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LED 120 Volt Pilot light

Discussion in 'Electronic Basics' started by Macdonald, Aug 11, 2005.

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  1. Macdonald

    Macdonald Guest

    I have used Diodes and resistors in several places to as indicator lights to
    tell me if an outside light is on etc. If it's on then the light lights up
    If not then its out. Simple.

    I have a 120 volt line that runs down to the lake and has a water pump
    running off of it. I want to use the same method e.g. leds, etc to tell me
    when the pump is running, drawing power from that 120 Volt line down at the
    lake. It is the only thing on that line. So it should work fine if I put the
    indicator up near the house. However, the outlet that the pump is plugged
    into is for obvious reasons a ground fault receptacle. It has a little pilot
    light of its own that just stays on all the time. My questions are as

    1. I guessing that if I put in my own LED power indicator it will light up
    whether the pump is on or not because of the pilot light at the pump drawing
    power. Is there a simple way around this.

    2. If I put in a different ground fault, e.g. one that had no light in it.
    Would that work. Im not exactly sure how they work, accept that they trip
    when there is a contact with ground I suppose. What I don't know is if they
    are drawing power to do their job which might light up my LED.

  2. Rich Grise

    Rich Grise Guest

    Use a current transformer. When the pump is drawing current, the
    secondary of the current transformer will want to cause a current
    flow - this is why the "burden resistor" is so important - it
    will develop as many volts as it needs to to make its current flow.

    But if you have diodes instead of resistors, the current can flow
    with Vf of the diode across it.

    Take the pump current, divide it by 0.02 (a typical LED current), and
    use that many turns on your CT. Put the LED directly across its
    leads, with another diode (LED or ordinary) in antiparallel.

    Piece of cake!

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