Three-Phase or AC Motor for Linear Actuators?

1. Electrical Connection of Single-Phase and Three-Phase Motors

An electric linear actuator (such as MINI actuators) can be equipped either with a single-phase AC motor or a three-phase motor, depending on the intended application. Both variants fulfill the same basic function, namely converting rotational motor movement into linear motion. However, they differ significantly in terms of electrical connection, running characteristics, and installation requirements. For electricians and installers, it's therefore important to consider these differences already during the planning and wiring stages.

As a general rule for both motor types, the electrical connection must always be carried out in accordance with the specifications shown on the respective nameplate. The wiring diagrams shown in maintenance and operating manuals are intended only as examples. The actual wiring must always follow the technical specifications and connection data of the respective motor or linear actuator.

2. Linear Actuators with Single-Phase AC Motors

Linear actuators with single-phase AC motors are typically operated on a single-phase 230 V power supply and are commonly used where no three-phase connection is available. They're particularly suitable for smaller systems, general automation tasks, or applications in building technology and special-purpose machinery.

Since a single-phase AC motor doesn't naturally generate a rotating magnetic field, it requires a capacitor to create starting torque. This capacitor creates a phase shift between the main winding and the auxiliary winding, thereby generating the rotating magnetic field required to start the motor. Without this capacitor, the motor would only hum and would not start independently.

Depending on the motor design, either a run capacitor alone or an additional start capacitor is used. The run capacitor remains permanently connected in the circuit and influences not only the starting characteristics but also the smooth running behavior of the motor.

When electrically connecting a single-phase linear actuator, electricians should pay particular attention to the following points:

1. correct wiring of the main and auxiliary windings
2. proper connection of the capacitor
3. connection in accordance with the nameplate specifications
4. correct motor rotation direction
5. adequate overload protection
6. proper protective grounding of the motor and housing
7. proper strain relief and EMC-compliant cable routing
8. correct grounding

Particular attention should be paid to the capacitor itself. An incorrectly sized or defective capacitor can lead to poor starting behavior, reduced lifting force, increased current consumption, or thermal overload. Since capacitors can lose capacitance over time due to aging, they are considered typical wear parts in single-phase drive systems.

Grounding also plays an important role in single-phase motors. The protective earth conductor (PE) connects conductive housing components to earth potential and protects people from dangerous touch voltages in the event of a fault.

3. Installation recommendations for Single-Phase Linear Actuators

For installation, a low-vibration mounting arrangement with sufficient space for heat dissipation from both the motor and the capacitor is recommended. The capacitor should be mounted away from direct heat exposure, as high temperatures can significantly reduce its service life. In addition, the terminal box should remain easily accessible to simplify maintenance and diagnostic work.

For applications involving high switching frequencies or heavy loads, it should be verified whether a single-phase drive is sufficiently dimensioned with regard to starting torque and thermal load capacity.

Screw jack systems with a rotating screw and traveling nut (traveling nut design) cannot be equipped with integrated limit position sensors. In such cases, the limit switches must be mounted externally on the lifting frame.

4. Linear Actuators with Three-Phase Motors

Linear actuators with three-phase motors are generally operated on a three-phase 400 V power supply. They are characterized by smoother running behavior, higher efficiency, better power density, and higher starting torque. Especially in industrial applications involving long duty cycles and high loads, three-phase drives are often the preferred solution.

Unlike a single-phase AC motor, a three-phase power supply inherently generates a rotating magnetic field. As a result, the motor doesn't require a capacitor for starting. This makes the motor design more robust and reduces maintenance requirements, since a typical wear component is eliminated.

Although this simplifies the motor connection for electricians, important electrical requirements still have to be considered. These include:

1. correct connection of the three phases L1, L2, and L3
2. verification of the rotation direction
3. suitable motor protection switches and overload protection
4. proper grounding
5. consideration of star or delta connection
6. suitable cable cross-sections for long cable runs

The direction of rotation of a three-phase motor can easily be changed by swapping two phases. However, especially with linear actuators, the correct direction of movement must always be verified before commissioning in order to prevent mechanical damage or collisions.

5. Installation recommendations for Three-Phase Linear Actuators

Three-phase linear actuators should preferably be operated on a stable and permanently available three-phase power supply. For industrial applications, the additional use of a motor protection switch with correctly adjusted rated current is recommended. In dynamic applications or where variable lifting speeds are required, operation via a frequency inverter may be beneficial. This allows acceleration, speed, and soft-start behavior to be controlled precisely.

Due to the higher performance capability of the motor, the mechanical mounting should also be sufficiently rigid in order to safely absorb vibrations and peak loads.

6. Conclusion

The choice between a single-phase and a three-phase linear actuator depends on the available infrastructure, the required performance, and the intended application. Single-phase solutions offer advantages where a simple 230 V power supply and lower installation requirements are desired. However, they require a properly sized capacitor for reliable operation. Three-phase linear actuators, on the other hand, provide higher efficiency, smoother operation, and lower maintenance requirements, but require a suitable three-phase power connection.