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Newbie for switching using relay

Discussion in 'General Electronics Discussion' started by buch11, Jul 20, 2011.

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  1. buch11

    buch11

    3
    0
    Jul 18, 2011
    hi all,
    I am new kid on the deck.I want to build a switching circuit using relay in such a way that the supply sholud flow through the circuit when relay is open and supply should get disconnected when the relay is on(closed).
    Any help will be appriciated.And I am unaware of the forum ethics so do mention if I am doing anything wrong...
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    Relays can have normally open (NO) and normally closed (NC) contacts.

    NO contacts are open (no current can flow) when the relay coil is not energised. They close (allow current to flow) when the coil is energised. These contacts allow something to be switched ON when power is applied to the relay coil.

    NC contacts are the reverse. They are closed (current can flow) when the relay coil is not energised. They open (prevent current from flowing) when the coil is energised. These contacts allow something to be switched OFF when power is applied to the relay coil.

    You are probably looking for a relay with at least one NC contact.

    As for ethics, being polite, staying on topic, and not posting anything potentially dangerous or offensive will keep you on the good side of the moderators. It's quite rare that we have problems with people who aren't spammers, so you should have little to concern yourself with. Oh, trying to get people to do your homework is another thing (and that may not apply to you). We have a special area for that with hints as to how to ask for help.
     
  3. Kaveyd

    Kaveyd

    15
    0
    Jul 10, 2011
    What do you plan to do with the relay? Getting a better idea of the "big picture" will help determine how the relay needs to behave.

    Relays are commonly used to switch on and off small house electronics (<10A) but this is not the only use. It's also possible that what you have in mind could be accomplished with a different component that is smaller/simpler/cheaper/etc.

    More data!
     
  4. donkey

    donkey

    1,293
    56
    Feb 26, 2011
    if i understand this correctly a spdt relay might work(dpdt are eaasier to find for me though) and if you give us a schematic or even a pic we could possibly help further. if you need help to explain what spdt means feel free to contact me cos this i can cover easily and even make a quick pic to show how it works
     
  5. buch11

    buch11

    3
    0
    Jul 18, 2011
    Thanks to all you ,it seems that the problem is solved as of now .I used the trick suggested by "(*steve*) Super Moderator" ...But i'll post back if there are any other issues.
     
  6. buch11

    buch11

    3
    0
    Jul 18, 2011
    I want to turn lights(220v AC,0.5A) on/off from the parallel port ,and want to use relay for the same.What kind of other components can we use for the same?
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    There are a number of devices used to switch the mains. The most important issue is isolation though. You do not want mains voltage getting into your PC -- and possibly from there into you!

    Relays provide intrinsic isolation between the contacts and the coil. However the coil requires a relatively large current necessitating some form of driver in most cases.

    Solid state relays also provide isolation, but require less drive, and *may* even be connected directly to a parallel port (for example).

    Triacs are probably the most common component used, however they are not isolated and require driving circuits that employ (typically) opto-isolators.

    Any mains wiring requires caution and is best not done unless you know what you're doing.
     
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