2 AC line inputs -> max 1 output

Discussion in 'The Projects Forum' started by MikeBD, Nov 25, 2008.

  1. MikeBD

    Thread Starter New Member

    Nov 25, 2008
    1
    0
    Hello,

    I'm looking to drive one AC line device when either or both of two AC line inputs are on. Any simple design ideas would be appreciated.

    Thanks.
     
  2. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Simpest design would require only two 120VAC relays. One would need to have 3PDT contacts and the other only needs to have 2PDT contacts. Contact current ratings would have to support the load you have in mind. Wire two small 120vac lamps across the relay windings and you will know which circuit is powering the load.

    Lefty
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It could be as simple as the attached, if your two 120v lines had a common Neutral.

    One SPDT relay. If L2 is not powered, output will be from L1.
    If L2 is powered, the relay will energize and output will be from L2.
     
  4. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    "if your two 120v lines had a common Neutral."

    Yes, but a design based on that assumption would be a safey hazard in waiting. Just an improperly wired AC plug or outlet would cause tripped AC protection breakers or worst. When dealing with this power level it's always best to design as safe and idiot proof as possible.
     
  5. lethalfalcon

    New Member

    Feb 15, 2009
    1
    0
    leftyretro, would it be possible for you to draw a simple wiring guide for using a 3PDT and a DPDT to achieve this? I can understand how the single neutral is a bad idea, but I can't figure out how to get the two relays to interact with each other to switch.

    Thanks
     
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