help required switching a LV circuit from a HV source

Discussion in 'General Electronics Chat' started by skydemon, Jan 1, 2007.

  1. skydemon

    Thread Starter New Member

    Jan 1, 2007
    3
    0
    Hi all, I need to build a circuit that will switch a low voltage signal when a high voltage (240VAC RMS) is detected. Basically I have an existing circuit as below:

    |----------/-------------|
    | |
    AC LOAD
    | |
    |------------------------|

    where the '/' is a switch on the active line. (sorry for the crappy drawing :). Once that switch is closed I need to close a circuit between an input and a 5V rail but I am unsure how to accomplish this. The best way I can think of doing it is to wire in a step down transformer/rectifier/filter to drive a relay but this seems overly complicated for the outcome I need to achieve. The other way is to use the 240V switch to connect the 5V rail to the input but I will need someway to isolate the high voltage portion of the circuit.

    Can anyone suggest the best way to do this?

    Cheers

    Mick
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    How about a relay with a 240 volt coil?
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Why would rectifier and filter be needed to drive a relay? A small transformer should be all that's needed for driving a relay.
     
  4. skydemon

    Thread Starter New Member

    Jan 1, 2007
    3
    0
    hmm...yeah in hindsight that was stupid, of course a relay coil could be driving off AC..silly me, however I had a bit of a look around and could not find a relay with a 240V coil. Every 240v relay I found was rated to 240v on the contacts but not the coil...
     
  5. wireaddict

    Senior Member

    Nov 1, 2006
    133
    0
    Howdy, welcome aboard! Potter-Brumfield/Tyco make small relays with 240 VAC coils with up to four "C form" contacts and NTE probably does, too. Check with Google.
     
  6. skydemon

    Thread Starter New Member

    Jan 1, 2007
    3
    0
    cool thanks! ill check it out :)
     
  7. KrisKizlyk

    New Member

    Jan 6, 2007
    8
    0
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