Starting Capacitor Calculation - Anhui Safe Electronics Co., Ltd.

Starting capacitors are used to help motors overcome initial inertia and startup load. They are commonly found in single-phase motors, such as fans, pumps, compressors, and other equipment. The capacity of the starting capacitor needs to be selected based on the motor's power and operating requirements. A capacitor that is too small or too large can affect the normal start and operation of the motor. The calculation of the starting capacitor involves several factors, including the motor's rated current, voltage, and power factor. Below are several common calculation methods:

Starting Capacitor Calculation Formula

Single-phase running capacitor:
$C = \frac{1950 \times I}{U \times \cos ϕ}$
$C = \frac{1950 \times I}{U \times \cos\phi}$
Starting capacitor:
$C = \frac{3500 \times I}{U \times \cos ϕ}$
I is the motor's rated current (amperes), U is the motor's rated voltage (volts), and cosϕ is the power factor (usually between 0.7 and 0.8).

Capacity Selection

The capacity of the starting capacitor is typically 1.5 to 2.5 times that of the running capacitor. For example, if the running capacitor's capacity is 34 microfarads, the starting capacitor's capacity can be selected between 51 and 85 microfarads.

Voltage Rating Requirements

1.5 to 2 times the rated voltage

For a 220V single-phase motor, the starting capacitor's voltage rating should be at least 330V or 440V.
For a 380V motor, the voltage rating should be 630V or higher.

Consideration of Surge Voltage

During startup, short-duration surge voltages may occur in the circuit. If the voltage rating is insufficient, the capacitor may break down. Therefore, it is recommended to choose a capacitor with a voltage rating higher than the standard rating, especially in heavy-load applications.

Practical Application

In practical applications, it is also essential to consider the capacitor's voltage and current stability, as well as the quality and brand of the capacitor to ensure the motor's stable operation and safety.

In conclusion, the calculation of the starting capacitor should be adjusted based on the specific motor specifications and working environment to ensure that the capacitor selected meets the motor's startup and operational requirements.

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