Allen-Bradley 1746-OB16 16-Point DC Output Module

Description

Product Introduction

The Allen-Bradley 1746-OB16 is a 16-point sourcing DC output module developed for the SLC 500 PLC platform. It switches 10 to 50 VDC field loads including solenoid valves, relay coils, indicator lamps, and interposing relays. The module installs in any standard 1746 I/O chassis slot except the processor slot and communicates through the SLC backplane.

In our field experience, the 1746-OB16 remains one of the most common output modules found in legacy packaging lines, water treatment plants, and material handling systems. It is simple to troubleshoot, responds quickly, and is well suited for applications requiring fast transistor switching rather than mechanical relay contacts. Verify the output type before ordering—this is a sourcing output module, not a sinking output module.

Key Technical Specifications

Application Scenarios & The “Trench” Experience

It always seems to happen during startup.

The PLC program indicates an output is ON, but the valve never actuates. Maintenance replaces the solenoid. Still nothing. Someone swaps the power supply. No improvement.

An hour later, somebody notices the replacement module is a 1746-OV16 sinking output instead of a 1746-OB16 sourcing output. Electrically, both fit the rack. Functionally, they’re completely different.

Typical applications include:

• Packaging — Driving 24 VDC solenoid valves and pneumatic manifolds where fast transistor switching reduces response time.
• Water & Wastewater — Operating chemical dosing pumps and alarm indicators from SLC 500 controllers.
• Material Handling — Controlling conveyor diverters, photo-eye outputs, and relay interfaces.
• Automotive Manufacturing — Switching relay coils and pneumatic cylinders on assembly equipment.
• Food & Beverage — Operating filling machine actuators and product reject mechanisms using 24 VDC control circuits.

Field Case

A beverage plant lost an entire packaging line after maintenance replaced a failed output module during the night shift. Every output remained inactive even though RSLogix 500 showed the correct logic.

The issue wasn’t the PLC program.

A sinking output module had been installed where the original system required a sourcing module. Once a tested 1746-OB16 was installed, every output returned to normal immediately. The repair itself took less than ten minutes. Finding the mistake had taken nearly three hours.

Transparency SOP: Quality Assurance & Testing

We don’t just ship boxes; we test them on actual Allen-Bradley SLC 500 racks.

• Inbound Inspection
  • Verify catalog number, hardware series, and serial labels.
  • Inspect terminals, PCB, and edge connector for damage or corrosion.
  • Screen for counterfeit labels and unauthorized repairs.
• Live Rack Testing
  • Install the module in a functioning SLC 500 chassis.
  • Verify processor recognition and diagnostic status.
  • Cycle all sixteen outputs repeatedly under electrical load.
• Electrical Parameter Verification
  • Measure output voltage.
  • Verify switching response time.
  • Confirm output current capability and isolation.
• Hardware Verification
  • Record hardware revision.
  • Confirm compatibility with supported SLC 500 processors.
• Final QC & Packaging
  • Clean connectors.
  • Complete functional inspection.
  • Package in anti-static shielding with impact-resistant cushioning.

1746-OB16

1746-

The Veteran’s Tech Trap Guide

⚠️ Don’t confuse sourcing and sinking outputs. The 1746- sources DC voltage to the load. Installing it where a sinking module is required will leave every field device inactive.

⚠️ Watch the output current. Each channel is limited to 0.5 A at 30°C. Loading multiple outputs near their maximum rating inside a warm enclosure shortens module life.

❗ Always install flyback protection across inductive DC loads. Relay coils and solenoids generate voltage spikes that gradually damage transistor outputs. A simple suppression diode is much cheaper than replacing an output card.

⚠️ Label every wire before removal. Sixteen identical DC outputs become surprisingly difficult to trace during a rushed shutdown.

Verify wiring diagrams, load polarity, and terminal assignments with the OEM installation manual before energizing the system.

Frequently Asked Questions (FAQ)

Q1. Can the 1746- be hot-swapped?

No. The SLC 500 platform is not designed for live replacement of digital output modules. Always remove chassis power before installing or removing the module.

Q2. Is the 1746- a sourcing or sinking output module?

It is a sourcing transistor output module designed for 10–50 VDC field devices. If your wiring requires a sinking output, you need a different module such as the 1746-OV16.

Q3. Is the 1746- still manufactured?

No. Rockwell Automation discontinued the 1746- on September 30, 2024. Most replacement units are now supplied from verified surplus inventory or professionally refurbished stock.

Q4. Can it drive solenoid valves directly?

Yes, provided the valve’s voltage and current requirements fall within the module’s specifications. For inductive loads, install a flyback diode across the coil to protect the output transistor.

Q5. Why is this module less expensive than buying directly from the OEM?

Since production has ended, available inventory typically comes from surplus stock, plant modernization projects, or excess distributor inventory. Market availability largely determines pricing rather than the original factory list price.

Q6. Are refurbished modules dependable?

They can be, provided every output channel is tested under load, electrical parameters are verified, and the module passes live rack testing. Cosmetic appearance alone is not evidence of reliability.

Q7. What warranty is typically provided?

Most reputable industrial automation suppliers offer a 12-month warranty on qualified new surplus and professionally refurbished 1746- modules, covering functional defects under normal industrial operating conditions. Always confirm the warranty terms before purchase.