Allen-Bradley 1756-PA75R – AC Redundant Power Supply | ControlLogix 1756 Platform
Engineering Background
The 1756-PA75R is Rockwell Automation’s dedicated redundant AC power supply for the ControlLogix 1756 chassis. Designed for mission-critical process control environments where unplanned downtime is unacceptable, it operates in a 1+1 redundant pair configuration — if the primary supply fails, the secondary assumes full load without interrupting backplane power or controller operation. This architecture is the backbone of high-availability DCS and safety-instrumented system (SIS) installations across oil & gas, chemical, water treatment, and advanced manufacturing.
Product Positioning
The 1756-PA75R targets automation engineers and system integrators who specify ControlLogix-based control systems under IEC 61511 / ISA-84 functional safety requirements or internal uptime SLAs exceeding 99.9%. It is the OEM-specified solution for redundant power in any 1756 chassis and is fully compatible with the 1756-PSCA2 Power Supply Chassis Adapter for external redundancy wiring.
Complete Technical Specifications
| Parameter | Value |
|---|---|
| Catalog Number | 1756-PA75R |
| Series | ControlLogix 1756 |
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Supply Type | AC Redundant |
| Input Voltage Range | 85 – 265 V AC (universal) |
| Input Frequency | 47 – 63 Hz |
| Output Voltage | 5 V DC (backplane) |
| Output Current (5 VDC) | 13 A |
| Output Power | 65 W |
| Backplane Current (1.2 V) | 3 A |
| Redundancy Mode | 1+1 Hot-Standby (automatic failover) |
| Chassis Compatibility | All 1756 chassis (4-, 7-, 10-, 13-, 17-slot) |
| Redundancy Adapter | 1756-PSCA2 (required for external redundancy) |
| Operating Temperature | 0 – 60 °C |
| Storage Temperature | -40 – 85 °C |
| Relative Humidity | 5 – 95% (non-condensing) |
| Vibration (operating) | 2 g @ 10–500 Hz |
| Shock (operating) | 30 g |
| Enclosure Rating | Open (panel-mount, IP20) |
| Dimensions (H × W × D) | 147 × 58 × 144 mm |
| Weight | 1.45 kg |
| Certifications | UL, CE, CSA, C-Tick, ATEX Zone 2 |
| Product Series | Series B |
Proven Application Environments
- Oil & Gas: Upstream wellhead control, midstream pipeline SCADA, downstream refinery DCS — where power interruption triggers emergency shutdown (ESD) sequences.
- Chemical & Petrochemical: Continuous batch reactor control requiring 24/7 uptime with SIL-rated power integrity.
- Water & Wastewater: Municipal SCADA systems with remote, unmanned pump stations where field service response time is measured in hours.
- Automotive Manufacturing: Body-in-white welding lines and paint shop conveyors where a single power fault halts an entire production cell.
- Pharmaceutical: FDA 21 CFR Part 11 validated environments requiring documented, uninterrupted process control.
- Power Generation: Turbine control and substation automation where grid-tied systems demand continuous availability.
Engineering Advantages
- Zero-interruption failover: Automatic hot-swap between primary and secondary supplies with no backplane voltage dip — controller execution continues uninterrupted.
- Universal AC input: 85–265 V AC range eliminates the need for separate SKUs for 110 V and 220 V installations; a single part number covers global deployments.
- Wide thermal envelope: 0–60 °C operating range supports installation in non-air-conditioned enclosures in tropical or desert climates.
- ATEX Zone 2 certification: Suitable for use in hazardous area control panels with appropriate enclosure selection.
- Diagnostic LED indicators: Dedicated OK and Fault LEDs on each supply provide instant visual status without requiring a connected HMI or FactoryTalk View session.
- Backplane-isolated output: Isolated 5 VDC output protects I/O modules and controller from AC-side transients and ground faults.
- Drop-in replacement: Identical form factor to 1756-PA75 (non-redundant) — retrofit existing chassis without mechanical modification.
