I need help with transistor operated relay

Discussion in 'The Projects Forum' started by *synonymous*, Nov 29, 2013.

  1. *synonymous*

    Thread Starter New Member

    Nov 29, 2013
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    Hello and thank you!

    I am making a circuit that uses a dual polarity power supply and relay and would like some help if possible. What I need is for the relay to use both the positive and negative taps and for the coil to be switched on based on a ground switch connection. Please take a look at the attached prospective image and offer any advice or magic that you have.

    Thanks
    S
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    How about this ?
    [​IMG]
     
    Last edited: Nov 29, 2013
  3. crutschow

    Expert

    Mar 14, 2008
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    3,229
    Here's a circuit that should do what you want. When the input is grounded both 12V supplies are connected to the relay.

    Switch.gif
     
  4. #12

    Expert

    Nov 30, 2010
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    This is another way to look at it.
    This might not be exactly what you need, but this is a conversation. You can tell us if this will not work for you.
     
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  5. crutschow

    Expert

    Mar 14, 2008
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    I like that. :) It's simple and works since the off switch position is open circuit.

    Unless there's some reason that both supplies have to be switched as the OP shows, but that seems unlikely.
     
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  6. #12

    Expert

    Nov 30, 2010
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    I think he gave us 2 options, not 2 requirements, and his drawing does show a switch that seems to go nowhere in one position. So, I took a stab at it.
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Are you saying that the coil must be connected between the + and - ; or that the relay contacts connect to the + and - ?
     
  8. *synonymous*

    Thread Starter New Member

    Nov 29, 2013
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    Hi and thank you to all the posts!
    #4 looks great, I love using few parts.
    Yes, it is the coil that is connected to the +12 and -12 but in this case, through the transistor. I suppose that I could have been a little clearer but it appears to have gotten the idea across. Yes also that the ground activates the circuit and that an open disables it. The main idea with this circuit is that I wish to load both rails equally using 24v relays and not use 12v overloading one or the other. I have another relay that will trigger this circuit that in one position grounds another device and when energized will ground this circuit into the on position. I will post that schematic when it grows closer to fruition.

    I really appreciate the abundance and quickness in responses
    Thanks again
    Scott
     
  9. *synonymous*

    Thread Starter New Member

    Nov 29, 2013
    22
    0
    Hello again and thank you!

    Would in the following attachment change your circuit create a delay on? If I were seeking about a 1 second delay, what value capacitor would I use? I may be able to swap this circuit in to reduce yet another part in the design!

    Thanks
    Scott
     
  10. #12

    Expert

    Nov 30, 2010
    16,267
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    The capacitor for this circuit turns out to be about 2200 uf but there are better ways to do this. A time delay is not the same as a switch. If you want a time delay, it is much easier done with a mosfet or a jfet. Start another thread so the other denizens will consider it.
     
  11. *synonymous*

    Thread Starter New Member

    Nov 29, 2013
    22
    0
    Thank you #12!
    I think I know what you are saying. The BJT isn't exactly an on/off device in this case. Ok I will start a new thread!!

    Thanks
    Scott
     
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