View Full Version : Need help to install VFD on small lathe

10-21-2013, 03:50 AM
I would like to install a VFD on a Emco V10P lathe.

My current lathe works well and is fitted with a single phase, two speed motor.
I also have a 3 phase 2 speed motor that i would like to fit to this machine.

I use my machine almost exclusively in the low speed range, but since i only have 4 gears to work with, this limits me to 60, 240, 315 and 1250 RPM.
I would like to employ a soft start function to take up backlash in the drivetrain, be able to adjust the speed of the motor to give infinite range of speeds and have an electrical braking function.

I think the 3 phase motor will be best for this, but some questions pops up with the wiring of it....
Should i include a relay to mechanically switch between the sets of windings on the motor?
Should i get a single - 3phase VFD (More convenient as this will not limit me to 3 phase) , or should i get a 3ph-3ph VFD (possible performance advantage) I do have 3 phase available

I plan on making a new panel for this machine with buttons for: Direction selector, Spindle start, Spindle stop, Brake on/off and E-STOP

Any advice or suggestion would be much appreciated.

10-21-2013, 10:50 AM
The problem with 1ph motor with VFD is the tendency to drop out of run on load when at low rpm's.
Run the 3ph motor on the high range and use the VFD for the lowering the RPM.
For this a phase/vector model will be worth paying slightly more that the V/hz only model.

10-21-2013, 03:24 PM
Thank you AL, I was told today that since the motor has 6 wires, it might be wired as star internally and that this will not work with a VFD. Can you see the reasoning behind this? Looking at the schematic of the 3 phase lathe head motor, Can you tell how you would wire the motor for high and low speed operation? I find it difficult to understand the wiring of the switch in the schematic. What i do know is that from left to right, the buttons are: Reverse, Forward, Stop, Low/ High Select, Milling head.

10-21-2013, 05:18 PM
Normally a two speed, single voltage motor wired for high speed, as per your drawing you would take the U2,V2,W2 and feed the 3 phase in to these, then take U4, V4,W4 and connect these all together in a star point.
The U2 V2 W2 would be fed from the VFD.

10-23-2013, 07:59 AM
Thank you Al, I will see if i can get hold of a phase/ vector VFD and put it to the test.