1768-PA3 Allen-Bradley CompactLogix 120/240V AC Power Supply

Product Overview and System Power Architecture

The 1768-PA3 (1768PA3) is a high-efficiency AC input power supply specifically designed for the 1768-L43 and 1768-L45 CompactLogix controllers. As part of the 1768-series architecture, this module provides the essential regulated DC voltages required to power the controller, the 1768 backplane, and any attached 1768 communication modules (such as the 1768-ENBT or 1768-CNB). The 1768-PA3 is engineered to handle the higher power demands of the 1768-series, which supports integrated motion and high-performance networking, making it a critical foundation for mid-range automation systems in conveyor control, assembly lines, and specialized process skids.

Hardware Architecture and Electrical Logic

The 1768-PA3 mounts directly to the left side of the 1768 controller. It converts standard industrial AC line power into the precise DC rails needed for internal logic and communication circuitry.

• Universal AC Input: Supports a wide input range of 85–265V AC, allowing for global deployment in both 110V and 220V power systems without the need for external transformers.

• Expansion Capacity: Specifically designed to provide sufficient current for up to two 1768-series communication or motion modules alongside the main processor.

• Regulated Output: Provides a stabilized 5V DC and 24V DC backplane output, ensuring that voltage fluctuations on the factory floor do not affect the deterministic performance of the PLC logic.

• Integrated Status Monitoring: Features a front-panel "DC OK" LED that provides immediate visual confirmation that the supply is outputting the correct voltages.

Technical Specifications

Integrated Technical FAQ

Can I use the 1768-PA3 with 1769-L3x controllers?

No. The 1768-PA3 is physically and electrically designed only for the 1768-L43 and 1768-L45 controllers. 1769-series controllers use 1769-PA2 or PA4 power supplies, which have a different form factor and backplane connector.

What causes the "DC OK" LED to turn off?

An unlit LED typically indicates one of three things: a loss of AC input power, an internal fuse failure, or an over-current condition on the backplane (often caused by a faulted communication module). Always measure the input terminals first to confirm line power is present.

Does this module provide power for the field I/O?

No. The 1768-PA3 powers the controller and the 1768-series modules only. If you have 1769-series I/O modules attached to the right side of the controller, those I/O modules may require their own 1769-series power supply (like a 1769-PA2) depending on the total current draw.

Engineering & Installation Protocols

• Wiring Safety: Use a minimum of 14 AWG (2.1 mm²) wire for AC input connections. Ensure the "Ground" terminal is connected to a clean, low-impedance earth ground to help filter out electrical noise and protect against surges.

• Thermal Clearance: The 1768-PA3 dissipates heat through convection. Maintain a minimum of 50 mm (2 in.) of clearance above and below the module. If the module is installed in a small, unventilated enclosure, the internal thermal protection may trip, causing the PLC to shut down.

• Finger-Safe Terminals: The terminal block features a protective cover. Always keep this cover closed during operation to prevent accidental contact with high-voltage AC terminals.

Engineering Advantages

The 1768-PA3 stands out for its robust power-to-footprint ratio. It is built to support the high-speed data processing and motion synchronization required by the 1768-L4x series, which was a pioneer in bringing high-end Logix performance to a compact form factor. Its ability to bridge the gap between heavy-duty industrial power and sensitive micro-electronics makes it a reliable choice for "Workhorse" applications in the packaging and material handling industries where power quality may be inconsistent.