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Switch 220V with a microprocessor

  1. Nov 1, 2004 #1
    Hello all,

    I would like to ask how one can switch on and off a device connected to 220 V using one microprocessor output (5V). I know I should use a relay but can I use only one relay, or a cascade of two relays? Any suggestion for what type of relay I should use?

  2. jcsd
  3. Nov 1, 2004 #2
    One relay on the hot side of the 220V line is sufficent. You will need a transistor to drive the relay though since I doubt the uP's port has enough current capacity to drive it.
  4. Nov 1, 2004 #3


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    Look into solid state relays (SSR), one of these will eliminate arcing and the resulting contact corrosion.
  5. Nov 1, 2004 #4


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    Might want to look into X10.
    All set up to do this.
  6. Nov 1, 2004 #5


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    You should probably use a contactor rather than a relay for such high voltages. A simple power MOSFET is all you'd need to drive it with a 5V uP signal.

    - Warren
  7. Nov 1, 2004 #6


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    Someone mentioned switching the hot side of the 220 volt line. In the U.S. BOTH sides of the line are hot on a 220 volt circuit. There IS no neutral. A clothes dryer for example is a 220 volt device and technically has a neutral because the motor runs on 120 volts. But a 220 volt device such as a water heater has NO neutral. There is a 3rd wire run but it is a ground and is not meant to carry current. In your case it is advisable to switch both of them regardless of the device used to switch.
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