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Solid State Relays

Discussion in 'General Electronics Discussion' started by andrewlines, Aug 1, 2013.

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  1. andrewlines

    andrewlines

    3
    0
    Aug 1, 2013
    Hi

    Hope someone is able to help me out with this project I have.

    Outline
    I have a plinth fan heater run through the hot water heating system that runs on 3a 240v. The fan itself has two speed settings normal and boost.

    What I'm trying to do is to connect this into the room thermostats and the home automation system so when the heating comes on so does the plinth heater. This part is easy by just connecting the heater to the power source and leave the fan on normal setting. But if the temperture in the room is below a certain level say 15C then the boost fan will come on until the temperature increases.

    The room temperature is read by the home automation system whcih can then trigger a 12v relay at certain intervals. So what I was thinking is to have two relays one normally closed that will run the normal fan and when the 12v trigger is received it will open this relay then close the second relay which is normally open for the boost. Though I'm having trouble finding a SSR that is normally closed and not sure how to create a time delay for the relays to switch over.

    Any help with trying to do this would be very much appreciated

    Thanks
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    SSRs are always normally open.

    If you want one that is "normally closed", you have to use your circuit to interrupt current to it.
     
  3. andrewlines

    andrewlines

    3
    0
    Aug 1, 2013
    Thanks Steve.

    Could someone in very simple terms explain how I could do this as a bit of a newb to this area.

    Or maybe there is an alternative solution to SSRs for what I'm trying to do?

    Thanks
    Andrew
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    Why not a normal relay?
     
  5. andrewlines

    andrewlines

    3
    0
    Aug 1, 2013
    Quite likely steve. Though having spent time looking I am now even more confused in the world of relays than before I started !! :)
     
  6. JMW

    JMW

    90
    3
    Jan 30, 2012
    Relays come in 2 flavors, N.O. means when the coil is NOT energized no current flows through the contacts. N.C. means current flows through the contacts when
    de-energized.
    Some relays will have both.
    Next is the coil voltage/current. This should be self explanatory
    Contact Rating. This is the maximum voltage/current the contacts can carry. There will be two ratings Surge and Continuous. Surge would be like a motor starting, continuous again, self explanatory.
    Relays should normally be configured so the de-energized state is the more common.
    For example, if you wanted a power on delay timer to protect a compressor from power transients you would want a timer relay that is N.O and closes when power is first applied, and opens once the predetermined time is reached. This in turn would operate a N.C. contactor to disable power to the compressor, during the delay period.
    A Contactor is a heavy duty relay for operating large motors.
    Then of course you have the mounting options. Many relays/sockets can be mounted on din rails and have screw terminals. Of course you must provide the box.
     
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