Movement of extruder motor (even without filament) causes temp reading to artificially dip and overshoot

[ceramichammer 0]

This is a very strange thing. I've been haunted by this issue by an original Ultimaker and an Ultimaker I built myself. I've had some intermittent temperature stability problems. In diagnosing this issue, I have discovered that when the extruder motor (and possibly other motors) is driven even without filament, the temp reading drops ~5C immediately. The temp controller compensates for this artificially low temp and pumps up the power. The instant the extruder motor stops driving, the temp snaps back up ~5C but by then it has overshot. This has happened on multiple Ultimakers with different hardware. I originally diagnosed it as a blown up stepper motor but now I'm not so sure.

 

[Dim3nsioneer 557]

Indeed interesting. Sounds like cross talk or (partial) short cut somewhere. Maybe you can check / answer a few things:

- Do you use an original UM shield PCB or a legacy board?

- Are the wires of the motor nicely twisted?

- Do the motor wires run in parallel with the sensor wires?

- Does the effect exist for any motor, i.e. also for x, y and z axis?

 

[ceramichammer 0]

Ultimaker 1.5.7 shield

motor wires are twisted nicely

motor wires do run in parallel with thermocouple amp board's power and signal wires

I'm still experimenting with other motors' effect