CNC spindle induced EMI and Duet boards
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I'm building a PrintNC at the moment, using a Duet 3 6HC board for the electronics, and a YL620A VFD to control the 2.2kw spindle. When I start to turn the spindle I get what appears to be quite serious EMI. My workshop all runs off of the same breaker / circuit, and my printer's Duet 2's LEDs start to pulse on and off slowly, and my router loses connectivity. I've installed an AC EMI Filter on the plug going in to my VFD, with the pins on the right in the included picture on the plug side and the other side on the load side, but this isn't helping. Maybe I need to flip it the other way around?
Have any of you had any experience with a problem like this? I'm quite concerned about running it, with this interference.
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@jrow Indeed, you have installed the filter in the wrong direction. The 3-pins end is for the load, as indicated on its label (though pretty uncommon!). Also, don't expect much from it as the common mode inductor and the X capacitor are pretty small. Better go for something like this one - https://www.conrad.com/p/schaffner-fn2090-16-06-emi-filter-250-v-ac-16-a-4-mh-l-x-w-x-h-1135-x-575-x-454-mm-1-pcs-554095. While it is significantly expensive, from my own experience it makes a huge difference.
But this filter just prevents electrical noise from getting back into the supply lines. You also need to insure that the VFD is properly grounded and also check that the spindle is really grounded. I had to make myself the ground connection into my spindle as the Chinese ones usually are not properly grounded.
On my CNC I have a Huanyang 1.5kW VFD inverter and a 24V power supply from Meanwell for the Duet. Never had any EMI problems and I have no line filter on the inverter. For connecting the spindle to the VFD I use a 4-core Lapp cable. The 4 cores are slightly twisted for maximum flexibility and that also helps a little bit on the electrical noise side.
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@catalin_ro yeah, I can definitely back you up on the grounding. The PrintNC instructions point out that a lot of these spindles are not 'properly' grounded, but what I wasn't expecting was for there to be no wire connected to ground pin at all! Had to solder one and screw it to the internal frame.
My Duet2 getting the pulses is using a legit Meanwell, but the Duet3 I've got for the CnC is running at 31.5v on a Meanwell clone.
And yeah, spindle is also double insulated! With a braided metal layer. I soldered the braid to the ground pin as well.
Is it likely just the inverter I got that's the source of all this woe?
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@jrow Ok, so I switched the line filter around the other way, and ran the VFD, and it caused interference again. So I switched over to another breaker, via long extension cord, and ran it again, and got an err4 warning (short circuit) then the VFD blew up. I think I might've fried the internals of the line filter when de-soldering it, before killing my VFD.
That is a very shitty outcome.
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@jrow Sorry to hear that!
Normally the filter, if connected the other way around, should be OK. The schematic has no component that would be in a critical condition if connected the wrong way, just that its characteristic would be slightly different. Among other things, I'm involved with a company that manufactures TEMPEST equipment (if you don't know what it means, just consider it EMI for paranoids!) and line filters are the first line of defense.
The VFD should have included a proper short protection toward the spindle, unless the spindle is "just slightly" broken. If you have a multimeter I would check the resistance between the 3 power wires and then the resistance between each of them and the ground. The 3 resistances between the power wires should be equal and pretty low. The resistances between the power wires and the ground should be really high, in the MOhm range. If one of the power wires has a significantly lower resistance to ground, there is your short circuit.
When using 3-phase spindles you don't really need a braided power cable. The beauty of AC engines is that they don't produce a lot of electrical noise unless they have a problem.
Now on the Meanwell clone power supply... It's like going for a Leadshine clone for your stepper! It is similar and covers most possible problems, but at some point it might hit you really hard! I have seen and I still see a lot of Chinese clones in various low cost, and not only, equipment. Usually they have a lot of empty places on the PCB, usually on the filtering side, either AC or DC.
Just for reference, I have used a Vigortronix 48V/10A PSU for a project (Vigortronix is anything but cheap!!!) where it was located in an enclosure on top of a building. 10 months later it was busted. In a similar location I have a Meanwell doing the same job for over 5 years.
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I've figured out what might've been my problem, and I suspect it's not related to my wiring, the filter, VFI or spindle. The wall outlet I was originally plugged in to had a faulty ground; confirmed by a plug tester. When I switched over to the extension lead from another breaker and a functioning ground, I may have let charge from the CNC itself exit via the new ground.
The reason I suspect this is because after discovering the faulty ground, I switched the power back over, and used a non-contact voltage detector all around my workshop, and found that the CNC, and even a wooden table had current in them. It's time to get the electrician over I think. This is above my paygrade.
Regarding the Meanwell clone; for now that's just handling my steppers, and the Duet. But I may have the budget for a proper supply in due course, and as you say it's probably a good idea.
I'll check the resistance on the spindle etc shortly. My VFD's UVW connectors are showing some continuance between one pair, but not between the other. I suspect that's going to be due to the component that blew up inside it.
