VFD interference problem

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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Attachment 17856

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.

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 :)

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

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

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.

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.

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Originally Posted by Clive S

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

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Fiber glass cabinet. Fireproof plate in the back. No metal.

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Originally Posted by JAZZCNC

Like Cheap nasty BOB.!!!!!

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

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Originally Posted by JAZZCNC

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

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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...

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Originally Posted by eurikain

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

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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.:grief:

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.

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Originally Posted by JAZZCNC

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.:grief:

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Okay but now, where do I go ?

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Originally Posted by m_c

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.

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

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Originally Posted by eurikain

Okay but now, where do I go ?

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

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Originally Posted by JAZZCNC

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

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

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Originally Posted by JAZZCNC

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

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

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Originally Posted by m_c

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

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Nobody puts Baby in the Corner.!! . . . . You keep on Dancing Mc

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Originally Posted by eurikain

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

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Well yes that would be my first choice but your talking different animal and cost depending on model.

Yes but if I order the PMDX 126, 160 Euros + tax when it gets here, you're looking at the same price than the 230 Euro 4 axis motion controller they've got at CSLabs. Plus, really, I think I can re-use it in the future for another build.

Are there any choices other than CSLab, for a decent controller ?

Yes there are but by time you have bought decent BOB to match they are not any cheaper than IP-M. While some like Ethernet Smooth stepper may beat IP-M on features(that you won't probably use) Nothing touches the IP-M on quality for same money.

Just be aware the IP-M isn't ideal if your using Slaved motors.

What if I buy an ethernet smooth stepper as you told me a few weeks back ? ESS smooth stepper ? That would prevent the ground loop going back to the PC since it's ethernet based.

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Originally Posted by eurikain

What if I buy an ethernet smooth stepper as you told me a few weeks back ? ESS smooth stepper ? That would prevent the ground loop going back to the PC since it's ethernet based.

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The Ess will help some but the ground loop will always cause issues. Have you powered the Bob with the USB cable? If so then have you tried to disconnect the cable and use a different 5v source?

Nope, the BOB is powered only using a 5VDC external power supply. Weird that I'm the only person with this issue.. I've got the exact same board as the one you sell on your website. Typical cheap Chinese BOB. But it works for everyone else.. why not for me :'( ?

I have a PCI parallel port expansion board. It might be interesting to install it and test if it improves or fixes the ground loop. It might be the native parallel port of my PC that's not working properly. I'll give it a try on Thursday.

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Originally Posted by komatias

The Ess will help some but the ground loop will always cause issues.

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It will with the ESS which think pulls Gnd from PC like the BOB but not with IP-M which is isolated from PC and pulls Gnd to Mains Earth. It also uses Differential signals with isolated Inputs which is why it's so very good at not being affected by noise.

That said you still need to be 100% sure it is the BOB and not some other cause.?

Have you tried getting rid of the ribbon cable and plugging the pp lead straight in to the BOB

Jazz, I'm not sure to understand what you are saying... will the ESS fix the issue IF it is a ground loop going to the PC ?

I have tried getting rid of the ribbon cable. Same problem, though I had disconnected the X axis motors because I didn't want to twist the gantry. But then it was a little more difficult to hear the noise but it was still there. I will do some more tests on Thursday, I'll connect everything back together to get the maximum noise, then disconnect the DB25 cable and see if that stops it. I'll let you guys know ASAP.

Any ethernet socket is galvanically isolated on both sides. So it will not pass direct currently to and from the computer. The ground loop will then not be present. But if there is an issue in the wiring then it may cause issues nonetheless.

Yes, but the ground loop could still flow through the cable from the BOB to the ESS, or not ?

It should not really unless the optos on the BOB are buggered or there is an issue on the board.

It looks like the board only has optos on the input signals though. But as you said, there are so many cases of people using this BOB without problem that we can't just assume it's the BOB that's the problem ^^.

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But then it was a little more difficult to hear the noise but it was still there

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What is noise you are hearing? You can't hear EMF

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Originally Posted by eurikain

Jazz, I'm not sure to understand what you are saying... will the ESS fix the issue IF it is a ground loop going to the PC ?

I have tried getting rid of the ribbon cable. Same problem, though I had disconnected the X axis motors because I didn't want to twist the gantry. But then it was a little more difficult to hear the noise but it was still there. I will do some more tests on Thursday, I'll connect everything back together to get the maximum noise, then disconnect the DB25 cable and see if that stops it. I'll let you guys know ASAP.

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In theory yes it should but like been said depends if this really is the source of trouble.? That said I'd still change the BOB because it's clearly not very good because shouldn't happen even with parallel port.

Now like Clive ask's What Noise.?

