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How big rheostat?

  1. Nov 20, 2008 #1
    I have a drymount press that runs on 110 V AC, and is rated at 400 W. It runs too hot and has no temperature control on it, so I need to build a simple control box with a rheostat in it to reduce the voltage reaching it. Not sure what size of rheo to look for. Typically the "work cycle" of the whole unit could run to an hour or more, so heat dissapation on the rheo will be a concern.

    Any suggestions?
  2. jcsd
  3. Nov 20, 2008 #2
    A good rule of thumb is to use a rheostat that is rated for at least 1.5 time the wattage that you are going to use. In this case that would be 110 V, 600 watt. But if heat is a big concern you could even use an 800 watt rheostat. It will be more expensive, but it will probably be worth it.
  4. Nov 20, 2008 #3


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    You mention the rated power of 400 watt. If this is for the heater plus the press, you might be able to get by with something less. Do you know the rating of the heating elements?
    Welcome to PF.
  5. Nov 20, 2008 #4
    You want a switched mode device like a lamp dimmer or motor speed controller. Rheostats haven't been used for power applications for decades.
  6. Nov 20, 2008 #5
    Yup -- I had a big "Doh" after starting the thread. A dimmer switch with a 600W capacity is the answer, and I rigged the whole thing up using a 10' extension cord with molded fittings, whacked off the receptical end and wired it into a 4x4x4 box with a standard recep and a nice faceplate. Life is beautiful -- thanks to everyone for the input!
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