Free 173 Best Homemade Tools eBook:  
Results 1 to 6 of 6

Thread: Variable Frequency Drive Noise Reduction

  1. #1
    Supporting Member rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    656
    Thanks
    225
    Thanked 1,233 Times in 363 Posts

    rgsparber's Tools

    Variable Frequency Drive Noise Reduction

    My Variable Frequency Drive (VFD) powers my mill's spindle motor. The mill is controlled by a Computer Numerical Control (CNC) system. As I used my mill in CNC mode, it quickly became evident that noise from the VFD was crashing the CNC. This article explains how I stopped the crashes and why the fix worked.

    If you are interested, please see

    https://rick.sparber.org/VFD_Noise_Reduction.pdf


    Your comments are welcome. All of us are smarter than any one of us.


    Thanks,

    Rick
    Rick

  2. The Following 4 Users Say Thank You to rgsparber For This Useful Post:

    JD62 (08-03-2018), JRock (08-03-2018), PJs (08-05-2018), Seedtick (08-03-2018)

  3. #2
    Supporting Member metric_taper's Avatar
    Join Date
    Mar 2017
    Location
    Marion, Iowa
    Posts
    229
    Thanks
    74
    Thanked 98 Times in 62 Posts

    metric_taper's Tools
    Ground straps that are made up of very fine braided wires can have the opposite results relative to high frequency (and expectations they work). It may appear they are all shorted together, but typically they have oxide, and oil film that insulates them. So these tiny wires with the RF skin depth makes this look like a large impedance. That is the same issue with stranded 12AWG SO cord ground.
    Your solid strap is the way to go. Should be interesting with installing motor leads in a coaxial Faraday shield. The only design issue is how to connect this shield with minimal inductance. Typical STP with ground drains (pigtails), will have around 25ohm impedance per inch at 100MHz (22AWG STP signal wire and drain wire gauge).
    There probably is some conducted emissions on the 220VAC power to the VFD. I don't know how good the EMI front end filters are in the VFD.
    It looks like you fixed your EMC issue.
    Very nice write up that should be helpful to many.

  4. The Following User Says Thank You to metric_taper For This Useful Post:

    PJs (08-05-2018)

  5. #3
    Supporting Member rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    656
    Thanks
    225
    Thanked 1,233 Times in 363 Posts

    rgsparber's Tools
    Quote Originally Posted by metric_taper View Post
    Ground straps that are made up of very fine braided wires can have the opposite results relative to high frequency (and expectations they work). It may appear they are all shorted together, but typically they have oxide, and oil film that insulates them. So these tiny wires with the RF skin depth makes this look like a large impedance. That is the same issue with stranded 12AWG SO cord ground.
    Your solid strap is the way to go. Should be interesting with installing motor leads in a coaxial Faraday shield. The only design issue is how to connect this shield with minimal inductance. Typical STP with ground drains (pigtails), will have around 25ohm impedance per inch at 100MHz (22AWG STP signal wire and drain wire gauge).
    There probably is some conducted emissions on the 220VAC power to the VFD. I don't know how good the EMI front end filters are in the VFD.
    It looks like you fixed your EMC issue.
    Very nice write up that should be helpful to many.
    My plan is to feed the braided tube through a hole in a sheet of copper foil and solder it all the way around. The copper will attach to the two ground screws inside the VFD. At the motor end, I will do the same but bolt the copper sheet to the box (paint removed at point of contact). Only problem at that end is that the cover has a gasket so it floats. May need to run a ground wire to it so the cover doesn't radiate.

    I know that soldering both ends of the braid will make it painful to remove but should give the best possible connection.
    Rick

  6. The Following User Says Thank You to rgsparber For This Useful Post:

    PJs (08-05-2018)

  7. #4
    rbjracing1's Avatar
    Join Date
    Jan 2017
    Posts
    12
    Thanks
    0
    Thanked 3 Times in 3 Posts
    Hi Rick, I get a screeching noise though my radio on some stations when I turn the VFD that powers my knee mill on. I wonder if this would fix that also I will have to give it a try.

    John

  8. #5
    Supporting Member rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    656
    Thanks
    225
    Thanked 1,233 Times in 363 Posts

    rgsparber's Tools
    Quote Originally Posted by rbjracing1 View Post
    Hi Rick, I get a screeching noise though my radio on some stations when I turn the VFD that powers my knee mill on. I wonder if this would fix that also I will have to give it a try.

    John
    That would be an interesting test. Just be sure to scrap all of the paint off on the mating surfaces.

    Rick
    Rick

  9. #6
    Content Editor
    Supporting Member
    DIYer's Avatar
    Join Date
    Aug 2013
    Posts
    3,091
    Thanks
    462
    Thanked 986 Times in 909 Posts
    Thanks Rick! We've added your VFD Noise Reduction to our CNC category, as well as to your builder page: Rick's Homemade Tools. Your receipt:



    Post your reply!
    Join 41,949 of us and get our 173 Must Read Homemade Tools eBook free.



    173 Must Read Homemade Tools

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •