Purchase now: Allen Bradley 1746-OB8 DC Output Module
Purchase now: Atlantechdrives provides you the 1746-OB8, an incredibly robust and highly dependable 8-channel digital DC output module designed by Allen Bradley for the SLC 500 programmable logic controller system. While high-density modules are built for space savings, the 1746-OB8 is built for rugged simplicity and thermal endurance. Operating on 24V DC with a Sourcing configuration, this module provides 8 solid-state transistor outputs capable of rapidly switching industrial actuators such as pneumatic directional valves, small DC motors, indicator beacons, and interposing relays. It is the ideal choice for smaller machine nodes, remote pump stations, or applications where maximum airflow and heat dissipation between outputs are prioritized over panel density.
Technical Specifications of the 1746-OB8
The 1746-OB8 utilizes high-quality optical isolation to separate the harsh electrical environment of the factory floor from the sensitive 5V DC processor backplane, preventing transient spikes from crashing the PLC. Its spacious terminal block makes it incredibly easy to wire and maintain.
- Part Number: 1746-OB8
- Module Type: Digital DC Output Module
- Compatible System: Allen Bradley SLC 500
- Number of Outputs: 8 Solid-State points
- Operating Voltage: 10…50V DC
- Wiring Logic: Sourcing (Provides V+ to load)
- Continuous Current per Point: 0.50 Amps at 60°C
- Signal Delay: On: 0.1 ms, Off: 1.0 ms
- Backplane Current Draw: 135 mA at 5V DC
Expert Tips: Reliable Wiring for Inductive Loads
Even though the 1746-OB8 is highly durable, solid-state transistors are always vulnerable to inductive voltage spikes. Expert Tip: When using the OB8 to switch inductive loads like relay coils or solenoids, the sudden collapse of the magnetic field when the output turns OFF creates a high-voltage reverse surge. If left unchecked, this surge will travel back up the wire and punch through the module’s output transistor, ruining the channel permanently. You must install a flyback suppression diode (such as a standard 1N4004) directly across the terminals of the field device (parallel to the coil) to clamp this voltage spike and ensure your module survives for decades.
Maintenance and Diagnostics
Maintenance on the 1746-OB8 is straightforward. The front panel features 8 bright red LED status indicators mapped directly to the logical state of each output. If the PLC program indicates an output is active, but the LED is OFF, the backplane connection or internal module logic may be faulty. If the LED is ON but the connected valve does not actuate, use a multimeter to check for 24V DC at the module’s screw terminal. If voltage is absent, the internal transistor has likely blown, or the external VDC supply wired to the module’s power terminal has failed.
Frequently Asked Questions (FAQs)
Q: Why would I choose an 8-point module over a 16-point module?
A: The 1746-OB8 has a lower backplane current draw (135 mA vs 280 mA for the OB16) and generates less internal heat. If you are close to the power limit of your SLC chassis power supply (like a 1746-P1), using an 8-point module can prevent an overload condition.
Q: Are the outputs individually isolated?
A: No. The 8 outputs on this module share a common VDC return internally. They are optically isolated from the backplane, but not from each other.
Do you need more references from this brand? Explore our full catalog of Allen Bradley here.
This compact 8-point DC output module is technically compatible with all SLC 500 racks, including the 1746-A4 chassis.
