Running a thermoelectric cooler.

Discussion in 'OT Technology' started by deusexaethera, Aug 12, 2006.

  1. deusexaethera

    deusexaethera OT Supporter

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    I picked up a Swiftech thermoelectric heatsink for about 1/4 of its original price (about $20) and I'm planning out how I'm going to set it up to keep my old Athlon XP 3000 a little cooler than it is right now.

    The thing is a monster. The cooling element can eat up to 226watts, which to me is just stupid, so I'd like to come up with a way to automatically control its power consumption based on the temperature of the CPU die.

    It would be nice if my motherboard had temperature-controlled fan sockets, because then I could use a simple power transistor to use the voltage at the fan socket to control the much larger power feed into the cooling element, but my fans run at full speed all the time so that's not an option.

    I'm going to have to measure the CPU temperature externally, using a flat thermosensor of some sort, but then the problem of how to use the thermosensor to control the power to the cooler crops up. There's no way I could pipe 200+ watts through a thermosensor -- I'd destroy it AND the CPU it's attached to.

    So what I need is some sort of magic box that is designed to accept input from a thermosensor and use that information to control a high-speed fan. The cooler is 12V, so matching the power supply won't be a problem, but the magic box will need to be able to withstand up to almost 20 amps if necessary. It would also be nice if the magic box could be programmed, so I could set the temp-to-voltage map myself.

    Does such a thing exist? Where can I get one?
     
  2. Doc Brown

    Doc Brown Don't make me make you my hobby

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    I'm guessing you are talking about a Peltier cooler?

    I don't know if there is some unknown factor that limits the ability
    to do that with a Peltier.
    But if not, then it would seem to be a basic electronics project.

    You would need some sort of meter for the temp so you could monitor realtime temperatures.

    I would think that a high capacity pot could control the wattage range.

    I don't know where to look for pots with that high of wattage rating, but you might try looking for them in car audio.
     
  3. Doc Brown

    Doc Brown Don't make me make you my hobby

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    Oh yeah, and if this is a Peltier cooler we are talking about,
    make sure you seal the cooler in tight with rtv silicone.
    You don't want any condensation getting to the board.
     
  4. deusexaethera

    deusexaethera OT Supporter

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    The whole point of having the cooler's wattage regulated is to avoid condensation by keeping the CPU within a comfortable range of, say 40 to 50 degrees Celsius. If the CPU is running cool, then the cooler will only use a few watts. If the CPU is running hot, then the cooler will use more watts. What I'm hoping is that there's a device that can do this kind of automated controlling.

    Isn't a pot just a volume control? I mean, that is what I need, but I need a volume control that can automatically adjust itself based on feedback from the thermosensor.
     
  5. Doc Brown

    Doc Brown Don't make me make you my hobby

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    Yep. A pot is a volume control.
    You can probably find a meter that will handle the adjustment too.

    Digikey is the biggest supplier that I know of. If anybody has it they do.

    http://www.digikey.com/
     
  6. Doc Brown

    Doc Brown Don't make me make you my hobby

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    One of the things that throws the project off is the amperage requirement.
    20 amps is huge.
    A controller that can handle 20 amps would cost a bundle.
    But you might be able to use a high amp relay with a decent controller and psu to get the job done.
     
  7. deusexaethera

    deusexaethera OT Supporter

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    I have no intention of using the full capacity of the thing. Considering that my Athlon tops out at 80-82 degrees -- or a full 30 degrees hotter than the rest of the case -- it should take only a modest amount of active cooling to bring it down around 60 degrees.

    The heat is the downside of having a fully sound-insulated case, with air filters on all intakes, and only a single exhaust fan in the power supply. Then again, the full-load temp is only 5 degrees above the idle temp, so despite the heat it's a very stable build. I love Swiftech heatsinks; they're the best non-heatpiped heatsinks I've ever seen.
     
  8. deusexaethera

    deusexaethera OT Supporter

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    Now, I figured out that you meant a volume control, but I thought "pot" was short for "potentiometer", which is a variable capacitor and is used for radio frequency tuning, whereas a volume control is a variable resistor and is used for amperage control. How did these terms get confused?

    Anyway, thanks for the link to the vendor. I'll check them out.
     
  9. Doc Brown

    Doc Brown Don't make me make you my hobby

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    Yeah, I probably use the term pot too loosely.
    Meanwhile to clarify further, I was talking about using an L-pad from a low pass filter,
    which is different than a simple volume control or potentiometer in that it can handle
    the direct signal.
    There might be some available for the kind of wattage you're talking about.

    But anyway, you are wanting to have the voltage varied automatically, so you need
    to use some sort of digital controller.
     
  10. Doc Brown

    Doc Brown Don't make me make you my hobby

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    Interesting. I just did a quick google pic search. Do they make them in all copper?
     
  11. deusexaethera

    deusexaethera OT Supporter

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    No, all their current models have copper bases and high-conductivity aluminum pins. To enhance the heat dissipation of the aluminum, they screw-thread the pins to increase surface area and they fan the pins out in all directions. They DO make a northbridge heatsink and RAM heatsinks with a similar design in all-copper, though.

    I think they made some early CPU heatsinks in all copper, but they were far too heavy. The copper base alone weighs a full pound! Making the pins out of copper would certainly exceed the torsional strength of the CPU socket, and rip the thing right off the motherboard.

    That said, a pound of copper does an amazing job at stabilizing the temperature of the CPU die, so that it doesn't undergo thermal expansion and contraction too fast and kill itself.

    They're expanding quickly into making watercooling blocks and radiators, as well; they've been reviewed favorably, and I'd buy them if I weren't adamantly against the idea of pumping liquid death through the inside of my machine. Besides, with one of their regular heatsinks, my CPU already has only a 5-8 degree range between idle temperature and full-load temperature; I wouldn't gain anything meaningful from watercooling at this point.
     

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