Start capacitors and run capacitors are two types of capacitors commonly used in electrical systems, particularly in electric motors. While both serve the purpose of storing and releasing electrical energy, they have distinct characteristics and roles in motor operation. Let’s explore in detail how start and run capacitors differ:
Start Capacitors:
- Purpose:
- Start capacitors are specifically designed to provide an extra boost of power during the starting phase of an electric motor. Their primary purpose is to assist in overcoming the inertia of the motor and initiate rotation.
- Placement:
- Start capacitors are typically connected in series with the motor’s start winding. This arrangement allows the start capacitor to be in the circuit only during the starting phase. Once the motor reaches a certain speed, a switch disconnects the start capacitor from the circuit.
- Capacitance Value:
- Start capacitors have a relatively high capacitance value. This high capacitance provides the necessary torque during motor startup by creating a phase shift in the current flowing through the start winding.
- Construction:
- Start capacitors are often designed with a non-polarized electrolytic construction. This allows for a higher capacitance value without the need for a polarized design.
- Duty Cycle:
- Start capacitors have a limited duty cycle. They are only active during the starting phase and are disconnected from the circuit once the motor reaches a predetermined speed.
- Voltage Rating:
- Start capacitors are designed to handle higher voltage levels, considering the initial surge of current during motor startup.
Run Capacitors:
- Purpose:
- Run capacitors are intended to maintain and optimize the efficiency of an electric motor during its run or continuous operation. They are not involved in the starting phase but contribute to the motor’s overall performance.
- Placement:
- Run capacitors are connected in parallel with the motor’s main winding. Unlike start capacitors, run capacitors remain in the circuit throughout the motor’s operation.
- Capacitance Value:
- Run capacitors have a lower capacitance value compared to start capacitors. The capacitance is optimized for continuous operation, providing a phase shift to maintain efficiency and power factor.
- Construction:
- Run capacitors are often designed with a metallized polypropylene or similar construction. This construction type ensures durability and reliability during continuous use.
- Duty Cycle:
- Run capacitors have a continuous duty cycle and remain active as long as the motor is running. Their design allows for prolonged use without the need for frequent disconnection.
- Voltage Rating:
- Run capacitors are designed to handle the standard operating voltage of the motor during continuous operation.
Summary of Differences:
- Function: Start capacitors assist in motor startup, while run capacitors optimize efficiency during continuous operation.
- Placement: Start capacitors are in series with the start winding, while run capacitors are in parallel with the main winding.
- Capacitance Value: Start capacitors have a higher capacitance for a significant power boost during startup, while run capacitors have a lower capacitance optimized for continuous operation.
- Construction: Start capacitors often use non-polarized electrolytic construction, while run capacitors use metallized polypropylene or similar designs for durability.
- Duty Cycle: Start capacitors have a limited duty cycle and are disconnected after startup. Run capacitors have a continuous duty cycle and remain active during motor operation.
- Voltage Rating: Start capacitors are designed to handle higher voltages during the startup surge, while run capacitors are designed for standard operating voltages.
In summary, the key distinction lies in their roles within the motor operation, the type of winding they are connected to, their capacitance values, construction, duty cycles, and voltage ratings, all of which are optimized for their specific functions in electric motor applications.
