Circuit to detect when a 220V device turns on/off

Discussion in 'The Projects Forum' started by stenaught, Apr 14, 2008.

  1. stenaught

    Thread Starter New Member

    Apr 14, 2008
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    I am trying to build a circuit that triggers when my 220V water heater turns on or off. Eventually I want to collect the data but for now detection would be fine. I think I know a little bit - a voltmeter should drop from 220 VAC to 0 when it's on, or an ammeter would work, but I don't know how to get from theory to a practical circuit.
    Thanks!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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  3. mik3

    Senior Member

    Feb 4, 2008
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    Take care with the 220V AC its dangerous if you dont know.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    At the most simple level, the heater coil's being energized will cause a voltage drop from the breaker panel to the heater, in porportion to the wattage of the heater and the gauge and length of the conductors between the heater to the panel.

    However, it would be much safer to use an inductive pickup to determine current flow on either L1 or L2.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you can get to the thermostat contacts, then a resistor and neon lamp (or resistor, diode and LED) can go across the contacts. Then you will have light output when the heater is off, and no light when on. Pretty easy to use that for a remote indicator.

    A low voltage transformer can also put out a safe 12 volts when the heater is off. Very easy and safe to use an isolated low voltage for signaling.
     
  6. stenaught

    Thread Starter New Member

    Apr 14, 2008
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    Thanks for the advice, everyone. Hgmjr, the example you sited was pretty much what I was looking for.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    The primary advantage to the circuit from discovercircuits is that it is non-invasive.

    hgmjr
     
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