Ghost voltage

Some parts of the frame of my printer are not grounded because they are isolated by plastic parts. Should fix it, but my problem is something else.

I have a multimeter with ncv (non contact voltage tester). It struck me that if it is kept close to my printer it indicates that there is voltage on it. So I measure between frame and earth, result: 30 volts ac.

Weird thing is that if I disconnect the stepper motors, the voltage goes back to 8 volts.

I've tried everything, like replacing psu and looking for short circuit but found nothing.

It is getting weirder. My other multimeter indicates 0 volts. You would expect that my first multimeter has a problem. However, if I connect the frame of my printer to earth, both millimeters indicate 0 volts. And if I execute exactly the same experiment on my other printer both multimeters indicate 0 volts.

What can be going on here?

Edited 1 time(s). Last edit at 08/30/2018 11:59AM by OrionNebula.

I got a little low voltage tingle from mine the other day, powered off, not plugged into PC, like the type I used to get from TV monitor bnc.
When my sensitive wrist skin touched arduino pins.

Edited 1 time(s). Last edit at 08/30/2018 07:32AM by MechaBits.

IIRC the shock you can get from TVs is them getting statically charged, used to happen to me with old CRTs but I haven't noticed it much with LCD/LED monitors.

Anyways, it sounds like your frame isn't grounded, and a wire somewhere is making it live. 8V is normal-ish I guess, from capacitive coupling and the likes. 30V is pushing it. Are the motors connected to the part of the frame that gets electrified? I.e. are they bolted to it? And is it only live when the motors are running or as soon as they are plugged in and doing nothing? Also, stupid question on my part, but any chance your other multimeter is set to DC? That would give you a 0V reading on the AC voltage your first meter was reading.

Either way, ground the frame. No excuse not to, it's just a flat out safety hazard with no benefits. It's not even all that hard.

All motors except for the extruder motor are bolted onto the frame. The extruder motor is bolted in plastic. Its live when the motors are connected and doing nothing.

Both multimeters were set to ac. I actually tested both with mains and they both gave 240 volt.

Definitely going to ground the frame but I must also find out which wire is making it live.

The psu which is earthed and control board are on my bench and are not physically touching the frame. And I measure 0 volt between those and earth. So how could the wires coming from the board going to the motors carry ac voltage?

... this could "be inductive coupling", where conductive parts acts as "antenna" for electromagnetic fields.

This EM-fields can be from the mains wire or even from a WLAN sender or repeater.

Some twenty years ago my day-job was below 1km away from a DXF-77-sender - IC's, lying open on the table had a "shelf-lifetime" of some weeks only ... and if touching not grounded metal frames, the high voltage sparks were up to some Millimeters long!

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Viktor
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The meter input is extremely high resistance. It will read capacitively coupled voltages that would go to zero if there was any measurable resistance to ground. I wouldn't worry about it.

As an experiment, try measuring the "voltage" on your bed frame.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Sometimes I feel the tickling sensation too, when I touch the frame of my printers.
The wall sockets in Germany aren't polarized, so we never know if Line and Neutral are connected the right way or crossed over. ( Doesn't seem to matter, tho )

Anyway, when I pull the wall plug of the Meanwell LED-PSU and put it in the other way round, the tickling is gone.

I don't feel anything when touching the frame

My bed is made of wood tho

I did the same thing with my heat gun and there was a 20ish volts.

You will measure non zero voltage between almost any piece of metal and ground, and probably between your body and ground. It doesn't mean anything in the context of safety or 3D printing.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]