Allen-Bradley 1746-P2 PLC Power Supply – SLC 500 Series

Allen-Bradley 1746-P2: AC Power Supply Architecture for SLC 500 Modular Control Systems

The Allen-Bradley 1746-P2 is a chassis-mount AC power supply engineered specifically for the SLC 500 modular I/O platform. It occupies the dedicated power supply slot on the left end of any SLC 500 modular chassis — 1746-A4, 1746-A7, 1746-A10, or 1746-A13 — and delivers regulated DC rails to the backplane bus, powering the processor and all installed I/O modules from a single, thermally managed unit. Unlike fixed SLC 500 controllers that integrate power internally, the modular chassis architecture separates power conversion from logic processing, allowing the 1746-P2 to be replaced independently without disturbing the processor or field wiring. This design principle directly reduces mean time to repair (MTTR) in production environments where unplanned downtime carries measurable cost.

The 1746-P2 accepts a universal AC input range of 85–265 VAC at 47–63 Hz, making it compatible with both 110 VAC North American infrastructure and 220/240 VAC industrial grids across Europe, Asia, and the Middle East without transformer intervention. Its switching power supply topology provides active power factor correction and tight output regulation across the full load range. The backplane receives +5 VDC at 5.0 A for logic and communication circuits, +24 VDC at 0.96 A for discrete I/O sourcing and sensor supply, and −5 VDC at 0.5 A for legacy analog modules that require a negative reference rail. Total backplane power capacity is 30 W, sufficient to support a fully populated 13-slot chassis under typical mixed I/O loading conditions.

In the SLC 500 backplane architecture, the 1746-P2 communicates power status to the processor via a dedicated power-good signal line. If output voltage on any rail drops below regulation threshold — due to overload, short circuit, or input undervoltage — the power-good signal de-asserts, triggering a controlled processor fault rather than an uncontrolled logic lockup. This deterministic fault behavior is critical in safety-adjacent applications where undefined processor states are unacceptable. The unit incorporates thermal shutdown protection with automatic restart, meaning transient overtemperature events caused by blocked airflow or ambient spikes do not require manual intervention to recover.

From a procurement standpoint, the 1746-P2 remains one of the most frequently replaced consumable components in aging SLC 500 installations. Electrolytic capacitor degradation in the primary switching stage is the dominant failure mode after 10–15 years of continuous operation, and the modular architecture makes field replacement a sub-30-minute task for a qualified technician. Maintaining one or two units as cold-standby spares is standard practice in facilities running SLC 500 systems beyond their original design life.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

The 1746-P2 employs a flyback switching converter topology operating at a fixed switching frequency in the 50–100 kHz range. This topology was selected by Rockwell Automation for its inherent galvanic isolation between the AC input stage and the DC output rails — a non-negotiable requirement in industrial control environments where ground loops between field devices and logic circuits can corrupt analog signals or damage I/O modules. The transformer primary and secondary windings are separated by a reinforced insulation barrier rated to withstand 1,500 VAC dielectric test voltage, consistent with IEC 61010-1 requirements for industrial control equipment.

EMC Design: The input stage incorporates a two-stage common-mode and differential-mode filter network. Common-mode chokes suppress high-frequency noise conducted from the AC line — particularly relevant in facilities where variable-frequency drives (VFDs) share the same distribution panel. X-capacitors across the line and Y-capacitors to chassis ground attenuate differential-mode switching noise generated by the converter itself. The result is a conducted emissions profile that meets EN 55011 Class A limits, ensuring the power supply does not degrade the signal integrity of analog I/O modules sharing the same chassis backplane.

Output Regulation and Cross-Regulation: Each output rail is regulated independently through optocoupler-isolated feedback loops referenced to the +5 VDC primary rail. The +24 VDC rail uses a secondary post-regulator stage to maintain tight tolerance even when the +5 VDC load varies significantly — a common scenario when the processor executes memory-intensive scan cycles. Cross-regulation error between rails under worst-case asymmetric loading is held within ±8%, preventing the +24 VDC sensor supply from sagging when the backplane logic demand peaks.

