Grounding kossel mini frame

leif · 20 Aug 2018, 14:12

Hi all,
I have have been having random head-crashes of my kossel mini between 2 - 4 hours into prints. I have been able to isolate it to one stepper motor that has now eventually failed, but was reading up in the doku when I came across paragraph to ground stepper :

"Note: it is highly recommended that the stepper motor casings be grounded, especially in belt-driven printers. Otherwise, motion of the belts causes static charge to build up, which eventually arcs over to the windings. If the motors are screwed to a metal frame, grounding the frame is sufficient."

There was anorther post on here to suggest to do it by attaching ground to frame which in turn is attached to the stepper through metal vertex of the kossel. My question is if I can ground it to mains ground as seen in quick illustration as attached.

dc42 · 20 Aug 2018, 15:38

I recommend that you also connect mains ground to the V- output of your PSU. Just watch out if you use a USB connection to the Duet, see the wiki page on USB ground loops.

leif · 21 Aug 2018, 08:26

Thanks for quick reply @dc42 . I was aware of ground loops and have been connecting to the Duet with laptop powered by battery alone which was suggested a safe option. I also think the new doku is very very good, so thank you very much for this

I updated the drawing as suggested and will wire up the rest of printer again shortly. I have also updated my steppers to 0.9 17HM19-2004S as suggested earlier in your blogpost. Practically my kossel mini came together by reading your blog, so thank you so much again

veng1 · 21 Aug 2018, 19:27

Why not use a large value resistor, say 1M, between V- and mains ground?

That will still bleed off a static charge but not, hopefully, impact ground loops as much.

c310 · 21 Aug 2018, 21:49

why not to ground stepper motors body directly to main earth?
...without connecting main ground to V-

i grounded mine and it seems to work without issues....

fcwilt · 22 Aug 2018, 01:28

Hi,

Just to be safe I would not connect the PS connections V- and G without checking with the manufacture first.

In many, if not most, cases I think it will be fine but there are PS designs (at least on paper) where this connection would not be a good idea.

Frederick

Phaedrux · 27 Aug 2018, 06:30

@veng1 said in Grounding kossel mini frame:

Why not use a large value resistor, say 1M, between V- and mains ground?

That will still bleed off a static charge but not, hopefully, impact ground loops as much.

I've also seen it recommended to use a diode between DC V- and Mains ground but I can't seem to find it anymore. I'm not an electrical wizard so I don't know if that's good advice or not. But the reasoning given was similar to what you mention.

c310 · 3 Sept 2018, 20:59

@phaedrux said in Grounding kossel mini frame:

I've also seen it recommended to use a diode between DC V- and Mains ground

@dc42 can you help us on this issue?

article WiKi_USB_ground_loops says that
"Disconnect the power supply negative output from mains ground. For safety reasons, this is not recommended."

So, questions:

Connect or not to V- to main ground? what is the risk of not connecting it?
put diode or resistor? what kind of parameters ?
if it is diode - which side / polarity ?

thanks!

dc42 · 4 Sept 2018, 08:00

@c310 said in Grounding kossel mini frame:

Connect or not to V- to main ground? what is the risk of not connecting it?

https://www.youtube.com/watch?v=3jYZDLOV4Jc

c310 · 14 Sept 2018, 05:56

@dc42 thanks for video.

it is clear with grounding PSU, but in the video ground is NOT connected to V-

should i connect it or not? if yes - diode (which polarity than) or resistor... ???

thanks!

dc42 · 14 Sept 2018, 06:55

I connect it directly on my delta.