ALLEN-BRADLEY 1747-L551 Series C | SLC 5/05 16K Controller

🔹 Product Introduction

The Allen-Bradley 1747-L551 Series C is an SLC 5/05 programmable controller with 16K words of user memory, designed for SLC 500 modular control systems. It provides Ethernet and RS-232 communication, supporting industrial programming, data exchange, and controller-to-device communication. Series C versions introduced enhanced Ethernet capabilities, with applicable firmware configurations supporting 10/100 Mbps Ethernet and increased connection capacity. The controller supports up to three local chassis and up to 30 local I/O module slots, making it suitable for machine control, process automation, material handling, and legacy industrial control-system maintenance. Rockwell Automation lists the 1747-L551 as discontinued effective December 31, 2021.

ALLEN-BRADLEY 1747-L551

📋 Product Datasheet

Parameter	Value
Brand	Allen-Bradley
Model	1747-L551
Series	SLC 5/05 Series C
Product Name	16K Controller / Processor
Place of Manufacture	Singapore
Product Status	Discontinued; surplus and refurbished units may be available
Dimensions	Approx. 56 × 165 × 249 mm
Weight	Approx. 0.42 kg
Original Country of Origin	Singapore
Power	5 VDC, 1.0 A and 24 VDC, 200 mA

The 1747-L551 provides 16K words of user memory and supports up to 4,096 discrete inputs and 4,096 discrete outputs within the SLC 500 architecture. It supports up to three local chassis with a maximum of 30 I/O slots. Communication includes Ethernet and RS-232, with the RS-232 port supporting protocols such as DF1, ASCII, and DH-485 depending on configuration.

🔧 Troubleshooting & Common Issues

• If the controller does not enter RUN mode, check the CPU status indicators and review the processor fault information.

• If the CPU Fault indicator is active, inspect the controller configuration, program integrity, firmware compatibility, and chassis power supply.

• If Ethernet communication fails, check the Ethernet cable, network configuration, IP settings, and controller firmware revision.

• If RS-232 communication is unavailable, verify the communication protocol, cable wiring, baud rate, and port configuration.

• If the Battery Low indicator is active, inspect the processor battery and replace it according to the applicable maintenance procedure.

• If connected I/O modules are not responding, check the chassis power supply, module seating, chassis configuration, and I/O addressing.

• Before replacing the processor, verify that the fault is not caused by the power supply, chassis, communication network, or I/O modules.

⚠️ Safety Precautions

• Disconnect power before removing or installing the processor.

• Follow applicable lockout/tagout procedures when servicing the SLC 500 system.

• Use appropriate ESD protection when handling the controller.

• Never remove or install the processor while the chassis is energized unless the system documentation specifically permits the procedure.

• Verify the processor catalog number and Series designation before installation.

• Back up the existing application program and controller data before replacing a processor whenever possible.

• Check firmware compatibility between the processor, programming software, and existing SLC 500 application.

• After replacement, perform controlled communication, I/O, and program-function tests before returning the machine to production.

📰 Product-Related News & Industry Context

The Allen-Bradley SLC 5/05 1747-L551 belongs to the established SLC 500 family of modular programmable controllers. Rockwell Automation officially lists the 1747-L551 as discontinued as of December 31, 2021, with an engineering replacement category. This makes identification of the exact catalog number, Series, firmware revision, memory capacity, and communication configuration particularly important when maintaining existing SLC 500 installations.

For Series C units, Ethernet capabilities depend on the specific firmware revision. Published technical information identifies later Series C configurations with 100 Mbps Ethernet auto-negotiation and increased Ethernet connection capacity, while older configurations can have different Ethernet limitations. Therefore, the physical label and firmware revision should be checked before specifying a replacement.

❓ Q&A

Q: What is the Allen-Bradley 1747-L551?

A: It is a 16K-word SLC 5/05 processor/controller used in Allen-Bradley SLC 500 modular automation systems.

Q: What does Series C mean?

A: Series C identifies a hardware/firmware revision of the 1747-L551 processor. Communication capabilities can vary according to the firmware revision.

Q: How much memory does the 1747-L551 have?

A: The controller provides 16K words of user memory.

Q: What communication ports are available?

A: The SLC 5/05 controller provides Ethernet and RS-232 communication. The RS-232 port can support DF1, ASCII, or DH-485 configurations depending on the application.

Q: How many I/O modules can the SLC 5/05 system support?

A: The SLC 500 architecture supports up to three local chassis and up to 30 I/O module slots.

Q: Is the 1747-L551 discontinued?

A: Yes. Rockwell Automation states that the 1747-L551 was discontinued on December 31, 2021.

Q: Can a Series C unit replace another 1747-L551?

A: Compatibility should be checked using the exact Series, firmware revision, application program, communication requirements, and existing SLC 500 hardware configuration.

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