Allen-Bradley 1791-OB16 24V DC Output Module

Allen‑Bradley 1791‑0B16 24V DC Block I/O Module

Overview and Key Features

The 1791‑0B16 belongs to the Allen‑Bradley 1791 Block I/O family. You get sixteen discrete DC output channels in one compact block. This module operates with a nominal 24V DC and accepts a wide range of 10‑30V DC.

Additionally, the 1791‑0B16 includes internal fusing. You do not need external power fuses. This saves panel space and reduces installation time. 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: 16

• 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: 12.5W

• Maximum thermal dissipation: 43 BTU/hr

Moreover, the 1791‑0B16 provides a fast response time. The 0.5 ms turn‑on delay suits high‑speed applications like packaging and material handling.

Environmental and Mechanical Ratings

• Operating temperature: 0 to 60 °C

• Dimensions: 6.95 x 2.7 x 3.85 inches

• Mounting orientation: Vertical (recommended) 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 prefer vertical mounting for higher current capacity. This ensures reliable operation in warm environments.

Wiring and Termination

For wiring, use 2 mm² (14 AWG) solid standard wire. Maximum insulation thickness should not exceed 3/64 inch. The module uses removable terminal strips. This design saves maintenance time because you do not need to rewire when replacing the block.

Important termination rule: If the 1791‑0B16 is the last block I/O module in a sequence, you must install a termination resistor. This prevents signal reflection on the RIO network.

Communication and Status Indicators

The 1791‑0B16 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 (one per channel)

These LEDs help you troubleshoot quickly without extra tools.

Common Applications

The 1791‑0B16 is cost‑effective for smaller 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 1 mA minimum on‑state current also supports high‑impedance loads.

Installation Guidelines

First, mount the 1791‑0B16 vertically for best thermal performance. Next, connect external power (19.2‑30V DC) to the appropriate terminals. Then wire your output devices to the 16 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.

Packaging List

• 1791‑0B16 module (1 unit)

• Removable terminal strip (pre‑installed)

• Product label

• 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 0.45 kg (1.00 lbs). All shipments include tracking and basic insurance.

Frequently Asked Questions (FAQ)

1. Is the 1791‑0B16 compatible with ControlLogix systems?
The 1791‑0B16 uses Remote I/O (RIO) protocol. It does not connect directly to ControlLogix. You need a RIO scanner module like the 1756‑DNB or 1756‑RIO.

2. Do I really need a termination resistor for the 1791‑0B16?
Yes, but only when this module is the last block on the RIO link. The resistor prevents data reflection and communication errors.

3. What happens if I mount the 1791‑0B16 horizontally at 60 °C?
The output current rating drops from 500 mA to 250 mA per channel. Exceeding this limit may cause overheating or shutdown.

4. Can I replace a 1791‑0B16 without rewiring everything?
Yes. The removable terminal strips stay attached to your field wiring. You simply unplug the old block and plug in the new 1791‑0B16.

5. Does the internal fusing cover all output channels?
Yes. The 1791‑0B16 has built‑in internal fusing for protection. You do not need external fuses on the power supply or outputs.