View Full Version : grounding via star connector

10-22-2011, 04:24 PM
I need to solve noise issues with my Chinese mill. The spindle stalls the motors for a short burst when I start her up and after checking the wiring I found that no shielded cables are used and high power travels close and parallel to PP cables and so on.

I did read most of the noise related posts but became confused over time, mainly because of the terminology used. I do understand some of it but would like to get things a bit more to the point.

I understand the advice about a star connector. But what exactly should I connect to it?
Here as I understand it:
1) I connect Earth that comes from the power point
2) I connect all the shields from the motor power cables and the switch cables and so on
3) It is best to connect the star connector to the case

Then I read about the common of the PS. My PS has a 48V out for the motors and a 5V out for the BOB. What does the term common stand for, is that actually the - (negative)?? Does that mean I connect the PS - (negative) to the star connector?

I can also see a grounding point on the BOB. Do I connect that to the star connector too?

Any help much appreciated.

10-22-2011, 04:57 PM
As you may have probably read there are two methods used, one is total isolation the other is grounding or making common to ground all parts of the system and their respective power supply commons (-ve's).
Regardless of what method you opt for, your PC MB is generally not isolated from your spindle.
The first thing I would look at with a Chinese mill is, is the spindle motor frame and VFD grounded to the star point?
The Earth Ground star connection should be set up at a convenient point in the enclosure or cabinet and the Service ground should terminate there.
Make sure your conductors to the spindle are at least tightly twisted if separate conductors.
Power supply -VE's are referred to as common, although often the term ground is used, which adds to the confusion.

10-23-2011, 03:51 AM
Thanks for your input, Al the Man.

First, there is no star connector yet in that box. Will have to do the complete job. Most of what you say I understand but would like clarification on some of it.
You say:

Regardless of what method you opt for, your PC MB is generally not isolated from your spindle.
What does this mean precisely?

"and the Service ground should terminate there"
What exactly is the Service ground?

10-23-2011, 11:20 AM
Unless you are using a Laptop, your PC. MB & P.S. and hence parallel port common is connected to earth ground via the MB. screws to the case, which is earth grounded by the ground conductor feeding the PC. P.S.

If using a mains fed spindle, one side of its supply (Neutral) is connected to earth ground, therefore the PC common and one side of the spindle are common to each other.

Service ground is the conductor that goes back to your earth ground entering your building, supplied by the service company or in lieu of that, any ground rod system you may have at the service entrance.

10-23-2011, 04:47 PM
Thanks Al the man, much appreciated.