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Do I really need 1 square inch per watt ???

Discussion in 'Electronic Basics' started by [email protected], Nov 13, 2005.

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  1. Guest

    I found these really cheap ($0.29) 10 ohm 20 watt power resistors in a
    TO-220 case. They are a TEPRO TO-220 style thick film heat sink
    devices. I was planning on combining these together in various
    configurations to make a power resistor in the neighborhood of about
    10-30 ohms 500-1000 watts. I plan on mounting a bunch of these on an
    aluminum plate as a heat sink. Using the 1 in^2 per watt rule of thumb
    I would need 500 in^2 - 1000 in^2 of surface area. Is this really true
    or could I get by with a smaller plate and a cooling fan? For the 500
    watts that would amount to about a 24" x 24" aluminum plate. What
    would be the best heat sink solution? I really like the small size and
    price of these TO-220 power resistors, but are they going to be too
    much of a hassle to heat sink? Should I maybe go with a bunch of
    $0.69 15 watt square prism shaped power resistors? Any advice would be
    greatly appreciated. Thanks
     
  2. For that power, you do need a REALLY GOOD heatsink - like a large
    aluminium extrusion (or two) with lots of fins, and a fan.

    A portable electric heater is about 1000 watts - that's the amount of
    heat you're talking about.



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  3. Doug McLaren

    Doug McLaren Guest

    | >Using the 1 in^2 per watt rule of thumb
    | >I would need 500 in^2 - 1000 in^2 of surface area. Is this really true
    | >or could I get by with a smaller plate and a cooling fan?
    ....
    | For that power, you do need a REALLY GOOD heatsink - like a large
    | aluminium extrusion (or two) with lots of fins, and a fan.

    The new dual core Intel paxville Xeon cpus use nearly 200 watts per
    chip at full power. All that heat goes through a square that's about
    one inch square into an elaborate heat sink, with a big fan. If the
    fan fails, the chip burns up in a few seconds.

    (At least the older Athlons did. I've heard that Intel P4s are better
    about throttling back on the power when they overheat, but even so, at
    200 watts, I wonder if it could shut down enough and quickly enough to
    save it's own skin.)

    Just an example of how not to do things :)
     
  4. Bob Eldred

    Bob Eldred Guest

    If you want to waste that amount of power, you are probably doing it on a
    short term intermittent basis for testing purposes and not continuously
    unless you are making a heater. Is that correct?

    For that, you can mount several of these resistors on a small aluminum plate
    and immerse the plate with resistors into a coffee can full of water. This
    will dissipate a KW easily for a while. As the water boils off, add more
    water. I've done a 10KW load this way and it works great. Depending on the
    voltage you may or may not have to insulate the leads and/or the can. For
    high voltages, oil can be used instead of water but water works better. It
    looks like your voltage is in the 100 to 200 volt range. I'd insulate the
    leads with RTV silicone goop and isolate the can from conduction to anybody
    or metal object. Be safe.
    Bob
     
  5. Jasen Betts

    Jasen Betts Guest

    so $15-$29 in parts plus heatsink, paste, bolts, interconnect, and 50-100
    holes to measure mark and drill. any reason why you're not planning on using
    a hank of nichrome wire and a fan.
    You may be able to run the resistors at a higher temperature than
    transistors can handle.
    one with fins and a fan?
    go with a heating element if you can find one with the right impedance,

    Bye.
    Jasen
     
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