Overview
The Allen-Bradley 1747-L20A is a fixed hardware style controller from the SLC 500 family of small programmable logic controllers. The 1747-L20A provides integrated processor, power supply, and I/O in a single compact module, eliminating the need for separate chassis and modules. With 20 I/O points—12 AC inputs and 8 AC/DC relay outputs—this processor is designed for straightforward control applications in small to mid-sized automation systems.
Key Features
- 20 fixed I/O points: 12 120V AC inputs, 8 AC/DC relay outputs
- 1K instruction memory capacity with capacitor-backed RAM
- Panel-mount design with support for 2-slot I/O expansion racks
- Five status indicator lights (POWER, PC RUN, CPU FAULT, FORCED I/O, BATTERY LOW)
- Optional lithium battery backup (5-year lifespan) and EEPROM/UVPROM memory options
- Fuse-protected at 1.25A, 120-240V AC line voltage
Technical Specifications
- Input Voltage: 85–265 VAC (nominal 120–240 VAC)
- Input Frequency: 47–63 Hz
- Input Specifications: 12 × 120V AC (on-state: 85–132V AC; turn-on/off time: 35–45 ms maximum)
- Output Specifications: 8 AC/DC relay outputs
- Memory Type: Capacitor-backed RAM (2-week hold-up); optional battery backup (5-year lifespan)
- Memory Capacity: 1K instruction capacity
- Program Scan Time: 8 ms per 1K instructions
- Load-Dependent Hold-Up Time: 20–700 milliseconds
- Operating Temperature: 0–60°C (32–140°F)
- Humidity: 5–95% non-condensing relative humidity
- Shock Rating: 30G at 10–500 Hz
- Vibration Tolerance: 2.5G at 10–500 Hz
- Mounting: Panel-mount
- Dimensions: 3.6 × 5.5 × 5.7 inches (91.4 × 139.7 × 144.8 mm)
- Weight: Approximately 0.4 pounds (180 grams)
- Fuse Protection: 1.25A at 120–240V AC
- Certifications: UL, CSA
Typical Applications
The 1747-L20A is well-suited for compact, fixed I/O automation tasks including:
- Simple sequential control and logic operations
- Equipment monitoring and status indication
- Small packaging and assembly line control
- Discrete process automation with limited I/O expansion needs
- Retrofit applications replacing legacy SLC 500 controllers
Compatibility & Replacements
Compatible With
- SLC 500 I/O expansion modules (via 2-slot expansion racks)
- DH-485 network communication
- Allen-Bradley SLC 500 programming software (APS, handheld terminals)
- DF1 serial communication (with optional interface modules)
- DeviceNet, ControlNet (with optional network scanner modules: 1747-SDN, 1747-SCNR)
Replaces / Drop-In Replacement For
Verify compatibility with your system integrator before ordering. The 1747-L20A is a direct replacement for damaged or failed 1747-L20A units in existing SLC 500 systems. Related models in the fixed controller family include the 1747-L30A (18 inputs) and 1747-L40A (larger configurations).
Works With
- SLC 500 APS (Allen-Bradley Programming Software)
- Hand-held terminal programming interfaces
- DH-485 industrial networks (integrated communication port)
- EEPROM and UVPROM memory backup modules
- 1747-BA optional battery assembly for extended data retention
- 1747-C13, 1747-CP3 serial cables for programming and communication
