CPU Cooling with Dual 172 Watt Peltiers

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Detailed article – many pics. — Ji Kuang.

I’ve been watercooling for 2 and a half years now. My first watercooled rig is an 80 watt peltier cooled by a cross-drilled waterblock on an Intel P3 600E @ 900mhz with a full load temp of 15C. When I went onto Thunderbirds, the cross-drilled
waterblock followed but I abandoned the 80 watt peltier because it was insufficient to keep up with the hot CPUs.

The block on the right is the cross-drilled block I used to use, seen here without the brass barbs.

From the cross-drilled waterblock, I
went onto a Danger Den Maze2 and then a home-made waterblock with 2 inlets, cooled
with my first evaporative cooler. This rig was cooling a Thunderbird 1000mhz
AXIA "B" chip which was overclocked to 1600mhz at 2.33v.

This was my previous rig and you can see more details of it here.

I ran this rig for about half a year before deciding to make another cooling rig upgrade. There weren’t many choices left. I didn’t think a waterblock upgrade was going to help much, since the block was besting a Danger Den Maze2. Therefore my next step would have to be some sort of supercooling that could get temperature of my CPU well below ambient.

I considered a few options: I could go with a phase-change system with a compressor ripped from an old fridge or air conditioner. Or I could go with direct peltier-cooling, or with peltier chilled
water, or a combination of both.

I decided on direct peltier-cooling. This was because I did not have the expertise on making a phase-change system as it required some skills in setting up and I don’t have enough confidence in doing a
good job. Water-chilling isn’t as efficient as a direct peltier cooled CPU, so I decided to go with direct peltier. I could add a water chiller later if I wanted to.

Next, I had to decide on the peltier that I was going to use. A highly overclocked Thunderbird at high voltages can put out near to 140-150 watts of heat. Clearly, a 156 watt peltier wasn’t going to cut it. A 172 watt peltier was pushing it also. Therefore, I decided to run 2 172 watt peltiers side by side.

This should keep a highly overclocked Thunderbird at a cool temperature. Next, I had to acquire the equipment to make this plan a
reality. Some of the pictures are pretty low quality due to the bad focus my camera gives me, so please bear with them.

The first thing that I contemplated was the waterblock that I was going to use. My previous waterblock was certainly out because of its design and the 4 holes. The only commercial waterblock designed to house dual peltiers is the Danger Den Maze2-2. I am a lover of high flow-rate and with dual peltiers, it was even more important to have fast flow.

Even though the new Maze2-2 has improved flow rate, I wanted something even faster. There was nothing that fitted this
out there, so I decided to make it. I had to come up with a design for the waterblock. Something with low flow rate cut and huge surface area would be good, something in the style of heater cores that perform so well compared to winding radiators. This is what I came up with:

It’s basically a watersink that is multichanelled. I decided to go with 5/8" fittings for this, firstly because my pump has a 5/8" output and I was confident in coming up with a 5/8" fitted evaporative cooler or radiator setup. Thus, the smallest fitting in my loop would be 5/8" and this would surely help flow rate.

This is the design of the top plate to cover the milled block. It measures 80 x 50 x 3. All measurements are in mm.

The hose barbs are without screw threads and they were to go into the plate and soldered underneath. This would make it look neater compared to if it was soldered on the outside.

This is the design of my coldplate. It measures 80 x 50 x 6.5.

Side A (The side facing CPU)

Note that the 6 holes for the screws on the cold plate are counter sunk for easier insulation.

Side B

Side view

I decided to use a 6.5mm thick cold plate because anything thicker wasn’t going to improve heat dissipation by much (according to thisarticle) and was going to add a lot of weight to my block. To get enough clamping pressure on the peltiers, I went with 6 screws instead of the usual 4 screws like in the Maze2-2. However, after the block was made, I realized that having the 2 center screws would make it impossible to hold a 50x50mm peltier.

This waterblock coldplate design can hold 2 40x40mm peltiers (such as
the 120 and 172watt peltiers). If you want to make one that can hold a 50x50mm peltier, then don’t incorporate the 2 center screws. Some people have said screwing down the Maze2 coldplate causes it to warp. With 2 screws in the middle, it is certainly not happening to mine.

I was going to use the 4 holes mounting technique and thus I had to incorporate 4 bolts to the coldplate. Thus, the side of the coldplate facing the CPU had to be drilled to around 4mm deep and tapped so that 4 bolts can be screwed in.

