This topic is not new, but I felt some here might have good insight. I have a plasma cutting CNC table that I built using a cheap control board (MKS DLC32 V2.1). I noticed that when I fire the plasma torch it disconnects the control board from the computer which is linked via a sheilded USB. I've had some luck preventing the interference by wrapping the torch lead and motor driver wires in tinfoil, and running a ground wire from the z-axis mechanism to the control board's power supply case, but I can only acheive about 60 seconds of run time before the usb connection fails. I was advised to try a USB isolator which I will order soon. The computer is connected to a different circuit than the 220 volt plasma cutter outlet but there could still be some interference happening inside the main panel I would assume. I did have a bit better luck running a laptop off battery power but would still error out after about a minute of plasma run time. The best performance so far has been running the g-code file directly off the SD card on the board via a wireless app. As long as the device (phone) doesn't get too near to the work table it will execute the cut without error. But I would still like to run the g-code from a computer since it has more functionality than the phone app/wireless connection.

It is my understanding that plasma cutters (like the cheaper inverter type I'm testing) operate in the 10 kHz to about 200 kHz range. I understand there are several types of USB isolators (galvanic, optical) and was wondering if anyone could shed some light on this situation? I have yet to test star grounding techniques and just want to try one idea at a time to see what method offers the greatest improvements. If the USB isolator doesn't solve the situation I will then go on to grounding the cutting table to an outdoor earth rod. If that doesn't solve the matter I will make a sheath for the torch lead using faraday fabric and ground it to the plasma cutter's case. I will be upgrading the motor wires to twisted pair shielded soon as well. I will also be moving the computer and control board enclosure further from the work area, but for now I want it close and failing so I can test the other options.

Thanks for any advice and tips.
Sincerely,
Robert Hosking

 

@ Robhoski

Did you tried running the USB cable through a metal conduit ?
I would prefer using a standard GI water Pipe perfectly grounded only on one end closer to the controller and leave the other end open and run your USB cable through it.
Plasma cutters are known for inherent EMI/EMC when its not properly engineered.
Faraday cage of Plasma cutter will be a good idea.
If you have access to spectral Oscilloscope see what band the noise is getting generated and tune the cage accordingly based on the wave length by 4.

Also if the signal to noise ratio is just above tolerance then using a simple ferite beed on USB cable can also resolve the issue.

Let us know which one actually helped ?