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Unread 12-20-2002, 03:37 AM   #1
Alchemy
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Default Peltier-powered double loop cooler plans

Okay, here at my folks' for the holidays. I have a lot of tools at my disposal here and maybe a bit of cash, so I'm going to go forward with my plans for my new cooling system. It's a dual loop system - a hot loop cooling a pelt and a cold loop being chilled by the pelt.

The cold loop is going to be a Danner Mag Drive 3 (350 gph, and with sealant mod around housing) pushing a cold liquid to a WB cooled with 220W pelt and then on to the CPU WB, then back to the pump. Second loop is a Maxijet pump pushing water to cool the hot side of the pelt (through another WB) and on to a radiator cooled by a couple 120mm fans, then back to the pump. The Maxijet is the Becooling setup inside its own reservoir.

The pelts and the fans will be powered by two 400W ATX PSUs with their 12V and ground rails spliced together. Each one is rated for 15A on the 12V rail. The pelt is rated for approximately 20A at 12V. The fans shouldn't pull more than 0.5A each.

I have enough parts around that all I need to purchase is the Mag Drive, tubing, the pelt, and the power supplies.

I have no scanner here, so I can't show you any of my sketches, but next time I get a chance to peruse the board I should have some bitmaps so you can get a better idea of what I'm trying to do. Right now I was mostly hoping some of you could look at these products I picked out and give me any opinions on them.

Hopefully, someone could also answer why this PSU is so frigging cheap.

http://216.136.224.156/hoct12/542.html

Unless it's prone to overheating or has a fan that sounds like a buzzsaw, I imagine it's suitable for my purposes. I'd like to know what's wrong with it to justify such a low price, though.

The pelt I plan to grab here:

http://becooling.safeshopper.com/10/121.htm?210

I vaguely remember someone offering the Mag Drive 3 for around $35 somewhere. I know petsmart sells them for about $10 more.

The tubing and fittings will come from US Plastics. I was planning on Norprene since it would work well at the sort of temperature range I was expecting and shouldn't mind the alcohol or whatever else I'll need to keep the viscosity of the cold fluid low. Plus, it might insulate a bit better, and it doesn't cost much more than regular vinyl tubing.

Total cost on this is running close to $150. I'd like to keep it that way.

So, any suggestions from the experts?

Alchemy
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Unread 12-20-2002, 08:52 AM   #2
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That psu has a limit of 180 W for the (combined) power to the 3.3 and 5 volt line: it's unusually low.

Interesting price: I'd rather assume that it's overrated, and work with the assumption that it's got a 300W rating, for safety's sake.

I think you can do better, for less than $20.
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Unread 12-21-2002, 10:10 PM   #3
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I wouldn't actually recommend using two cheap PC PSU's, but if you want to try it, I would recommend the following:

First of all, cut the pelt leads off about an inch away from the device itself. (or less if you feel comfortable doing so) The leads on the pelt are not really adequate for carrying the roughly 19A current draw. (The manufacturers use the small leads so that they fit between the hot and cold plates.)

Run 12V and Ground wires all the way from each supply, to the wire stubs left connected to the pelt. Don't connect the two supplies together and then run a single pair of wires to the pelt. The reason for this, is that most likely the two supplies will be trying to regulate their outputs to slightly different voltages. The resistance of each set of power supply leads will help to balance the system so that one supply isn't carrying a much higher percentage of the total current load than the other.

If there is enough difference between the two supplies, one might source the whole current. Use the same length and gauge of wire (16 AWG at the smallest) to connect each supply to the pelt. Measure the voltage drop across the wire from each supply to the pelt. If one pair of wires has a much higher voltage drop than the other pair, then one of the supplies is carrying a disproportionate amount of the load.

If possible (unlikely with cheap supplies) adjust the output voltages of the two supplies so that they are as close to identical as possible. (Ideally you would do this with each supply loaded for 10A output - 1.2 Ohms.)

Be aware, that the colder your water, the greater the amount of heat leaving your pump via the water. This pump heat will limit the effectiveness of the waterchilling. It may be worthwhile trying each of your pumps on the coldside to see which configuration gives better temps.
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Unread 12-22-2002, 01:39 AM   #4
Alchemy
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Quote:
Originally posted by Since87
I wouldn't actually recommend using two cheap PC PSU's, but if you want to try it, I would recommend the following:
Thanks for the advice, though I don't quite understand entirely how it makes any difference how close the junction of the two PS leads and the pelt lead are to the pelt, given the fact that the resistance of the leads shouldn't be much at all. But I'll try it.

