Variable speed motor.

I've got three phase motors and drives from Newton Tesla on both of my lathe and my milling machine and wouldn't consider not having them The milling machine in particular went from very noisy due to motor induced vibration to eerily quiet. You can get cheaper than Newton Tesla, but you get what you pay for, and their after sales is top notch

HI I am new tonight so if I get it wrong sorry.

As an Development Engineer we use Invertek optidrive E2 Single phase inverters these ramp up to full speed and then slow to the set speed (amount depends on quality of motor), yes on single phase motors! I have reduced speed quite a lot, on several motors.

They are not cheap but do what they say on the box!

Nigel B

I'm not sure what size of motor you need but there are plenty on the market and an ad here or on Home Work page will I think get some response. Many motors have provision for reconnecting to Delta within the terminal box, usually there is a label under the terminal box lid explaining what to do. Locating the STAR point is not so difficult either, but it does need the motor to be dismantled. Scratch mark the stator and end shields so that it is easy to reassemble, two marks one end one mark the other. Be careful when with drawing the rotor, not to scratch the varnish off the copper windings. Look at the stator winding ends and you should find a lump, not a big one but a lump never the less. That is the STAR point where the three wires are connected together, they need separating and extending so that all three will extend into the terminal box, together with the other three,6 in all. Make sure that you insulate the new connections very well. Next you have to get the Delta connections correct, for this you will need some form of continuity tester, a multi meter, battery and bulb or battery and buzzer. There are three separate circuits, for every circuit there must be a one end and a two end of the winding. Identify and label all three using the meter and some coloured tape or masking tape with writing on. The original ends will all be the two ends, mark them U2, V2, and W2.Now connect together U1 to W2,W1 to V2 and V1 to U2 using a block connector. Job done. Sorry I don't know how to included a diagram. Regarding an inverter, there are plenty of used one advertised and I've never heard of anyone being ripped off. One of mine is more than 25 years old and it wasn't new at the time. Making a remote control box is easy as well. The control circuit is low voltage so cheap pushed and other switches are available from hobby shops. I suggest you do include a relay to give isolation from the main in the event of mains or other supply failure. give it a go, sorry about the protracted write up.Ted

I can imagine that being able to vary the speed of a standard single phase motor could be indispensable in some cases, ie cases where the motor of a lathe or mill is not amenable to being replaced with a 3 phase motor. My Emco mill has a very non standard motor with a long splined shaft so could be a candidate. I have not checked the inverter price but I expect it will be very expensive.

I think the fact that the motor starts up at full speed would rule out it being used on a lathe (unless it has a clutch). In my workshop I have mostly 3 phase motors with VFDs and I use the ability to start at just a few RPM every time mainly for safety reasons. Even if I had left the chuck key in the odds are it would just fall out rather than being flung across the workshop, same applies to fly cutters or something held in the four jaw. At very low RPM there is very little torque so its unlikely any damage will occur.

The consensus always seems to have been, that you cannot usefully vary the speed of single phase induction motors. Invertek have blown that myth out of the water.

Ian P