In a capacitor-start motor, the start capacitor is larger than the run capacitor. Which option shows the correct statement?

In a capacitor-start motor, the start capacitor is larger than the run capacitor. Which option shows the correct statement?

• A. Start capacitor larger than run capacitor
• B. Run capacitor larger than start capacitor
• C. They are equal in value
• D. Both are absent in some designs

Answer: (A)

In a capacitor-start motor, the starting torque comes from the start capacitor being in series with the starting winding to create a larger current phase shift. Making the start capacitor larger gives a bigger surge of current to the starting winding, which produces the strong torque needed to get the rotor moving from rest. Once the motor starts, a switch or device disconnects the start capacitor, so it’s not in the circuit during running. The run capacitor, when used, stays in the circuit but is smaller, just enough to improve running efficiency and power factor without supplying a strong starting surge. Therefore, the start capacitor is larger than the run capacitor to provide the high starting torque, while the smaller run capacitor optimizes running performance. If the run capacitor were larger, starting torque would be reduced and starting reliability would suffer; if they were equal, you wouldn’t have the extra torque needed for a robust start.

In a capacitor-start motor, the starting torque comes from the start capacitor being in series with the starting winding to create a larger current phase shift. Making the start capacitor larger gives a bigger surge of current to the starting winding, which produces the strong torque needed to get the rotor moving from rest. Once the motor starts, a switch or device disconnects the start capacitor, so it’s not in the circuit during running. The run capacitor, when used, stays in the circuit but is smaller, just enough to improve running efficiency and power factor without supplying a strong starting surge. Therefore, the start capacitor is larger than the run capacitor to provide the high starting torque, while the smaller run capacitor optimizes running performance. If the run capacitor were larger, starting torque would be reduced and starting reliability would suffer; if they were equal, you wouldn’t have the extra torque needed for a robust start.