Thread: Attention BobL

With old motors one can never be sure what they are.

The wiring does look like a Delta connection but given it is a biggish lathe it could also be a "415V Delta" which is different from a "240V Delta".

If it is a "415V Delta" and you connect that to a 240V SP-3P VFD, it should still run BUT will generate less than half the power.
This will mean if you try and load the motor up by trying to take deep cuts with the lathe it will damage the motor and possibly the VFD although they usually take care of themselves.

This is what I would do.
Get a sparky to connect up a 240V Sp-3P VFD. Remember this should be a 5HP rated VFD
Careful start taking ever deeper cuts with the lathe, if it stalls, or trips the VFD then it is most likely a 415V Delta wired motor
There is naught you can do about this except replace the motor.
If it is a 415V Delta motor and you convert this motor to Star it will produce even less power.

If you do not intend to ever use the lathe to take deep cuts you can derate the motor by current limiting the VFD. This decision and the current limit used is best done by a sparky for your given situation.

My preference would be to replace the motor with a new or decent second hand one.

Remember with a VFD you have to strip out all switches including reverse between the VFD and the motor and connect the VFD directly to the motor. Figure to do this might damage the motor and VFD. A big lathe like this probably has a coolant/lube pump. f it is a 3P pump there will be issues connecting it to the same VFD - but lets leave that for another time.

Thank you
Dick