CNC spindle control VFD problem

Quote:

Originally Posted by djc

Hello All,

I am having problems controlling my VFD with my Spindle 2 board and Mach3.

Let me hasten to add that the problem is neither Mach nor the Spindle board: testing the output with a voltmeter gives a rock steady voltage that varies linearly and correctly from 0-10v with the speed selected in Mach.

The problem occurs when I connect the positive and negative wires from the spindle board to the VFD. Suddenly the output voltage (and hence the frequency displayed on the VFD) jump about (oscillate) all over the place and proper control of the motor is impossible. With the spindle off (and the board disconnected from any signals, the VFD shows about 5Hz. When under Mach control, the voltage never reaches 10v at maximum speed.

The inverter is a Dinverter by Control Techniques (manual date is 1995) and works perfectly well when controlled by a 10k pot from its own 10v supply pin. The ends of the pot connect across 10v and ground and the wiper goes into the speed control terminal.

Any suggestions?

Should I connect a 10k resistor between 10v and ground in the VFD? Is the VFD pulling too much or too little current out of the Spindle board? Should I try an externally-powered 10k pot (i.e independent of the VFD)? Should I try the same set-up with a different VFD (Altivar)? Would a diode in the feed to the VFD have any effect (could there be a back EMF)?

Thanks for reading.

djc

i wonder if you have a ground loop issue and thats injecting ground noise into the link. measyre the AC voltage between the ground on the VFD (spindle running and spindle off) and the ground on the spinlde board. anything more than 100mV or so and you'll have a problem...