Introduction to the 1746-OB8 Output Module
When your SLC 500 control system needs reliable high-current DC switching, the Allen-Bradley 1746-OB8 delivers. This 8-channel digital DC output module handles demanding industrial loads without compromising backplane integrity. As part of the proven SLC 500 platform, it integrates seamlessly into existing installations and offers a straightforward replacement path for legacy systems.
Technical Specifications That Matter
The 1746-OB8 operates with a voltage range of 10-50 Volts DC source. Each output can handle 1 amp or 0.5 amp, depending on your configuration. The module supports a total current of 8 amps or 4 amps per module. Backplane current consumption is 135 milliamps at 5 Volts DC. Heat dissipation reaches 6.9 Watts total, with 0.775 Watts per output point. Step response is 60 milliseconds in and 2.5 milliseconds out. The maximum off-state leakage is 1 milliamp, and the minimum load current is 1 milliamp. An on-state voltage drop of 1.2 Volts at 1 amp ensures efficient switching. The module includes 1500 Volt electro-optical insulation between I/O terminals and control logic.
Key Parameter Comparison
| Feature | 1746-OB8 | Typical 8-Channel DC Output |
|---|---|---|
| Voltage Range | 10-50V DC | 24V DC only |
| Current per Output | 1A or 0.5A | 0.5A |
| Current per Module | 8A or 4A | 4A |
| Backplane Current | 135mA at 5V | 100mA at 5V |
| Heat Dissipation | 6.9W | 5W |
| Step Response | 60ms in / 2.5ms out | 10ms in / 10ms out |
This comparison highlights the 1746-OB8’s advantage in high-current applications and its flexible voltage range.
Industry Applications
In automotive assembly lines, the 1746-OB8 controls solenoid valves and motor starters that require reliable high-current switching. The 10-50V DC range accommodates various actuator voltages. For material handling systems, this module drives conveyor diverters and sortation gates. Its 8-amp module capacity supports multiple outputs simultaneously. In packaging machinery, the fast 2.5-millisecond turn-off response ensures precise timing for glue guns and cutters. The robust design handles the electrical noise common in these environments.
Installation and Setup
Mount the 1746-OB8 in any SLC 500 chassis slot. Ensure the backplane connector seats firmly. Wire outputs according to your field device requirements, respecting the 10-50V DC source range. Use separate power supplies for isolated groups if needed. Verify that load currents do not exceed 1 amp per point or 8 amps total. The module draws 135 milliamps from the 5V backplane. No external 24V backplane current is required. For transient protection, follow the user manual recommendations. Always power down the chassis before inserting or removing the module.
Maintenance and Reliability
Periodic inspection of terminal connections prevents loose wires and overheating. Check for dust accumulation and clean with dry compressed air if necessary. The operating temperature must stay between 0°C and 60°C. Storage temperature ranges from -40°C to 85°C. Humidity should remain between 5% and 95% non-condensing. The 6.9W heat dissipation requires adequate panel ventilation. Replace modules showing signs of discoloration or erratic output behavior. With proper care, the 1746-OB8 provides years of dependable service.
Compatibility and Integration
The 1746-OB8 works with all SLC 500 processors and I/O chassis. It communicates through the backplane, so no special configuration is needed beyond addressing. The module is UL-listed, CE compliant, CSA certified, and C-Tick certified. It integrates with existing 1746 series I/O for mixed systems. For new installations, pair it with 1746-IB8 input modules for a complete control solution.
Selection Guide
Before purchasing, verify your system uses SLC 500 hardware. Confirm that your field devices operate within 10-50V DC and do not exceed 1 amp per point. Check that your chassis has available slots and sufficient power supply capacity. The 1746-OB8 suits high-current applications where standard 0.5A outputs fall short. SpareTechPLC stocks this module and can advise on compatibility. Contact them for current availability and lead times.
Frequently Asked Questions
Q: Can I use the 1746-OB8 with a 12V DC power supply?
A: Yes, the voltage range is 10-50 Volts DC source, so 12V DC falls within the acceptable range.
Q: What is the maximum current per output point?
A: Each output handles 1 amp or 0.5 amp, depending on your configuration and ambient temperature.
Q: Does this module require external 24V DC backplane power?
A: No, backplane current consumption is 135 milliamps at 5 Volts DC and 0 milliamps at 24 Volts DC.
Q: What is the step response time?
A: The 1746-OB8 has a step response of 60 milliseconds in and 2.5 milliseconds out.
Q: Is the 1746-OB8 still available?
A: Please verify current lifecycle status and availability with SpareTechPLC before ordering.