If I can get a hold of a multimeter (I really should!) I'll check the current through each PSU. I'll be borrowing my dad's workshop for a few days, so I'm not terribly worried if I blow the PSUs or do anything else that doesn't result in me electrocuting myself. At worst I'm out about $20, or a few drinks at the bar. Or both.

If I check the voltages and find one PSU is giving me more than another, I should be able to correct it by inserting an appropriately sized resistor, correct? And how large a discreprency would you worry about? One volt? Half a volt?

Would it be foolish to try to wire a 120mm case fan parallel to the pelt? It would only draw off half an amp or so.

Also with the PSU, to get an ATX running without a mobo I need a resistor (10 Ohms? Higher?) on the 5V line and a short on the 5V standby, correct? I remember seeing the exact instructions somewhere but I can't seem to remember them, and don't want to try anything until I'm sure.

Finally, putting the more powerful pump on the hotside is a very good idea, but it's not feasible right now since I know I'll have most of the equipment in a wooden box nearly 3 feet below the CPU, and I really think my cheaper pump doesn't have the strength to get the water up there. I'll try to switch them out just to see, though.

And bigben2k, maybe you can find a better deal, but a 30A 12V supply for $16 plus shipping and a few minutes of wire splicing seems about the best I can hope for.

I'll be buying everything online tomorrow, and I'm estimating a total cost of $130 plus shipping. I may pick up a disposable camera for pics in case I might want to write about it later. It's surely not an original idea, but with the case mods I'm planning and the classy wooden chest I'm fitting most of the equipment in, I think it will look nice enough to warrant some pictures.

And on a personal note, I'm bumming off my family's computer while mine sits on the workbench, and I just now realized the right shift key and menu button on the keyboard of this computer seemed to be glued together.

Ew.

Alchemy
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Unread 12-22-2002, 10:55 AM   #5
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Quote:
Originally posted by Alchemy
Thanks for the advice, though I don't quite understand entirely how it makes any difference how close the junction of the two PS leads and the pelt lead are to the pelt, given the fact that the resistance of the leads shouldn't be much at all. But I'll try it.
At the high currents these pelt run at, the resistance of the wiring becomes a fairly significant issue. I've heard people tell of the insulation on the pelt leads melting with these pelts before.

My 172 Watt Pelt appears to have 20 gauge leads. 20 gauge wire will dissipate 4.2W/foot at 20A. Also, the voltage drop across the wire will be fairly substantial at 0.21V/foot. (From the Becooling picture, it looks like the 220 Watt pelt they sell has thicker wire, but I can't say for sure.)

Here is a link showing resistance at different wire gauges.

Quote:
Originally posted by Alchemy
If I can get a hold of a multimeter (I really should!) I'll check the current through each PSU.
Yes, I'd definitely recommend getting ahold of a voltmeter. I wouldn't use the current measurement mode of a multimeter though. Most handheld multimeters are going to be fused at 10 Amps, and the fuse will blow if you try to measure the full 20A. As you can see from the numbers I mentioned above, the voltage drop across a known length of wire will be easily within the measurement range of any decent voltmeter. Knowing wire length, gauge and voltage drop gives you the current. (V=I*R)Also, the added resistance of the current input to the multimeter will probably be large enough to throw off any measurement of how well the two supplies share the load.

Quote:
Originally posted by Alchemy
If I check the voltages and find one PSU is giving me more than another, I should be able to correct it by inserting an appropriately sized resistor, correct? And how large a discreprency would you worry about? One volt? Half a volt?
I would be seriously worried about a 0.2V difference between the two supplies if the measurements were done at 10 Amp load. I would suggest doing something like this:

Get the pelt setup with watercooling running on the hotside.

Connect both supplies to the pelt with 10 foot of 16 gauge wire between each supply and the pelt.

Connect the voltmeter between the +12V outputs of each supply.

Turn the supplies on as close to simultaneously as you can manage. Note the voltage reading and turn the supplies off quickly.

If the load is balanced between the supplies, the voltage reading will be 0V. If one supply is carrying the full load, the voltage reading will be 0.84V. You are most likely going to see something in between these two readings.

