Noise problems. Would like some advice.
So here's my setup. I have a 120 line going to my KFlop controller box. I have a 240 line going to my Hitachi inverter, and then to the spindle (actually, it goes to a disconnect, and then to the inverter). There is a ground going from the inverter to the spindle.
So the cnc chassis is essentially grounded through the spindle, and the controller is grounded through a completely different circuit. This is putting a ton of noise on the chassis as referenced to KFlop and is tripping one of my limits. I think I need to somehow get the KFlop box at the same ground potential as everything else.
My thought is to run a ground from 120 line and bond it to the disconnect. I think that will essentially give me a star ground with everything bonded to the enclosure and then my problem will go away. I would have a ground loop between the 120 line and the 240 line through the disconnect, but everything downstream would only see ground referenced at the disconnect.
What do the experts think?
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Well you definitely should have a star common earth ground point set up, this should include the service ground conductor and any ungrounded metallic part of the machine should be taken back to this point.
http://www.automation.siemens.com/do.../emv_r.pdf?p=1
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
If I had it to do again, I would have bought a large enclosure and mounted everything in there. Then I would have bonded everything to one common ground. Unfortunately, everything's not mounted in the same enclosure so there's going to be a ground loop SOMEWHERE. I did confirm that clipping the controller case to the chassis is enough to make the noise problems go away, so I think my scheme will work even though it will look a little funny.Originally Posted by Al_The_Man
Yes, often this is the case, the PC, spindle, servo's are in some cases all fed off of different outlets.
Rather than the customary mounting of everything off a common source, and this is usually the cause of 'noise' problems.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
So that worked perfectly. Now I can home with the spindle running and I don't have any false trips. So as an application note for the future, the way I would do this (and the way I will rewire my system in the next few days) is to bring the 120 for the logic into the disconnect box and loop it right back out, but bond the grounds to the ground bus in the disconnect. What I quickly did to get over the hump was wire up a plug with nothing but the ground lug attached, brought that into the disconnect and bonded it to ground. Then I plugged it into the same outlet as my power strip for the logic/steppers. That's basically the same thing but it's ugly. It would be much neater if I just had a 120 plug hanging out of the box.
What screwed me up is I didn't realize that the spindle would really need to get grounded to the inverter...I imagined that the spindle would see the 3 phases, and that everything else would see ground from the logic/steppers. Oh well. Live and learn. The next will one will be neater
Hey, thanks for the help, Al!
It is usual to take the ground to the inverter and carry on to the spindle.What screwed me up is I didn't realize that the spindle would really need to get grounded to the inverter...I imagined that the spindle would see the 3 phases, and that everything else would see ground from the logic/steppers. Oh well. Live and learn. The next will one will be neater
Some use shielded cable from VFD to motor, I usually use TEW/MTW tightly twisted and run in metallic flexible conduit.
Another catch if using the 400hz Chinese hi-speed spindles, the ground pin on the 4 pin plug on the motor is not actually grounded.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
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