[Quada]

I am in the process of building a plasma tube cutter and ran into an issue that I can't seem to resolve. My plasma cutter is a cheap ebay cut 50F pilot arc that has served me well so far. It is running on 220V and my stepper motors are running on 110V. When my plasma cutter turns on (arcs), my stepper motors go haywire. Sometimes they go back and forth, sometimes they go one direction but it doesn't stop until I turn the plasma cutter off. First I thought I would try to isolate the stepper motors from the "table" so no residual current would flow through the casing. I did this by using plastic hardware between the stepper motors and the table. This did not work. I removed the stepper motors from the table and placed them away on a piece of plastic away from any metal. When I turned the plasma cutter on the stepper motors went haywire again. I thought the feedback must be going through the 220V circuit through the breaker panel and into the 110V circuit. To try to eliminate this I bought a battery backup (UPS) for the 110V components. That didn't fix the problem, even when I completely unplugged the battery backup from the supply power and just ran the stepper motors and computer from the battery. So at this point the stepper motors are completely removed from the plasma table sitting in some far off land not making any contact whatsoever with the plasma cutter, everything connected to the stepper motors (computer, breakout board, stepper drivers) is running on battery power from the UPS (UPS is unplugged from the wall), and somehow still when I turn the plasma cutter on the motors start turning! There can't possibly be that much inductance in the air, can there be? Am I missing something simple?

A few things to note:
- no other 110V components (lights, drills, TV) have had issues when running the plasma cutter until now
- When the computer turned is off (drivers and breakout board still on), the stepper motors do not exhibit any weird behavior, even when connected to the table
- Stepper motors operate flawlessly when the plasma cutter is not arcing and I can run through g-code just fine

I attached a few pictures of my setup for reference.

[Maglin]

It doesn't appear you are running shielded wires on your stepper motor wiring. You can try wrapping your wires in aluminum foil and ground it at the same grounding point that you are using for all of your other electrics. If you use a different grounding point you can end up with a differential potential and still exhibit emi on your steppers.


Or just spend a few bucks and get shielded cable. For how much you've spent already you could have done several upgrades. Good luck.

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[Quada]

It doesn't appear you are running shielded wires on your stepper motor wiring. You can try wrapping your wires in aluminum foil and ground it at the same grounding point that you are using for all of your other electrics. If you use a different grounding point you can end up with a differential potential and still exhibit emi on your steppers.


Or just spend a few bucks and get shielded cable. For how much you've spent already you could have done several upgrades. Good luck.

Sent from my iPhone using Tapatalk

Can you expound on the upgrades other than the shielded cable? I have some shielded CAN cable laying around that I can try.

[flyinwilly]

When I first built my table, I used the CUT40D plasma cutter. It worked great but I would occasionally get strange motions from the steppers. I had used shielded cable with a drain wire on ALL of my circuits and would still get an occasional misstep. The solution for me was to add a ground rod to the table. I sunk a 8' rod connected with 6 GA stranded wire to the table frame. Never had a problem after that.

Willy

[Torchhead]

Sheilding on motor wires stops SOME of the PWM noise from the motors from feeding back to the control circuits, but you cannot force erratic motion in a motor from external plasma EMI inot the motor wires. Workclamp on plasma is NOT ground so if your table is not grounded the plasma noise gets injected on the table side. You are getting false steps from noise getting into the control (Logic side) before it gets to the drivers. If the axis Readouts (DRO's) do not move then its between the PC/Breakout board and the motor drivers. If they do move then its coming from the PC itself or even its keyboard.