Purchase now: Allen Bradley 1747-L40F Fixed Controller
Purchase now: Atlantechdrives provides you the 1747-L40F, a high-capacity and remarkably versatile «Fixed Hardware» programmable controller from the Allen Bradley SLC 500 family. What sets the 1747-L40F apart from the rest of the fixed controller lineup is its primary power source. While most brick PLCs require standard 120V AC wall power, the 1747-L40F operates entirely on 24V DC Line Power. This makes it an absolute necessity for mobile industrial equipment, solar-powered remote pumping stations, AGVs (Automated Guided Vehicles), and critical facilities that rely on centralized 24V DC battery backup systems to maintain automation control during massive plant-wide power outages. Furthermore, it boasts the maximum fixed footprint of 40 I/O points, eliminating the need for bulky expansion racks in tight cabinets.
Technical Specifications of the 1747-L40F
The 1747-L40F combines 24 inputs and 16 highly adaptable AC/DC mechanical relay outputs. The relay outputs allow the 24V-powered PLC to safely switch external 120V AC or 220V AC loads without any issue, acting as an excellent voltage bridge.
- Part Number: 1747-L40F
- Controller Type: Fixed Hardware Style
- Total I/O Points: 40 Points
- Line Power Requirement: 24V DC (Ideal for battery systems)
- Inputs: Twenty-four (24) 24V DC Sinking (NPN logic)
- Outputs: Sixteen (16) AC/DC Relay (Normally Open dry contacts)
- Memory Capacity: 1K Instructions
- Communication Port: DH-485 via RJ45 jack
- Expansion Capability: Supports a 2-slot external chassis
Expert Installation Advice: Managing DC Power Drops
Powering a PLC with 24V DC requires strict attention to cable resistance. Expert Tip: The 1747-L40F draws its operational current directly from your 24V DC grid. If your DC power supply is located far away from the PLC cabinet, the resistance of the long copper wires will cause a «voltage drop.» If the incoming voltage sags below the module’s minimum operating threshold during a heavy load surge (like several solenoids firing at once), the CPU will fault and the machine will crash. Always use thick-gauge wire (minimum 14 AWG) for your main 24V DC power feed, and keep the run as short as possible to ensure the processor receives a stable voltage supply.
Maintenance and Relay Protection
Because the 1747-L40F utilizes 16 mechanical relays for its outputs, it can switch both AC and DC loads with ease. However, when switching inductive loads like large motor contactors, the inductive kickback creates an electrical arc that will eventually burn out the internal relay contacts. During maintenance windows, always verify that your field devices have surge suppressors installed (RC snubbers for AC loads, or freewheeling diodes for DC loads) across the coil. This prevents the internal relays from pitting and welding shut over time.
Frequently Asked Questions (FAQs)
Q: Does the 1747-L40F provide a 24V DC «User Power» output?
A: No. Unlike the AC-powered models (L40A, L40E), the DC-powered L40F does not output user power. You must power your field sensors directly from the same main 24V DC power supply that is running the PLC.
Q: What software do I need to program this controller?
A: You will need Rockwell Automation’s RSLogix 500 software and a DH-485 interface adapter (like the 1747-UIC) to connect your PC to the RJ45 port on the controller.
Do you need more references from this brand? Explore our full catalog of Allen Bradley here.
For high-density fixed control, this 40-point unit offers the maximum I/O count available for the fixed SLC family.
