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zero cross function

Discussion in 'General Electronics Chat' started by westhomas, Sep 19, 2008.

  1. westhomas

    westhomas New Member

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    I'm shopping for the right relay for my project on Digikey: I want to use a DC signal from a IR sensor to turn on a high voltage (1000W) inductive load. I know what the zero-point crossing means in terms of alternating current, but I can't parse any explanation on the datasheets about what it means to have or not have this functio-zero cross-on the relay. Can anyone articulate this for me?

    Oh, i'm looking at G3NA series and Sharp S102S11 or S102S12 series...
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The advantage of connecting the load at the zero voltage crossing point is that for the current in the load would be zero.
    If you switched on the load at any other time during the cycle, say at maximum voltage of the ac, this would switch the maximum current thru the load.

    If the load was inductive this would generate a voltage spike, recall Lenzs Law
    Emf= - L * di/dt.

    These inductive spikes can damage semiconductors and also cause RFI.

    I would recommend zero point switching for the 1000W inductive load.
    Does this cover what you are asking.?
     
    Last edited: Sep 19, 2008
  3. westhomas

    westhomas New Member

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    ahhh....I see now.

    that answers it perfectly. thanks!
     

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