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IndustryArena Forum > CNC Electronics > CNC Machine Related Electronics > Enclosure / VFD / Grounding / EMI
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  1. #1
    Join Date
    Apr 2014
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    3

    Enclosure / VFD / Grounding / EMI

    Would anyone mind having a quick look at this....Worried about my enclosure being to small, and getting EMI noise problems.



    1. Is the VFD in this enclosure a problem in your mind. ?

    UC300 Motion control and KK01 Breakout board would be mounted on a shelf above the drivers.
    I have bought belden shielded mains cable for mains wiring within the enclosure.
    I will also use the shielded belden cable for connection to the spindle - Grounded both ends.

    I was thinking of trying to shield the VFD within the enclosure with dividers from the rest of the contents with steel or foil or something.


    2. Should i be using shielding the power / signal lines to the stepper drivers from the transformer / breakout board within the enclosure ?


    3. Does my grounding look right in the schematic ?

    Rough Schematic attached.

    Thanks for any input...

  2. #2
    Join Date
    Sep 2010
    Posts
    1765

    Re: Enclosure / VFD / Grounding / EMI

    Nice schematic!

    Encl way way waby too small to dissipate the heat imo. There are online calculators for min encl size. My gut says 4x large needed if sealed, 3x if vented....

  3. #3
    Join Date
    Jun 2014
    Posts
    777

    Re: Enclosure / VFD / Grounding / EMI

    Quite similar to my enclosure and devices however I did opt to install a conductive partition between ac and dc devices to avoid this issue and not had any issues whatsoever. Just used twisted pair inside the enclosure, and like I say no issues at all, even with a toroidal In there and the vfd is 2.2kw.

    See pic

    http://s26.postimg.org/3rqeewhcp/image.jpg

    For cooling I used two 48v fanson the bottom blowing hot air upwards, no bigger than standard pc 12v fans but these things shift some air. Very pleased with them, infact initially I had 4 but it was completely overkill.


    You have a possible ground loop in your schematic tho, I'd suggest you run one mains cable to your vfd (+,-,ground) and that terminates at the vfd, the vfd has a plastic case and your spindle is not grounded by vfd so that ground terminates within the vfd. Which is what you want. The other mains you run through your kettle connector and switch, you then run + and - to your psu and you fit a bolt with plenty of thread into your case and connect the ground to it. You then connect all your device ground terminals including psu to that point/thread. Always keeping in mind that any device that is fixed to the case must be isolated from the case if the devices ground terminal is grounded to the devices enclosure or board fixing holes, if it is then you may opt to just fix the device case unisolated and in turn grounding the device and no need to wire a ground wire to terminal. Use the buzz or isolation test on most multimeters to determine if a devices enclosure is grounded before installing into case.

    To power the other devices with mains positive and neutral, you make your connections at the source which is the power switch.

    Also connect all your screen wires to the cases ground point described above.

    Hope this helps

  4. #4
    Join Date
    Apr 2014
    Posts
    3

    Re: Enclosure / VFD / Grounding / EMI

    Wow Jon

    That is tight.. I think i will have a bit more room than that, but i do like your shields. What material are they made of - Ali ?
    I have removed the buttons of the VFD and mounted them on the front as well.

    How long has your machine been running like that ? If it's been working for a while it tells me that mi might just get away with it.

    Cheers
    Martin

  5. #5
    Join Date
    Jun 2014
    Posts
    777
    Quote Originally Posted by mturneruk View Post
    Wow Jon

    That is tight.. I think i will have a bit more room than that, but i do like your shields. What material are they made of - Ali ?
    I have removed the buttons of the VFD and mounted them on the front as well.

    How long has your machine been running like that ? If it's been working for a while it tells me that mi might just get away with it.

    Cheers
    Martin
    2 years, never a noise blip on a limit switch or miss step I think it looks tighter than it actually is, all the wires run to the bottom of the front and back panel so for access a few bolts and they just fold down. yeah just Ali,

    Used to build medical equipment with similar stuff in them which were much tighter. If you were cleaver about it you could squeeze all that in a 2u rack no problem.

    I've edited my previous post with some advice on your wiring, hope it helps.

  6. #6
    Join Date
    Apr 2014
    Posts
    3

    Re: Enclosure / VFD / Grounding / EMI

    Thanks Jon.
    Trying to understand what you've said. I'm no electronics engineer!
    Could you clarify.

    Quote Originally Posted by Jon.N.CNC View Post
    I'd suggest you run one mains cable to your vfd (+,-,ground) and that terminates at the vfd, the vfd has a plastic case and your spindle is not grounded by vfd so that ground terminates within the vfd. Which is what you want.
    So are you saying do away with the kettle chassis switch / connector / fuse - How will i turn the VFD off ?
    What about the EMI Filter I was going to put in the mains line to VFD?
    Also not understanding "The spindle is not grounded by the VFD"
    Can you explain where the ground loop is ?

    Quote Originally Posted by Jon.N.CNC View Post
    The other mains you run through your kettle connector and switch, you then run + and - to your psu and you fit a bolt with plenty of thread into your case and connect the ground to it.
    You then connect all your device ground terminals including psu to that point/thread.
    Can I not just connect grounds to the ground terminal on the PSU ?
    Other than the drivers not sure what else i need to connect to ground here.


    Quote Originally Posted by Jon.N.CNC View Post
    Always keeping in mind that any device that is fixed to the case must be isolated from the case if the devices ground terminal is grounded to the devices enclosure or board fixing holes.
    I have been testing with my multimeter.
    The 48V power supply metal case is grounded. Should I isolate this from chassis? As it stands I have just bolted it to the chassis with no isolation, which in turn means the chassis case is grounded automatically.
    The drivers cases are not isolated. These are also bolted direct to the chassis. Should these be isolated from the case ?

    Quote Originally Posted by Jon.N.CNC View Post
    To power the other devices with mains positive and neutral, you make your connections at the source which is the power switch.
    Not sure what other devices you mean? The UC300 / KK01 breakout board is powered from USB isn't it?


    Quote Originally Posted by Jon.N.CNC View Post
    Also connect all your screen wires to the cases ground point described above.
    Stepper motor cables ?

    Thanks Jon

  7. #7
    Join Date
    May 2014
    Posts
    182

    Re: Enclosure / VFD / Grounding / EMI

    You want to ground all shields to the case - but not with a ground or drain wire, you want a full 360 degree metal clamp around the wire to create a low impedance ground connection.
    http://www.focusondrives.com/wp-cont...eldingGood.jpg

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