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  1. #1
    Hello everyone,

    I've been struggling with EMI problems with my VFD. The second my spindle starts spinning, my motors start doing uncommanded moves. Last week it was obvious since I didn't use any shielded cable for the spindle and inside the control box.

    However, yesterday I replaced ALL the cables going out of my control box with CY cable. Also, all small uncovered sections (close to the motors for example) are wrapped in aluminium foil and covered by a protective sleeve. In the control box, I replaced most signal wires with CY cables: drivers to connectors, VFD to spindle connector, BOB to VFD (FOR and speed control). I also connected all the screens inside the control box to the earth.

    Still getting EMI, and it hasn't changed one bit.

    I don't have good pictures of the control cabinet after I changed to CY cable, because I don't have a proper camera with me today. However, I did take a photo with my laptop so the quality is not goo but it'll give you a good idea. Plus, I add older photos of the control cabinet that were made BEFORE I used CY cables.

    Before CY:
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    After CY:

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    I'm pretty depurate now.. the only solution I see really is to take the VFD out of the control cabinet, power it completely separately from it and just pulling a connection from the control cabinet / BOB to the VFD for Mach3 control.

    Can anyone please advise me ? Please don't judge my machine or control cabinet, this is my first build ever, and I am far from being an expert and this is the best I could do with what I know so far.

    Thanks a lot !

    All the best,
    G.

  2. #2
    Maybe I'm wrong but I dont see any grounding wires for your control cables, so I think you have to do that first. and perhaps a power line filter for the VFD and ferrite beads on all of them as well, also physically separating power lines from control lines.

    maybe someone with more experience can comment as well :)

  3. #3
    I am not surprised that you have emf problems I think I would remove the vfd from the control box plus sort out the rats nest of wires try to keep or the signal wires away from the power wires and avoid running them side by side.

    If you have to cross power wires do so at 90' if possible. Have you connected all the screens to one star point? I don't think it helps having the PP ribbon cable I would try and replace that by connecting the PP cable from the PC direct to the BOB without the ribbon cable.

    You have the basis of a good control box but you have not made the best use of the cable management in there.

    edit: Is that a plastic control box? have you mounted everything on to a backplane (ie metal plate) I think one of your main problems will incorrect grounding
    Last edited by Clive S; 06-03-2016 at 11:52 AM. Reason: add text
    ..Clive
    The more you know, The better you know, How little you know

  4. #4
    Different VFDs generate different levels of interference, I have a .55kW Omron on a small manual mill in the workshop that kills the radio and knocks the benchtop CNC mill about and yet the .75kW Siemens on the CNC mill itself causes no interference from 750rpm through to 7000.
    It is fairly standard to have all the kit in one box but if it's a dirty VFD it may be worth relocating it if problems persist after you add an RF filter on it's mains input

    - Nick
    Last edited by magicniner; 06-03-2016 at 01:54 PM.

  5. #5
    Geoffrey got to be methodical to find this. Make one change then test before making another.

    Start with small trivial things first like removing the Tie raps holding cables together around the machine and separate the VFD cable from Stepper or signal cables.
    Next make sure the screens from the long cables go to the Star Earth not just the cables inside the box.

    I See you have 4 wires going to the spindle and suspect one of them you have connected to the Spindle for Earth.? Remove this at the VFD end and try.
    Also Only connect the spindle cable Shield at the VFD Earth not both ends.

    After doing these I would remove the VFD from the Box as a test. If solves then fit a Line filter and try again but it still may not work if you have sensitve elelctronics in the control box.?. . Like Cheap nasty BOB.!!!!!

    One last thing you haven't earthed the PC case to control box have you.? If so remove.

  6. #6
    Alright, so after spending the day trying to fix this with Graeme on Skype, we seem to have found the source of the problem.


    I have connected all screens to the star point. I've taken the VFD out of the box, power is separate, it's completely diconnected from the control box, and still, no improvements.


    Turns out disconnecting the PC solves the issue. So it seems like there is a grounding problem with the BOB. As JAZZ said, it's a cheap chinese BOB, so I might have to change it.


    Quote Originally Posted by Clive S View Post
    edit: Is that a plastic control box? have you mounted everything on to a backplane (ie metal plate) I think one of your main problems will incorrect grounding
    Fiber glass cabinet. Fireproof plate in the back. No metal.


    Quote Originally Posted by JAZZCNC View Post
    Like Cheap nasty BOB.!!!!!
    Jee JAZZ, you don't like them.. :D !


    Quote Originally Posted by JAZZCNC View Post
    One last thing you haven't earthed the PC case to control box have you.? If so remove.
    Nope, not intentionally, but apparently it is through the BOB.


    One thing to note. When there is no power to the control cabinet, but the PC is plugged and turned on, the BOB receives 5V, but the 5VDC PSU led turns on, apparently because it receives power through the BOB ! Weird...

  7. #7
    Quote Originally Posted by eurikain View Post
    Jee JAZZ, you don't like them.. :D !
    Nope and now you know why. You have been lucky to find it quickly this isn't always the case, in fact often not the case. Which is exactly why when these troubles come my way first thing I do is rip out the BOB.

  8. #8
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 4 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    You're most likely getting a ground loop through the parallel cable shield. As you're using a ribbon cable internally, try unscrewing the parallel connector from the cabinet and see what happens. If it cures the problem, you can either come up with some way of insulating the connector, or just cut the cable shield near the connector.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  9. #9
    Quote Originally Posted by JAZZCNC View Post
    Nope and now you know why. You have been lucky to find it quickly this isn't always the case, in fact often not the case. Which is exactly why when these troubles come my way first thing I do is rip out the BOB.
    Okay but now, where do I go ?

  10. #10
    Quote Originally Posted by m_c View Post
    If it cures the problem, you can either come up with some way of insulating the connector, or just cut the cable shield near the connector.
    It's Fibre Glass cabinet so won't be that.!!

    Quote Originally Posted by eurikain View Post
    Okay but now, where do I go ?
    The good old US of A. . . . . PMDX126.

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