I think you miss under stand what is meant by Noise. It's not audible so if your hearing any noise that's something else.?
If your using AM Digital drives then I suspect it's because you haven't tuned them. Or what your hearing is the current reduction in the drive working while motors are stood still. This will make an Hissing sound.

Electrical noise or EMF is a Silent Killer.!!

Very difficult to help from distance when it comes to noise. All you can do is be meticulous with wiring and gnding. Ensure separation between signal and power cables.
If still present then fit EMF Filters etc.

If still present then start back tracking.

I was helping (well trying) to help Geoffroy over the weekend with his "noise" issue. His current problem is that when he runs the spindle all the steppers start making random moves. It is these rapid random stepper moves that is the noise he is hearing.
We started looking into the shielding of the spindle cable and he managed to improved it, but no change to the random stepper movements. He then removed the VFD unit and all VFD wiring from his control cabinet -still the same issue. So it does not look like it is caused by the cable radiating noise into the BOB.
The last thing we tried was to disconnect the parallel port cable from the BOB. This did seem to stop the steppers from moving when the VFD was run.
The reason I suggested he disconnected his slaved X axis motors was when the spindle was run these motors were sometimes going in opposite directions causing his gantry to twist. Removing them kept his machine safe, but did lower the "noise" from the steppers.
It looks like the BOB is seeing noise on the signals from the PC when the spindle is run, which is then being used to send random STEP and DIR pulses to the stepper drivers. This could be caused by an earth loop between PC and control cabinet or by a poor 0v connection between the two. More testing will be required to find out which.
Hope that clears up the meaning of the "noise", any suggestions welcome as to how to solve this one.

Thanks Graeme, you couldn't explain it better :)

You may well have a ground loop, however you would do well to relocate your BoB so that the PP cable from the computer plugs directly into it (get rid of the unshielded flat form cable).

A good principle to follow when wiring up a cabinet is to put signal cables on one side of the cabinet and power cables on the other.

Cheers,

Rob

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Originally Posted by Graeme

The last thing we tried was to disconnect the parallel port cable from the BOB. This did seem to stop the steppers from moving when the VFD was run.

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Does the BOB have Charge pump.? If so then disconnecting from PC will kill the Outputs so you won't get any movement.!!

Going to sound obvious but have you tried another parallel port cable.? Also you are using a proper straight thru cable not some Old printer cable.?

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Originally Posted by JAZZCNC

Does the BOB have Charge pump.? If so then disconnecting from PC will kill the Outputs so you won't get any movement.!!

Going to sound obvious but have you tried another parallel port cable.? Also you are using a proper straight thru cable not some Old printer cable.?

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Hi Jazz,

This BoB does not have a charge pump. I have suggested that the OP uses the cable that came with the BoB (these are generally sold with PP and USB cables) if there was one. Also that flat PP cable inside the box needs to go or at least be shielded.

Cheers,

Rob

Goffroy,

you did some work on the spindle if I remember from your other thread. You sure that the grounding is still intact in there?

Also I cannot tell from your photos if the shield of your stepper motor cables is grounded. Each of the sockets in the control box should have a solder tang to allow them to be grounded too unless they are designed to be used with a metallic box.

Finally, is your actual house wiring set up correctly with a good ground to real ground?

This is how the cabinet is set. All hight voltage power cables are on one side of the cabinet. Signal cables are close to the BOB, there is only 5V power cables that run next to them.

I'll get rid of the ribbon cable, but that doesn't solve my ground loop. Why would I have a ground loop while other don't ? Is it the computer that's the problem ?

Quote:

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Originally Posted by JAZZCNC

Going to sound obvious but have you tried another parallel port cable.? Also you are using a proper straight thru cable not some Old printer cable.?

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I haven't. I have a PCI PP card that I will try to install and use on Thursday, this might prevent the ground loop, who knows :)

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Originally Posted by eurikain

I haven't. I have a PCI PP card that I will try to install and use on Thursday, this might prevent the ground loop, who knows :)

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It is important as others have said to try a different pp cable or at least check the continuity from pin one to pin one etc at both ends of the cable.

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Originally Posted by eurikain

This is how the cabinet is set. All hight voltage power cables are on one side of the cabinet. Signal cables are close to the BOB, there is only 5V power cables that run next to them.

I'll get rid of the ribbon cable, but that doesn't solve my ground loop. Why would I have a ground loop while other don't ? Is it the computer that's the problem ?

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I think it is down to the fact that many use metal cabinets to house the electronics and also for the machine frame. Spurious currents then have an easier path to earth.

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

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Originally Posted by eurikain

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

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have you got an oscilloscope to probe the parallel port?

Nope, sorry ! I have a voltmeter though :) Probably won't be of any help huh :'(