Allen-Bradley 1746-OB32 Overview
The Allen-Bradley 1746-OB32 is a high-density digital DC output module designed for the SLC 500 programmable controller platform. This module provides thirty-two 24VDC output channels, arranged in two isolated groups of sixteen points each. Engineers commonly select this module for applications that require energizing discrete devices such as pilot lamps, buzzers, horns, sirens, solenoids, and small motors. Because it delivers a nominal output of 24VDC, it integrates directly with many industrial loads that operate within the 5-50VDC range.
Key Technical Specifications
The 1746-OB32 operates with a sourcing voltage range from 5 to 50VDC, making it versatile for various DC control circuits. Each output point can handle a nominal current of 0.25A at 0-60°C, with a maximum of 0.5A per point. The module supports a total current of 8A per module, and each common group can carry up to 2A. Backplane current draw is only 190mA at 5VDC, which helps manage power budgets in a SLC 500 chassis. Signal delays are minimal, with an ON delay of 0.1ms and an OFF delay of 1.0ms, ensuring fast response for time-critical processes.
Isolation is a crucial feature of this module. The output circuits are tested to withstand 1500V AC for one minute, providing robust protection against voltage transients. The module also includes a maximum leakage current of 1mA in the OFF state, which prevents unintended actuation of connected devices. In addition, the 1746-OB32 meets NEMA ICS 2-230 noise immunity standards and carries UL and C-UL certifications for Class I, Division 2 hazardous locations, making it suitable for demanding industrial environments.
Wiring and Installation Best Practices
For reliable operation, use the recommended Allen-Bradley 1746-N3 or 1492 wiring systems with the module. These pre-assembled connectors ensure proper termination and adequate wire size, reducing the risk of loose connections or overheating. They also help maintain a clean front panel, allowing easy access for troubleshooting. If you choose alternative wiring, be cautious: large wire sizes can obstruct the module door and make maintenance difficult.
When connecting output devices, verify that their operating voltage matches the 24VDC output. For AC-operated devices, implement an interposing relay with a 24VDC coil. The relay contacts can then switch the AC voltage, while the module drives the coil. This approach also provides electrical isolation, protecting the module from noise and ground loops common in older wiring systems.
Applications and Practical Value
The 1746-OB32 excels in high-current switching applications, thanks to its per-point surge capability of 1.0A for 1ms, repeatable every 2 seconds. This feature is particularly useful for energizing solenoids and contactors that draw high inrush currents. With a step response of 60ms in and 2.5ms out, the module handles rapid on/off cycles effectively. Its compact design fits any available slot in a 1746 chassis (except slot 0), allowing easy expansion of your SLC 500 system.
In summary, the Allen-Bradley 1746-OB32 offers a reliable, high-density solution for DC output control. Its robust electrical specifications, fast switching, and isolation features make it a solid choice for both new installations and upgrades. For engineers seeking a proven output module for discrete control, this model delivers consistent performance and long-term dependability.