Allen-Bradley 1791-OB32 24V DC Output Module

Allen‑Bradley 1791‑0B32 High‑Density 24V DC Block I/O Module

Overview and Key Features

The 1791‑0B32 belongs to the Allen‑Bradley 1791 Block I/O family. You get thirty‑two discrete DC output channels in one block. This module operates with a nominal 24V DC and accepts a wide range of 10‑30V DC.

Additionally, the 1791‑0B32 includes internal fusing for protection. You do not need external power fuses. This saves panel space and simplifies installation. The module works as a slave device using Universal Remote I/O (RIO) communication. You can place it at remote locations away from the main controller.

Furthermore, this module is compatible with multiple controllers. For instance, it works with PLC‑2, PLC‑3, PLC‑5/250, PLC‑5 series, and SLC 5/02 modular controllers. Specifically, it connects to scanners like the 1771‑SN, 1772‑SD, and 1775‑S5.

Technical Specifications

• Outputs per block: 32

• Output voltage range: 10‑30V DC (nominal 24V DC)

• External power required: 19.2‑30V DC

• Minimum on‑state current: 1 mA per output

• Maximum on‑state current: 500 mA (vertical mounting at 60 °C)

• Maximum on‑state voltage drop: 1V at rated current

• Off‑state leakage current: 0.5 mA maximum

• Output signal delay ON: 0.5 ms maximum

• Output signal delay OFF: 1.0 ms maximum

• Maximum power dissipation: 19.2W

• Maximum thermal dissipation: 65.5 BTU/hr

Moreover, the 1791‑0B32 provides fast response times. The 0.5 ms turn‑on delay suits high‑speed applications like packaging and material handling. The 1 mA minimum on‑state current also supports high‑impedance loads.

Environmental and Mechanical Ratings

• Operating temperature: 0 to 60 °C

• Dimensions: 6.95 x 4.35 x 3.85 inches

• Mounting orientation: Vertical (preferred) or horizontal

• Vertical mounting output rating at 60 °C: 500 mA per channel

• Horizontal mounting output rating at 60 °C: 250 mA per channel

Therefore, always mount vertically when possible. If you must mount horizontally, ensure adequate ventilation space around the module for air‑cooling. This prevents overheating and maintains reliable operation.

Wiring and Termination

For wiring, use 2.0 mm² (14 AWG) solid standard wire. Maximum insulation thickness should not exceed 3/64 inch. The 1791‑0B32 uses removable terminal strips. This design saves maintenance time because you do not need to rewire when replacing the block.

Important note: If this module is the last block I/O device in a sequence, you must install a termination resistor. This prevents signal reflection on the RIO network.

Communication and Status Indicators

The 1791‑0B32 uses Universal Remote I/O protocol. Two switch assemblies let you configure:

• Starting I/O group

• I/O rack number

• Communication rate

• Last state behavior

• Last chassis setting

For monitoring, the front panel includes:

• 1 COMM status indicator

• 1 STATUS indicator

• 16 I/O status indicators (note: 16 LEDs for 32 channels; each LED typically represents two channels or groups)

These LEDs help you troubleshoot quickly without extra tools. Additionally, the module comes with identification labels. You can use these labels to clearly mark the module and list its specifications.

Common Applications

The 1791‑0B32 is cost‑effective for smaller, less expensive enclosures. Typical applications include:

• Packaging machines

• Material handling systems

• Operator interface panels

• Remote I/O distribution in large factories

You can connect this module to solenoid valves, indicator lights, relays, and small DC motors. The high channel density (32 outputs) saves panel space compared to using multiple lower‑density blocks.

Installation Guidelines

First, mount the 1791‑0B32 vertically for best thermal performance and maximum output current. Next, connect external power (19.2‑30V DC) to the appropriate terminals. Then wire your output devices to the 32 channels. Finally, set the I/O rack number and communication rate using the switch assemblies.

If this module is the last device on the RIO trunk, add a termination resistor. Always verify the output current does not exceed the derated value for your mounting orientation and temperature. For horizontal mounting at 60 °C, limit each output to 250 mA.

Packaging List

• 1791‑0B32 module (1 unit)

• Removable terminal strip (pre‑installed)

• Identification labels (set)

• Quick start guide (printed)

Note: No certificates or warranty documents are included. These items are available upon request.

Shipping Information

We ship worldwide via FedEx, UPS, or DHL. The gross weight is 0.79 kg (1.75 lbs). All shipments include tracking and basic insurance.

Frequently Asked Questions (FAQ)

1. Is the 1791‑0B32 compatible with CompactLogix?
The 1791‑0B32 uses Remote I/O (RIO) protocol. It does not connect directly to CompactLogix. You need a RIO scanner module like the 1756‑DNB or 1734‑RIO.

2. Why does the 1791‑0B32 have only 16 status indicators for 32 outputs?
The 1791‑0B32 uses one status LED per two output channels in some configurations. Refer to the user manual for exact LED mapping.

3. Do I need external fuses for the 1791‑0B32 outputs?
No. The 1791‑0B32 has built‑in internal fusing for protection. You do not need external fuses on the power supply or output circuits.

4. Can I mount the 1791‑0B32 horizontally in a sealed cabinet?
You can mount it horizontally, but you must provide adequate ventilation. For horizontal mounting at 60 °C, the output current rating drops to 250 mA per channel. In a sealed cabinet, consider derating further.

5. How do I replace a failed 1791‑0B32 without rewiring?
The removable terminal strips stay attached to your field wiring. You simply unplug the old block and plug in the new 1791‑0B32. Then verify the switch assembly settings match the original configuration.