Allen-Bradley 1746-OB8 Overview
The Allen-Bradley 1746-OB8 is a digital DC output module from the SLC 500 product line. It delivers eight outputs with a voltage range of 10-50 Volts DC, making it a flexible choice for high-current applications. This module suits engineers who need reliable switching for solenoids, contactors, and other inductive loads. Its compact design fits seamlessly into existing SLC 500 systems, providing a straightforward upgrade path for older installations.
Key Technical Specifications
This module operates with a 24V DC nominal voltage, though it accepts a source range of 10-50V DC. Each output can handle 1 amp at 30°C or 0.5 amps at 60°C, with a total module current of 8 amps or 4 amps respectively. The backplane draws only 135 milliamps at 5V DC, which keeps power consumption low. Additionally, the module dissipates 6.9 Watts of heat, so proper ventilation in the enclosure remains essential.
Signal response times are quick: 60 milliseconds for input and 2.5 milliseconds for output. This fast switching makes the 1746-OB8 ideal for processes that require rapid actuation. The module also features a maximum off-state leakage of 1 milliamp, ensuring minimal current flow when outputs are off. Its on-state voltage drop stays at 1.2V at 1 amp, which helps maintain efficient power delivery to connected devices.
Compliance and Environmental Ratings
The 1746-OB8 meets international standards, including UL listing, CE compliance, CSA certification, and C-Tick approval. This broad compliance simplifies integration into global projects. The module operates within a temperature range of 0°C to 60°C and can be stored from -40°C to 85°C. It also tolerates humidity from 5% to 95% non-condensing, so it works reliably in varied industrial environments. The electro-optical insulation between I/O terminals and control logic is rated at 1500V, providing robust isolation for sensitive electronics.
Practical Applications
Because of its high-current capability, the 1746-OB8 excels in applications like motor starters, valve control, and lighting systems. Its eight outputs can drive multiple devices simultaneously, reducing the need for additional modules. The module's step response of 60 milliseconds in and 2.5 milliseconds out ensures precise timing for sequential operations. Engineers can configure the module easily through a connected computer, which streamlines setup and reduces downtime during commissioning.
When installing the 1746-OB8, technicians should be aware of transient pulses that may occur when external DC supply voltage is applied to the output common terminals. The user manual provides detailed guidance on mitigating these effects. Proper wiring and shielding can prevent false triggering and extend module life. With its robust design and clear documentation, the Allen-Bradley 1746-OB8 remains a dependable choice for modern automation systems.