Allen-Bradley 1747-L551 SLC 5/05 CPU Controller | Replacement, Equivalent & Selection Guide
The Allen-Bradley 1747-L551 is a SLC 5/05 series CPU module manufactured by Rockwell Automation. It features an Ethernet communication port, enabling direct integration into modern industrial networks. This page provides full technical specifications, compatible replacement models, application guidance, and a structured selection guide to help engineers and procurement teams make informed decisions.
Technical Specifications
- Manufacturer: Allen-Bradley / Rockwell Automation
- Series: SLC 500
- Model Number: 1747-L551
- CPU Type: SLC 5/05
- Communication Port: Ethernet (10/100 Mbps), RS-232 (Channel 0)
- User Memory: 64K words
- Data Memory: 32K words
- I/O Capacity: Up to 4,096 I/O points
- Scan Time: ~1 ms/K (typical)
- Power Supply: Supplied via SLC 500 chassis backplane
- Operating Temperature: 0°C to 60°C (32°F to 140°F)
- Storage Temperature: -40°C to 85°C
- Relative Humidity: 5% to 95% (non-condensing)
- Certifications: UL, CE, CSA
- Weight: Approx. 1,200 g
- Form Factor: Single-slot SLC 500 chassis module
Compatible Replacement & Equivalent Models
The following models are commonly evaluated as replacements or equivalents for the 1747-L551. Compatibility depends on firmware version, chassis type, and application requirements — always verify before substitution.
- 1747-L552 — SLC 5/05, 64K words, same Ethernet port; direct drop-in replacement in most applications
- 1747-L553 — SLC 5/05, 64K words, extended memory variant; backward compatible
- 1747-L541 — SLC 5/04, DH+ communication; functional equivalent without Ethernet, suitable for legacy DH+ networks
- 1747-L531 — SLC 5/03, RS-232/DH-485 only; lower-tier replacement for non-networked applications
- 1756-L71 (ControlLogix) — Migration path for modernization projects; requires chassis and I/O adapter changes
- 1769-L30ER (CompactLogix) — Modern Ethernet-based alternative; suitable for new system designs replacing SLC 500 architecture
Note: Cross-brand equivalents (Siemens S7-300, Mitsubishi Q-series, etc.) require full re-engineering and are not drop-in replacements.
Why Choose the Original Model
- Proven Reliability: The SLC 5/05 platform has decades of field-proven performance in demanding industrial environments.
- Native Ethernet Connectivity: Built-in 10/100 Mbps Ethernet eliminates the need for additional communication modules.
- RSLogix 500 Compatibility: Fully supported by Rockwell’s RSLogix 500 and Studio 5000 migration tools.
- Large Installed Base: Extensive ecosystem of compatible I/O modules, chassis, and power supplies.
- Spare Parts Availability: Widely stocked globally, reducing lead times for maintenance and repair.
Typical Applications
- Discrete manufacturing automation (assembly lines, conveyors, packaging)
- Process control in food & beverage, chemical, and water treatment plants
- HVAC and building automation systems
- Material handling and warehouse automation
- Oil & gas upstream and midstream control panels
- Machine tool control and CNC integration
System Compatibility
- Chassis: Compatible with all SLC 500 modular chassis (1746-A4, 1746-A7, 1746-A10, 1746-A13)
- Power Supplies: 1746-P1, 1746-P2, 1746-P3, 1746-P4, 1746-P5, 1746-P6
- I/O Modules: All 1746-series digital and analog I/O modules
- Programming Software: RSLogix 500 (v8.0+), RSLinx Classic, FactoryTalk Linx
- Communication Protocols: EtherNet/IP, DF1, DH-485
- HMI Compatibility: PanelView, PanelView Plus, third-party Modbus/TCP HMIs
Selection Guide
Use the following criteria to determine whether the 1747-L551 is the right choice for your application:
- Need Ethernet connectivity? → 1747-L551 or 1747-L552/L553 (SLC 5/05 family)
- Need DH+ network only? → Consider 1747-L541 (SLC 5/04)
- Replacing a failed unit in existing SLC 500 chassis? → 1747-L551 is a direct replacement; verify firmware revision compatibility
- Planning a new system? → Evaluate CompactLogix 1769-L series for a modern, scalable architecture
- Budget-constrained retrofit? → Refurbished 1747-L551 units are available; request test reports and warranty documentation
- Memory requirement > 64K words? → The SLC 5/05 platform maximum is 64K; consider migrating to ControlLogix
Quality Assurance & Sourcing
- All units sourced from authorized distributors or verified surplus channels
- Each module undergoes functional power-on testing prior to shipment
- Firmware version documented and provided with each unit
- Anti-static packaging with humidity indicator cards
- Traceability documentation available upon request (COO, test reports)
- Warranty: 12 months from date of shipment (new units); 90 days (refurbished units)
How to Order
- Step 1: Confirm your chassis model and available slot count
- Step 2: Verify your current firmware version (if replacing an existing unit)
- Step 3: Select new or refurbished unit based on budget and lead-time requirements
- Step 4: Add to cart or contact us for bulk pricing and lead-time confirmation
- Step 5: Provide PO number or request a formal quotation via email
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Replacement & Compatibility FAQ
Q: Is the 1747-L552 a direct replacement for the 1747-L551?
A: Yes, in most cases. Both are SLC 5/05 CPUs with Ethernet and 64K user memory. Verify firmware compatibility with your RSLogix 500 project file before swapping.
Q: Can I use a 1747-L551 in any SLC 500 chassis?
A: Yes, it is compatible with all standard SLC 500 modular chassis (1746-A4 through 1746-A13). It occupies slot 0 (leftmost slot).
Q: Does the 1747-L551 support EtherNet/IP?
A: Yes. The SLC 5/05 supports EtherNet/IP messaging, enabling communication with other Logix controllers, HMIs, and SCADA systems over standard Ethernet infrastructure.
Q: What is the difference between 1747-L551 and 1747-L553?
A: The 1747-L553 offers extended memory options in some firmware revisions. Both share the same hardware platform and are functionally interchangeable in most applications.
Q: Can I migrate my SLC 500 program to a ControlLogix system?
A: Yes. Rockwell Automation provides migration tools within Studio 5000 to assist with converting RSLogix 500 programs. Hardware changes (chassis, I/O adapters) are required.
Q: Do you provide a warranty?
A: Yes — 12 months for new units, 90 days for refurbished units, from date of shipment.
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