Relay Switch From Transistor

Discussion in 'General Electronics Chat' started by scmojks, Nov 14, 2012.

  1. scmojks

    Thread Starter New Member

    Nov 14, 2012
    6
    0
    Hi

    Attached is a section from a manual from an industrial camera.

    The following is also a snippet from the manual:

    The camera is equipped with one physical output line designated as Output Line 1. The output line
    is accessed via the 6-pin connector on the back of the camera.
    The output line is opto-isolated.
    recommended operating voltages. The absolute maximum voltage is +30.0 VDC. The maximum current allowed through the output circuit is 50 mA.
    A low output signal from the camera results in a non-conducting Q1 transistor in the output circuit.


    Voltage Significance
    < +3.3 VDC The I/O output may operate erratically.
    +3.3 to +24 VDC Recommended I/O output voltage.
    +30.0 VDC Absolute maximum; the camera may be damaged, if the absolute maximum is exceeded.

    A high output signal from the camera results in a conducting Q1 transistor in the output circuit. [/I

    I want to switch a 24VDC relay coil with output line 1 and was wondering where do i connect A1 & A2 of the relay so that when the ouptut is turned on the relay will switch on,
    Also if using a 24VDC 2.1 A do i need a resistor to limit the current in the circuit to 50mA?

    Any advise would be appreciated

    Thanks
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Connect your relay between pins 4 and the battery positive,measure the resistance of the relay coil,and divide it into 24 volts to see how much current it takes, so if your coil is over 480 Ohms your ok, if its less then i would use a slave npn transistor like this..
     
    Last edited: Nov 14, 2012
  3. scmojks

    Thread Starter New Member

    Nov 14, 2012
    6
    0
    thanks i should have mentioned, i would not be switching the led shown in the attachment. The contact of the coil would be connected to a light drawing 2A
    What i am trying to achieve- is when the output is turned on it closes the coil of the relay which fires on a light connected to the relay contacts (pin 11, 14 of the relay)

    So i connect A1 to the +24V 2.5A supply and A2 to pin 4.
    Then connect pin 5 to GND of the power supply.

    Below are the specs on the relay, it sais the input impedance is 3200 ohm, does this mean its okay so without a current limiting resistor to 50mA


    SSR, 2A, 24VDC
    Control Voltage Range: 16V DC to 30V DC
    Operating Voltage Range: 1.5V DC to 24V DC
    Contact Configuration: SPST-NO
    Load Current: 2A
    Relay Terminals: Through Hole
    SVHC: No SVHC (19-Dec-2011)
    Approval Category: UL Recognised
    Control Current Typ: 7mA
    Control Voltage DC Max: 24V
    Control Voltage DC Min: 2V
    Control Voltage Type: DC
    External Depth: 5mm
    External Length / Height: 15.5mm
    External Width: 28mm
    Input Impedance: 3200ohm
    Input Voltage Max: 30V
    Input Voltage Min: 16V
    Isolation Voltage: 2.5kV
    Load Current RMS Max: 20A
    Load Voltage DC Max: 24V
    Load Voltage DC Min: 1.5VDC
    Load Voltage Range: 1.5V DC to 24V DC
    Must Release Voltage: 10V
    Operating Temperature Max: 55°C
    Operating Temperature Min: -20°C
    RMS Load Current Min: 2A
    RMS Load Voltage Max: 24V
    Series: 34
    Terminal Type: Through Hole
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    745
    yes its ok to put the relay on direct
     
  5. scmojks

    Thread Starter New Member

    Nov 14, 2012
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    so this is the correct layout and i wont blow the camera
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
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    yes, but put the back emf diode across the relay , cathode to +24volts anode to pin 4, this will prevent the transistor blowing.
     
  7. scmojks

    Thread Starter New Member

    Nov 14, 2012
    6
    0
    sorry which diode? You wouldn't be able to explain how the circuit works and why there is no need to limit the current to 50mA

    Thanks
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    The diode prevents the collapsing voltage from damaging the transistor output, when the relay is de-energised, it produces a high voltage opposite in polarity to its source. Any IN4001 to IN4007 diodes will do

    http://www.progeny.co.uk/Back-EMF-Suppression.aspx


    As for the current limit the relay coil is 3200 Ohms, so it will only draw 7 mAmps at 24volts.
     
  9. scmojks

    Thread Starter New Member

    Nov 14, 2012
    6
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    thanks attached is what i think is the suggested circuit?
    is the diode still needed if the relay is a solid state?

    Thanks
     
  10. scmojks

    Thread Starter New Member

    Nov 14, 2012
    6
    0
    anyone have any further suggestions on this?
     
  11. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    try this circuit.....if its a simple relay driver you need,one uses a mosfet in place of your relay
     
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