Husnen Rupani:
In this video, we’ll look at locked rotor torque of a single-phase induction motor in four different configurations. Let’s get started.

Hi, I’m Hus. In this video, we’ll connect a single-phase motor in split phase, permanent split cap, cap start, and cap start/cap run configuration and compare the locked rotor torque in each of those configurations. To do this experiment, we’ll use the single-phase induction motor in the motor fault prac box and this dynamic torque sensor. Let’s start with the split phase motor.

This is the circuit that we’ll connect for the split phase motor. To power this motor, we’re using the porter phase, and on the distro box we’ve connected across line one and line two to get about 41.5 volts. We’ve connected the power supply directly to the main winding, and then the auxiliary winding is connected in series with this resistor and this toggle switch. This resistor and this winding in series is basically creating a start winding for us with higher resistance. And this toggle switch is basically our centrifugal switch so we can control when it turns on and off. Let’s turn it on. Now that the motor is running, I’m going to stall it, which is giving us the locked rotor torque, and we’re seeing about 0.02 Newton meters of locked rotor torque.

Let’s now connect a permanent split cap motor, or also known as cap run motor. For permanent split cap, this is the circuit that we’ll use to connect our motor. So we’ll use the main winding, auxiliary winding, and the run capacitor. Let’s turn on the motor. Now that the motor is running, I’m going to stall it and I’m seeing a locked rotor torque of about 0.029.03 Newton meters.

Let’s now connect a cap start motor. For cap start motor, this is the circuit that we will connect. So we’ll use our main winding, the auxiliary, or our start winding, in series with this resistor to simulate the start winding, the centrifugal switch, which will be our toggle switch, and the start capacitor. Let’s turn on the motor. Now I’m going to stall the motor and I’m seeing about 0.04748 Newton-meter torque for the cap start mode.

And finally, for the cap start/cap run motor, this is the circuit that we’ll connect. We will use the main winding, auxiliary winding, toggle switch to simulate the centrifugal switch, start capacitor, and the run capacitor. Let’s turn on the motor. I’m now going to stall the motor and I’m seeing the locked rotor torque of about 0.110 Newton meters.

As we compare the locked rotor torque of the four configurations, we see that the split phase motor has the lowest torque, which is about 0.02 Newton meters, then is the permanent split cap, which is about 0.03, and then the cap start motor which is about 0.048. And finally the cap start/cap run motor has the highest locked rotor torque, which is about 0.11 Newton meters.

And we can understand this because split phase motor only has the two windings. One of the windings has slightly higher resistance which is giving you a very small face shift, hence giving you the least amount of torque, as compared to permanent split cap which has one small capacitor which is giving you a slightly higher face shift and giving you slightly higher torque. And comparing that to cap start motor, has a bigger capacitor, which is then giving you slightly bigger face shift and the bigger torque. And finally, the cap start/cap run has two capacitors in parallel while the motor is still starting, giving you the highest amount of locked rotor torque.

I hope you enjoyed this video comparing the locked rotor torques of a single phase induction motor in four different configurations. If you have any questions or feedback, please feel free to contact us. Thanks for watching.