View Full Version : Grounding help, UCCNC, UC300 and connection loss

13-10-2015, 07:05 PM
Hi all,

I need some help regarding grounding. I have a system which is based on 4 G203V + HDBB2 (BOB) + UC300 + Altivar 12 (VFD).
Every time when I input a M3 or M4 or M5 command in the UCCNC software the UC300 loose connection with the controller. The spindle start (CW or CCW depending on which command is given), but to stop it (since the connection is already lost) I need to use the stop button from the VFD panel. If the controller box (with stepper drives) is not connected (with the BOB and UC300) everything is running as expected. I suspect it is a noise related problem.

My controller (with his own power supply) is in one box, the HDBB2, UC300 and power supply in another.

I have a plug extension from main. From that I have another 2 plug extension's. One is for controller, the box with HDBB2 and UC300 and VFD. All plug's are MasterPlug.

VFD and motor are earth connected to their terminals.
Connection are made it with shielded cable (CY Cable 4 core's 1.5mm) between VFD and motor, controller and stepper's, power for the second box (with UC300 + HDBB2).

On the second plug extension (which is powered from the other one) I have the pump for spindle an USB hub for controller.

The router (made entirely from aluminium) stand on a big table with MDF top.

How do you suggest to ground all of that?


13-10-2015, 09:36 PM

13-10-2015, 10:31 PM
Ye of little faith,

this is an inherent issue with any USB type communication device. That is why many of us prefer to use the Ethernet variety of motion controllers.

That said, you do not need to spend money on a controller, I am sure the UC300 is more than adequate.

So things to check/do just listed as they pop into my head:

1)Put a ferrite filter thingy on you USB cable if it does not already have one.
2)Ensure that the ground of the VFD is connected
3)Try to increase the distance between the VFD and the UC300/laptop
4)Plug the VFD directly to the wall socket
5)Ground your machine.

Seems you have already done the obvious and used shielded cable

Are you using a laptop to run the UC300? I seem to remember my USB data logger used to not like being on powered by a desktop, something to do with the 5V line being linked through to ground so it would pick up nearby motor noise and flake out

13-10-2015, 10:45 PM
Hi Komatias,

I have some ferrite filters and I put one on the USB cable. That make things even worse. The machine start to be unresponsive. The axis movement become erratic. Do I need to put one on each end?
Grounding the machine you mean put a wire from machine and something which is already grounded (the garage door will do it)?
Yes I use a laptop.

13-10-2015, 10:55 PM
Hi Gabi,

Ok well you could have a few issues going on here.?

The Uc300 is USB and some USB cables are better than others regards there shielding and ground. So use a good quality cable and keep it short has possible.
Then you have the VFD which is most likely the cause. The Shield of the Spindle Cable should connect to the VFD ground. Some say Ground both ends of the cable and others just one end, the VFD end. Personally I only ground the VFD end and never have any troubles.

Then you have the fact your control system is spread over several areas meaning your probably not using one Central Star ground point. This leaves you open to introducing ground loops.
The cables in your total system act like huge antena sending or recieving signals so if they are not shielded or there shields not grounded correctly to single point then stray signals will be recieved and wrongly seen then acted upon. Which is why your getting troubles because the VFD is a Bad boy when it comes to making noise and infecting any poorly shielded or grounded cable.

So ideally you want one Earth point that all earths are taken from and shields etc run to. Also run a Earth lead from the machine Frame to this same point.
Make sure you run all High power cables separate from Signal cables, so don't run spindle or power cables next to limit or E-stop or drive signal cables.

Ground issues are always hard if not impossible to track down with certainty in situations like this where spread over several places so My suggestion is to get everything BUT the VFD into one box. Keep the VFD separate away from signal wires.
This will make it much easier to use Star ground setup. It will also allow you to get rid of the extension cables which don't always help matters.

Edit: Here's a quick knock up to show principle of Star ground. Notice only one path back to the Earth pin on Wall socket.!
Also Notice how the DC power supplys Ground drawn has black wire is different to Mains Earth. Very easy to mixup DC Ground with AC earth when they are completely different things. DC Ground finds it's path to Earth thru the DC supply so not be confused with AC earth.
We are only taking about AC Earth here and Signal Shield paths to Earth often mistakenly called Ground.


14-10-2015, 06:45 PM

Thanks to Dean I was able to make it work. Everything is working as it should be.

I post in the wrong thread. I was asking about how I can mount the spindle cable without having the noise problems again. I have a cable chain with cables from X, Z axis and water hoses for spindle.
I intend to put another chain cable uplifted on some aluminium brackets for spindle motor cable.
What I try to find out is what is the safe distance between noisy cable and quiet ones (stepper signal)?


14-10-2015, 07:42 PM
Great stuff...:toot:

See other thread for reply to Cable routing.!