Nc/no contacts

Discussion in 'General Electronics Chat' started by jerrymyersmills, Apr 25, 2011.

  1. jerrymyersmills

    Thread Starter New Member

    Mar 22, 2011
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    0
    Hi
    folks, i have bought an optico isolated relay board for a project.The relay board is going to wired to thermostat.I done majority of the work.What is left now is how to wire the alarm to the relayboard.I want the alarm to sound when tempereture rises too high or goes too low and when there is power outage.
    The problem is the alarm uses 12VDC (it runs on car battery)whilst the output of relay board (fitted with general purpose relay)is 240VAC.I am the 240VAC will damage the alarm .I have seen this type of thing work somewhere else some years back.I heard it is called 'battery backed control circuit'.
    I do not know how to wire the alarm leads to relay board and whether to use 'NC' or 'NO' contacts.
    Any questions welcome!
     
    Last edited: Apr 25, 2011
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Is there some reason why you can't put 12 VDC in place of the 240 VAC? I doubt if the relay cares what voltage is on the contacts.
     
    Last edited: Apr 25, 2011
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
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    If you are trying to use a solid-state relay designed for AC switching in a DC circuit, then it probably will not work. Typically these things use SCR or TRIAC switch elements, and these do not turn off with DC.

    That said, it's not really clear what you are trying to do. Can you please post a schematic?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    As said before, are the relays solid state or mechanical?
    If they are mechanical, AC or DC should be no problem.

    About the NC and NO connections, see the picture I made:

    [​IMG]

    Bertus
     
  5. jerrymyersmills

    Thread Starter New Member

    Mar 22, 2011
    29
    0
    Hi the relay board is equipped with general purpose relays not solid state relays.
    Now half of my problem is solved.The only problem left now is that i want to back up the system with a 12VDC car battery so that in case of power failure the siren will sound .
    Thanks for all your inputs.
     
  6. jerrymyersmills

    Thread Starter New Member

    Mar 22, 2011
    29
    0
    Bertus you are right!AC/DC must not be a problem.How do i back the system with car battery?
     
  7. jerrymyersmills

    Thread Starter New Member

    Mar 22, 2011
    29
    0
    My timeZONE is GMT
     
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