Suppose you target a maximum imbalance of 12Amps-8Amps; the voltage measured between the two supply outputs should be less than 0.17 Volts. If the voltage difference isn't much greater than that, you can probably get the load balanced adequately just by using different wire lengths between the supplies. If you need help doing this let me know.

Quote:
Originally posted by Alchemy
Would it be foolish to try to wire a 120mm case fan parallel to the pelt? It would only draw off half an amp or so.
The only concern I would have here are, "What are the consequences if the power supply fails and thus the fan does also." Unless, the fan continuing to run, could protect some hardware in the event of a supply failure, I wouldn't worry about it.

Quote:
Originally posted by Alchemy
Also with the PSU, to get an ATX running without a mobo I need a resistor (10 Ohms? Higher?) on the 5V line and a short on the 5V standby, correct? I remember seeing the exact instructions somewhere but I can't seem to remember them, and don't want to try anything until I'm sure.
I believe you need to short the "Power Good" line of the power supplies to ground to get them to start. It would probably be a good idea to connect both Power Good lines through the same switch so that the supplies start as simultaneously as possible.

I don't recall what you need as a load resistor, but 10 Ohms sounds about right. You may need a lower resistance but certainly not higher. Keep in mind the power dissipated in the resistor. (P=V^2/R) And definitely search around for more information. Hopefully the supplies will come with documentation telling what they need.

Quote:
Originally posted by Alchemy
Finally, putting the more powerful pump on the hotside is a very good idea, but it's not feasible right now since I know I'll have most of the equipment in a wooden box nearly 3 feet below the CPU, and I really think my cheaper pump doesn't have the strength to get the water up there. I'll try to switch them out just to see, though.
It's my understanding that if it is a closed loop, the additional three feet doesn't matter much. I could be wrong though. Because you don't have a very large difference between your pumps, the temperature difference due to pump heat would probably be very small. I just wanted to toss that thought out there. Other issues very likely will be more significant than the difference in pump heat.
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Unread 01-03-2003, 12:02 AM   #6
Alchemy
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Default Update!

Peltier and most of my plastics have arrived. Got a good deal on Norprene tubing. Yay.

Still looking for a pump and power source, both of which I of course got fvx0red on.

Case work is nearly complete. Still have one more hole to drill in the back. I'm amazed at how well that battery-powered dremel goes through steel.

Most of the components are going to be mounted inside a small wooden chest, and I'm fairly satisfied with the drilling on that as well.

Tomorrow I'll be running by Petsmart to get a Mag Drive 3 and will seal up the CPU area for condensation. I plan to use Neoprene inside the socket, household Goop for the back, layers of electrical tape between the CPU board and the WB, and more Neoprene around the block and socket.

I'm looking forward to getting my computer back together. ProcionRed has been in pieces around the house for over a day now. It makes me sad.

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Unread 01-03-2003, 08:01 AM   #7
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Don't forget the dielectric grease (petroleum jelly) in the socket, for the CPU pins.
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Unread 03-01-2003, 12:48 AM   #8
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maybe i'm a little late on this, but why use 2 pumps? it just seems more complicated. you're using basically a chiller, correct? so, why not this:

res-->pump-->chiller(cold)-->cpu-->chiller(hot)-->rad-->res

or even

res-->pump-->cpu-->chiller(hot)-->rad-->chiller(cold)-->res


make sense?
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Unread 03-01-2003, 01:31 AM   #9
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What I would like to know if why you are not just using the TEC directly on the CPU. It's more efficient, and since you're only cooling the CPU with the water, then there are no drawbacks in comparison.
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Unread 03-01-2003, 08:49 PM   #10
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Quote:
Originally posted by iroc409
res-->pump-->chiller(cold)-->cpu-->chiller(hot)-->rad-->res
I tried that - didn't work...

Using two 172 watt Pelts sandwiched between two Maze 2 waterblocks an E-1250, two BIE in parallel and a Maze3 on CPU. The water actually got much hotter with the Pelt "chiller" than running without it. Proved a valuable lesson to me though. It really drove home the point that Pelts consume 3 to 4 times the power that they pump! So with two Pelts, each dumping 180 watts of waste heat into the water plus about 70 watts from the CPU - way more than two relatively small rads could handle => so the water temp went up instead of down.

You have to go with two seperate loops: hotside and coldside...
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