Description

The Allen-Bradley 1756-PA72 is a standard AC power supply designed to provide regulated backplane power directly to compatible ControlLogix chassis. Operating on a nominal input voltage of 120V or 240V AC at 50/60 Hz, this module delivers multi-rail DC outputs across the 24V DC, 5.1V DC, 3.3V DC, and 1.2V DC lines to power processor, I/O, and communication modules. It features reinforced insulation providing continuous 250V isolation between the power input and the backplane, protecting sensitive control circuitry from line-side electrical anomalies. The unit is designed with an open-style enclosure and mounts directly on the left side of the ControlLogix chassis, utilizing internal card guides for precise alignment.

Features

• Auto-Sensing Input: Automatically detects and adapts to 120V AC or 240V AC input line voltages without manual jumper settings.
• Multi-Output Backplane Support: Supplies simultaneous current capacities of 2.8A at 24V, 10.0A at 5.1V, 4.0A at 3.3V, and 1.5A at 1.2V up to a 100W maximum total power limit.
• High Isolation Voltage: Features 250V continuous reinforced insulation from the power input to the system backplane.
• Visual Status Diagnostics: Integrated green power indicator LED provides immediate local visual feedback of correct module operation.
• Integrated Circuit Protection: Accommodates external 15A time-delay fusing on ungrounded lines to protect internal power elements.

Applications

• Main chassis power sourcing for industrial factory automation systems.
• Powering distributed I/O chassis in wastewater treatment, chemical processing, and packaging facilities.
• Infrastructure assembly power for complex machinery using high-density ControlLogix module layouts.

Technical Specifications

Connections and Interfaces

Alternative Models & Compatibility

The standard 1756-PA72 functions within identical chassis form-factors as the 1756-PA75 power supply, though it presents distinct total output current limits (75W maximum output versus 75W backplane limits with variance across specific rails). For systems running under extended temperature profiles or requiring conformal coatings, standard units do not substitute for the K-suffix (e.g., 1756-PA72K) or XT series variations (e.g., 1756-PA30XT) which support operating spectrums from -25 degC to +70 degC.

Application Pitfalls & Engineering Notes

A common field risk involves failure to remove the temporary protective label from the top vents of the power supply housing prior to commissioning. This label must remain intact exclusively during panel fabrication to block airborne metallic shavings from entering the module circuitry. Operating the module with the label attached blocks passive air convection, forcing thermal buildup beyond the maximum 60 degC surrounding air limit and triggering premature electrical stress or module shutdown. Additionally, users must avoid wire daisy-chaining on single terminals; use external distribution blocks for multiple line configurations.

Installation Guidelines

Installation Considerations

Before installing the ControlLogix AC Power Supply, verify that the chassis is properly mounted and connected to protective earth ground. Disconnect all incoming power sources and follow applicable lockout/tagout procedures before performing installation or maintenance work.

Mounting

• Install the power supply on the left side of the ControlLogix chassis.
• Align the circuit board with the chassis card guides.
• Slide the module fully into position until flush with the chassis front.
• Secure the unit using the top and bottom mounting screws.
• Keep the protective cover in place until enclosure fabrication is complete.

Power Wiring

• Use 14 AWG (2.5 mm2) copper conductors rated for at least 90 degC.
• Protect ungrounded power connections with a 15 A time-delay fuse.
• Tighten terminal connections to 0.565 N.m (5 lb-in).
• Connect only one conductor per terminal.
• Input voltage is automatically sensed and does not require manual voltage selection.

Grounding and Safety

• Verify proper chassis grounding before energizing the system.
• Do not connect or disconnect wiring while power is applied.
• Prevent metal shavings, dust, or debris from entering the power supply during installation.
• Ensure adequate enclosure ventilation for long-term reliability.

Status Indicator Check

The front-panel green status indicator should remain illuminated during normal operation.

If the indicator is off:

• Verify incoming line voltage.
• Check backplane loading requirements.
• Reseat the power supply in the chassis.
• Replace the unit if the indicator remains off after troubleshooting.