VFD spindle interferences issue

Hello everyone,

I recently implemented a 1.5kW VFD spindle on one of my machines and everything works very smoothly, except for one problem occurring randomly.

It happens mostly during longer jobs, where everything is going well and the cuts are great, until the Z-axis of the machine suddenly drops, as if the idle current of the driver was going down to 0 and the Z-axis motor could no longer bear the weight of the spindle. The odd thing is that the driver doesn't give me any error, but my PC is unable to connect to it using the USB port (unknown USB device error). One thing I observed, is that the driver green LED is not blinking in sync with the other drivers anymore. The problem disappears if I simply switch off the power supply and put it back on again.

I'm using the Mk3/4 controller and 6.0A 256 motor drivers.

I highly suspect interferences because of the VFD, but all my cables are shielded and connected to the ground, the spindle as well. I also installed an EMC Filter in my VFD control circuit that didn't help much.

If anyone has a clue that could help me, I would greatly appreciate it!

Thanks

I don’t think the Z axis would drop due to gravity, or it would drop when the machine is off. Is the stepper getting very hot? Can you try another power supply?


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Quote:

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Originally Posted by mgravet

Hello everyone,

I recently implemented a 1.5kW VFD spindle on one of my machines and everything works very smoothly, except for one problem occurring randomly.

It happens mostly during longer jobs, where everything is going well and the cuts are great, until the Z-axis of the machine suddenly drops, as if the idle current of the driver was going down to 0 and the Z-axis motor could no longer bear the weight of the spindle. The odd thing is that the driver doesn't give me any error, but my PC is unable to connect to it using the USB port (unknown USB device error). One thing I observed, is that the driver green LED is not blinking in sync with the other drivers anymore. The problem disappears if I simply switch off the power supply and put it back on again.

I'm using the Mk3/4 controller and 6.0A 256 motor drivers.

I highly suspect interferences because of the VFD, but all my cables are shielded and connected to the ground, the spindle as well. I also installed an EMC Filter in my VFD control circuit that didn't help much.

If anyone has a clue that could help me, I would greatly appreciate it!

Thanks

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Need to see some photos of the wiring, Correct Grounding of the shields are very important, did you check that the Spindles 4th pin ( Ground ) has continuity to the spindle body, most are not connected and need to be corrected

The EMI Filter has to be installed correctly also and be a quality filter, so some photos will help to see if you have the correct installed filter

When the machine is off, the Z-axis doesn't drop because of gravity, but almost (I can push it down manually easily). The reason behind this is that I use a 10mm pitch ball screw. So I suspect that the driver stops delivering current, so the Z-axis motor isn't powered at all anymore, and that the vibrations generated by the cutting operation make it moves down. It actually doesn't drop at once, I can see a ramp inside the material.

I tried using another power supply, no luck there unfortunately.

Do you think Z would loose power if you ran the program without cutting? If it does it without cutting (no loads) it’s noise or program (doubtful bc drives are always on).
While cutting indicates heat, noise or loose connectors.


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Here is a picture of the wiring attached.

I also tried two different methods to connect the shield of the cable to the ground: the pigtail method and a 360° shield termination (also 2 pictures attached).

I just checked and indeed the 4th pin of the connector isn't connected to the spindle body (see pics attached too). Do you really think that this could be the cause, although the cable shield is properly grounded on the driver side?

Thank you for the help!

Yes it already did it without cutting. I also monitored the drivers temperature and they never go above 50°C.
So I agree with you, the source should be noise.

Quote:

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Originally Posted by mgravet

Here is a picture of the wiring attached.

I also tried two different methods to connect the shield of the cable to the ground: the pigtail method and a 360° shield termination (also 2 pictures attached).

I just checked and indeed the 4th pin of the connector isn't connected to the spindle body (see pics attached too). Do you really think that this could be the cause, although the cable shield is properly grounded on the driver side?

Thank you for the help!

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You made a nice tail there with the shield, but unfortunately doing this a disaster for shield Grounding you can not use a tail for shield Grounding this will create problems

The spindle will have to have a Ground wire connected to the 4th pin it is unsafe to use like it is, what most do with these Air cooled spindles where one of the cap screws are you add a Ground wire with a lock nut at that point then solder to the 4th pin, so you will need to make a custom stud ( just a piece of threaded rod ) cutaway clearance where the cap mounts at this point to give the Ground wire lug and lock nut some clearance

Your Spindle Cable Shield Ground need to be clamped under the cable restraint clamp, this is not ideal but the only choice you have with this type of plug

The shield at the VFD Drive end needs to be clamped to the Ground Plane, The Ground Plane is the metal plate that everything is mounted on, this must be paint free where you do any component mounting

Your Ground main junction, is not suitable, you need a ( star Point Ground Bus ) where this is connected to the Ground Plain, ( Metal Plate that all your components are mounted )

The EMC Filter you have is not what I would recommend suitable for VFD Drive use, not all are created equal I would have to see the spec. sheet to know for sure

It would be very dangerous to think that the Shield can be used as a Ground it can not and must not be any part of a Safety Ground circuit

You must install a Ground Bus where all Ground wires are connected at this on point ( Star Ground )

Some snips to give you an Idea of what and how to correctly ground Shields, if you need more snips I have lots to help with your wiring

Thanks a lot for all these tips, I'll try to implement them and see if it helps!