VFD interference problem

[magicniner]

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

[JAZZCNC]

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.

[eurikain]

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.

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.

Like Cheap nasty BOB.!!!!!

Jee JAZZ, you don't like them.. :D !

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...

[JAZZCNC]

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.

[m_c]

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.

[JAZZCNC]

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.!!

Okay but now, where do I go ?

The good old US of A. . . . . PMDX126.

[eurikain]

The good old US of A. . . . . PMDX126.

How about NOT USA ? CSLab ? And while I'm at it, why not go with ethernet motion controller instead of a BOB ?

[m_c]

It's Fibre Glass cabinet so won't be that.!!

Good point. I'll just go back to sitting in the corner and keeping quiet!

[eurikain]

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 ?