Allen-Bradley 1746-OB8 DC Output Module SLC 500

1746-OB8 8-Channel Sourcing Output Module

Product Introduction

The 1746-OB8 from Allen-Bradley provides eight high-current DC sourcing outputs in a compact SLC 500 form factor. This output module handles loads up to 1A per point or 8A per module at 30°C, making it suitable for driving solenoids, relays, and indicator lights. Its wide 10-50V DC voltage range offers excellent flexibility across different system voltages. With a total heat dissipation of 6.9W and a backplane current draw of only 135mA at 5V DC, this output module maintains efficient power usage within your control cabinet. Furthermore, the module includes optical isolation of 1500V between I/O terminals and the logic side, significantly enhancing system reliability.

Key Technical Specifications

The 1746-OB8 operates with eight output points sharing a common return. Each point delivers either 1A at 30°C or 0.5A at 60°C, with corresponding module currents of 8A and 4A. The maximum on-state voltage drop measures 1.2V at 1A, which minimizes power loss during normal operation. Off-state leakage current stays below 1mA, effectively preventing unintended actuation of sensitive loads. Meanwhile, each output can withstand a surge current of 3A for 10ms, providing extra margin for inrush events.

Additionally, this output module demonstrates a step response of 60ms for turn-on and just 2.5ms for turn-off. This fast switching supports precise timing sequences in automated processes. The minimum load current required is 1mA, ensuring compatibility with high-impedance devices. For transient suppression, remember that applying external DC supply voltage to the common terminals may generate transient pulses—consult the user manual for proper snubbing techniques.

Environmental and Mechanical Ratings

Operating temperature for the 1746-OB8 ranges from 0°C to 60°C, while storage allows -40°C to 85°C. Humidity tolerance spans 5% to 95% non-condensing, accommodating diverse factory floor conditions. This output module holds UL listing, CE compliance, and CSA plus C-Tick certifications, confirming adherence to international safety and EMC standards. Its electro-optical insulation rating of 1500V ensures robust isolation between field wiring and backplane logic, protecting your controller from external faults.

Installation and Configuration

Installing the 1746-OB8 is straightforward with the SLC 500 chassis. Simply slide the module into any available slot and secure it with the retaining screws. The backplane provides 5V DC power automatically, requiring no external logic supply. All field wiring connects via the front-facing terminal block, with each output point clearly labeled. Configuration happens through your programming software, where you map the outputs to your control logic. Importantly, the module draws 0mA from the 24V DC backplane supply, which simplifies power budgeting considerably.

For optimal performance, mount this output module away from high-heat sources and maintain proper airflow around it. Ensure that the total load current does not exceed the module's thermal capacity, especially at elevated ambient temperatures. Moreover, verify that external DC supplies match the 10-50V range to prevent damage to internal circuits.

Typical Applications

This output module excels in high-current switching tasks within manufacturing lines, packaging machinery, and material handling systems. For instance, it directly drives hydraulic valves, motor contactors, and alarm annunciators. Its wide voltage acceptance also accommodates battery-powered or unregulated DC sources common in older installations. Consequently, the 1746-OB8 remains a popular choice for retrofit projects and new SLC 500-based control panels.

Furthermore, the module's fast turn-off response benefits applications requiring precise timing, such as clutch/brake controls or stepper driver enable signals. When paired with inductive loads, external flyback diodes are strongly recommended to protect the output transistors. This practice extends module life and significantly reduces electrical noise on the DC bus.

Packaging List

• 1 x Allen-Bradley 1746-OB8 output module

• 1 x Removable terminal block (installed)

• 1 x Slot filler label (for unused slots)

• 1 x Quick-start guide (printed)

Note: Cables, mounting hardware, and programming software are sold separately.

Shipping Information

All orders ship via FedEx, UPS, or DHL with full tracking and insurance coverage. Expedited shipping options are available upon request. Domestic deliveries typically arrive within 2–3 business days, while international shipments take 5–7 days depending on customs clearance.

Frequently Asked Questions (FAQ)

Q1: Can the 1746-OB8 drive AC loads?
No. This output module provides DC sourcing outputs only, with a voltage range of 10-50V DC. For AC loads, please consider the 1746-OA series modules instead.

Q2: What happens if I exceed the 1A per point rating?
Exceeding 1A per point may trigger thermal shutdown or cause permanent damage. Each output is protected but not fused internally. You should use external fusing or circuit breakers for overload protection.

Q3: How do I address transient pulses on the outputs?
Transient pulses appear when the external DC supply connects to common terminals. Install a suppression diode (flyback diode) across inductive loads and add a capacitor (0.1µF) across the supply terminals as recommended in the user manual.

Q4: Is the 1746-OB8 compatible with newer ControlLogix systems?
Not directly. This output module fits only SLC 500 chassis. However, you can use a 1746-to-1756 adapter chassis (such as the 1756-CNB) to interface with ControlLogix controllers.

Q5: How many 1746-OB8 modules can I install in one chassis?
The limit depends on the chassis backplane current capacity. Each unit draws 135mA at 5V DC, so a 10-slot chassis with a 5A supply can accommodate up to 37 modules, though physical slot count restricts this to 10 or fewer.