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Thread: Possible interference from dimmers

  1. #1
    Join Date
    Jul 2018
    Location
    Poplar Bluff, MO USA
    Posts
    2

    Possible interference from dimmers

    Hello everyone. First post here. I was recently contacted by a church group saying they were having problems with lines and interference showing up on the projector screen any time they used any of the 5 dimmers (round dial type) on the wall located about 6' away from the projector and sound equipment. The receptacle the projector is plugged into is a dedicated circuit run with romex and is about 3' from the dimmer bank. The dedicated receptacle circuit is fed from one panel while the lights with dimmers are fed from another. As stated when the dimmers are used lines begin to move around on the projector screen. The lines are always there but only move when you wiggle the dimmers. I took the dedicated recep out of the box and it has a ground (bare copper). If I disconnect the ground from the recep all lines disappear even when wiggling the dimmers. Reconnecting the ground causes the lines to reappear. The dimmers themselves are older and have no ground wire or ground screw (2 wire). The lights the dimmers control are roughly 60' away from the dimmers and control booth. Does anyone have any experience with this? My first thought is to replace the dimmers with modern ones that have a ground. I would also like to try to temporarily remove the dimmers from the equation and just wire nut the wires in the box together just to see if the interference goes away but i didn't have time. I don't have much experience with interference and any suggestions you guys might have is appreciated.

  2. #2
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    7,123
    180728-1027 EDT

    username5000:

    Any dimmer that uses phase shift switching to control average voltage to a load will create RFI (Radio Frequency Interference). This results from the fast switching from "off to on" or "on to off" of current every cycle. The points in the cycle where switching occurs determines the dimming level, and how your interference shows up.

    Unless the dimmer has some sort filtering in it a change of dimmers will probably be no help.

    I may comment more later.

    .

  3. #3
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    38,500
    Try using some sort of RF filter for the projector.
    I live for today, I'm just a day behind.

  4. #4
    Join Date
    Jul 2018
    Location
    Poplar Bluff, MO USA
    Posts
    2
    Thanks for the suggestions guys. I'll see what they've got at the parts house.

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