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  1. #1
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    MB2 ESS relay connection

    Hi guys,
    I am trying to connect a 24Vrelay to the MB2, to operate a pump on spindle start. I have configured the output y302 as a 2nd output for the spindle forward output, and the light follows the on/off as expected.

    Problem is i have connected the coil of the relay to Y302 and 24V on the BOB, but the coil stays energised no matter what the status of the output is... Am i doing something wrong?

    Thanks in advance
    Tim

  2. #2
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    Re: MB2 ESS relay connection

    Did you remember to add the flyback diode to the relay coil? If not, you may have fried the optocoupler.

  3. #3
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    Quote Originally Posted by CitizenOfDreams View Post
    Did you remember to add the flyback diode to the relay coil? If not, you may have fried the optocoupler.
    Dr forgive my ignorance but not sure how or what is needed for a flyback diode.. so no, I didn't add one.
    Could you explain a little please?

  4. #4
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    Re: MB2 ESS relay connection

    A relay coil is an inductive load. When you switch off an inductive load, there is a large voltage spike that can (and does) destroy sensitive electronic elements such as transistors.

    Whenever you control a relay with a transistor (or an optocoupler, which contains a transistor), you must shunt the relay coil with a diode. The diode dissipates the back EMF and prevents the voltage from spiking to dangerous levels.

    The MB2 manual mentions the diode on page 14: http://www.cncroom.com/downloads/MB2...al%20E16R5.pdf

  5. #5
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    Re: MB2 ESS relay connection

    If you need a suggested part, 1N4007 is the popular one.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  6. #6
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    Re: MB2 ESS relay connection

    Thought about using one of the relay contacts on your VFD instead?

  7. #7
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    Re: MB2 ESS relay connection

    Quote Originally Posted by Sterob View Post
    Thought about using one of the relay contacts on your VFD instead?
    That is a good idea. (Most) VFDs have one or two relays that can be programmed for different functions, such as "Alarm", "Spindle rotating", "Spindle at speed" and so on.

    Depending on the current rating of the pump, you may connect the pump directly to the VFD, or use an external relay.

  8. #8
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    Re: MB2 ESS relay connection

    It is always advisable to use an external relay or operator, if you overload and damage the internal relay, it is costlier to fix!
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  9. #9
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    Re: MB2 ESS relay connection

    Quote Originally Posted by Al_The_Man View Post
    If you need a suggested part, 1N4007 is the popular one.
    Al.
    Thanks Al

    I have a curious situation going on..;l
    I bought one of these
    https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

    After the advice yesterday - i think it should be ok for the task.... i have set the y305 output to come on when i activate the spindle (for the pump) and though i see the output light on/off when commanded, the relay state does not change...

    For learning and incase i wanted extra i also purchased this

    https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

    If i wire this up it is the same behavior... and i was curious though the 'input side' only has to COM terminals, and its says pnp/npn input, am i right in thinking that 24V to the COM?

    Whichever is correct i can not get any change of signal lights on the relay or optocoupler board even though the MB2 light is active on/off....

  10. #10
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    Re: MB2 ESS relay connection

    IIRC, the MB2 states a sinking opto output, if using it with a external relay board that has opto input, the recieving opto has to be set to sourcing input.
    Al.
    Attached Files Attached Files
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  11. #11
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    Quote Originally Posted by Al_The_Man View Post
    IIRC, the MB2 states a sinking opto output, if using it with a external relay board that has opto input, the recieving opto has to be set to sourcing input.
    Al.
    So the relay board is opto isolated inputs with a high/low jumper. Am I correct in saying the high would be sourcing?

  12. #12
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    Re: MB2 ESS relay connection

    I would read it that way, see if it works, it should not cause any problems either way, just only one way will work.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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