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One on-off switch for 2 circuits ?!

Discussion in 'General Electronics Discussion' started by Mr.K, Apr 28, 2016.

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  1. Mr.K

    Mr.K

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    Apr 28, 2016
    Hello there. I'm new user in the forum and this is my first thread!:rolleyes:

    Is it possible to have one switch for 2 circuits with different voltages ?!
    I have a simple LED circuit (Imagine the LED is a 12-volt) with 12-volt power source and one 220-volt lamp circuit. I want the leds to get on when the lamp gets on. Would there be any voltage interference ?!

    * I tested the idea in Edison , here is the result . It seems to be no problem , but I'm not sure about real world test!
    Switch : Off
    1.png

    Switch : On
    2.png

    Thanks in advance
     
    Last edited: Apr 28, 2016
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Welcome to EP.

    Never ever try this combination, it is very dangerous!!!

    You can use a relay to isolate the high voltage side from thelow voltage side. Use a relay with a 12V coil and contacts reated for 220V operation and the required current for your 220V load. Make sure the relay has "normally open" contacts contacts.
    Connect the coil side in parallel to the LEDs.
    Connect the contact side to the 220V circuit such that the contacts are closed when the relay is energized.
    Turning on the 12V to the LEDs will activate the relay, the contacts will close and the 220V will be interrupted.

    Make sure everything is safely stored in an insulating box. In addition, as your question indicates you are not well versed in this topic, have your setup checked by an expert (electrician, expert friend or similar) to ensure safety for the user(s) of this setup.
     
    Last edited: Apr 28, 2016
  3. dorke

    dorke

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    Jun 20, 2015
    There are so many ways to do this.
    Do you use the 12V only for the LED?
    Are the LED and Lamp far apart or in different boxes?
     
  4. BobK

    BobK

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    Jan 5, 2010
    Easiest way is to use a DPST switch rated for 220V and the current needed for the high voltage lamp.

    Your circuit will put 220V acroos LED when the switch is off. Also, the LED needs a resistor for current limiting.

    Bob
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    This will pysically work as long as the 220V and 12V are separate (isolated).

    It is very unsafe, however!

    1. I assume the 220V is your mains and 12V are from a transformer operating off mains. In this case it is an illusion to assume these volategs are completely isolated. The 12V power source (e.g. transformer) is at least capacitively coupled to mains. Therefore leackage currents through this capacitance caused by teh AC mains voltage can create a closed circuit (from an AC point of view) making the theory of insulated circuits moot.
    2. You'd bring the dangerous potential (voltage) of the 220V circuit in direct contact with the 12V circuit. The 12V circuit is most probably not designed to withstand such a high voltage . You will thus risk exposing parts of the 12V circuit (which would otherwise be safe to human touch) with a dangerous voltage.
    I really urge you to use an insulated means of switching the 220V (e.g. a relay aas I recommended) and to get expert help in checking your setup before you put it into operation!
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Well noticed.
     
  7. Mr.K

    Mr.K

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    Apr 28, 2016
    Thank you all for your nice explanations ...
     
  8. Mr.K

    Mr.K

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    Apr 28, 2016
    Yes , they are in different boxes
     
  9. Mr.K

    Mr.K

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    Apr 28, 2016
    Imagine that the led is indicator of power on/off status of the lamp. (I know the lamp emits light when it is on , I need another indicator like a LED!)
     
  10. Bluejets

    Bluejets

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    Oct 5, 2014
    BobK likes this.
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