Triac PC Linuxcnc

[Doddy]

John, I've looked at the link to that board and I can't work it out - but it looks probable (PCB underside image) that the 0V reference for the 0-10V analogue output is common with the other 0V references on the board. In that case - I understand your concern with effectively raising the 0V reference to some hundreds of volts that the Spindle Controller operates. If that 0V cannot be isolated (between the logic and the analogue output) then, yes, you have a problem. I understand your argument of adding an isolation transformer to allow the 0V rail to be raised to that of the spindle-controller, but - of course - at that point you're raising the common 0v reference, back to the logic supply and ergo the short-circuit hazard remains at the point that you connect to another system - the connecting PC. It crossed my mind whether you could do the opposite and provide an isolation transformer (1:1) to the supply to the spindle controller, but you would wonder if there's any internal bonding of earths to line neutral anywhere on the spindle controller - either direct or indirect through EMF caps. Considerable care is needed going in this direction.

These https://www.amazon.co.uk/Isolation-Q.../dp/B082NXR4PR look interesting and useful. I've no experience of them, but understand the description rather better than the BOB.

[JohnT]

Thanks Doody. Yes I checked with a multimeter and the Bob shares it's grounds. I was looking at those isolation boards. I checked the motor controller and measured the 0-10v terminals against each other and to machine ground. I'm getting 270v DC and 9v AC with the multimeter. I don't have an oscilloscope. I'm leaning towards ordering one of those isolation boards. But if it doesn't work I could blow the motor controller etc. I'm thinking feeding one end of the isolation board to the 0-10v terminals on the motor controller and the other end to the 0-10v output on the Bob. Use a transformer power supply to feed the vcc and ground. Or else not risk it and let linuxcnc control the SGR relay and use a potentiometer to control the speed.

[Doddy]

Thanks Doody. Yes I checked with a multimeter and the Bob shares it's grounds. I was looking at those isolation boards. I checked the motor controller and measured the 0-10v terminals against each other and to machine ground. I'm getting 270v DC and 9v AC with the multimeter. I don't have an oscilloscope. I'm leaning towards ordering one of those isolation boards. But if it doesn't work I could blow the motor controller etc. I'm thinking feeding one end of the isolation board to the 0-10v terminals on the motor controller and the other end to the 0-10v output on the Bob. Use a transformer power supply to feed the vcc and ground. Or else not risk it and let linuxcnc control the SGR relay and use a potentiometer to control the speed.

From what I squinted at with that particular board the circuitry was visible separate from the LV and HV sides. You’d supply the LV from the general machine supplies and the HV from the reference voltage provided by (most) spindle controllers (is these that you’d otherwise write a speed control pot to). It’s low risk and you can test with a meter easily. I wouldn’t have much fear of going this route.