Thermal Management: The unit uses a combination of aluminum heat-sink extrusion bonded to the primary switching transistors and a thermistor-based thermal monitoring circuit. When junction temperature approaches the shutdown threshold (typically 85°C case temperature), the controller reduces switching duty cycle before initiating full shutdown, providing a soft-derating behavior rather than an abrupt cutoff. This protects downstream I/O modules from the voltage transients that would otherwise accompany a hard power loss.

Inrush Current Limiting: A negative temperature coefficient (NTC) thermistor in series with the AC input limits cold-start inrush current to below 30 A peak, protecting upstream circuit breakers and contactors from nuisance tripping during power-up sequences in multi-chassis control panels.

System Integration Benefits

• Direct chassis compatibility: The 1746-P2 installs into the dedicated power supply slot of all SLC 500 modular chassis variants (4, 7, 10, and 13-slot) with no adapter hardware, no firmware configuration, and no software parameter changes required.
• Universal AC input eliminates transformer cost: The 85–265 VAC input range covers every major industrial grid voltage globally, removing the need for step-down or step-up transformers in international installations and reducing panel BOM cost.
• Deterministic power-good signaling: The power-good output to the SLC 500 processor ensures that any rail fault produces a logged, recoverable processor fault rather than an undefined logic state, preserving program integrity and simplifying post-fault diagnostics.
• Independent replaceability reduces MTTR: Because the power supply occupies its own chassis slot, field replacement requires no rewiring of I/O modules or processor connections. A trained technician can swap the unit and restore power in under 30 minutes.
• Multi-rail output supports mixed I/O architectures: The simultaneous availability of +5 VDC, +24 VDC, and −5 VDC from a single module supports digital I/O, analog I/O, and legacy modules within the same chassis without auxiliary power supplies.
• Thermal shutdown with auto-restart: Transient overtemperature events — caused by momentary airflow blockage or ambient temperature spikes — trigger a controlled shutdown followed by automatic restart once thermal conditions normalize, avoiding unnecessary maintenance callouts.
• EMC-compliant design protects analog signal integrity: The input EMC filter network prevents VFD-generated conducted noise from propagating onto the backplane, maintaining the accuracy of analog input modules measuring 4–20 mA or 0–10 VDC process signals.
• Inrush limiting protects upstream protection devices: The NTC-based inrush limiter prevents nuisance tripping of upstream MCBs during panel energization, a common failure point in older installations where breaker ratings were sized to running current rather than cold-start inrush.
• Spare parts standardization: A single 1746-P2 unit serves as a common spare across all SLC 500 modular chassis sizes, simplifying spare parts inventory management for maintenance departments operating multiple chassis configurations.
• Long-term availability from verified distribution: siemensplc.com maintains stock of the 1746-P2 sourced through documented supply chains, providing procurement continuity for facilities that cannot migrate legacy SLC 500 systems to newer ControlLogix or CompactLogix platforms on short timelines.

Quality Assurance & Global Logistics

Every 1746-P2 unit dispatched from our Xiamen, China facility undergoes a structured pre-shipment inspection protocol. Label authenticity, housing integrity, connector pin condition, and serial number format are verified against Rockwell Automation factory standards. Output voltages on all three rails are measured under representative load conditions using calibrated bench equipment, and results are recorded in a unit-level inspection log available to enterprise buyers on request.

Units are packed in anti-static ESD shielding bags, placed in foam-lined cartons with corner protection, and sealed with tamper-evident tape. Export documentation — commercial invoice, packing list, certificate of origin, and HS code declaration — is prepared as standard for every international shipment. Customs HS code 8537.10 applies to this product category for most destination markets.

Shipping is executed via DHL Express, FedEx International Priority, and UPS Worldwide Expedited, with typical transit times of 3–5 business days to Europe, 4–6 days to North America, and 2–4 days to Southeast Asia and the Middle East. Bulk orders and blanket purchase agreements are accommodated with dedicated account management and volume pricing. All units carry a 12-month warranty from the date of shipment, covering manufacturing defects and verified functional failures under normal operating conditions.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
© 2026 siemensplc.com. All rights reserved.