When a ControlLogix Chassis Loses Its Power Supply
A Gulf Coast gas processing plant faced a familiar problem: a ControlLogix chassis running critical compressor monitoring had only one power supply. A single failure would drop the whole rack. The fix was not a bigger supply, but a redundant pair built around the Allen-Bradley 1756-PA75R.
What the 1756-PA75R Actually Does
The 1756-PA75R is a ControlLogix redundant power supply from Allen-Bradley / Rockwell Automation. Unlike a standard supply, it mounts outside the chassis and pairs with an identical unit to share the load automatically. Each supply takes 85-265VAC input at 47-63 Hz and delivers 75W of output power at 0 to 60 degrees Celsius.
Backplane current capacity is split across four rails: 1.5A at 1.2VDC, 4A at 3.3VDC, 13A at 5.1VDC and 2.8A at 24VDC. That 13A at 5.1VDC rail is the workhorse for most ControlLogix I/O and communication modules.
Technical Specifications
| Specification | Value |
|---|---|
| Input Voltage Range | 85-264VAC |
| Nominal Input Voltage | 120/240VAC |
| Input Frequency | 47-63 Hz |
| Output Power | 75W at 0-60 degrees C |
| Current Capacity | 1.5A at 1.2VDC; 4A at 3.3VDC; 13A at 5.1VDC; 2.8A at 24VDC |
| Max Inrush Current | 20 Amperes |
| Isolation Voltage | 250V continuous, reinforced insulation |
| Hold Up Time | 2 cycles at 60 Hz; 2 cycles at 50 Hz |
| Dimensions | 17.5 x 14.5 x 13.7 cm |
| Weight | 1.45 kg |
| Chassis Compatibility | 1756-A4, 1756-A7, 1756-A10, 1756-A13, 1756-A17 |
| Operating Temperature | 0-60 degrees C |
Building a Redundant Pair
A working redundant setup needs two 1756-PA75R supplies, two redundant power supply cables such as 1756-CPR2, and one chassis adapter module such as 1756-PSCA2. The cable uses two female ends to connect the male connectors on the supply and the adapter. A solid state relay on the supply can wire to an input module, giving you a status signal when the pair is running correctly.
This is where hands-on technical selection help pays off. Getting the cable and adapter matched to your chassis the first time avoids a stalled startup.
Where This Supply Earns Its Keep
Redundant supplies matter most where a rack outage stops production. On offshore platforms, pipeline compressor stations and refinery unit controls, the 1756-PA75R keeps the chassis alive if one supply drops. The automatic load sharing means neither unit runs at full stretch, which supports longer service life.
Maintenance and Reliability Notes
Inspect the supply periodically for dust buildup and secure connections. The unit uses a non-replaceable fuse soldered in place, so a blown fuse means the supply needs replacement rather than field repair. Keep the panel environment within the 0-60 degrees C operating range and follow the manufacturer’s safety manual for all service work.
Please verify current lifecycle status and availability with Oil AutoTech before ordering.
Sourcing the 1756-PA75R
When a redundant supply fails, every hour of downtime costs money. Oil AutoTech focuses on fast dispatch, worldwide, for oil, gas and industrial automation spares. Contact Oil AutoTech today for pricing and availability.
