Denford Novamill Mach3 conversion

[Miller]

I took ownership of this about a week ago and I've already spent some time chasing the wiring and figuring out what components to order. I decided on an AKZ250 Mach3 USB controller (leafboy77) and already ordered it, plus 3 stepper drivers to go with it.

I am planning to use the existing spindle driver which is a Sprint 400 unit.

I have a question about the control signal going to the Sprint 400, the manual says 0-10V. Does that mean pulse with modulation, or literally 0-10V as if it were potentiometer control?

[JAZZCNC]

I have a question about the control signal going to the Sprint 400, the manual says 0-10V. Does that mean pulse with modulation, or literally 0-10V as if it were potentiometer control?

Means 0-10v so either potentiometer or 0-10V analog signal from speed controller.

[Miller]

This is what I found in the controller manual. So it looks like a 10v source through an 1k resistor, joint with the PWM output, turns into 0-10V analog?

[irving2008]

That's exactly what it does. The PWM output is active low, i.e. a pull-down to GND. The wider the pulse the lower the average voltage.

[JohnHaine]

Normally you would have a smoothing filter to convert the PWM to an average voltage, presumably that must be in the vfd?

The other thing to be careful of is to check the vfd is ground referenced. My Novamill came without its control box so I had to build the whole thing, using a KB Electronics thyristor controller. In this the 0V rail is not connected to ground but floating with 100v or so of rectified ac. Not a good idea to connect to a controller with its 0V common earthed! Currently I use manual speed control, will have to rig up an opto isolator to allow M3 to control the speed.

The Novamill is a great little machine, much nice than a converted Sieg machine, enjoy!

[irving2008]

All commercial VFD control inputs are referenced to signal ground, which shouldn't be confused with safety earth. The AC input and UVW outputs are isolated/floating.

The VFD has effectively got a low pass filter on the speed control inputs as it has a limited slew rate on speed. You could add an external capacitor but it's not needed.

[EddyCurrent]

The VFD has effectively got a low pass filter on the speed control inputs as it has a limited slew rate on speed. You could add an external capacitor but it's not needed.

Irving, are you referring to the ramp settings here ? which basically use a capacitor integrator. I say this because some drives can trip on overcurrent if the ramp is set too low which implies the input itself is not filtered.

[irving2008]

Not specifically, I know my VFD couldn't respond fast enough to recognise individual pulses at low duty cycles even on a 100Hz pwm. So no capacitor needed.

[JohnHaine]

I think you're being a bit categorical here Irving! You can't rely on a limited slew rate to do the smoothing for you. And your comment on ground referencing isn't helpful because by definition "signal ground" is what the control inputs are referenced to! The question is, can the 0v on the controller be safely connected to the signal reference on the vfd?

The Novamill does not use a vfd since the motor is a dc permanent magnet type and the original controller I think is thyristor based. There may or may not be isolation between the trigger circuit and the speed control circuitry, on the KB Electronics one I have there isn't.

Miller, I suggest that you ask the question on the Denford forum, denfordata.co.uk .

[Miller]

Thanks, so it's not as easy as it looks then. I have couple more diagram, one for the spindle driver and another one where it shows the breaker board's own 5V supply used to form an analog signal. Can we draw some definitive conclusions over the above issues?


Breakout board's own analog signal.






Sprint 400 spindle driver schematics below, pot goes on terminals 1/2/3 on the left.