How to Wire a Single-Phase Dual-Capacitor Motor?

A single-phase dual-capacitor motor is a commonly used motor type in industrial and civil equipment. It is equipped with two capacitors: a running capacitor and a starting capacitor. The core of wiring lies in distinguishing the leads of the motor’s main winding (running winding), auxiliary winding (starting winding) and centrifugal switch. The following are standardized wiring steps and precautions.

1. Clarify Motor Lead Markings First

A single-phase dual-capacitor motor generally has 6 leads. The markings vary slightly among different manufacturers. The common markings and their corresponding windings are as follows:

Supplementary Note: Some motors use simplified markings M (main), S (auxiliary), C (common terminal). In this case, a multimeter is required to measure the resistance for distinction (the resistance of the main winding is less than that of the auxiliary winding).

1. Core Wiring Principles
2. Running capacitor: Connected in parallel between the main winding and the auxiliary winding, it participates in motor operation at all times, with a relatively small capacity (usually several microfarads to tens of microfarads, and the withstand voltage is ≥450V AC).
3. Starting capacitor: Connected in series with the centrifugal switch first, then in parallel across the running capacitor. It only works during startup, with a relatively large capacity (usually tens of microfarads to hundreds of microfarads, and the withstand voltage is ≥450V AC).
4. The live wire (엘) and neutral wire (N) of the power supply are connected to the main winding and the common terminal respectively. The forward and reverse rotation of the motor can be achieved by switching the terminals of the main and auxiliary windings.

III. Step-by-Step Wiring Operations

Step 1: Distinguish Windings with a Multimeter (Critical to Avoid Wrong Wiring)

1. Set the multimeter to the resistance range (Ω) and measure the resistance value between any two leads.
2. The resistance of the main winding (U1-U2) is the smallest; the resistance of the auxiliary winding (Z1-Z2) is larger; the series resistance of the main winding and auxiliary winding is the largest.
3. Centrifugal switch (V1-V2): In the normal state (motor stationary), the resistance is 0 (closed); after the motor rotates, the resistance is ∞ (open).

Step 2: Basic Wiring (Forward Rotation Mode)

1. Connect the centrifugal switch to the starting capacitor: Connect the V1 terminal of the centrifugal switch to one end of the starting capacitor, and connect the other end of the starting capacitor to the Z2 terminal of the auxiliary winding.
2. Connect the running capacitor: Connect one end of the running capacitor to the Z2 terminal of the auxiliary winding, and connect the other end to the U2 terminal of the main winding.
3. Connect the power supply to the common terminal of the main and auxiliary windings:

Connect the live wire (엘) of the power supply to the U1 terminal of the main winding;

Connect the neutral wire (N) of the power supply to both the U2 terminal of the main winding and the Z1 terminal of the auxiliary winding (short-circuit U2 and Z1 as the common terminal);

4. Fix the lead of the centrifugal switch: Connect the V2 terminal of the centrifugal switch to the U1 terminal of the main winding.

Step 3: Achieve Forward and Reverse Rotation of the Motor

To change the rotation direction, you only need to swap the two terminals of the auxiliary winding (i.e., swap Z1 and Z2 before connecting to the circuit), while keeping the wiring of the main winding unchanged.

1. Safety Precautions
2. Must disconnect the power supply before wiring, and use a test pen to confirm that there is no electricity; the motor housing must be reliably grounded to prevent electric leakage.
3. The withstand voltage value of the capacitor must match (≥450V AC). It is forbidden to use capacitors with insufficient withstand voltage, 그렇지 않으면, the capacitors may break down and explode.
4. The starting capacitor and running capacitor cannot be interchanged: The starting capacitor has a large capacity, and long-term connection will burn out the windings; the running capacitor has a small capacity and cannot provide sufficient starting torque.
5. After completing the wiring, perform a no-load test run first: If the motor fails to start, makes abnormal noise, or generates excessive heat, cut off the power immediately for inspection, and eliminate faults such as wrong winding connection, damaged capacitors, or faulty centrifugal switches.
6. If the motor has no centrifugal switch (some small dual-capacitor motors), the starting capacitor must be controlled to turn on and off via a time relay to avoid long-term power-on.
7. Common Fault Troubleshooting

The motor is difficult to start and makes a buzzing sound: Most likely, the starting capacitor is damaged or the centrifugal switch has poor contact.

The motor heats up quickly after startup: It may be due to incorrect connection of the running capacitor, short circuit of the main and auxiliary windings, or mismatched capacitor capacity.

The resistance values of the main winding and auxiliary winding of a single-phase dual-capacitor motor do not have a unified fixed value. Their values are directly related to the motor’s power, winding wire diameter, and number of turns, and always follow the core rule that the resistance of the main winding is less than that of the auxiliary winding.

Resistance Range Reference (Divided by Motor Power)

The core influencing logic of resistance is: the higher the motor power, the thicker the winding wire diameter and the smaller the resistance; conversely, the lower the power, the thinner the wire diameter and the larger the resistance. The resistance ranges of common power segments are as follows:

1. Micro-motors (power ≤ 100W)

Main winding resistance: 5Ω ~ 20Ω

Auxiliary winding resistance: 10Ω ~ 30Ω

Such low-power motors are mostly used in small fans and household appliance accessories, with thin winding wire diameters and a large number of turns, resulting in relatively high resistance.

2. Small motors (power 200W ~ 1000W)

Main winding resistance: 1Ω ~ 8Ω

Auxiliary winding resistance: 4Ω ~ 15Ω

They are commonly used in household washing machines, small water pumps, single-phase air compressors and other equipment, and are the mainstream specifications for civil and light industrial use.

3. Medium-sized motors (power 1.5kW ~ 3kW)

Main winding resistance: 0.5Ω ~ 3Ω

Auxiliary winding resistance: 2Ω ~ 8Ω

They are mostly used in industrial small fans and conveying equipment, with thicker winding wire diameters and further reduced resistance.

Key Identification Method (Multimeter Practical Operation)

Even if the motor power is unknown, the main and auxiliary windings can be distinguished by the resistance relationship:

1. Use the multimeter resistance range (Ω) to measure three groups of resistance values between any two winding leads (assuming the leads are three common combination terminals: 에이, B, C).
2. The group with the smallest resistance is the main winding; the group with medium resistance is the auxiliary winding; the group with the largest resistance is the series resistance of the main winding and auxiliary winding (theoretically equal to the sum of the resistance values of the previous two groups).
3. Winding resistance is affected by temperature: After the motor runs, the windings heat up and the resistance will increase slightly. It is recommended to measure when the motor is cooled down.
4. Due to differences in motor manufacturing processes among different manufacturers, the resistance of motors with the same power may have a deviation of about ±20%, so there is no need to insist on exact consistency.
5. If the measurement shows that the resistance of the main winding is greater than that of the auxiliary winding, or the resistance of a certain group is infinite (∞), it indicates that the windings are connected incorrectly or have an open circuit fault.