KL2791 BECKHOFF Single-Phase AC Motor Speed Controller Bus Terminal

Product Overview

The KL2791 (KL2791) is a specialized 1-phase AC motor speed controller designed to be integrated directly into the Beckhoff Bus Terminal system. Operating at a nominal voltage of 230 V AC, this terminal provides a compact, DIN-rail mounted solution for controlling small single-phase AC motors with a power rating of up to 200 VA. Unlike standard digital output terminals, the KL2791 utilizes advanced phase/full-wave control logic to adjust motor speed with a fine resolution of 1%. This makes it an ideal choice for B2B industrial applications such as ventilation fan control, small pump modulation, and conveyor speed synchronization in HVAC systems or light assembly lines.

Hardware Architecture and Control Logic

The KL2791 is engineered to bridge the gap between low-voltage PLC logic and high-voltage motor actuation. It features a high degree of safety with 3750 V AC electrical isolation between the power circuit and the K-bus logic, protecting the upstream bus coupler and CPU from voltage spikes.

The terminal operates via a 16-bit data process image, allowing for precise speed setpoints. The control electronics are powered via the K-bus, while the motor load is supplied through the 230 V AC power contacts. Its "Direct Motor Connection" technology eliminates the need for external triacs or interposing controllers, significantly reducing the complexity of the control cabinet. With a maximum output current of 0.9 A, it is optimized for small-displacement motors where traditional frequency inverters would be cost-prohibitive or physically too large.

Technical Specifications

Technical FAQs

What is the difference between Phase Control and Full Wave Control on the KL2791?

Phase control (leading or trailing edge) clips the AC sine wave to reduce the effective voltage delivered to the motor, suitable for speed regulation. Full wave control can be used for zero-cross switching to minimize electromagnetic interference when toggling the motor state.

Can the KL2791 be used for 3-phase motors?

No. The KL2791 is strictly designed for 1-phase AC motors with a maximum load of 200 VA. For 3-phase applications, a Beckhoff frequency inverter (Distributed or Drive series) should be utilized.

Is external fuse protection required?

While the terminal is robust, it does not feature integrated reverse voltage protection. It is highly recommended to install a fast-acting fuse or motor starter upstream on the 230 V AC supply line to protect the terminal and motor from short-circuit conditions.

Engineering & Installation Guide

• Motor Compatibility: Ensure the motor is compatible with phase-cut dimming or voltage regulation. Some capacitor-start motors may require a minimum speed setting in the PLC program to ensure sufficient torque for starting and to prevent overheating at low RPMs.

• Wiring and Termination: Use the pluggable KS series wiring for easier maintenance. Ensure that the 230 V AC supply is connected to the correct power contacts. Given the high-voltage nature of this terminal, use wires with a minimum insulation rating of 300 V and keep motor leads as short as possible to reduce EMI.

• Thermal Management: The KL2791 generates heat when operating near its 0.9 A limit. Maintain vertical installation on the DIN rail to allow for natural convection. If multiple KL2791 terminals are installed side-by-side, ensure the cabinet temperature does not exceed 55 Celsius to prevent thermal derating.

Engineering Advantages

The KL2791 stands out for its ability to integrate high-voltage motor control into a standard 12 mm I/O slice. By eliminating the need for standalone speed controllers, it reduces the total bill of materials (BOM) and panel labor costs. Its compliance with EN 61000-6-2/4 for EMC immunity and emission ensures that the phase-cutting noise does not disrupt sensitive analog signals in the same terminal block. For engineers, the 16-bit resolution provides granular control over airflow or fluid pressure, making it a "smart" alternative to simple ON/OFF relays for AC motor management.