Allen-Bradley 1746-P1 SLC 500 Rack Mount Power Supply

Description

Product Introduction

The Allen-Bradley 1746-P1 is a rack-mounted power supply designed for the SLC 500 PLC platform. It converts incoming AC power into the regulated DC voltages required by the chassis backplane, supplying processors and I/O modules throughout the control system. It installs directly into the left side of a 1746 chassis and serves as the foundation of the entire rack.

To be honest, when an SLC 500 rack suddenly goes dark, experienced technicians often check the power supply before suspecting the processor. The 1746-P1 has proven dependable over decades of service, but like any power supply, electrolytic capacitor aging and heat eventually take their toll. Before replacing the unit, calculate the total backplane current to ensure the selected power supply has sufficient capacity.

Key Technical Specifications

Application Scenarios & The “Trench” Experience

Here’s one many maintenance teams have experienced.

An entire SLC 500 rack loses power without warning. The processor LEDs are dark. Every I/O module appears dead. Operators immediately assume the CPU has failed.

After replacing the processor, nothing changes.

The actual failure turns out to be the chassis power supply. Because every module depends on it, one failed power supply can make an entire PLC rack appear completely inoperative.

Typical applications include:

• Water Treatment — Supplying power for SLC 500 racks controlling filtration, pumping, and chemical dosing systems.
• Packaging Machinery — Powering processors and distributed I/O controlling conveyors, sealers, and labeling equipment.
• Food & Beverage — Supporting continuous production lines where reliable backplane power is essential for process uptime.
• Automotive Manufacturing — Providing chassis power for machine cells controlling robotic fixtures and transfer systems.
• Power Generation — Supporting legacy SLC 500 control cabinets used in auxiliary plant systems.

Field Case

A wastewater treatment facility experienced an unexpected PLC shutdown during peak operation. Maintenance initially suspected the SLC 5/04 processor because the rack showed no signs of life.

Voltage measurements confirmed proper AC input, but no regulated backplane voltage was present. After installing a tested 1746-P1, the processor booted normally, all I/O modules initialized correctly, and the plant returned to service within minutes. The original processor was never faulty.

1746-P1

1746-P1

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 revision, and serial identification.
  • Inspect the enclosure, terminals, cooling vents, and connectors.
  • Screen for counterfeit labels, corrosion, or previous repair work.
• Live Rack Testing
  • Install the power supply in a functioning SLC 500 chassis.
  • Verify proper startup and processor initialization.
  • Confirm stable operation under representative backplane loads.
• Electrical Parameter Checks
  • Measure 5 VDC and 24 VDC backplane outputs.
  • Verify AC input operation across the specified voltage range.
  • Confirm output stability during load changes.
• Hardware Verification
  • Inspect fuse condition.
  • Record hardware revision.
  • Confirm compatibility with supported SLC 500 chassis.
• Final QC & Packaging
  • Perform a complete functional inspection.
  • Clean all connectors.
  • Package in anti-static materials with protective cushioning.

The Veteran’s Tech Trap Guide

⚠️ Calculate the backplane load before installing a replacement. The 1746-P1 provides 2 A at 5 VDC and 0.46 A at 24 VDC. Adding too many high-current modules can overload the supply.

⚠️ Don’t assume the processor has failed. If the entire rack is dark, measure the power supply outputs before replacing expensive CPUs.

❗ Always check the fuse before condemning the unit. A blown 1746-F1 fuse may indicate a downstream fault rather than a defective power supply. Replacing the fuse without identifying the cause often results in another failure.

⚠️ Verify the input voltage selection and wiring. Applying the wrong AC supply or incorrect wiring can damage the power supply immediately.

Always compare the total chassis current requirement with the power supply rating and verify installation using the official Rockwell documentation before energizing the rack.

Frequently Asked Questions (FAQ)

Q1. Can the 1746-P1 be replaced while the PLC is energized?

No. Disconnect AC power before removing or installing the power supply. Replacing it under power can damage the chassis or connected modules.

Q2. What input voltage does the 1746-P1 accept?

It operates from 85–132 VAC or 170–265 VAC at 47–63 Hz, making it suitable for both 120 VAC and 230 VAC industrial control systems.

Q3. How much backplane current can it provide?

The 1746-P1 supplies 2.0 A at 5 VDC and 0.46 A at 24 VDC, plus 200 mA of user 24 VDC power. Always total the current requirements of every installed module before selecting the power supply.

Q4. Is the 1746-P1 still manufactured?

No. Rockwell Automation discontinued the 1746-P1 on September 30, 2020. Most replacement units are sourced from verified surplus inventory or professionally refurbished stock.

Q5. Can I replace the 1746-P1 with a third-party power supply?

Generally, no. The 1746-P1 interfaces directly with the SLC 500 chassis backplane and is not designed to be replaced by a generic DIN-rail power supply. Field experience from maintenance professionals consistently recommends using compatible 1746-P series power supplies.

Q6. Are refurbished power supplies dependable?

Yes, provided they undergo load testing, output voltage verification, thermal stability testing, and full rack operation before shipment. Cosmetic condition alone does not indicate electrical reliability.

Q7. What warranty is typically offered?

Most reputable industrial automation suppliers provide a 12-month warranty on qualified new surplus and professionally refurbished 1746-P1 power supplies, covering functional defects under normal industrial operating conditions.