Description
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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Model | 1756-PA72C |
| Brand | Allen-Bradley |
| Product Family | ControlLogix (1756) |
| Module Type | AC Input Power Supply |
| Input Voltage | 120/240V AC (selectable via jumper or wiring — verify) |
| Input Frequency | 47 – 63 Hz |
| Input Current (Max) | 2.5 A at 120V AC / 1.2 A at 240V AC (typical — verify) |
| Output Voltage 1 | 5V DC |
| Output Current 1 | 10 A (verify on label) |
| Output Voltage 2 | 24V DC |
| Output Current 2 | 5 A (verify on label) |
| Output Voltage 3 | 3.3V DC |
| Output Current 3 | 10 A (verify on label) |
| Power Consumption | 100 VA typical |
| Isolation | 2500V AC (input to output, 1 minute) |
| Backplane Connector | 1756 backplane edge connector |
| Status Indicators | Power OK (green LED), Fault (red LED), 5V/24V/3.3V OK indicators |
| Operating Temperature | 0 °C to +60 °C |
| Storage Temperature | –40 °C to +85 °C |
| Humidity | 5% – 95% RH, non-condensing |
| Mounting | ControlLogix chassis slot (leftmost slot for power supply) |
| Weight | Approx. 1.0 kg (2.2 lb) |
| Certifications | UL 508, CSA C22.2, CE, ATEX (verify on unit label) |
4. Product Introduction
The Allen-Bradley 1756-PA72C is a 120/240V AC power supply for the ControlLogix chassis. It mounts in the leftmost slot and provides regulated 5V, 24V, and 3.3V DC to the backplane, powering the controller, communication modules, and I/O cards in the same rack. It accepts both 120V and 240V AC input, so it works in North American and international panels without a step-down transformer.
The engineering value is power margin and diagnostics. The module provides front-panel LEDs for each output rail, so you can see at a glance whether the 5V, 24V, or 3.3V rail is sagging under load. In my experience, the most common cause of a “failed” ControlLogix chassis is not the controller—it is a power supply that cannot hold the 5V rail under the inrush of a full rack of I/O. The 1756-PA72C gives you the headroom to avoid that trap.
1756-PA72C
1756-PA72C
1756-PA72C
1756-PA72C
5. Application Scenarios & Field Experience
Part 1 – Narrative Paragraph
The failure that stops a ControlLogix line is rarely a dead power supply—it is a supply that browns out under load. The chassis powers up, the controller runs, and then an output card energizes and the 5V rail drops below the module’s threshold. The controller faults, the line stops, and the maintenance crew replaces the controller. I have seen that movie three times. The 1756-PA72C solves it by providing a stiff 5V rail with enough current for a fully loaded chassis. Check the total backplane load before you assume the supply is oversized.
Part 2 – Numbered List (Application Scenarios)
- Automotive Assembly – ControlLogix Main Rack – The power supply feeds a chassis with a 1756-L7x controller, EtherNet/IP communication modules, and analog and digital I/O. The 5V @ 10A capacity handles the inrush when multiple output cards energize simultaneously.
- Food Processing – Line Controller Panel – Used in washdown environments where the panel is sealed. The 120/240V AC input allows the same part number to be stocked for domestic and export machines.
- Water Treatment – SCADA RTU Cabinet – The module powers a ControlLogix rack that collects flow, pressure, and level signals. The front-panel LEDs let a technician verify all three rails without opening the cabinet.
- Material Handling – Conveyor Control Rack – The supply powers a rack with digital input cards for photo-eyes and output cards for motor starters. The 24V @ 5A rail feeds field devices through the I/O cards, reducing external power supplies.
Part 3 – Short Field Story
A bottling plant in the Midwest had a ControlLogix line that would fault every Monday morning after a weekend shutdown. The crew had replaced the controller and the communication module. The fault kept coming back. We asked them to measure the 5V rail with a scope during startup. It dropped to 4.6V for 200 ms when the output cards energized. The original power supply was a lower-current model. We supplied a 1756-PA72C, they swapped it in, and the Monday faults stopped. The old supply had been marginal from day one.
6. Standard Operating Procedure (SOP) for Quality Control
Every 1756-PA72C passes this QC sequence:
- Visual & Origin Inspection – We verify the Allen-Bradley marking, the 1756- catalog number, and the date code. We inspect the backplane connector for bent pins and the housing for cracks. A module with a damaged connector or evidence of moisture is rejected.
- Input Voltage Verification – We power the unit at 120V AC and 240V AC and confirm it operates on both settings. We measure input current at no load and full load.
- Output Rail Test – We load each output rail (5V, 24V, 3.3V) to its rated current and measure voltage regulation. Ripple must stay below the OEM specification.
- Protection Circuit Test – We verify overvoltage and overcurrent protection engages at the specified thresholds. We also test thermal shutdown.
- LED Verification – We confirm each status LED illuminates correctly for normal and fault conditions.
- Backplane Communication Test – The module is installed in a live ControlLogix chassis with a controller. We verify the chassis powers up and the controller recognizes all modules without a power fault.
- ESD-Safe Packaging – The module is wrapped in anti-static film, seated in a foam insert with the connector protected, and packed in a double-wall carton.
7. Frequently Asked Questions (FAQ)
Q1: Can I use this power supply in a chassis that originally had a 1756-PA75?
A: Mechanically, yes—both are single-slot ControlLogix power supplies. Electrically, check the total backplane current draw. The 1756-PA75 provides more current on the 5V rail. If your chassis is fully loaded, the may not have enough margin. Add up the backplane current for every module in the rack and compare it to the ratings on the label.
Q2: What is the warranty on this module?
A: We offer a 12-month warranty from the ship date. It covers output rail failure, overvoltage protection failure, and backplane connector failure under normal operating conditions. It does not cover damage from connecting 240V AC to a unit set for 120V, physical damage, or ESD damage from handling without a wrist strap. Every unit is load-tested before it ships.
Q3: Do you have this in stock?
A: ControlLogix power supplies are active products but inventory fluctuates. Confirm availability before you plan an outage. If we are out, we will give you a realistic restock window. We do not quote placeholder dates.
Q4: What happens if I install this in the wrong slot?
A: The 1756- must go in the leftmost slot of the chassis. It will not fit any other slot because the backplane connector is keyed differently. If you force it, you will damage the connector. If the chassis does not power up, verify the module is fully seated and the input voltage selector is set correctly.
Q5: Any installation pitfalls I should watch for?
A: Three. First, verify the input voltage selector is set for your actual supply—120V or 240V—before you apply power. Second, do not hot-swap the power supply with the chassis energized. Third, after installation, check the 5V rail with a meter under full load. A supply that reads 5.1V at no load can sag below 4.9V when the rack is fully loaded.
