Single-phase motors with slightly higher power typically have two capacitors: a starting capacitor and a run capacitor. Single-phase motors manufactured before the 1970s typically had only one capacitor: the starting capacitor. After the motor starts, a centrifugal switch disconnects the capacitor, leaving only the primary winding active. The secondary winding is idle.
To improve the efficiency of single-phase motors, dual-capacitor single-phase motors appeared after the 1970s.
What causes a single-phase motor's starting capacitor to burn out? I will focus on the causes of starting capacitor burnout.
Starting capacitors are generally less likely to burn out because their operating time is very short. They are disconnected by the centrifugal switch at the moment of startup, leaving no current flowing through the starting capacitor, making them less susceptible to burnout. However, this vulnerability does not mean they will never burn out.
What causes a starting capacitor to burn out?
(1) The capacitor's withstand voltage is low or its quality is poor. A capacitor with a withstand voltage of 500V should be selected.
(2) Arcing often occurs when the centrifugal switch is disconnected, potentially burning the switch and causing it to stick. After the motor starts, the switch cannot be disconnected, and current continues to flow through the capacitor, which can easily burn out the motor's secondary winding and the starting capacitor over time.
(3) The selected capacitor capacity is too small, and the starting current exceeds the capacitor's allowable value.
(4) The motor has a scratched bore or bearings are damaged, making it difficult for the motor to start for a period of time, and the centrifugal switch has difficulty reaching the disconnect speed, which can easily burn out the starting capacitor.
These are my four humble opinions on why starting capacitors burn out.