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Relay

Discussion in 'General Electronics Discussion' started by Stoneww, Jun 28, 2017.

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  1. Stoneww

    Stoneww

    42
    2
    Apr 18, 2017
    Hey I've been trying my best to get this relay circuit working for about a week now, help would be very much appreciated :)

    I've managed to get the comparator working as well as the transistor. However the transistor wasn't enough to power a motor. I've tried the motor with a relay but even after numerous guides I couldn't do it. As I understand the principle is that if the coil is powered an EM field will pull a switch and activate a circuit which has a different power source.

    I haven't been able to successfully connect this on my breadboard. Could anyone show me how it would be done? Below is a circuit diagram of how I think it works and also a diagram I used as a reference.
    [​IMG][​IMG]
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,316
    2,593
    Nov 17, 2011
    Your diagram is o.k.
    What's missing is: where does IO1 or IO2 come from? This should be a signal that switches between 0 V (relay on) and open circuit (relay off). An I/O port of a microcontroller will not work. You'll need a more powerful driver, e.g. a transistor.

    By the way: do not use the breadboard for the mains side of the relay. A breadboard isn't menat to be used with mains voltage. Use some wire and solder it t o the relay's terminals, then connect only the coil side to the breadboard.
     
    Stoneww likes this.
  3. Minder

    Minder

    3,066
    657
    Apr 24, 2015
    The .png pic shows it, you could also use a 2n7000 fet if driven from a comparitor.
    M.
     
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  4. Stoneww

    Stoneww

    42
    2
    Apr 18, 2017
    Oh dude not that diagram, I mean't the diagram that I have left as an attachment
     
  5. AnalogKid

    AnalogKid

    2,485
    715
    Jun 10, 2015
    The circuit will work better if you swap the two comparator inputs (to change the output logic polarity to go high when you want the motor to run) change the transistor to an NPN (with base resistor) or N-channel MOSFET (2N7000, 7002). The gate or emitter goes to GND and the collector or drain goes to the coil. This drives the relay with a saturated switch instead of an emitter follower. This reduces power dissipation in the transistor and puts more voltage across the relay coil.

    ak
     
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  6. duke37

    duke37

    5,364
    770
    Jan 9, 2011
    You need a npn transistor (2N2222) or n channel fet.(2N7000)

    Edit. Nothing like saying the same thing twice:)
     
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  7. Stoneww

    Stoneww

    42
    2
    Apr 18, 2017
    Thanks for the help :) , turns out the problem was just that 9V wasn't enough for the coil but 18V did the trick.
     
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  8. Minder

    Minder

    3,066
    657
    Apr 24, 2015
    The relay didn't have a rating on it??
    M.
     
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  9. Stoneww

    Stoneww

    42
    2
    Apr 18, 2017
    It did but clearly I am blind :D
     
    [email protected] likes this.
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