suddenly remembered what had happened to the CPU when I first used the peltier. I turned the machine off and pulled the assembly apart but there was no ice in sight - however, some small droplets of water were forming on the edge of the peltier. Hmm. Condensation occurs when warm moisture-laden air comes in contact with something that cools it rapidly (like, the cold side of the peltier). So I figure if I can stop air getting to the peltier, I can stop condensation. I bought some "Dow Corning RTV Sealant - 732 Electrical Sealant" in a big tube for $7.00 at Dick Smith.
This stuff is great - it's like liquid Minties or very thick toothpaste - you squeeze it on, smooth it around etc and in 24 hours it's turned into silicone rubber. It has a heat tolerance of -54C to 200C (they warn you that at >150C it will give off formaldehyde odours, which will basically kill you, though). I used this to completely fill the gap between the CPU's ceramic casing (the black bit with the pins in it) and the bottom of the watercooler. This completely enclosed the peltier in an airtight seal. I made sure to push it under the peltier so the cold side should have no air in contact with it now. Also, it covers the back of the CPU's pins in a non-conductive waterproof shield. That has to be a good thing. Lastly, it sucks moisture out of the air during the curing process - so I figure any air trapped inside the assembly will be dry by the time the sealant has set. Maybe.
the white stuff is the sealant
So! For now, I'm pretty happy. My current issues are:
(a) How to keep the water at room temperature or below (small radiator, another stage of peltiers or similar)
(b) Getting a more powerful peltier - this one (40W) is only just coping, I think
(c) A more accurate way of measuring the temperature..
(d) Build the reservoir+pump unit into a minitower case to put next to the computer, or a little box that fits under the mid-tower.
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