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IndustryArena Forum > CNC Electronics > General CNC Machine Related Electronics > Issue with shielded wires on DIY machine
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  1. #1

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    Issue with shielded wires on DIY machine

    Hello,

    I recently finished building my controller for a DIY router machine (image attached).

    I am using 3x these closed loop steppers: https://www.omc-stepperonline.com/cl...5Bnema%2024%5D
    When they arrived I noticed that the motor cable was not shielded.
    I made my own shielded cable assembly for one of the motors, but I am getting some very strange behavior with this (strange for me at least...)

    When I connect the drain wire from that cable to my ground terminal (controller side) and power-on the system the stepper makes a loud whiny noise and nothing really works.
    Any ideas what might be happening ?

    Thanks in advance!!

  2. #2
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    Re: Issue with shielded wires on DIY machine

    did you only connect the shield on one side ??? otherwise you might have a ground loop, or worse some short.

  3. #3
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    Re: Issue with shielded wires on DIY machine

    Unless the stepper motor lines are ran together with sensors etc, twisted conductors should be sufficient, the EMI is self canceling when this is done.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  4. #4
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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Xenofon9 View Post
    Hello,

    I recently finished building my controller for a DIY router machine (image attached).

    I am using 3x these closed loop steppers: https://www.omc-stepperonline.com/cl...5Bnema%2024%5D
    When they arrived I noticed that the motor cable was not shielded.
    I made my own shielded cable assembly for one of the motors, but I am getting some very strange behavior with this (strange for me at least...)

    When I connect the drain wire from that cable to my ground terminal (controller side) and power-on the system the stepper makes a loud whiny noise and nothing really works.
    Any ideas what might be happening ?

    Thanks in advance!!
    You should never run a Drain wire to a Ground terminal a shield needs to be Grounded Direct to the Ground Plane, for a motor cable if you are using a shielded cable, you need to clamp both ends of the cable
    Mactec54

  5. #5
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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Toinvd View Post
    did you only connect the shield on one side ??? otherwise you might have a ground loop, or worse some short.
    Both ends of a shielded motor cable , must have the shield directly clamped to Earth / Ground, this can not cause a Ground loop
    Mactec54

  6. #6
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    Re: Issue with shielded wires on DIY machine

    Actually the theory behind the old established practice of only grounding one end of a shielded cable is to prevent any ground loop that may be present in different parts of a machine and another to impose a field into the shielded conductors. IOW one end of the cable GND may differ from the GND potential of the other, thereby inducing a voltage in the shield if grounded at both ends.
    The now common practice of earth grounding a machine with sensitive electronic equipment is to ground bond all metalic parts of the machine, known as Equi-Potential bonding, this essentially eliminates any difference of potential between grounded points, allowing the new practice of grounding any and all shielded cables at both ends.
    As per the Siemens paper on equi-potential bonding - section 3.
    CNC, Mechatronics Integration and Custom Machine Design

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

  7. #7
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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Al_The_Man View Post
    Actually the theory behind the old established practice of only grounding one end of a shielded cable is to prevent any ground loop that may be present in different parts of a machine and another to impose a field into the shielded conductors. IOW one end of the cable GND may differ from the GND potential of the other, thereby inducing a voltage in the shield if grounded at both ends.
    The now common practice of earth grounding a machine with sensitive electronic equipment is to ground bond all metalic parts of the machine, known as Equi-Potential bonding, this essentially eliminates any difference of potential between grounded points, allowing the new practice of grounding any and all shielded cables at both ends.
    As per the Siemens paper on equi-potential bonding - section 3.
    We are talking motor cables if a Shielded Cable is used, this has nothing to do with whether there whole system is bonded or not, a Ground loop can not be formed this is standard industrial practice and a requirement in most countries

    Analog circuits using a shielded cable are connected at one end only even if everything is bonded
    Mactec54

  8. #8
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    Re: Issue with shielded wires on DIY machine

    There is two version of cables, ones that are either affected or ones that produce EMI, the ones that produce it are DC motors, VFD's etc, The former ones were traditionally shielded at one end only, the emitters of radiated fields, the higher energy types, the conductors were mainly just twisted together which is quite effective at reducing radiated energy, with the onset of VFD's that used higher out put frequency, the custom has been to use specialized shielded cables GND bonded at both ends.
    As per the Siemens paper, if equi-potential bonding is observed then low signal cables can be connected at both ends, i.e no ground loop is present to cause imposed EMI.
    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: Issue with shielded wires on DIY machine

    Thanks for all the answers guys.

