Purchase now: Allen Bradley 1746-OW16 Relay Output Module
Purchase now: Atlantechdrives provides you the 1746-OW16, an exceptionally versatile 16-channel digital output module designed by Allen Bradley for the SLC 500 platform. Unlike solid-state DC or AC modules, the 1746-OW16 features electromechanical relay outputs (Normally Open, dry contacts). This design makes it the ultimate «universal» output card, capable of switching both alternating current (AC) and direct current (DC) loads interchangeably. It is the perfect hardware choice for mixed-voltage control panels, allowing a single module to control 120V AC motor contactors, 24V DC pneumatic valves, and 220V AC warning sirens simultaneously, drastically simplifying your system architecture.
Technical Specifications of the 1746-OW16
The 1746-OW16 isolates the processor backplane from the field wiring using both optical isolators and the physical air gap of the mechanical relay contacts. The 16 outputs are divided into two isolated groups of 8, allowing you to use two completely different power sources on the same module.
- Part Number: 1746-OW16
- Module Type: Digital Relay Output Module
- Compatible System: SLC 500 (1746 Chassis)
- Number of Outputs: 16 Relay points (Normally Open)
- Operating Voltage (AC): 5…265V AC
- Operating Voltage (DC): 5…125V DC
- Continuous Current per Point: 2.5 Amps (Resistive load)
- Maximum Module Current: 16.0 Amps total
- Backplane Current Draw: 170 mA at 5V DC, 180 mA at 24V DC
Expert Installation Advice: Inductive Kickback and Snubbers
Mechanical relays are tough, but they have a fatal weakness: inductive loads. Expert Tip: When you use the 1746-OW16 to turn off an inductive device—like a large AC motor contactor coil or a DC solenoid—the collapsing magnetic field generates a massive voltage spike. This spike causes a high-temperature electrical arc to jump across the tiny metal relay contacts inside the module just as they are opening. Over time, this arcing causes pitting, carbon buildup, and eventually causes the contacts to physically «weld» shut, meaning your machine will not turn off. To prevent this, you must install surge suppression. For AC loads, install an RC network (snubber) in parallel with the load. For DC loads, install a reverse-biased freewheeling diode across the load. This simple step will increase the life of your module from a few months to over a decade.
Maintenance and Relay Lifespan
Unlike solid-state modules which theoretically last forever, electromechanical relays have a finite mechanical and electrical lifespan. If an output on the 1746-OW16 fails, it is usually because the internal relay contact has either welded shut (stuck ON) or oxidized completely (stuck OFF). During troubleshooting, disconnect the field wire and use a multimeter in continuity mode to test the terminal. If the PLC commands the output ON but there is no continuity, the internal relay is dead and the module (or the internal relay board) must be replaced.
Frequently Asked Questions (FAQs)
Q: Can I put 120V AC on Group 1 and 24V DC on Group 2?
A: Yes. The 1746-OW16 is divided into two electrically isolated banks (Outputs 0-7 and Outputs 8-15). You can safely feed an AC voltage common to one bank and a DC voltage common to the other without interference.
Q: Does this module require an external power supply to operate?
A: The relays’ internal coils are powered by the 24V DC drawn from the chassis backplane. However, you must provide external power (AC or DC) to the output terminals to actually drive your field devices.
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For universal load switching, these isolated relay outputs integrate seamlessly into a 1746-A7 7-slot chassis.