Ji Kuang

This is the design of the waterblock itself. It measures 80 x 50 x 19.

Side A (The side facing the hotside)

Side B

Side view

I decided that the base was to be milled to 2mm deep because I’ve had better temperatures with a thinner base plate before. Some people argue that a thicker base plate is better but this is not what I found from my own experience. Also, with the same thickness of block, a thinner base would mean higher surface area.

Special thanks to weazel666 from the
tekforums for helping me with the graphics.

Now that the design was on paper, I went shopping for the parts to make them. Here are the materials to make the block and coldplate.

These materials cost me around US$6. Together with the design, I passed them over to a machinist who helped me make my block. I did not do it myself this time because I wanted to save myself some time and effort.

While I was waiting for the waterblock to be made, I was rather worried that he might get some parts wrong, especially the distance of the 6 screws from the edge of the block and I would end up with a block that was unable to house the 2 peltiers. Thank God the end product was exactly as I had wanted. I paid him about US$27 for his service – well worth it, I feel. Here’s the picture of it before I polished it up. Beside it is my previous waterblock:

Here are some more pictures of it.

Here it is with the 2 peltiers with a layer of Arctic Silver II on both hot side and cold side of the peltiers:

Before I screwed the cold plate onto the waterblock, I dipped the metal screws into some silicone grease to prevent thermal leak between the cold plate and the block. I also cut some insulation tape to act as insulative washers before I screwed the metal screws into the counter-sunk cold plate.

I fitted the cold plate with nylon bolts instead of metal ones because I didn’t want the cold plate to lose its coldness to the bolts. Also, if I had used metal bolts, I would have to insulate them from condensation. From my experience, nylon bolts can offer strong retention power if they are used with tough springs and washers.

Yes, they bend easily, but the weight of the block and cold plate should not be resting on the bolts but on the springs, washers
and the screw threads.


Ji Kuang

Now, I had to decide on the setup to cool the water. I could use my bong, as evaporative coolers can take care of the huge heat load the 2 peltiers and CPU put out.

However, with the high water temps, evaporative rate is going to be very high and the constant refills could become a chore in the long run. Therefore I decided to go with a radiator setup. However, not many radiators can cool the water effectively and the big ones were going to cut down flow rate a lot.

Thus, I decided to go with a dual loop setup since I have an extra pump collecting dust. One loop will be the main waterblock loop on a 3000L/hr pump and the other will be a loop cycling reservoir water on a 1200L/hr pump. I decided to go with a multi radiator setup this time. Here’s the 3000L/hr pump I was going to use, modded to be inline with some plumbers goop and a hose barb.

Here’s the 1200L/hr submersible pump also modded to be inline with plumbers goop and hose barb, so that the pumps do not heat up the water much with their heat:

Time to pick the radiators I was going to use.

I was using this dual loop setup to cool my Thunderbird 1333 at 1780 MHz, AYHJA at 2.16V and water temperatures stabilized at 3-4C above ambient. I burned in with CPU K7Burn program running my chip at 1780 MHz, 2.25V with the 2 172 watt peltiers at 20.5V and the water temperature rose to 5-6C above ambient.

I wanted to lower the temperature of the water and, in so doing up, the peltier voltage to try to get a drop in CPU temperature. Therefore I did what most people think is an overkill: I added another loop.

This is the 2200L/hr pump I used for the third loop, modded to be inline as well with some plumber’s goop and JB weld like substance. The reason why my pumps are all submersible is because they cost much less than pumps that are able to work inline. I bought the 3000L/hr pump for US$25, the 1200L/hr pump for US$13 and the 2200L/hr pump for US$16.

Here’s my collection of radiators:

Most of them are used and I got them for free from a neighbour who deals with auto parts. I can just visit his shop and get 2-3 radiators per week. Some of them I bought from motorbike shops for cheap. Look at the big black one here:

It can hold 8 120mm fans with some room left for a shroud. However, it is not the multichanelled heater core type but a flat-tubed winder, so I gave it a pass as flow rates would be hugely impacted.

This is one of the radiators I’m using on my third loop. It’s designed in the style of heater cores with flat parallel tubes.

This is the other heater core I was using on my third loop. It developed a leak one day at the copper elbow epoxy connection, so I removed it.

Fitted with 2 strong 120mm fans, it cools very well. Here’s the flat-tubed winder I chose for my second loop: