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Thread: Encoder for stepper motor

  1. #49
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,

    Hmmm. Here are some thoughts:

    The USB cable seems like it is excessively long and coiled up.

    The USB cable doesn't seem to have a Ferrite ring

    The USB cable seems very thin? You might check the shield continuity from one end to the other (should be less than 1 ohm)

    You might check the USB shield connections as it goes through your panel. The shield might not have connectivity from both sides of the panel and/or it may be connected to the panel which may not be desirable.

    The diode across the Relay coils must be fast switching

    What power supply are you using for the relay coils? Is it is isolated from everything else?

    Consider using Solid State Relays to possibly avoid the issue.

    Try disconnecting whatever the relays are controlling to determine if it is the coils causing the problem or the device the relay is controlling.

    Is the PC earth grounded?

    Regards

    TK
    http://dynomotion.com


  2. #50
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    Default Re: Encoder for stepper motor

    Quote Originally Posted by TomKerekes View Post
    Hi ssjantonio,

    Hmmm. Here are some thoughts:

    The USB cable seems like it is excessively long and coiled up.

    The USB cable doesn't seem to have a Ferrite ring
    I have already changed it for a shorter cable with ferrite ring , thank you for the recommendation.

    The USB cable seems very thin? You might check the shield continuity from one end to the other (should be less than 1 ohm)
    I have checked it with the new cable and it has continuity, 0.1ohm

    You might check the USB shield connections as it goes through your panel. The shield might not have connectivity from both sides of the panel and/or it may be connected to the panel which may not be desirable.
    From computer to the USB Isolator it has continuity with the ground Earth, then, from de USB Isolator to KFLOP it has continuity with DC Ground hole of KFLOP but does not have continuity with earth ground.

    The diode across the Relay coils must be fast switching
    Ok, I have UF5408 and NTE569, wich of them do you recommend? Or another model?

    What power supply are you using for the relay coils? Is it is isolated from everything else?
    I have a 24V Delta power supply, it is used only for the external buttons and the coils.

    Consider using Solid State Relays to possibly avoid the issue.
    Ok, I will to replace them.

    Try disconnecting whatever the relays are controlling to determine if it is the coils causing the problem or the device the relay is controlling.
    After changing the USB cable the problem is still present.

    The three contactors that you can see in the picture are controlling:
    1.- A trifasic async motor of 1/8HP (Screw conveyor transporter)
    2.- A monofasic 120V motor of 1/8HP (Coolant pump)
    3.- A monofasic 120V motor of 80W motor (Oil pump)

    I have disconnected them, and the problem is gone, so it is not problem of peak voltaje in the coil, right?


    Is the PC earth grounded?
    Yes, it is connected to earth ground.

    Best Regards!



  3. #51
    Gold Member TomKerekes's Avatar
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    Default Re: Encoder for stepper motor

    Hi ssjantonio,


    I have checked it with the new cable and it has continuity, 0.1ohm
    Did you measure through the shield (shell to shell)? Or through the GND wire?

    Ok, I have UF5408 and NTE569, wich of them do you recommend? Or another model?
    I'm not an expert but I think those are a little slow (50ns and 250ns). I've seen references that show the voltage spike rising in 200~300ns. Something like a 1N4148 should start conducting in 4ns before the voltage has time to rise much.

    The three contactors that you can see in the picture are controlling:
    1.- A trifasic async motor of 1/8HP (Screw conveyor transporter)
    2.- A monofasic 120V motor of 1/8HP (Coolant pump)
    3.- A monofasic 120V motor of 80W motor (Oil pump)

    I have disconnected them, and the problem is gone, so it is not problem of peak voltaje in the coil, right?
    I think that is probably correct. However there might be a possibility the coil sparking is radiated through the wiring. Disconnecting the wiring would then cause the problem to go away. Did you leave the wiring intact to the relay but disconnect the power? Or did you disconnect the wiring from the relay contacts. You might also try them one at a time to see if it is one that causes the problem.

    Regards

    TK
    http://dynomotion.com


  4. #52
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    Default Re: Encoder for stepper motor

    Hi tom, I have changed the coil relays for solid state relays, and the problem was gone, I post my comments for reference of other users. Thank you very much!

    Quote Originally Posted by TomKerekes View Post
    Hi ssjantonio,
    Did you measure through the shield (shell to shell)? Or through the GND wire?
    I checked Shell to Shell and GND wire too, both of them has near to 0 ohm (I say near to 0 because my ohmetro shows 0 when the resistance is below 1ohm).

    I'm not an expert but I think those are a little slow (50ns and 250ns). I've seen references that show the voltage spike rising in 200~300ns. Something like a 1N4148 should start conducting in 4ns before the voltage has time to rise much.
    Yes you are right, those models was slower, I changed the diodes for 1N4148, and the problem still persist after that.

    I think that is probably correct. However there might be a possibility the coil sparking is radiated through the wiring. Disconnecting the wiring would then cause the problem to go away. Did you leave the wiring intact to the relay but disconnect the power? Or did you disconnect the wiring from the relay contacts. You might also try them one at a time to see if it is one that causes the problem.
    With the monophasic motors the problems was much less frequently, maybe 1 in 50, but with the trifasic the problem happends 1 in 10, or sometimes more frequently, I think the theory of the coil sparking is correct.


    Thank you very much for your help!

    Regards.



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