single phase Motor Centrifugal switch

[dnem]

So heres what Im reading in this book
"A split-phase motor is a single-phase AC motor that includes a run winding and a resistive start winding that creates a phase-shift for starting. The two windings are placed in the stator slots and spaced 90 degrees apart...... In addition, a centrifugal switch is located inside the motor. The centrifugal switch is used to disconnect the start winding as the motor approaches full-load speed."

So heres my question, if the start winding is in the stator, how is the centrifugal switch, located on the rotor shaft, used to disconnect it.? The start winding gets its power from an exterior source and it is located in the stator, so does that circuit enter the rotor thru slip rings, go thru the centrifugal switch, and then re-exit the rotor to finally be in series with the stator start winding.? That cant possibly be true but Im stumped to envision what the actual configuration is.

 

[GoldDigger]

That cant possibly be true but Im stumped to envision what the actual configuration is.

You may find it impossible, but it appears to be fact. The slip rings will only have to carry current during starting and will be continuous rings, avoiding a lot of the potential problems associated with a commutated connection as in a universal motor.

It is also possible to have a centrifugal switch mechanism that actuates a switch mounted on the stator, but that would involve slipping mechanical contact 100% of the time that the motor is running and would be a lot more complex.

 

[Jraef]

There are many different methods of making centrifugal switches, some involving slip rings, but most do not. The switch mechanism itself, and thereby all of the electrical circuit parts, remain mounted to the frame. On the motor shaft is a mechanism that typically changes shape with the centrifugal force, either by moving ball bearings into a weighted wedge arrangement or by using a conical shape or weighted spring that flattens out, something like that. So in its resting state, the contacts are held closed by that mechanism with springs trying to open them, so when the shaft speed causes the shaft mounted part to change shape, it gets out of the way and the contacts open.



Hard to tell from a static photo, the best way to understand it is to take one apart. It's the same mechanism used for Split Phase or Capacitor Start motors.