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auto-sensing voltage switch

Discussion in 'Electronic Basics' started by 440roadrunner, Dec 14, 2005.

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  1. I need to find or design a circuit that detects the input line voltage (i
    will be either 110vac or 24vac), and then toggle a switch (or relay) t
    the output path to the proper circuit.

    The logic of the circuit would be something like:

    If line-in voltage is 110v then switch position A
    If line-in voltage is 24v then switch position B

    Unit should handle 2amp max current draw.

    Is anything like this commercially available?
    If not, any ideas?

    I know this is probably something quite simple for you guys...

  2. ehsjr

    ehsjr Guest

    It's a 120 VAC relay. When 24 VAC is applied to its coil,
    nothing happens, and the relay stays de-energized. When
    120 VAC is applied to its coil, the relay is energized,
    and the contacts transfer.

    +------Normally Open
    | +------ Common
    | |
    o o o------ Normally Closed
    ----- | | |
    Vin ------|Relay| | | |
    ------|Coil | |> |<-+

    Shown de-energized. A path for current exists from Common
    to Normally Closed. When energized, that path is opened,
    and a new path is created from Common to Normally Open.

    You can see such a relay at
    Put RLY-453 in the search box. That particular relay
    has two sets of contacts, and the contacts can handle
    12 amps.

  3. Rich Grise

    Rich Grise Guest

    I saw a guy do this to switch from 120V to 240V mains, but
    he added a diode and a cap for some reason, and every time
    I plugged one in to 240 to test, I kinda cringed expecting
    an explosion. It did seem to work OK, however. :)

  4. Pooh Bear

    Pooh Bear Guest

    SGS-Thomson once made an IC specifically to do this ( except it was 120/240V
    ). One important thing to note is that the status needs to be latched once
    detected or you may get a loud band under brown-out recovery conditions !

  5. Jasen Betts

    Jasen Betts Guest

    like Deep Purple -

    Smoke Upon the Water


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