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Yet another Cut-off Relay Switch

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Elecnoob, Oct 22, 2008.

  1. Elecnoob

    Elecnoob New Member

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    Hello all, new to this forum.

    I'm looking project that will cut off 120v AC 15am plug-in type device when another 120v 15am plug in device is energized. I tried googling it but found nothing. Anything simple a non-EE type guy like me can build? A link to a project would be perfect. Thank you.
     
  2. Willbe

    Willbe New Member

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    A current sense resistor on the second 15A circuit that drives a normally closed relay for the first one, through a transistor? If so, what minimum current must the second circuit draw in order to cut off the first?
     
  3. Elecnoob

    Elecnoob New Member

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    One goes on, one goes off..that simple. Im looking for a simple solution without having to spend $100+ for a whirlpool type componment. Something that could fit into a large junction box.
     
  4. dave

    Dave New Member

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  5. KMoffett

    KMoffett Well-Known Member

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    Here's a circuit that I used to turn my ShopVac ON when I turned ON the table saw...except I modified the schematic to meet your spec. The Switched Outlet is normally ON. When the Sensed Outlet device it turned ON the Switched Outlet device is turned OFF.

    Ken
     

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    Last edited: Oct 22, 2008
  6. Boncuk

    Boncuk New Member

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    Here is a transformerless version.

    L1 is a kind of 'antenna' sensing the electric field around the cable to the master device. T1 through T3 make a 'super transistor' activating the relay when the electric field is sensed.

    Make L1 using 5 to 10 turns of stranded isolated wire wound around the master cable.

    To reverse the function of the circuit connect the slave load to terminal 14 of the relay.

    Boncuk
     

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  7. Willbe

    Willbe New Member

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    So wrapping 5 to 10 turns around a wire inside your house circuit breaker panel can make a current sensing xformer for much less than Grainger wants.
    There was a much earlier post about a guy who wanted such a transformer.
     
  8. Boncuk

    Boncuk New Member

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    this is a current sensing transformer. The black wire is the secondary side. Current flows across the enamelled copper wire.
     

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  9. Willbe

    Willbe New Member

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    L1 is disconnected at the top end in your diagram. Is this really a capacitively coupled voltage sensor or a typo?
     
    Last edited: Oct 22, 2008
  10. D-cat

    D-cat New Member

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    As long as you wrap around a power lead... Most house wiring includes a power lead and a ground return path, wrapping around both in the typical wire casing should cancel eachother's EMF to effectively zero. If you wrap around only a power lead (typically black), then yes, you can get the desired effect.

    Hmmm, good Q. It might work as drawn with sufficient current through an AC circuit. Otherwise, I'd think it'd have to connect to ground as a typical transformer?
     
  11. Boncuk

    Boncuk New Member

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    L1 represents an antenna receiving the electric field around the supply wire. So only one end has to be connected.
     
  12. Boncuk

    Boncuk New Member

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    Master-slave-circuit

    The sensor wire around the master cable is not a transformer. The transistors connected to the wire are high impendance amplifiers. The sensed voltage is rectified at the base-emitter junctions and charges C3. (not included in the preceeding picture)

    Sensitivity might be adapted by changing the value of R2.

    Life and Neutral must not be changed. Otherwise the relay might be activated at all times. Also, if a single pole switch is used for the master life must be switched. Switching neutral has no effect.

    Boncuk
     
  13. Boncuk

    Boncuk New Member

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    Here is the revised circuit and a picture how to connect components.

    To prevent electric shock isolate the open end of the "coil" using heatshrink.

    Boncuk
     

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    Last edited: Oct 23, 2008

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