Need help with unexpected/random stops on basic Parport/5 axis BOB setup

Lezard wrote: I've noticed also that the PC screen is a bit unstable, with some sort of diagonal ripples going through the image.

That means there is something very wrong with the wiring/shielding/grounding, but at least you have something to test with.
Looks like there is something drawing quite some power through the ground on that machine.
Use a DVM and measure the voltage from the ground of the outside socket ( the one that has no issues) and the one inside, i would bet that you will have quite a difference, most probably around 60V AC.
You will have to get that sorted before starting to use that machine as any grounding mishap in the shop can cause some issues with the machine .

Hello,

I've made some measures today :
- voltage between GND of outside socket and cabinet chassis (resistance to cabinet GND arrival = 0) :
- with all equipment powered, _not_ enabled : 0 Vac
- same, enabled : readings between 110 and 440Vac (!!), from a multimeter set to 500Vac scale
- readings depend on which var is powered : I've tried to connect each one in turn to see if one might be the sole bad guy.

- I've also checked the resistance between various points supposed to be grounded inside the cabinet, the chassis, and the GND arrival in the cabinet : everything seems OK, except for a 5 Ohm reading between the common GND of the vars and the GND source itself. These are mounted on the same DIN rail, and are supposed to be connected through the rail.

- I will check again that the resistance between the outside socket GND and the cabinet is close to 0.

Any thoughts ?

Thank you for your help,
Laurent

Lezard wrote: - same, enabled : readings between 110 and 440Vac (!!), from a multimeter set to 500Vac scale

That is not good, but at least now you have a route to follow :
Check the breaker boxes for loose ground wires,
Check all the sockets/plugs en route to the machine for proper ground wiring,
Check if you have a ground fault interrupter, if you do not, install one immediately, that is a must, not an option.
Then you have to check the equipment and find what is causing all that potential to run to the ground.
BTW, do not touch the machine while powered on and enabled and wear good isolating shoes, ruining shoes do just fine.

VFDs and servo drives can often send a lot of interference back up the main power lines. Sometimes it may be necessary to add an EMI filter before them.

That said, I am also having the exact same trouble with the same Chinese BOB. The input I am/was using for e-stop suddenly went intermittent. I've worked around it for now by connecting a 2nd unused input in parallel then to an or2 in hal. Mostly I think it is just a design defect or bad module on these cheap boards.

Hi,

Todd Zuercher wrote: ... I've worked around it for now by connecting a 2nd unused input in parallel then to an or2 in hal. Mostly I think it is just a design defect or bad module on these cheap boards.

Thank you for your suggestion. I've done the same, it sort of improved things a bit, but I still had unexpected stops. I've read also about the debounce function, this might also help, haven't tried that yet. This cheap Bob was intended as a stepping stone towards a more robust solution, I stll plan to upgrade it as soon as cash allows...

tommylight wrote: Check the breaker boxes for loose ground wires,
Check all the sockets/plugs en route to the machine for proper ground wiring,
Check if you have a ground fault interrupter, if you do not, install one immediately, that is a must, not an option.

I appreciate your concern re. safety. I do have a 30mA ground fault interrupter installed at the main electrical panel in the workshop, if that is what you mean ( not sure about the correct translation here) It does work : I just triggered it when I inadvertently touched a phase wire with a ground connected wire... All parts of the machine are also connected (including gantry and Z-axis) and grounded at the CNC cabinet ground.

I've attached a thick copper wire from the CNC cabinet chassis, and pulled it near the electrical panel from where the CNC is wired. Resistance between the end of this cable and the GND on the electrical panel reads as 2 Ohms (control wire is 10mm diameter copper strand, +/-20m long). So I believe the cabinet is grounded, at least it's connected to the GND at the electrical panel.

Am I wrong ?

I have also pulled the same thick wire directly from the CNC cabinet chassis to the building ground stake, to bypass all the ground wiring : this has no effect on the ripples on the PC screen.

The friend who helped me with the wiring can"t join me, as we are under travel restrictions due to the COVID-19...
I'm a bit lost !

@ Todd,
Had the same problem with a cheap BOB, the optocouplers would weaken with time and needed more current to open properly. Adding some resistors parallel to the existing ones on the inputs did remedy that and luckily had no issues with it anymore.
@ Lezard,
Yes, that is the GFI in US or FID here in Europe. To test it's functionality just short the ground to the neutral, they are both located at the bottom of the socket and open to access, here in Europe.
If i remember correctly, whenever i measured between two grounds in my shop, i always get less than 1 Ohm.