Rf-emi problems possible..arduino-ramps 1.4

For several yrs now have been using arduino mega 2560 with ramps 1.4 for cnc plasma machine.just recently i have had a few loss of connection issues while actually cuting..When the plasma cutter is not on things work perfect then when the cutter is on it will do the first couple of cuts then freeze up.These are not high frequency start.. the cutters are blow back start made specially for cnc cutting..I am thinking it is an rf or emi interference problem..And even more so just with certain computers.. So far i have had this issue with two out of maybe 60 machines.. I put ferrite cores on the wires on the last machine but it was to late the computer was already damaged....I hooked up one of my other computers and it runs flawless.. SO here are my questions.???Is anyone else running arduino for cnc plasma?If so have you had any similar issues and what did you end up finding to be the cause of the problem?
Have you noticed your connection is more stable with one opperating system than with another?I personally noticed better connections with repetier 1.5.6 than with the previous versions..I was having pretty good luck running win 7 as long as the computer origonally came with win 7..IF it came with xp or vista and had win 7 installed it seemed to be a much weaker connection an very easily lost connection if everything else was not exactly perfect..The funniest thing of all these issues is it will run for hrs without a problem as long as the plasma is not on.. I am considering getting netbooks to give with the machines but seems most of them have pretty slow processor speeds ..Is anyone running a netbook that is really happy with thier system?

The usual culprit for this sort of disconnection is current transients in the ground loop that is formed when you connect the 3D printer (or in your case the plasma cutter) to a PC through a USB cable.

To mitigate the problem, my usual advice is to power the PC and printer and nothing else from the same power distribution block, and use a USB cable with a ferrite bead on it. But your plasma cutter may be generating too much ground noise for that to be enough.

To eliminate the ground loop, instead of a mains powered PC you could use a laptop or tablet powered from batteries. Alternatively, instead of RAMPS you could use more modern electronics that provides an Ethernet connection and use that instead of USB. Ethernet provides galvanic isolation, unlike USB.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Another plus for Ethernet is, you can move the PC further away from the EMI-source.

-Olaf

Being a PC repair guy, my first thought was maybe it is just a dirty USB connection. It sounds like it / they worked for an extended period, and started to just recently fail? If it were EMI, I would expect that to show up quickly, unless something has changed in the surroundings. By putting a new PC in place and the problem goes away, just enforces that that thought.

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dc42
The usual culprit for this sort of disconnection is current transients in the ground loop that is formed when you connect the 3D printer (or in your case the plasma cutter) to a PC through a USB cable.

To mitigate the problem, my usual advice is to power the PC and printer and nothing else from the same power distribution block, and use a USB cable with a ferrite bead on it. But your plasma cutter may be generating too much ground noise for that to be enough.

To eliminate the ground loop, instead of a mains powered PC you could use a laptop or tablet powered from batteries. Alternatively, instead of RAMPS you could use more modern electronics that provides an Ethernet connection and use that instead of USB. Ethernet provides galvanic isolation, unlike USB.

i did put ferrite beads on the usb cable after i noticed the issue with this last machine.. Butt it still messed up. i switched computers and it worked fine.i am guessing it already hurt something in the computer.. i was just thinking this would most likely not be a problem running wifi or bluetooth but didn't think about an ethernet set up?this customer has some of the worst wiring i have ever seen in a shop they had a 50 amp 3phase converter powering a 105 amp cutter from a 30amp breaker using number 10 wire for a 50ft run? I am now running a hypertherm powermax 65 on that machine .. I told them to wire in the 220 outlet properly they stuck a 50 amp extension cord thru plastic pvc pipe going back to the electrical panel.. so am pretty certain there is a ground loop problem even without hooking up a meter or scope.

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cat.farmer
Being a PC repair guy, my first thought was maybe it is just a dirty USB connection. It sounds like it / they worked for an extended period, and started to just recently fail? If it were EMI, I would expect that to show up quickly, unless something has changed in the surroundings. By putting a new PC in place and the problem goes away, just enforces that that thought.

These customers had issues right from the start both have what we will call less than perfect wiring in there shop..The one machine was a used machine and my old hypertherm powermax 45 that i had used for 2 yrs without problem. the machine was roughly 3 months of use and worked fine in someone elses shop. moved both to the guys shop and bam it is messing up..The cutter shut off twice and flashed the low voltage indicator.. and the computer losses connection and freezes up like the other one did

I worked with Automatic cash machines for years, we had issues with EMF noise being generated by stepper motors from within the ATM's.
It was always a requirement to use shielded USB cables within the ATM as well as shielded ethernet external cables.

Often a ATM would go for years and then you would end up with intermit problems when someone had installed non shielded Ethernet wiring in a building. The buildings had PC's on the network wouldn't be affected.
I think what would happen with Ethernet that the Ethernet driver chips would slowly degrade and output signals would reduce and then the ATM EMF noise would start causing errors.

If you think that there is a ground loop issue, try running your mega 2560 on a power backup unit which is disconnected from the mains power, Isolated a few faults that way in the past.


Cheers.