Description
Product Introduction & Engineering Value
When an SLC 500 rack starts throwing intermittent CPU faults or dropping analog channel reads across multiple cards simultaneously, the culprit is almost always a failing power supply rail. The Allen-Bradley 1746-P2 serves as the heavy-duty power backbone for multi-slot SLC 500 chassis, delivering up to 5.0 Amps on the 5V DC backplane logic bus.
Mounting directly to the far left of any 1746 chassis, it provides clean, filtered power with built-in ride-through capability to withstand line voltage sags during motor start-ups. Plant maintenance teams swap in the 1746-P2 to eliminate random rack resets and restore rock-solid backplane voltage regulation.
Technical Specifications
| Specification | Parameter Value |
| Input Voltage Range | 85 to 132V AC or 170 to 265V AC (jumper selectable) |
| Line Frequency | 47 to 63 Hz |
| Max Real Input Power | 110 VA |
| Internal Backplane Current (5V DC) | 5.0 A max |
| Internal Backplane Current (24V DC) | 0.96 A max |
| User Auxiliary Power (24V DC) | 0.20 A (200 mA) max |
| Fuse Protection | 120/240V AC user-replaceable fuse (3AG 3.0A 250V Slow-Blow) |
| Inrush Current | 20 A max for 1/2 cycle |
| Hold-Up Time (Power Ride-Through) | 20 ms at full load |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Field Application & The “Trench” Experience
A critical wastewater treatment plant experienced erratic rack shutdowns every time the main effluent pumps kicked across the line. The voltage sag dropped line power to 92V AC for a few cycles, causing an aging 1746-P1 power supply to lose its 5V logic hold-up and fault the SLC 5/04 processor. Replacing the degraded supply with a fresh 1746-P2 restored the required 20 ms ride-through window, keeping the processor running seamlessly through heavy pump start-up transients without dropping process telemetry.
- Heavy Industrial Motor Control Centers (MCC): Supplying clean backplane power to multi-card SLC racks subject to line voltage fluctuations and industrial noise.
- Grain Terminal Conveyor Control: Powering high-density 32-point transistor output cards and analog modules across 13-slot expansion chassis.
- Chemical Skid Batch Controllers: Providing steady logic power and auxiliary sensor excitation in elevated ambient heat panels.
- 1746-P2
- 1746-P2
- 1746-P2
Transparency SOP: QA & Testing
- Capacitor & Bridge Rectifier Audit: Inspecting internal filter capacitors for ESR degradation, swelling, or electrolyte leakage, and checking the main power transformer for thermal stress.
- Line Jumper & AC Input Test: Verifying continuity and correct positioning of the 120V/240V input selector jumper before energizing.
- Dual-Rail Full Load Stress Test: Connecting precision active electronic loads to both the 5V DC (5.0A) and 24V DC (0.96A) output rails simultaneously on a test chassis.
- Thermal & Ripple Voltage Verification: Running the supply under 100% rated load for 12 hours in an environmental test chamber while monitoring DC output ripple voltage using a digital oscilloscope to ensure noise stays well below factory limits.
The Veteran’s Tech Trap Guide
- ⚠️ 120V / 240V Jumper Switch Trap: The 1746-P2 features a physical input voltage selection jumper located under the top protective shroud. If you plug a unit jumpered for 120V AC into a 240V AC utility feed, you will instantly blow the internal fuse and risk destroying the primary switching stage. Always verify jumper position before applying line power!
- PRO TIP: Backplane Power Budgeting: Never exceed 5.0A on the 5V rail or 0.96A on the 24V rail. High-density analog modules (like the 1746-NO8I or 1746-NT8) and relay modules (like the 1746-OW16) draw significant 24V DC backplane power. Sum up the 5V and 24V draw for every module in your chassis using RSLogix 500 I/O Config before powering up.
- ⚠️ Auxiliary 24V DC Terminal Limits: The front screw terminals provide an auxiliary 24V DC output (200 mA max). Do NOT attempt to run loop power for multiple 4-20 mA transmitters or heavy solenoid valves off these auxiliary terminals—overloading this circuit will trip the power supply’s internal shutdown protection, taking down the whole PLC rack.
Dynamic FAQ
Q: What is the primary difference between the 1746-P1 and 1746-P2 power supplies?
A: The 1746-P2 offers higher output capacity (5.0A @ 5V DC and 0.96A @ 24V DC) compared to the smaller 1746-P1 (2.0A @ 5V DC and 0.46A @ 24V DC), making the P2 essential for larger or higher-density chassis.
Q: Can I use the 1746-P2 on a 24V DC input source?
A: No. The 1746-P2 requires an AC power input (120V AC or 240V AC). If you need to run your SLC 500 chassis off a 24V DC battery or panel supply, you must use a DC-input power supply like the 1746-P3 or 1746-P6.
Q: What type of replacement fuse does the 1746-P2 use?
A: It uses a standard 3AG slow-blow fuse rated at 3.0 Amps / 250 Volts, accessible directly behind the front protective flip cover.
Q: Are these replacement power supplies bench-tested under full electrical load before dispatch?
A: Yes. Every 1746-P2 is thoroughly audited, ripple-tested on an oscilloscope under maximum rated amperage, and thermal burn-in certified prior to shipment.
Start Chat
