Plasma EMI Problems help/advice

[wiltshire_chris]

I knew all along the electric side of things was going to be a steep learning curve. I Ran many dry runs with a marker pen zip tied to the torch. Turned the plasma cutter on and hit start, it arced then cut out, no movement, tried again and the g code file was empty on the sd card, uploaded the code again and hit start. Well, let's just say it cost a chunk of money, my 18v power supply is out putting nearly 40v now and the magic smoke came out of the stepper drivers. The cutter is about 12 feet away from the control box, and the laptop a few feet on from that. From what I've read it was going to be hit and miss if I was going to have EMI issues but wasn't expecting it to be that bad. I've used the cutter with a hand torch for a few years with no EMI issues to surrounding computers. So, if I could have got it working later in the year I was going to get a jasic cut45, it looks like that will be happening sooner than later, those of you that are running these machines (same as razor cut45) with arduino what steps did you take to get rid of EMI if you even get any due to it being blow back start. 1 step forward 4 steps back this week.

[acourtjester]

Sorry to here about that, running a G-code will not blow things up. I would say you have things connected wrong somewhere, or what is called infant mortality (things blow up when first starting). I think that Plasma unit is used by Langmuir tables so you should get a reply from member here. EMF will cause errors but should not blow things up either, shorts are another thing. Using shielded wires for the motors and switch signals is mainly what is used for EMF protection some also use ferrite cores on cables too.

[wiltshire_chris]

It was very weird, I understand the g code itself can't do damage, and the only connection between them is signal wires, I can only imagine the PSU went wrong when the gantry started to move, so now I'm at replacing the PSU, both controllers (basic 2 axis table) the stepper motors and probably the arduino for good measure, annoying all the electrics where bought second hand, so no come back on anyone. The buget table build went from about £500 to £1700. How do you go about shielding the wires that come out of the motors? I wrapped these ones in foil tape but I'm now not sure if it worked

[weldguy]

"Magic smoke"...that's funny but not funny. What a bummer. I am not sure how that could happen with the Razorcut 45. Is your plasma cutters input power on a separate circuit than your 18v cnc power supply?

[wiltshire_chris]

It's on the same ring main in the workshop. Yup when the smoke comes out, the magic stops.

[weldguy]

And are you using a Razorcut 45 or a different plasma? I was not sure from reading your posts.

[wiltshire_chris]

I was using a cheap Chinese cut50, I've read mixed reports if it will work. I can confirm, for me it didn't. I'll order the cut45 over the weekend after a few beers so it won't hurt as much.

[weldguy]

Ah ok, I thought you had a Razorcut, makes sense now. I could see one of those cut 50's causing a lot of issues and never actually producing a good cut.

[Plasma-art]

The motors are probably fine, they can handle that voltage, just measure the coils for resistance to check.
Arduino's are extremely hard to shield when it comes to EMI.
I would not bother with them because they are going to be a continued source of frustration with plasma.
A second hand computer with a 5 dollar Chinese parralel breakout board is already way more resistant to EMI

For stepper shielded wire it's the easiest to get liycy 4x0.75 shielded cable, its totaly worth the expense.
Don't connect the shield at the motor side and connect the other side to the star ground.

Use star grounding to a good ground rod that has been checked by an electrician.
I have 15 meters of ground rod underneath my table and zero issues with a similar no name chinese plasma EMI due to proper grounding and no ground loops.
The material clamp goes from plasma to ground rod to material, so any stray current and EMI goes into the ground.

[wiltshire_chris]

thanks for the informative reply, for did you shield the short bits of wire from the stepper motors before the added shielded cable?

[Plasma-art]

Not yet, still in the testing phase.
Need to shorten the wires, put proper plugs on them and put steel motor covers over them.
Just wrapped them around the steppers temporarily and I should be ashamed I haven't fixed it yet.

Good optical isolation between the computer and plasma and solid grounding is what helping the most.

20221230_161724_compress73.jpg

[acourtjester]

this is the motor cables I buy you may need to find another vendor of your in Europe. You ground the shield at the controller end. Cut the motor leads to about 4" long and put a connector there. I use water proof auto type connectors
https://www.ebay.com/itm/144902876897?h ... R-r01L-5YQ

[N2 Welding]

this is the motor cables I buy you may need to find another vendor of your in Europe. You ground the shield at the controller end. Cut the motor leads to about 4" long and put a connector there. I use water proof auto type connectors
https://www.ebay.com/itm/144902876897?h ... R-r01L-5YQ

Is this good for power wires to the stepper motors and Is it rated for any amperage rating the motors could draw ?

[acourtjester]

Yes Stepper motors used on the size CNC tables used by most here would not need more current then this cables will carry. I have use a 1600 OZ-IN motor on a few tables using this wire.

[wiltshire_chris]

Small update, I pulled the control box apart earlier, it was second hand and used on a mill before me. The 18v PSU is actually 2 18v in 1 case with a bridge to make 36v. So that's where the big voltage I got came from. I pulled the drivers apart and it's fried the contacts that drive the motors, I'm guessing that when the plasma arc and caused mass EMI the arduino rebooted itself and sent both push and pull signals to the drivers, the drivers did what was asked but the stepper motors acted a short/bridge and burnt the drivers out

IMG-20230126-WA0055.jpeg

[weldguy]

Good find and good info, thanks for posting back, may be helpful to someone in the future.