Grounding!

wilriker

@wilriker FYI, If you have a plastic spool holder, it will transfer static charges via the filament onto the ungrounded) extruder motor (2 users recently have been hit by this problem)

That is interesting, I would have never thought of that!

Currently I am still using the crappy Anet A8 acrylic frame but I will switch to an aluminium frame (similar to AM8) somewhen in the next two weeks. I already planned to ground the motors then as part of wire-management-redo. I would probably left out extruder as I had not seen how this could be charged up.

SnowCrash

@hey_allen said in Grounding!:

In the interest of getting rid of the stray electrical charge developed from the moving belts, I suspect that it would be best to route it to earth ground, rather than the common rail of the power supply.
This would minimize the chances of the static possibly causing any issues, and dissipate it direct to ground, rather than routing it through whatever electrical path before eventually, hopefully, being tied to ground.

This reminds me that I need to double check my grounding...

Thanks, @Hey_Allen. Makes perfect sense!

ShiftingTech

@snowcrash I think safety ground is the way to go. Since that's where your frame should nominally be connected anyway. And you're basically just extending your frame grounding to your motors. Connecting to DC or AC negative / ground creates some non-zero possibility of having something go wrong, and the motor casings ending up energized to one voltage or another!

DocTrucker

@dc42 said in Grounding!:

The earth spade on the Ethernet module is for when the Duet Ethernet is mounted against a metal plate that forms part of the printer case, so that you can ground the Ethernet connector to the case. PCs use a spring metal tab for the same purpose.

I was originally thinking about two things; cancelling out the filters in the PSU if the earth tag was directly tied to - VIN and setting up an earth loop in machines (like ormerod2) where the build instructions directly tie the earth and PSU negative.

I've had a look at the wiring diagram and assume the capacitor C12 and resistor R1 are there to sink induced AC and DC voltages that build up on the Ethernet socket body. This would be shorted out if you had earthed the machine and linked the PSU - and earth together.

Phaedrux

When building my printer I took extra steps to ensure everything was grounded form the frame, to the build plate and motors. Everything is tied to earth. I also tied DC- to mains ground as well as it seemed to be recommended for safety. The only downside of that I saw discussed was the potential for creating a ground loop, especially when using the USB port.

https://duet3d.dozuki.com/Wiki/USB_ground_loops

My solution for the ground loop is to only connect to the USB port from my laptop when on battery power, which happens very rarely now that setup is complete.

Are there any other negatives (Pardon the pun) from connecting DC- to mains ground?

dc42

@phaedrux said in Grounding!:

When building my printer I took extra steps to ensure everything was grounded form the frame, to the build plate and motors. Everything is tied to earth. I also tied DC- to mains ground as well as it seemed to be recommended for safety. The only downside of that I saw discussed was the potential for creating a ground loop, especially when using the USB port.

https://duet3d.dozuki.com/Wiki/USB_ground_loops

My solution for the ground loop is to only connect to the USB port from my laptop when on battery power, which happens very rarely now that setup is complete.

Are there any other negatives (Pardon the pun) from connecting DC- to mains ground?

I recommend connecting DC- to mains ground, and taking appropriate precautions when using a USB connection (see https://duet3d.dozuki.com/Wiki/USB_ground_loops). If you don't then you risk getting a mild electic shock under normal conditions (see the video by Makers Muse), and a severe one if the PSU develops a fault.

DocTrucker

I thought a voltage build up that was large enought to cause a safety issue on the earth would trip an RCD disabling the whole machine as soon as possible?

You wouldn't use normal RCD on an AC servoed system due to the filters being designed to leak to earth, but that isn't an issue with our systems is it?

DocTrucker

Reading up on this and I can see it is a mine field with huge learning curves on some bits if you let youself drop too deep!

I had heard in the past about people worrying about the failure mode of switched power supplies causing mains on the DC out but this appears to be mitigated by an internal fuse. Float between multiple PSUs would not be great but I've commoned my PSUs.

So the earth tie must be to try and stop the DC floating higher than the expected 'safe' 24VDC, but this is also potentially done internally by a similar RC circuit to that between your ethernet socket and -VIN? Tieing the earth to the -DC does potentially reintroduce the noise kicked out of the non-linear switch mode supplies to your -VDC and so screwing with your temp readings.

Are there no standards that we can look for that indicate the earth is tied with an appropriate RC circuit internally and there is no additional need to tie? Is this a product of buying cheap PSUs? Or perhaps is it my PSU which needs an RC circuit because of the noise that it kicks back to the mains that is confusing me?

Edit: I've made a few references to RC circuits (resistor capacitor), but apprecieate the internal circuits in the power supplies may be more complicated with over voltage shunts and transient suppression to mention a couple of things. I guess the main question is if it is safer to tie why don't the PSUs all arrive like that?

DocTrucker

@dc42 said in Grounding!:

I recommend connecting DC- to mains ground, and taking appropriate precautions when using a USB connection (see https://duet3d.dozuki.com/Wiki/USB_ground_loops). If you don't then you risk getting a mild electic shock under normal conditions (see the video by Makers Muse), and a severe one if the PSU develops a fault.

Makers muse issue was no ground connection to the mains. Nothing todo with DC - to earth unless he has been nearly shocked twice?

Video makers muse references:
https://m.youtube.com/watch?v=3jYZDLOV4Jc

Makers muse video #1:
https://m.youtube.com/watch?v=Lt-0n95GvQo

Makers muse video #2:
https://m.youtube.com/watch?v=v1OuYg7AJjw

gen2eng

I'm been slowly commissioning a CoreXY machine. I've been using a carbon fiber filled PETG filament for rigidity and better heat resistance. The stepper brackets are fastened securely to a 20x20 anodized aluminum frame and the steppers are fastened to brackets using the usual 3mm screws. I've not attached any bonding wires between the frame and motors.

On a whim this morning after reading this thread, I check for continuity between my printer frame and the steppers and I have about 30 KOhms resistance between the body of the steppers and the mains ground. It's not highly conductive, but it's enough to be considered static dissipative and prevent a build up.