Over running 3ph motor

[robgraham]

I've just bought an older wood working lathe (Wadkin Bursgreen BZL) which has been converted to an electronically controlled 3ph motor.

One thing that wasn't made clear in the advert was that there was a size constraint in the conversion and the largest pulley of the motor's 4 block was machined off with the result that the maximum turning shaft speed is 1400 rpm. The seller has now told me that he was advised by the motor supplier that the motor can be run quite happily up to 100Hz from the electronic controller, which would allow the lathe to run at its designed maximum of 2300rpm easily - 82Hz being required for this speed.

On the basis that the motor will be a 4 pole one and that 2 pole 3 ph motors run at 2,800 with the same type of rotor, this seems plausible,but I would appreciate some 3rd party opinion.

Thanks Rob

[Andy Dingley]

Then away you go.

My only concern would be cooling, bearings and balance. As this is "big iron" I'm guessing that your Wadkin is a similar '60s vintage to my own cabinet saw. Was the motor of that period designed to cope with running at 3krpm? Will it have sufficent airflow through the case, and are the bearings still in a state to handle it (although minor vibration in a lathe motor is less trouble than for a saw).

Electrically it will be fine. The magnetic losses will actually be lower, so it might even run a bit cooler and happier. If you have an inverter drive that supports it, pushing the frequency up is a well- established practice.

[Rob G]

Many thanks, Andy

Just to clarify - the motor is modern as the previous owner wasn't capable of doing the star /delta reconnection so bought a new one. The reason for cutting down the pulley block was that the shaft was short.

As a passing comment, I had no bother reconnecting the coils in a friend's 3ph lathe motor. Like all things older, it was easy to take the case end off, get access to the coil connections and change from star to delta. The biggest pain was re-lacing the windings.

Rob