Allen-Bradley 1771-PA Power Supply Module

The 1771-PA is a standalone AC power supply module manufactured by Allen-Bradley for the PLC-5 and Mini-PLC-2 automation platforms. Designed to mount directly alongside or above a Bulletin 1771 I/O chassis, it accepts a dual-voltage AC input rating of 120/220 V AC and converts it into a regulated 16 A backplane output at 5 V DC to power local processors, communication adapters, and I/O modules.

Power Conversion and Voltage Flexibility

The module supports nominal input voltage selections of 120 V AC (1 A input current) and 220 V AC (0.5 A input current) over an operating frequency range of 47 to 63 Hz. It accommodates input voltage tolerances between 97–132 V AC or 195–264 V AC, drawing up to 108 W of real input power and 176 VA of apparent input power under maximum operating load. Output protection is reinforced via an internal 3 A, 250 V normal-blow fuse.

Mechanical Installation and Chassis Mounting Requirements

As a standalone, open-type module, the unit requires installation within an industrial enclosure to safeguard against electrostatic discharge and environmental contamination. To maintain proper natural convection cooling, installers must maintain a minimum vertical clearance of 6 inches and ensure the module is placed adjacent to or above the 1771 chassis—never directly beneath it. Interconnection with chassis adapters or processor modules is established using 1771-CP1, 1771-CP2, or 1771-CP3 interface cabling.

Operational Restrictions and Configuration

Before mounting the 1771-PA, ensure the chassis power supply configuration jumper is set to the N position. This standalone unit is engineered to power a single 1771 I/O chassis independently and must never be wired in parallel with another power supply. Parallel operation can cause unstable voltage delivery, resulting in equipment damage, processor memory loss, or uncommanded machine behavior.

Frequently Asked Questions

Q: Can the 1771-PA power supply be connected in parallel to increase chassis output current? A: No, the 1771-PA is strictly a standalone power supply and must not be connected in parallel, as doing so can cause system instability and memory loss.

Q: Where should the 1771-PA be mounted relative to the 1771 I/O chassis? A: It must be mounted directly above or beside the I/O chassis with a minimum 6-inch vertical clearance; mounting it below the chassis disrupts convection thermal cooling.

Q: What cables are used to connect the 1771-PA to the chassis or processor?A: The module connects via 1771-CP1 local cabling or 1771-CP2 / 1771-CP3 remote cabling assemblies.