800W Chinese spindle - earth coming live

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superfrog
Posts: 19
Joined: Tue Sep 08, 2015 6:50 pm

800W Chinese spindle - earth coming live

Post by superfrog » Sat Sep 19, 2015 1:24 pm

Hello everyone, first post, I hope I won't be breaking too many rules.

I got myself a 800W spindle:
- connected the VFD to mains, checked there was no L/N inversion, checked that neutral is close to earth. All good.
- assembled the cable going to the spindle with foil and braid shielded cable, 4x1mm2 (3 phase + earth), earthed shield at VFD side as well as on spindle side (as to earth the metal plug). The actual earth wire is spliced out at the VFD to allow for remote earth connection.

The casing of the spindle and the plug are not connected. There is no connection between any of the wires and the casing at any angle.

When I run the spindle, the earth potential goes high relative to casing after a while (meter says around 160V at 100hz decreasing to 110 V at 300Hz). I am starting to blame the VFD or the earth at the plug but it could also be charge building up in the floating casing. The fact that it keeps its potential when measured (the meter is likely a 10Mohm sense resistor) makes me think that simple parasitic charge is unlikely.

Anyone experienced something similar? Anyone has and Idea what the issue could be.
eShapeko #377: "Uncle Bob" 500x1000 deluxe frame, with nicely coloured plates.
Arduino Due + GAUPS 1.1 + 4xDRV8825 at 30V running G2
800W ER11 "Ol' Sparky" Chinese spindle + VFD

AnonymousPerson
Posts: 758
Joined: Sun Apr 26, 2015 1:16 pm
Location: 3753 Cruithne

Re: 800W Chinese spindle - earth coming live

Post by AnonymousPerson » Sun Sep 20, 2015 2:10 am

Has the vendor got any ideas what it might be? :)
Shapeoko 3 #516

superfrog
Posts: 19
Joined: Tue Sep 08, 2015 6:50 pm

Re: 800W Chinese spindle - earth coming live

Post by superfrog » Sun Sep 20, 2015 5:56 pm

I am going to ask the reseller; I suspect that it is going to be a rather long process: it took me five emails to ascertain where they were shipping from. I doubt they will be able to provide me with much assistance. I may have to contact the manufacturer of either VFD or spindle to understand what is going on. I suspect they will say that it is probably because of the other part of the system.

I am well curious as to how I could get such a buildup (which will shock you) without obvious electrical path.

The more I think about it, the more I thin it is a badly cabled earth in my electrical installation, I am going to check that my dwellings actually have functional earthing (plug tester is on order).
eShapeko #377: "Uncle Bob" 500x1000 deluxe frame, with nicely coloured plates.
Arduino Due + GAUPS 1.1 + 4xDRV8825 at 30V running G2
800W ER11 "Ol' Sparky" Chinese spindle + VFD

voneiden
Posts: 1
Joined: Tue Nov 11, 2014 4:58 am

Re: 800W Chinese spindle - earth coming live

Post by voneiden » Tue Feb 02, 2016 11:04 am

It's an old post but FYI in case it might be relevant to anyone, Chinese spindles often have a ground pin that is not connected anywhere.

superfrog
Posts: 19
Joined: Tue Sep 08, 2015 6:50 pm

Re: 800W Chinese spindle - earth coming live

Post by superfrog » Tue Feb 02, 2016 11:13 am

Thanks.

In this case there is some magical(probably capacitive, but I'll call it magical for simplicity's sake) coupling between body and something inside. As a result you get large voltage spikes on the body. As there is indeed no connection between plug ground and metal body, you get zapped on contact to the body, repeatedly and rather painfully.

Properly grounding the body solves the problem. I am already running 4 core CY cable to the spindle, I am planning on changing the plugs to have a pin connection for ground rather than relying on a dirty hack at the plug. LUMBERG SGV 40 and related look like they should be good enough (if a bit under for peak current rating, they are definitely better that what is currently on)
eShapeko #377: "Uncle Bob" 500x1000 deluxe frame, with nicely coloured plates.
Arduino Due + GAUPS 1.1 + 4xDRV8825 at 30V running G2
800W ER11 "Ol' Sparky" Chinese spindle + VFD

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