Calling @MaxHeadRoom

I thought I would post this in case someone else find them self in the same situation.
I bought a used Beaver wood lathe and it came with a 1/4hp AC motor. I needed to mount the motor in such a manner that required the motor direction to be reversed. I could not find a capacitor so I opened the motor and found a contact that opens and closes as the rotor turns. As it turns out there was no need to open the motor. When I reverse the windings leading out to the terminals the rotation is reversed.

I have never seen a phase switching scheme like this before. How long would the contacts last? The lathe and motor is about 90 years old.

 

That switch is a centrifugal switch that disconnects the start winding once the RPM's get high enough. Switching the phase of the start winding will change the rotation. Those contacts will open and close once for each time the motor is started and will probably outlast the shaft bearings.

 

And I dont think there should be a capacitor on that motor. The capacitor is determined by the power factor which will vary with the load, and as the load on a lathe is always changing, the proper capacitance would always be changing too. Capacitors are for motors that see a fairly stable load (thus power factor). In those situations, the cap is chosen to adjust the PF to about 92-95%.

 

That appears to be a Repulsion-Induction motor, they were fairly common some decades ago, they are never seen today usually.
On second thoughts, if it was such a motor, the rotor would have windings and brushes,
It does appear to be a staring cap, it is not unusual to see the centrifugal switch on modern motors.

 

Post #2 is correct, it is an induction motor with a starter switch and a starting winding. So to control it you need connections to both the run winding and the start circuit, (switch + start winding).
So that will be a 3-pole, double throw, center off switch. One section to power the run winding and the other two sections to power the start winding for either direction. Such switches are available with the required jumpers already installed, saving some work.

 

I don’t need to select the direction of rotation. I only have to reverse direction permanently.

 

I don’t need to select the direction of rotation. I only have to reverse direction permanently.

OK, then I did not understand the comment about reversing made in post #1 correctly. Sorry about that.
So then, once you have the direction you need, only a simple OFF/ON switch will be needed. Motor start capacitors are mostly for improved starting torque, which they provide by creating a greater phase shift.

 

It is a pain to change lathe speed by moving the V-belt to a different pulley and retightening the belt. Now I am thinking about a variable speed treadmill motor. Any tips on this would be much appreciated.

 

Variable speed controllers for brush type motors have been around since triac devices have been available. So there are a lot of those circuits published, although not recently. They are quite similar to the light dimmer circuits presently available. The only problem might be if the brush motor available is intended for less than 120 volts. But if you can recover the treadmill motor controls and transformer as well as the motor then you will be all set.

 

The most popular T.M. motors/drives for machine use is the MC2100 and the Johnson DC motors that usually come with that controller, they are PWM controlled.
A simple 20Hz PWM control input is needed for the control signal which is also PWM, this replicates the signal coming from the T.M. console.
There are some circuits out there that use a 555 to generate it, A while back I put one togethe using a 8 pin Picmicro.

Motor start capacitors are mostly for improved starting torque, which they provide by creating a greater phase shift.

Without the phase shifted start winding there will be no rotation as the field operates across 180°, the motor will usually just sit and Buzz!

 

The other option is a 220v/240v 3ph motor and VFD.

 

The most popular T.M. motors/drives for machine use is the MC2100 and the Johnson DC motors that usually come with that controller, they are PWM controlled.
A simple 20Hz PWM control input is needed for the control signal which is also PWM, this replicates the signal coming from the T.M. console.
There are some circuits out there that use a 555 to generate it, A while back I put one togethe using a 8 pin Picmicro.

Without the phase shifted start winding there will be no rotation as the field operates across 180°, the motor will usually just sit and Buzz!

The required phase shift in a non-capacitor induction motor is provided by the higher resistance and inductance of the starting winding. It has been that way for many years.

 

The required phase shift in a non-capacitor induction motor is provided by the higher resistance and inductance of the starting winding. It has been that way for many years.

I am not disputing that, it was your statement "Motor start capacitors are mostly for improved starting torque," which I had issue with, I can't count the number of times i have come across motors where the start cap has failed, the motor sits stationary until a spin is given to the shaft!
The start capacitor is to provide phase shift in the start winding, no other reason.
And Why they are called split-phase motors.

 

OK, and YES, Max, the capacitor -start scheme does provide greater starting torque than the motors that use the two different windings. On many of those capacitor motors, the three terminal variety, the windings are identical, which means that reversing is much simpler. That might be part of the reason for the change. Also, having two identical windings makes production cheaper.

 

The ones with identical windings are PSC (permanent start cap) motors and can easily be controlled/reversed by a SPDT centre off switch.
Generally 1/2hp maximum.

 

The ones with identical windings are PSC (permanent start cap) motors and can easily be controlled/reversed by a SPDT centre off switch.
Generally 1/2hp maximum.

You'll never win an argument with him about motors. Did you miss where he holds the word "expert" under his name? He actually believes it....

 

The ones with identical windings are PSC (permanent start cap) motors and can easily be controlled/reversed by a SPDT centre off switch.
Generally 1/2hp maximum.

Certainly that is the correct name for what I was talking about. I was not attempting to argue about it at all.

 

Max, the capacitor -start scheme does provide greater starting torque than the motors that use the two different windings.

This statement is what had me confused??

 

This statement is what had me confused??

The reason it provides more starting torque is because the capacitor provides a greater phase shift than can be typically obtained using only the inductance and resistance of the start winding. And it is that phase shift that produces the starting torque.
So it is no argument with anybody, it is an explanation of why it works so well.

 

The reason it provides more starting torque is because the capacitor provides a greater phase shift than can be typically obtained using only the inductance and resistance of the start winding. And it is that phase shift that produces the starting torque.
So it is no argument with anybody, it is an explanation of why it works so well.

Funny though that no text book on electric motors says that. They all say it's due to the slight time that the voltage is delayed by the cap. But then what do professors and electrical engineers know, they don't have expert next to their names. I salute you higher knowledge!