Description
Product Introduction
The Allen-Bradley 1756-PA75 is a standard 75-Watt AC power supply module engineered for ControlLogix I/O chassis. Mountable directly on the far left side of any 1756 chassis (such as the 1756-A7, 1756-A10, or 1756-A13), it accepts a wide universal AC input voltage range from 85 to 265V AC. It converts incoming utility or transformer power into four regulated DC voltage rails (1.2V, 3.3V, 5.1V, and 24V DC) required by the backplane.
Unlike specialized redundant power supply configurations (such as the 1756-PA75R paired with a 1756-PSCA2 adapter), the 1756-PA75 serves as a self-contained, standalone power source for standard control enclosures. Its 75-watt rating provides ample power headroom for chassis populated with high-density CPU processors, Ethernet bridges, and digital/analog I/O cards.
Key Technical Specifications
| Parameter | Value / Specification |
| Input Voltage Range | 85 to 265V AC (nominal 120V/240V AC) |
| Input Frequency Range | 47 to 63 Hz |
| Maximum Input Power | 100 VA / 100 W |
| Output Power | 75 W @ 0 to 60°C (140°F) |
| Backplane Current (1.2V DC) | 1.5 A |
| Backplane Current (3.3V DC) | 4.0 A |
| Backplane Current (5.1V DC) | 13.0 A |
| Backplane Current (24V DC) | 2.8 A |
| Inrush Current | 30 A max |
| Hold-Up Time | 35 ms @ 120V AC | 40 ms @ 240V AC |
| Isolation Voltage | 250V continuous (tested at 3500V DC for 1s) |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Application Scenarios & The “Trench” Experience
A main continuous packaging line goes completely dark without warning. All chassis diagnostic LEDs drop out, shutting down the controller, remote bridge cards, and motion controllers simultaneously. You open the enclosure and smell burned electrical insulation near the power supply. A voltage spike tripped the internal primary circuit, killing the 5.1V DC rail. The entire line is halted, losing thousands of dollars every fifteen minutes. Keeping a replacement 1756-PA75 on hand allows you to pull the damaged power unit, land the AC input line, and restore backplane power in under ten minutes.
Target Application Scenarios
- Main Control Cabinets: Powers local 1756 chassis housing high-performance CPUs (like 1756-L73 or 1756-L75) and communication cards.
- Remote I/O Drop Panels: Supplies regulated backplane voltage to distributed chassis containing high-density digital and analog I/O modules.
- Stand-Alone Machine OEM Skids: Serves as the primary AC power interface for standalone packaging, converting, and assembly machinery.
- Water Treatment & Telemetry Skids: Operates reliably in utility panels running off standard 120V AC field distribution transformers.
Field Case Study
An automotive stamping facility experienced intermittent backplane communication resets across its primary 13-slot chassis during peak summer shifts. Diagnostic logs pointed to momentary voltage sags on the 5.1V DC rail caused by an aging 1756-PA75 unit operating at elevated panel temperatures. We dispatched a bench-tested, new-surplus 1756-PA75. The maintenance team swapped the power supply during a scheduled shift change, stabilizing backplane DC rail voltages and eliminating nuisance bus reset faults across the stamping line.
- 1756-PA75
Transparency SOP: Quality Assurance & Testing
We don’t just ship boxes; we test them on actual Allen-Bradley racks. Every 1756- module passing through our workshop endures a strict 5-step verification process:
- Inbound Physical Inspection: Checking chassis mounting lever alignment, edge connector pins, housing heat vents, and verifying line terminal block screw conditions.
- AC Line Inrush & Hold-Up Verification: Wiring the unit to a variable AC source (Variac) to test operation across the full 85V to 265V AC spectrum under load.
- Full Backplane DC Load Bank Test: Connecting all four output rails (1.2V, 3.3V, 5.1V, 24V DC) to a simulated 75W resistive load bank to measure voltage regulation, ripple noise, and thermal dissipation.
- Thermal Stability Audit: Operating the power supply under full 13A backplane load for two hours while monitoring housing temperatures with thermal imaging equipment.
- ESD Isolation & Packaging: Discharging static risks at an ESD-certified workstation before sealing the supply in heavy-duty protective static shielding bags with fresh desiccant.
The Veteran’s Tech Trap Guide (Crucial Value-Add)
⚠️ Watch Out for DC Backplane Power Budgets: The 1756- delivers 75 Watts total, but you must verify that your combined module draw does not exceed individual rail limits—specifically the 13.0A max on the 5.1V DC rail and 2.8A max on the 24V DC rail. Populating a 17-slot chassis with multiple high-draw analog or specialty cards can exceed the 24V rail budget even if total power stays under 75W. Use Integrated Architecture Builder (IAB) to verify your rack power budget!
❗ Don’t Confuse 1756- with 1756-PA75R: The standard 1756- mounts directly onto the left end of a single chassis. It cannot be used in a redundant power supply system. If your rack requires dual power supplies feeding a 1756-PSCA2 adapter for high-availability applications, you must purchase the 1756-PA75R redundant power supply.
⚠️ AC Input Wiring Safety: Always make sure incoming 120V/240V AC power is de-energized before removing the protective green terminal block cover on the front of the unit. The terminals sit close together, and accidental shorting against the metallic chassis frame will blow the internal non-serviceable primary fuse.
Frequently Asked Questions (FAQ for Conversion)
Q: Can I replace a 1756-PA72 power supply with a 1756-?
A: Yes. The 1756- is the direct successor to the older 1756-PA72 (which provided 50W output). The 1756- provides higher power output (75W) in the same physical footprint, making it a drop-in upgrade for chassis requiring additional backplane current.
Q: Is the 1756- power supply hot-swappable while the PLC is running?
A: No. The 1756- supplies all DC operating power to the backplane. Removing or disconnecting the 1756- while the chassis is energized instantly shuts down the processor and all I/O modules in that rack.
Q: What is the input voltage selector switch setting on the 1756-?
A: There is no manual voltage selector switch. The 1756- features an auto-ranging universal power supply circuit that automatically adjusts to any incoming AC input voltage between 85V and 265V AC at 47 to 63 Hz.
Q: What does a solid green status LED on the front door indicate?
A: A solid green POWER LED indicates that incoming AC line voltage is present and all internal DC backplane rails (1.2V, 3.3V, 5.1V, and 24V DC) are operating within proper regulated output tolerances.
Q: What warranty is provided with this power supply module?
A: We back every New Surplus and fully tested replacement 1756- power supply with a full 12-month operational warranty. If the module experiences hardware failure under standard operating conditions within one year, we issue an immediate replacement or full credit.
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