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ESD and 3D printers from filament?

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A few days ago I came across this thread on the Prusa forum and I thought it could be of interest to folks here too.
This might apply to many other printers and might be the cause of "mysterious" resets in the middle of a long print.
My printer is a Prusa MK3S and has been working well for about two years.

Although it started about ESD corrupting the display I remember other comments in various forums about a dry carpet ESD resetting the printer and in some cases having to replace the controller board. In winter the house has very low humidity and, although very good for the filament spools, it is nasty for ESD. I remember having to scratch the paint off to ensure all the parts of the printer were well bonded to the PSU ground (as well as the powerline ground) and ran a ground wire to my metal baseplate and table (as the four printer feet are isolating it). The LCD screen and rotary controls are housed in a PETG enclosure so any ESD from the display metal edge would be carried out the circuit readily.

If you get deeper in the thread I got to check to see if the build plate was grounded. It is not, nor is the all metal extruder assembly. Everything around there is made of plastic so none of the rails, stepper motors, bearing/rods are bonded to AC ground but all interconnected to the controller board eventually from floating assemblies. Easy to see how an ESD could get to the control board.

I ran a simple experiment with a Keithley 617 electrometer attached to the extruder cooling fins. There are two cartridges clamped on the extruder. The heater and the thermistor are both insulated from the extruder assembly; however it is easy to see that an ESD either from touching it or from touching the metal build plate could get to the control board jumping through the devices.

I used the Coulomb mode and then the voltage mode to monitor what happens during the process. Nothing, apart from random noise happened during the heating phase and the self leveling phase, but the moment the extrusion of the filament started charges appeared. I used the built-in first layer test pattern. It is basically a zigzag across the build plate with a simple 1x1 cm stamp at the end. The Coulomb mode went in overload in the middle. The voltage went to 50 to over 100V during the process. Even got over 150 in some runs to nearly 200-300 by using a tissue to induce a small charge on the filament prior to extrusion, probably similar to the filament cleaning things used by some people. This is for one layer.

I suspect that with a dry environment and a floating extruder head during a long print the accumulated charge could jump the thermistor and zap the controller board causing a uP reset and such. It does looks a lot like a van der Graff generator accumulating charge from an insulated belt carrying it to the globe for me. Depends on so many factors it is hard to tell.

How many other brand of 3D printers could be affected? Anyone has checked if the extruder assembly is grounded?

Thanks to the comment from Joan in the Prusa forum for seeding this inquiry!
Comments welcome.



I have a Creality CR-10 Mini.
There is no continuity between any of the printer assemblies where there are V-slot wheels.

No continuity between any of these:
  1)  Control box
  2)  Main frame
  3)  Build plate
  4)  X-axis gantry
  5)  Hot end

Interesting ESD problem.  My printer is in a small bedroom with carpeted floors. 
I have zapped it before but never had any issues.

Creality has a official grounding method for Ender 3 V2 to solve the layer shift issues people see.   Fixed the layer shift for me once it was installed.

Just found this link where someone does make the van der Graaf comparison...
So... I was not the first one to think about it looks like :-[

So the issue of shifted layers or resets in the middle of a long print might be related to ungrounded extrusion heads. There are so many factors such as the filament, its initial charge on the spool, if it was cleaned by rubbing a soft cloth on it, humidity and temperature, electronics sensitivity...

I just grounded my setup with a 100k resistor to the frame and a thin wire attached to the extruder cooling fins via the ombilical.

I have an Ender 3 pro. All the rails are linear rails after I upgraded them, so they all have continuity between each other. However the aluminum plate on which the glass build plate rests is not "grounded" to the rest of the system. Also, the metal parts have no continuity to the AC line ground.

I have noticed (and this is simply an annoyance) something when I start a print and need to cancel it after a few layers. The very thin and flimsy plastic waste I need to toss has a very high static charge and I can't flick it off my tool or fingers very easily. So, I'm going to look into getting a connection between the aluminum plate and rails, and if advised, grounding the metal parts of the case and rails to actual earth ground.


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