Logic Level Mains Switching

Discussion in 'General Electronics Chat' started by Mad Professor, Aug 29, 2009.

  1. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Good Day All.

    Upto now whenever I have needed to switch mains powered items on and off I have always used SPST or DPST relays.

    I now need to be able to switch a mains unit on and off via a microcontrollor, the problem is that it can't be a mechanical switch like a standard relay due to the risk of sparks, as the room with this unit does at times have flammable liquids and gases.

    The liquids and gases are unliky to get close to the unit in question, but I want to limit any meny risks as possible.

    The mains powered unit is 240volt 75watt.

    Could you please advice.

    Thanks for your time.

    Best Regards.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Try a solid sate relay
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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  4. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Thank you for your replys.

    I am just reading the wikipedia link.

    As I have never used SSR's before are they just wired in like a standard would be, or does it need extra circuit.

    How meny amps is 75watts at 240vac?

    Best Regards.
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    Depending on the input configuration it may or may not need a current limiting resistor for the input's LED. If the input is spec'd as "3-32VDC", it already has a built in resistor. If the input is spec'd as a voltage drop and a minimum and maximum current, you will need to add the appropriate resistor in series. Unlike (most) DC electromechanical relays the input has a polarity. Also, if you are switching an inductive load like a motor, the output rating should be at least twice the maximum current rating of the motor. And maximum ratings with heavy loads only apply when heavily heat-sinked. But, for your load a 1A rating should be fine.

    Ken
     
  6. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Should work fine.

    Ken
     
  8. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    You best be checking with your local electrical code as they most certainly will have regulation that affects your need.
     
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