    My motor has the drain connected to ground only on one side (controller side).

    Can you explain a little more about why the "pigtail" wiring is a bad approach? Unfortunately this is the method I am using for all my shielded wiring at the moment.

    I am puzzled because all of the limit switch sensor wiring is done in exactly the same way. It's just the motor that's misbehaving when i connect the drain to ground.

    Still no luck with fixing this. The whole cnc is stable without the shielded motor cable, but now I am stubborn to understand what the problem exactly is...

    Is there a method to cross-check if a ground loop is indeed taking place ?

  10. #10
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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Xenofon9 View Post
    Thanks for all the answers guys.

    My motor has the drain connected to ground only on one side (controller side).

    Can you explain a little more about why the "pigtail" wiring is a bad approach? Unfortunately this is the method I am using for all my shielded wiring at the moment.

    I am puzzled because all of the limit switch sensor wiring is done in exactly the same way. It's just the motor that's misbehaving when i connect the drain to ground.

    Still no luck with fixing this. The whole cnc is stable without the shielded motor cable, but now I am stubborn to understand what the problem exactly is...

    Is there a method to cross-check if a ground loop is indeed taking place ?
    Give them time and they all will cause problem's, they are not doing much at the moment and are low voltage, so my not show any problems

    Motors and there drives are very noisy and higher voltage

    A Pig tail is unshielded and becomes an antenna and emits noise, shielding terminated at one end also becomes and antenna so in effect your shielded cables are causing you more problems than if you did not even have them, and you just used twisted pairs for your wiring which will work much better in your case

    The longer you make the tail the more noise that will be everywhere

    A Question are you using ( 1 ) Main Power source to supply your machine with Power ???
    Mactec54

  11. #11

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    Re: Issue with shielded wires on DIY machine

    Thank you Mactec54. That's a good explanation.

    Quote Originally Posted by mactec54 View Post

    A Question are you using ( 1 ) Main Power source to supply your machine with Power ???
    I have 1 mains AC cable coming in the controller through an IEC connector which is then distributed by DIN terminals to the following PSUs:

    - 3x 48Vdc PSUs. each of these powers a motor driver
    - 24Vdc PSU for powering sensors, fans etc
    - 12Vdc PSU for micro-controller (arduino in my case)

    All of these have a shared common ground, which is also connected to the AC earth and the Controller metal enclosure.
    Attached a picture for reference.
    Attached Thumbnails Attached Thumbnails 20201124_210511.jpg  

  12. #12
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    Re: Issue with shielded wires on DIY machine

    Did you actually draw up a schematic for the system, always wise for trouble shooting later.
    Nice tidy cabinet BTW.
    Do you have stop/start circuit and E_stop?
    I don't see anything on the cabinet front where you would commonly see them.?
    CNC, Mechatronics Integration and Custom Machine Design

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

  13. #13
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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Xenofon9 View Post
    Thank you Mactec54. That's a good explanation.



    I have 1 mains AC cable coming in the controller through an IEC connector which is then distributed by DIN terminals to the following PSUs:

    - 3x 48Vdc PSUs. each of these powers a motor driver
    - 24Vdc PSU for powering sensors, fans etc
    - 12Vdc PSU for micro-controller (arduino in my case)

    All of these have a shared common ground, which is also connected to the AC earth and the Controller metal enclosure.
    Attached a picture for reference.
    You mean the input power PE to the power supplies is Grounded / to Ac Earth , each Dc common must be able to return to the source before it can be connected to Ground /Earth and in some cases should not be connected to Earth Ground or this can generate noise

    You will need a EMI Power Filter for the VFD Drive and this needs to be connected close as posable to the input power of the VFD Drive sometimes it is good to have one for the Power supplies also

