Allen-Bradley 1746-P1: The Power Behind Your SLC 500 Rack
When an SLC 500 chassis loses its power supply, every module in the rack goes dark. The Allen-Bradley 1746-P1 is the module that prevents that downtime. As a dedicated SLC 500 power supply, it mounts in the leftmost slot of a 1746 chassis and delivers the backplane power that every attached module needs to operate.
This is not a generic power brick. The 1746-P1 accepts a nominal input of 120/220 Volts AC and provides an internal current capacity of 2A at 5VDC and 0.46A at 24VDC. It also offers a 24VDC user-power output with built-in fuse protection, so your rack stays energized and protected.
Technical Specifications That Matter
| Specification | Value |
|---|---|
| Input Voltage | 120 to 220 Volts AC |
| Input Power | 42 Watts |
| Frequency | 47 to 63 Hertz |
| Backplane Current (5V) | 2 Amps |
| Backplane Current (24V) | 0.46 Amps |
| Output Voltage Range | 18 to 30 Volts DC |
| Inrush Current | 20 Amps |
| Operating Temperature | 0 to 60 Celsius |
| Dimensions | 5.5 x 2.3 x 5.7 inches |
| Weight | 2 pounds (0.9 kilograms) |
| Fuse Protection | 1746-F1 or equivalent |
Three specs deserve a closer look. First, the dual backplane current of 2A at 5VDC and 0.46A at 24VDC determines how many modules your chassis can support. Second, the 18 to 30VDC output range gives you flexibility for user-power devices. Third, the 20A inrush current tells you the supply can handle startup surges without tripping upstream protection.
How the 1746-P1 Compares to Other SLC 500 Power Supplies
Buyers often weigh the 1746-P1 against other SLC 500 supply options. Here is a quick comparison:
- 1746-P1: 120/220V AC input, 2A at 5VDC, 0.46A at 24VDC, 42W input power.
- 1746-P2: Higher input power rating, suited to larger rack configurations.
- 1746-P4: Designed for 24V DC input applications, not AC line power.
If your facility runs on standard AC line voltage and your rack draws within the 1746-P1 current budget, this model is the direct fit. Always verify your total module load before selecting a supply.
Where the 1746-P1 Fits in Real Applications
Manufacturing Cells With Mixed I/O
A typical SLC 500 rack might hold a processor, several digital I/O cards, and an analog module. The 1746-P1 supplies the 5VDC backplane rail those cards need, plus 24VDC user power for field devices. Its 42W input power and 47 to 63Hz frequency range suit standard industrial mains.
Remote I/O Racks
The 1746-P1 installs in the leftmost slot whether the chassis is a main, expansion, or Remote I/O rack. Only one power supply is needed per chassis. That simplifies spare-parts planning across a plant with multiple SLC 500 racks.
Upgrade and Replacement Projects
When a legacy SLC 500 rack needs a new supply, the 1746-P1 is a drop-in replacement. Its 5.5 x 2.3 x 5.7 inch footprint and 2 pound weight match the original chassis slot, so no re-engineering is required.
Installation and Setup Essentials
Before applying power, set the input jumper. The exposed pins carry hazardous voltage once power is on, so this step protects both you and the equipment. Mount the supply in the leftmost slot of the 1746 chassis. Only one supply is required per chassis, regardless of rack type.
The 1746-P1 includes fuse protection, but note that this guards against fire hazards from short circuits only. For user-power overcurrent conditions, behavior differs by manufacturing origin. The Series A made in Japan shuts down the supply and faults the CPU, requiring a user program reload. The Series A made in Malaysia keeps the CPU running but shuts down 24VDC user power, and you correct the overcurrent condition to recover.
Reliability, Hold-Up Time, and Maintenance
One standout feature is CPU hold-up time. When input voltage drops below the operating range, the 1746-P1 continues powering the controllers briefly. Hold-up time is 20 ms at full load and 3000 ms at no load. If normal voltage returns, the processor continues operating normally.
For maintenance, inspect the supply periodically for dust buildup and secure connections. The operating temperature range is 0 to 60 Celsius, but current capacity derates by 5% above 55 Celsius. Keep cabinet airflow adequate in hot environments. The internal fuse may be replaced with a 1746-F1 or equivalent.
What to Verify Before You Buy
Confirm your chassis type and total module current draw. Check that your input voltage falls within the 120 to 220 Volts AC range and your line frequency is between 47 and 63 Hertz. Verify the 24VDC user-power load stays within the 200 mA capacity. Also confirm whether your unit is Series A from Japan or Malaysia, since overcurrent recovery differs.
SpareTechPLC stocks the Allen-Bradley 1746-P1 and can help you confirm compatibility with your existing SLC 500 rack. Please verify current lifecycle status and availability with SpareTechPLC before ordering.
Frequently Asked Questions
What input voltage does the 1746-P1 require?
It accepts a nominal 120/220 Volts AC input with a frequency range of 47 to 63 Hertz.
How much backplane current does the 1746-P1 provide?
It supplies 2 Amps at 5VDC and 0.46 Amps at 24VDC to the chassis backplane.
Can I use the 1746-P1 in a Remote I/O rack?
Yes. It installs in the leftmost slot of main, expansion, or Remote I/O racks, and only one supply is needed per chassis.
What happens during a power dip?
The 1746-P1 provides CPU hold-up time of 20 ms at full load and 3000 ms at no load, letting the processor ride through brief voltage drops.
What fuse replaces the internal one?
Use a 1746-F1 or equivalent fuse for replacement.
