RF interfering with stepper motors

[Bradnicent]

Hi all ,I believe my plasma machine is causing emi interference to my motors, When switch is triggered all motors move until plasma arc makes contact with the plate then stops moving .. I’ve tried moving the plasma machine 5meters away from the table with no luck .my table is grounded with a threaded rod hammered into the ground, plasma machine is plugged in a power source isolated from the Pc power source. Does anyone have a solution to this problem?

Thanx


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[coherent]

This is a common problem with the lower cost imported plasma cutters. There a few models and those from companies like hypertherm that play well with cnc machines and are recommended. Folks have tried just about anything you can think of to eliminate the interference (shielding, grounding etc) with limited or no success. Your mileage may vary, but a plasma cutter that has been tested and recommended for CNC use will save you lot of headaches. Yep, they cost more, but like everything else, you get what you pay for.

[Bradnicent]

R u saying there’s no way at all I can illuminate this problem? ... I just need some pointers and guidance to what options I have that will possibly work


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[rodw]

You have not really given us much to go on. What is your CNC controller? USB, Ethernet, Parport? What voltages are you using for your home switches etc?
What THC?
Are you using shielded stepper cables?
Is the cable shield unconnected at the plasma end?
Has the shield been passed through any connectors on your control box and grounded as close to the stepper controller as possible?
Have you followed the Hypertherm tech document on table grounding?
Have you got a centralised star ground on your table?
Do you have seperate grounding cables from the case of every stepper back to the star ground?
How long are your 5 volt signal cables to your stepper drives?
Do they run along any mains cables?
Also consider fitting a mains EMI filter to your control box. That and properly grounding my table were the biggest wins I had.

From the list above, you can see there are a lot of things you can do to improve interference from noise and I only know about these things because I had problems on my system.

[widgitmaster]

Noise is a big problem in most machines, I've built several from scratch!
All cables MUST be stranded copper with a braided shield, only one end of the shielding is grounded.
You can buy a coil of braided shielding, and slide it over many of the wires in your motion control box.
https://www.mcmaster.com/5537k27
This will help greatly, as simply grounding the machines frame is not enough!
Also, don't coil the plasma cable and motion cables on the floor, as this will create a noise field in everything!

Hope this helps!
Widgit

[Bradnicent]

Thanx guys I will look into all of this


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[coherent]

You don't say what make and model plasma cutter you are having the issue with. So, as i said... with some of the lower cost imported models like the Lotos, Cut-50 etc and their variants it is nearly impossible to eliminate the interference issues. There may be ways to do so, but the expense and work to do so would exceed the cost of a CNC compatible cutter. These cutters are great for the price for hand cutting and I have one myself for simple hand cutting jobs, but I tried about everything to get it to work with a cnc machine for a friend (grounding, isolation etc etc.) and finally gave up. They just put out way to much interference. I suppose if you had a custom computer and cabling setup made for high interference conditions it may work, but that option was beyond my budget and time. A good plasma cutter like the Hypertherm 45xp (or many other models and makes tested and recommended for CNC) will work perfectly and I've never had an interference issue with any of the Hypertherm models I have owned with any computer setup I've used near it or on a CNC plasma table.

[bamwa]

You are a ninja.