System Architecture & Signal Flow
In a redundant power configuration, two 1756-PA75R units are installed in adjacent slots of the same 1756 chassis and connected via the 1756-PSCA2 Power Supply Chassis Adapter. The adapter provides the inter-supply communication bus that arbitrates primary/secondary roles and monitors health status. Both supplies share the backplane load equally under normal operation; upon detection of a fault on either unit (over-voltage, under-voltage, over-temperature, or input loss), the healthy supply assumes 100% of the load within the hold-up time window (<20 ms), preventing any detectable voltage sag on the 5 VDC backplane rail.
System integrators should note that the 1756-PA75R occupies two chassis slots (one per supply) plus the PSCA2 adapter slot — plan chassis slot budgets accordingly when specifying 17-slot vs. 10-slot chassis for high-I/O-count applications.
Sourcing & Quality Verification
- OEM traceability: All 1756-PA75R units sourced by Konmask.com carry full Rockwell Automation OEM documentation including date code, series designation, and country of manufacture.
- Functional test: Each unit undergoes bench power-on verification (input voltage sweep, output voltage measurement, LED status check) prior to shipment.
- Counterfeit screening: Physical inspection against Rockwell Automation’s published authenticity markers — label typography, PCB color, connector finish, and holographic serial label.
- Condition grading: Units are graded as New (factory-sealed), Surplus New (unused, original packaging), or Refurbished (tested, warranted). Grade is stated explicitly on each order confirmation.
- Documentation package: Certificate of conformance, test report, and packing list provided with every shipment on request.
Procurement Process
- Submit RFQ: Contact [email protected] or call +0086 19859288691 with your required quantity, condition grade, and delivery timeline.
- Receive quotation: Formal quotation issued within 1 business day including unit price (HKD/USD), lead time, and shipping options (DHL Express, FedEx International Priority, sea freight).
- Order confirmation: Purchase order accepted via email; proforma invoice issued for prepayment or net-terms accounts.
- Quality inspection & packing: Unit inspected, photographed, and packed in anti-static foam with moisture barrier bag.
- Shipment & tracking: Tracking number provided within 24 hours of dispatch; export documentation (commercial invoice, packing list, COO) included for customs clearance.
- After-sales support: 12-month warranty on all units; Konmask technical team available for installation guidance and compatibility verification.
Technical FAQ
Q: Can the 1756-PA75R be used without the 1756-PSCA2 adapter?
A: Yes — a single 1756-PA75R operates as a standard (non-redundant) power supply without the PSCA2. The redundancy adapter is only required when configuring a 1+1 redundant pair.
Q: Is the 1756-PA75R compatible with all ControlLogix chassis?
A: Yes. It is compatible with all standard 1756 chassis (4-, 7-, 10-, 13-, and 17-slot). It is not compatible with the 1756-A5XT or 1756-A7LXT extended-temperature chassis, which require the 1756-PB75 (DC input) variant.
Q: What is the hold-up time during a supply failover?
A: Rockwell Automation specifies a minimum hold-up time of 20 ms at full load, which is sufficient to prevent any backplane voltage dropout during automatic failover between the two supplies.
Q: Can I hot-swap a failed 1756-PA75R while the system is running?
A: Yes — with the redundant pair active and the healthy supply carrying full load, the failed unit can be removed and replaced without powering down the chassis or interrupting controller operation.
Q: What is the difference between 1756-PA75 and 1756-PA75R?
A: The 1756-PA75 is a single (non-redundant) AC power supply rated at 13 A / 5 VDC. The 1756-PA75R adds the redundancy interface connector and internal arbitration logic required to operate in a 1+1 pair with the PSCA2 adapter. The output ratings are identical.
Q: Does Konmask.com provide export documentation for international orders?
A: Yes. Standard export documentation includes commercial invoice, packing list, certificate of origin, and HS code declaration (HS 8537.10). Additional documentation (ECCN classification letter, material safety data) available on request.
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Contact: [email protected] | +0086 19859288691