    This is a Filter to buy TDK Lambda RSEN-2030
    Mactec54

  14. #14

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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Al_The_Man View Post
    Did you actually draw up a schematic for the system, always wise for trouble shooting later.
    Nice tidy cabinet BTW.
    Do you have stop/start circuit and E_stop?
    I don't see anything on the cabinet front where you would commonly see them.?
    Thank you man
    I do have a wiring diagram yes (bear in mind I am not an electrical engineer though). I need to find a way to access it because I created it in Visio through my previous work and now can't open it since I have switched jobs :P I'll find a way and upload it later today.

    You are right in the image the cabinet is finished except the interfacing panel.
    I have this located at the top of the cabinet. See some more images below.
    Of course E-stop is present you can't see it in the images but it's tethered and goes to the front of the machine so I can smash it nice and quick.
    Attached Thumbnails Attached Thumbnails 20201201_214213.jpg   20201203_190352.jpg  

  15. #15

    Re: Issue with shielded wires on DIY machine

    Greetings! If it's a standard VSD Visio file LibreOffice will open it. Microsoft has or had a free Visio viewer app as well. LibreOffice can open but not save, so you'll need to convert to some other format if you want to continue editing the file. Depending on how fancy or simple you kept things, your results will range from perfect to not so great. I believe Inkscape can import VSD files as well.

  16. #16
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    Re: Issue with shielded wires on DIY machine

    When I saw you had a safety relay I new you would of had all the other important connections like Estop extra
    Mactec54

  17. #17
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    Re: Issue with shielded wires on DIY machine

    Xenofon9, the schematic may provide some insight.
    Normally if you have set up a star ground point to terminate all grounds including the service supply ground, and bond all metallic parts of the machine, eliminating ground loops, you can ground all shields at each end,
    The origin of l grounding one end of low signal shielded cables was to prevent the possibility of ground loops that might exist, imposing an external signal on the cables if shields were grounded at both ends.
    By using the bonding practice above it is now possible to ground both ends.
    Also it is made a little more confusing due to most DIY CNC is made up of several different parts and components from different sources, all having their own position on, for example grounding of the common supply conductor.
    Most, possibly to avoid any problem where other equipment is connected to theirs, usually specify no ground bonding.
    I have always ignored this where possible and earth grounded all power common conductors to the star ground.
    So far, with no issues. and often cured many spurious tripping of L.S. inputs etc experienced by other posters here.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  18. #18

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    Re: Issue with shielded wires on DIY machine

    Apologies for the delay. Had a hectic work week

    Here's the visio wiring diagram: https://we.tl/t-v2vqJsG2a6

    Unfortunately I left it at a semi-finished state (....as you typically do with these things...)

    In the diagram, my shield drain, GND distribution block, Earth distribution block are not connected. Attached is an "amendment" picture of how they are connected in reality.

    Hope this makes sense. Comments/feedback are very welcome.

  19. #19
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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by Xenofon9 View Post
    Apologies for the delay. Had a hectic work week

    Here's the visio wiring diagram: https://we.tl/t-v2vqJsG2a6

    Unfortunately I left it at a semi-finished state (....as you typically do with these things...)

    In the diagram, my shield drain, GND distribution block, Earth distribution block are not connected. Attached is an "amendment" picture of how they are connected in reality.

    Hope this makes sense. Comments/feedback are very welcome.
    As I said before you can not have a shield terminal block all shields must clamp direct where the cable ends to the Ground Plane, with a 360 degree clamp, what you have will never work like this, there will be noise every where
    Mactec54

  20. #20

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    Re: Issue with shielded wires on DIY machine

    Quote Originally Posted by mactec54 View Post
    As I said before you can not have a shield terminal block all shields must clamp direct where the cable ends to the Ground Plane, with a 360 degree clamp, what you have will never work like this, there will be noise every where
    Understood!
    Any tips for improvement with the current set-up? I am in no position to restart the wiring as we stand with the proper ground plane and clamp. In particular how can you do a panel mount connector with this method though ?

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