Product Overview

The 1756-PB72 is a high-performance 24V DC Power Supply designed for the Allen-Bradley ControlLogix 1756 chassis system. This module is responsible for converting an external 24V DC source into the specific backplane voltages (1.2V, 3.3V, 5.1V, and 24V DC) required to power ControlLogix processors, I/O modules, and communication adapters. Engineered for maximum reliability in industrial environments, the 1756-PB72 provides enhanced ride-through capabilities and robust protection against electrical transients, ensuring stable operation for critical control architectures.

Functional Engineering & Load Capacity

The 1756-PB72 is designed to support high-density chassis configurations. It provides a total current capacity of 13 Amps at 5.1V DC and 2.8 Amps at 24V DC to the backplane. Its "slim" yet powerful design allows it to be mounted on the left side of any standard 1756 chassis (4, 7, 10, 13, or 17-slot), efficiently distributing power across the entire backplane. The module features integrated circuit protection and a front-panel status LED, allowing maintenance teams to instantly verify the health of the DC input and internal conversion logic.

Technical Specifications

Technical FAQs

What is the "Hold-up Time" for the 1756-PB72?The module is designed with a hold-up time of approximately 35ms @ 24V DC. This ensures that the ControlLogix processor can perform an orderly shutdown or "ride through" momentary power sags and micro-interruptions without causing a system fault or losing volatile data.

Can I use the 1756-PB72 in a redundant power configuration?No. The 1756-PB72 is a standard power supply. For redundancy, you would require the 1756-PB72R (Redundant) power supply along with a 1756-CPR2 cable and a 1756-PSCA2 chassis adapter. The standard PB72 is intended for single-supply applications where high amperage is required but physical redundancy is not a project mandate.

How do I calculate if the 1756-PB72 is sufficient for my chassis?You must sum the backplane current requirements (at 5.1V and 24V) for every module in your chassis. If the total exceeds 13A at 5.1V or 2.8A at 24V, the system may experience intermittent resets. Rockwell Automation’s Integrated Architecture Builder (IAB) is the recommended tool for performing these power budget calculations accurately.

Field Engineering & Installation Guide

• Wiring Requirements: Use a minimum of 14 AWG (2.5 mm²) solid or stranded copper wire rated for at least 75°C for the DC input connections. Ensure the 24V DC source is properly fused or protected by a circuit breaker to prevent damage during a sustained overcurrent event.

• Chassis Attachment: The power supply mounts to the left end of the 1756 chassis. Ensure the two chassis mounting screws are tightened to the specified torque (1.16 N•m) to maintain a solid ground connection, which is vital for the module's internal EMI filtering.

• Environmental Clearance: Maintain a minimum of 2 inches (50 mm) of clearance above and below the power supply for airflow. Excessive heat is the primary cause of power supply failure; ensuring proper convection cooling will significantly extend the life of the internal electrolytic capacitors.

Engineering Advantages

The 1756-PB72 offers a robust and space-efficient power solution for DC-powered control cabinets. Its high isolation rating (250V continuous) ensures that field-side electrical noise and ground loops do not reach the sensitive backplane electronics. For B2B procurement, choosing the original Allen-Bradley 1756-PB72 ensures full compatibility with the 1756 chassis series and maintains the system's UL, CSA, and CE certifications, providing a reliable foundation for any ControlLogix-based automation project.