Product Overview

The Allen-Bradley 1746-OBP8​ is an eight-channel high-current DC output module for the SLC 500 programmable controller platform. The “P” in its catalogue number designates it as the high-power variant of the SLC 500 transistor output range, and that description is fully justified: each of its eight sourcing outputs delivers a continuous 2.0 A at any ambient temperature from 0 to 60 °C, with no thermal derating, and the module as a whole handles up to 8.0 A. This is roughly four times the per-point capability of a standard SLC 500 DC output module, which is why the 1746-OBP8​ is specified wherever field devices demand real current rather than just a control signal.Internally, the Allen-Bradley 1746-OBP8​ is organised into two electrically isolated groups of four outputs each. Every group has its own supply terminal and its own common return, so the module can switch two separate 24V DC power domains, or the same supply can be landed on both groups when a single distribution is preferred. The sourcing topology means the module switches the positive side of the load; the field device is connected between the output terminal and the DC common. Isolation between the I/O terminals and the logic circuitry is rated at 1500V AC, which protects the processor backplane from field-side faults.Speed and diagnostics round out the module’s value proposition. The 1746-OBP8​ turns on in 1.0 ms and turns off in 2.0 ms under resistive load, the fast turn-off characteristic being important when driving inductive devices such as solenoid coils and relay actuators, where sluggish release translates directly into cycle time. Front-panel e-fuse LED indicators give immediate per-channel status, and a jumper setting allows the CPU to be notified when a fuse condition occurs. Installed in a single slot of any 1746 fixed or modular chassis and compatible with every SLC 500 processor from the 5/01 to the 5/05, the Allen-Bradley 1746-OBP8​ is the standard answer to high-current discrete output requirements on this enduring platform.

Technical Specifications

Main Features and Advantages

Genuine high-current capability: The reason to choose the Allen-Bradley 1746-OBP8​ over a general-purpose output module is current. Two amps continuous per point is enough to energise large solenoid valve coils directly, to drive stacks of pilot lights and annunciator lamps, to sound industrial horns and buzzers, and to hold in contactors and relays without an interposing device. Critically, the 2.0 A rating holds across the full 0–60 °C operating range, so a panel that runs warm in summer does not force a de-rating exercise. The 4.0 A per point surge allowance for 10 ms further absorbs the inrush of lamp filaments and coil pull-in currents that would otherwise stress a lesser module.Fast turn-off for cycle-time-sensitive machines: The 1746-OBP8​ releases its outputs in 2.0 ms, a characteristic Rockwell specifically labels as fast turn-off. On solenoid-driven equipment, the release time of the output transistor adds directly to the mechanical drop-out time of the valve, so a slow output module quietly steals milliseconds from every cycle. In packaging, indexing and pick-and-place machinery where those milliseconds accumulate over thousands of cycles per shift, the 1746-OBP8​ protects throughput in a way that is rarely captured on a specification sheet comparison.Two isolated groups for design freedom: The eight outputs of the Allen-Bradley 1746-OBP8​ are split into two isolated groups of four, each with its own positive supply and common terminal. This lets a designer separate a safety-related or clean-control supply from a noisy actuator supply within one module, or shut down one half of a machine’s outputs while the other half remains live. It also means the module can be wired with two independent external supplies, which simplifies panels where different voltage domains must be kept apart.Clear per-point diagnostics: Every channel of the 1746-OBP8​ carries an e-fuse LED on the front panel, so an operator can see at a glance which outputs are commanded on and which have dropped out. A jumper setting additionally allows the module to report a fuse condition to the CPU, turning a local indicator into a system-level alarm that can annunciate on an HMI or trigger a controlled stop rather than leaving a machine in a half-operated state.Efficient, cool-running design: Despite its current capability, the Allen-Bradley 1746-OBP8​ draws only 135 mA from the 5V backplane and dissipates 3.08 W as a fully loaded module, with an on-state voltage drop of just 1.0 V at 2.0 A. The low voltage drop means less heat is generated inside the module and more of the supply voltage reaches the load, which matters when long cable runs to remote solenoid manifolds already erode the available voltage.