Purchase now: Allen Bradley 1747-L30C Fixed Controller
Purchase now: Atlantechdrives provides you the 1747-L30C, a highly durable and incredibly versatile «Fixed Hardware Style» programmable logic controller (PLC) from the legendary Allen Bradley SLC 500 family. Often referred to as a «brick» PLC, this unit brilliantly houses the system processor, the 120/240V AC power supply, and a high-capacity 30-point I/O circuit board within a single, ruggedized enclosure. The 1747-L30C is widely considered the «sweet spot» configuration for legacy machine builders because it pairs 18 modern, safe 24V DC Sinking inputs with 12 highly flexible, isolated AC/DC mechanical Relay outputs. This exact combination allows automation engineers to control a diverse array of mixed-voltage field devices—such as 120V AC motor contactors and 24V DC pneumatic solenoid valves—all from the exact same controller, eliminating the need for external interposing relay boards.
Technical Specifications of the 1747-L30C
Powered directly from standard factory AC line voltage, the 1747-L30C features 1K of embedded instruction memory and utilizes the robust DH-485 network for both software programming and seamless integration with PanelView operator interfaces.
- Part Number: 1747-L30C
- Controller Type: Fixed Hardware Style (Brick PLC)
- Total I/O Points: 30 Points
- Inputs: Eighteen (18) 24V DC Sinking (NPN logic)
- Outputs: Twelve (12) AC/DC Relay (Normally Open dry contacts)
- Line Power Requirement: 120 / 240V AC (50/60 Hz)
- Memory Capacity: 1K Instructions (Capacitor-backed RAM)
- Communication Port: DH-485 (RJ45 connector)
- Expansion Capability: Supports a 2-slot expansion chassis
Expert Installation Advice: Sinking Inputs and Sourcing Sensors
Integrating sensors correctly is the key to a successful installation. Expert Tip: The 18 inputs on the 1747-L30C are configured as «Sinking» inputs. This means the controller’s internal circuitry provides the path to DC ground for the input signal. Therefore, you must use «Sourcing» (PNP) field devices—such as PNP proximity sensors, photoelectric eyes, and standard 24V DC pushbuttons. A PNP sensor will output the positive +24V DC signal when activated, which travels into the PLC input terminal to complete the circuit. If you attempt to wire a Sinking (NPN) sensor to this controller, the input will never trigger because neither device is supplying the necessary positive voltage.
Maintenance and Relay Protection
While the 12 mechanical relays on the 1747-L30C are exceptionally versatile, they are susceptible to damage from inductive kickback. When you use these relays to turn off a large inductive load (like an AC motor starter coil), a massive voltage spike is generated that arcs across the internal relay contacts. To prevent the contacts from pitting or welding shut, you must install surge suppression. For AC loads, wire an RC snubber in parallel with the load. For DC loads, wire a freewheeling diode across the load. This simple maintenance step will extend the life of your controller by decades.
Frequently Asked Questions (FAQs)
Q: Does the 1747-L30C provide 24V DC power for my sensors?
A: Yes. The unit features a small «User Power» terminal block that outputs an isolated 24V DC at approximately 200 mA. This is perfect for powering a handful of low-draw field sensors without needing to buy a separate DIN-rail power supply.
Q: Can I add an analog input module to this fixed controller?
A: Yes. By removing the side cover, you can attach an interconnect ribbon cable to an external 2-slot 1746 expansion chassis, allowing you to add any standard SLC 500 specialty modules.
Do you need more references from this brand? Explore our full catalog of Allen Bradley here.
The 1747-L30C fixed controller is technically engineered for 24V DC industrial environments, similar to the 1746-P3 supply.
