Stepper motor wire causing interference



  • Hey there, first thanks for reading. I appreciate your time.

    I have an Ender 5+ running a Duet Maestro with a hemera direct drive setup inline with a Duet MFM. The hemera is a running a volcano hot end setup. Everything was working well, but I have had weird issues that I believe is being causing by the stepper motor wire being in close proximity with the thermistor wire and the Duet MFM wire.

    The problems I have seen: Initially I was seeing weird issues with the MFM. It would be working well, then all of sudden throw weird low to no movement errors followed by high movement errors. On checking the filament all was well, and I was starting to think that the MFM was bad or malfunctioning since I have not gone to 3.0 yet on the board. I read in the forums that perhaps proximity to the stepper motor wire was causing interference. This seemed to be the issue as I had all wires in a bundle wrapped in a prusa cable wrap and zip tied for good measure. I removed the duet wire from the bundle and had it run outside this bundle for some short prints. Voila, this fixed the issue! No more false readings. So I set out to separate the MFM wire from the stepper motor by putting the other wires between it. (I know, I can see my folly).

    That was when the thermistor errors started. Up until this point, my temps had been rock solid. I mean, boring. After PID tuning, things were just working well. I made the change with the bundle of wires, and now my thermistor was doing weird things. Running at the right temp, then dropping 15 degrees in a second then back up until eventually it would drop enough for a heater fault.

    On examining my hotend, it had come loose, which I figured was the problem. I reseated my nozzle, heat tightened it, made sure the wiring was good and then did another print. No problems at all! Problem solved! Yeaaaaah not so much. One print later, same issues.

    So I got a new thermistor, rewired the entire Duet to be the right ends, no jumpers etc. Got everything stock and kosher. Reseated all the wires in the bundle, making sure to keep the MFM away from the stepper motor wire. Made sure the nozzle was seated well, started a print.

    Heater fault. Same issue, sharp drops then return right back to the right temp.

    Scratching my head, I started searching the forums and found out that the stepper motor wire can also interfere with the thermistor. I slapped my forehead.

    Question; How do I shield the stepper motor wire from everything else effectively? This is the stock Ender wire that came with the unit with an extension I got from filastruder so I could go direct drive. I need to separate them out I think so I can avoid the cable noise and from getting false readings. What is the best way to prevent this?

    Again, thanks in advance for your advice and time.


  • Moderator

    I do a 4 wire braid on my stepper wires and regular braid on 3 wire devices and twist on 2 wire devices. This is usually enough. I have everything running through tight bundles and have never had an issue.



  • @Phaedrux said in Stepper motor wire causing interference:

    I do a 4 wire braid on my stepper wires and regular braid on 3 wire devices and twist on 2 wire devices.

    i do as well. its strange when this topic comes up and ask why i know how to braid, and i says its because of electronics wiring.



  • I think I saw a review on YT when this (or similar) problem was shown. In most extruders stepper is isolated from other parts. With hemera all is ALU, so there is a connection between motor and the thermistor housing. I would try to grounding hemera.


  • administrators

    I suggest using shielded cable for the MFM if it will be running next to a stepper motor cable. Alternatively, use 4 core shielded cable for the stepper motor.



  • @Phaedrux forgive my ignorance, but you are literally just doing a braid of the existing wires like you would long hair?



  • @Walternate thats how i braid mine



  • I do mine as two twisted pairs, twisted together. So the two wires for each coil are twisted together and then those two sets are twisted together. No idea if this is any better/worse than braiding them all together though.


  • Moderator

    @gloomyandy I've done both. It's easier and faster to twist the two wires of a phase then it is to braid. I haven't had problems with either way.

    The physics of it all is pretty complex and interesting. I had a good link for it a while ago, but can't find it now. But here's one that covers most of it. https://www.dataforth.com/protecting-signal-lines-against-electromagnetic-interference.aspx



  • Man, thank you everyone so much. I appreciate your responses and the time you took to do so. I am going to first try the braid/twisting, then will go to shielded if I have no luck there. Thank you again!



  • Okay coming on back for anyone reading this with possibly the same issue. The suggestion of twisting the wire pairs looks like it has fixed the issue so far. I have a 6-wire stepper cable that adapts on down to four to the Duet. I took an extension out since I really didn't need it, then popped the wires out of the molex connector two at a time. I then twisted those, putting them back into the ends when done. I ended up with 3 twisted pairs.

    Hooked everything back up, have run 3-straight days of prints and am back to boring flat temp lines and the MFM hasn't errored once. A HUGE thank you to the people who gave suggestions, they were right on. Thank you all!!



  • I've run into a similar problem, came here looking for answers. I'm converting a cheap xvico printer to a duet 3 board. (yes, the board costs more than the entire printer, but it'll work!)

    I only have the X and Z steppers connected so far, and the X limit switch. It already wont home properly. I found the limit switch is bouncing erratically when the stepper turns on.

    I thought I'd try twisting the stepper wires together, as suggested here, but I look at my printer and find it's using a 6 conductor cord to each stepper. 4 wires for the stepper and 2 more for the limit switch, bundled nicely in a black cord.

    I'll replace these wires. A few alligator jumpers to the limit switch and it works properly now.



  • @lorenzop said in Stepper motor wire causing interference:

    I found the limit switch is bouncing erratically when the stepper turns on.

    see this marlin page about hardware solutions for that.
    https://marlinfw.org/docs/hardware/endstops.html


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