Description
Product Introduction & Engineering Value
When operating remote control cabinets or off-grid skids running on battery banks and 24V DC industrial power buses, AC-input power supplies simply aren’t an option. The Allen-Bradley 1746-P4 is the high-capacity DC solution for heavy-density SLC 500 racks, delivering an impressive 10.0 Amps on the 5V DC backplane rail.
Mounting directly into the left-most slot of any 1746 chassis, it powers large multi-slot configurations packed with high-density analog and communication cards. Plant technicians count on the 1746-P4 to deliver stable backplane power without requiring line-in AC transformers inside field enclosures.
Technical Specifications
| Specification | Parameter Value |
| Nominal Input Voltage | 24V DC |
| Input Voltage Range | 19.2 to 28.8V DC |
| Inrush Current | 30 A max for 2 ms |
| Max Real Input Power | 100 W |
| Internal Backplane Current (5V DC) | 10.0 A max |
| Internal Backplane Current (24V DC) | 2.88 A max |
| Fuse Protection | Internal 250V / 10A fast-acting input fuse |
| Power Ride-Through (Hold-Up Time) | 10 ms at full load |
| Isolation | 1500V DC input-to-backplane |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Field Application & The “Trench” Experience
A solar-assisted off-grid pipeline valve site in a harsh desert environment relied on a 24V DC battery bank to power its remote terminal unit (RTU) enclosure. During an unseasonable heat wave, an older DC power supply began shutting down due to thermal degradation on its 5V rail, causing the SLC 5/05 processor to lose communication with SCADA. Swapping in a heavy-duty 1746-P4 restored the RTU’s backplane power stability, effortlessly driving the 13-slot chassis filled with high-density analog modules while operating reliably under elevated cabinet temperatures.
- Solar & Battery-Powered Remote Telemetry: Supplying clean backplane power to SLC 500 controller racks on off-grid pipeline monitoring stations.
- Mobile & Marine Equipment Automation: Powering onboard control systems running directly off 24V DC generator/battery buses on dredging vessels or heavy machinery.
- 24V DC Safety Instrument Panels: Driving high-density I/O configurations in plants utilizing centralized, uninterruptible 24V DC battery backup power loops.
Transparency SOP: QA & Testing
- DC Input Stage & Circuit Board Inspection: Inspecting internal switching transistors, input filter chokes, PCB traces, and gold-plated chassis backplane edge connectors for thermal or mechanical stress.
- Voltage Range Regulation Audit: Supplying variable DC input voltages across the full operating range (19.2V DC up to 28.8V DC) on a test bench to ensure output voltage rails stay perfectly regulated.
- 10A High-Load Stress Testing: Connecting active electronic loads to the 5V DC (10.0A) and 24V DC (2.88A) backplane outputs simultaneously to verify full power delivery.
- Oscilloscope Ripple & Thermal Chamber Burn-In: Running the unit at 100% rated capacity for 12 hours inside a thermal chamber while verifying that output noise and voltage ripple remain strictly within factory limits.
- 1746-P4
- 1746-P4
- 1746-P4
The Veteran’s Tech Trap Guide
- ⚠️ Input Polarity Critical Warning: Unlike AC power supplies, DC input modules are sensitive to wiring polarity. Connecting +24V DC to the negative terminal will immediately blow the internal input fuse or trip protection circuitry. Always double-check wire tagging and measure voltage polarity with a multimeter before landing wires on the power supply terminals.
- PRO TIP: Inrush Current Cable Sizing: The 1746-P4 can draw an inrush current spike of up to 30 Amps upon startup. Ensure the 24V DC feed wire gauge (typically 14 AWG minimum) and upstream DC circuit breakers are appropriately sized to prevent instantaneous voltage drops during rack power-up.
- ⚠️ Backplane Current Budgeting: Even though the 1746-P4 provides a massive 10.0A on the 5V DC rail, you must still ensure total chassis draw does not exceed 2.88A on the 24V DC rail. High-density relay output modules (such as the 1746-OW16) draw heavily on the 24V DC rail, so sum up both rails in RSLogix 500 I/O Configuration before commissioning.
Dynamic FAQ
Q: What is the primary difference between the 1746-P3 and 1746-P4 power supplies?
A: Both are 24V DC input power supplies, but the 1746-P4 is a high-capacity supply delivering up to 10.0A @ 5V DC and 2.88A @ 24V DC, whereas the 1746-P3 delivers lower capacity (3.6A @ 5V DC and 0.87A @ 24V DC) suited for smaller chassis.
Q: Does the 1746-P4 provide an auxiliary 24V DC output terminal for field sensors?
A: No. Unlike some AC-input models (like the 1746-P1 or P2), the 1746-P4 uses its entire power stage to convert incoming 24V DC to internal backplane power rails and does not feature an auxiliary field output terminal.
Q: Can I run the 1746-P4 off a 12V DC battery system?
A: No. The minimum operating threshold for the 1746-P4 is 19.2V DC. Attempting to power it with a 12V DC system will result in an under-voltage lockout fault.
Q: Are replacement 1746-P4 units bench-tested under full electrical load before dispatch?
A: Yes. Every 1746-P4 undergoes full input voltage range testing, high-current load verification on both DC rails, and oscilloscope ripple checks on a live SLC test rack prior to shipment.
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