What size VFD

I have a 4kw speed motor on my mill with a 1.5kw table drive motor in the base. What size VFD would be recommended.

Abeneman

Depends. Are you running the machine on 3 phase or single?

If you're running on three phase power, size the VFDs to suit the motor ratings.

If you're running on single phase power and can find single phase rated VFD's, size them to suit the motor ratings.

If you're running on single phase power and can find only three phase rated VFD's, size them 1 1/2 time or more larger than the motor ratings.

If you plane to use the VFD as a phase converter to run both spindle and feed motors be sure to adjust the parameters to defeat the built-in economizer circuitry. VFD's prefer to run a single motor. They don't like to run two motors differently loaded but you can force them to if you set the unit's parameters correctly.

If you plan to use the VFD on both spindle and feed motors varying the speed of the spindle will vary the feed as well.

I suggest you ontain two VFD's: one for the spindle and one for the feed - if they will fit in the budget.