Allen-Bradley 1747-BA PLC Battery – SLC 500 Series

Allen-Bradley 1747-BA: Lithium Memory-Retention Battery for SLC 500 Processor Platforms

The 1747-BA is the factory-specified lithium battery for the Allen-Bradley SLC 500 programmable controller family, engineered to sustain SRAM data integrity across the full SLC processor range — from the entry-level 5/01 to the high-performance 5/05. Within a modular PLC architecture, the processor’s internal SRAM holds the user program, data table values, and I/O configuration. When AC power is interrupted and the internal capacitor charge dissipates, the 1747-BA assumes sole responsibility for maintaining that volatile memory state. Without a serviceable battery, an unplanned power event results in complete program loss, forcing a cold-start reload from an external programming device — an outcome that carries measurable downtime cost in any continuous-process environment.

The 1747-BA operates at a nominal 3 VDC with a lithium manganese dioxide (Li-MnO₂) electrochemical cell. This chemistry was selected by Rockwell Automation for its flat discharge curve, which maintains output voltage within a narrow band across the majority of its service life, and for its low self-discharge rate — typically less than 1% per year at 20 °C — which supports a rated shelf life of up to 5 years under proper storage conditions. The cell is housed in a compact, keyed connector assembly that mates directly to the battery connector on the SLC 5/01 through 5/05 processor boards, requiring no tools and no configuration changes at installation.

In the context of the SLC 500 control loop, the 1747-BA functions as a passive but operationally critical component. The processor continuously monitors battery voltage through an internal supervisory circuit. When voltage drops below the low-battery threshold — typically around 2.5 VDC — the processor asserts a battery-low fault bit in the status file (S:5/11 on most SLC models), which can be mapped to an alarm output or HMI indicator through standard ladder logic. This diagnostic transparency allows maintenance teams to schedule battery replacement during planned downtime rather than reacting to an unplanned fault condition.

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Technical Parameters

Hardware Logical Analysis

The SLC 500 processor board integrates a dedicated battery supervisory circuit that operates independently of the main CPU execution cycle. This circuit samples the battery terminal voltage at fixed intervals and compares the reading against a hardwired threshold reference. The design ensures that a degrading battery is detected well before voltage drops to a level that would compromise SRAM retention — typically providing a warning window of several weeks to months depending on the rate of discharge.

The Li-MnO₂ cell chemistry contributes directly to this supervisory reliability. Unlike alkaline cells, which exhibit a sloping discharge curve that makes remaining capacity difficult to predict, the Li-MnO₂ cell maintains a relatively stable output voltage for the majority of its discharge cycle before entering a steep terminal drop. This characteristic means the processor’s threshold comparator triggers at a consistent, predictable point in the battery’s life, reducing the risk of false-early warnings or missed detections.

From an EMC standpoint, the battery circuit is isolated from the processor’s digital logic planes by the board’s internal layout design. The battery supply rail feeds only the SRAM retention circuit and the real-time clock (where fitted), not the main logic supply. This isolation prevents battery-side noise — which is negligible for a passive cell but relevant in high-vibration or high-EMI environments — from coupling into the processor’s instruction execution path. The keyed connector assembly also provides mechanical polarity protection, eliminating the risk of reverse-insertion damage during field replacement.

For installations in environments with elevated ambient temperatures — common in steel, foundry, or petrochemical applications — the accelerated self-discharge rate of the Li-MnO₂ cell at temperatures above 40 °C should be factored into preventive maintenance intervals. Rockwell Automation’s published guidance recommends annual inspection in such environments, with replacement triggered by the S:5/11 fault bit or by calendar interval, whichever occurs first.

System Integration Benefits

• Deterministic memory retention: The 1747-BA sustains SRAM state through power interruptions of indefinite duration, ensuring the processor resumes execution from a known program state on power restoration without requiring a manual reload cycle.
• Integrated fault diagnostics: The battery-low status bit (S:5/11) provides a machine-readable signal that can be wired into existing alarm management logic, enabling condition-based maintenance scheduling rather than time-based replacement.
• Zero-configuration replacement: The keyed connector and standardized form factor allow field technicians to complete a battery swap in under two minutes without a programming device, reducing mean time to repair (MTTR) for this maintenance task.
• Broad processor compatibility: A single part number covers the entire SLC 5/01 through 5/05 processor range, simplifying spare parts inventory management for facilities operating mixed SLC 500 fleets.
• Low self-discharge chemistry: The Li-MnO₂ cell’s sub-1% annual self-discharge rate supports long-term storage in maintenance stock without capacity loss, reducing the cost of carrying safety stock.
• Stable voltage profile: The flat discharge curve of the Li-MnO₂ cell ensures the SRAM retention voltage remains within specification for the majority of the battery’s service life, avoiding the gradual data corruption risk associated with cells that exhibit early voltage sag.
• Thermal operating range: Rated operation from 0 °C to +60 °C covers the majority of industrial panel environments, including those without active cooling, without requiring derating of the rated service life.
• Traceability and audit compliance: Genuine OEM parts supplied with verifiable sourcing documentation support ISO 9001 maintenance record requirements and facilitate audit responses for regulated industries including food processing, pharmaceuticals, and utilities.

Quality Assurance & Global Logistics

Every 1747-BA unit supplied through siemensplc.com is sourced from verified industrial distribution channels and subjected to a structured pre-shipment inspection protocol. Open-circuit voltage is measured on each unit to confirm the cell retains full charge within the OEM-specified tolerance band. Physical inspection covers label integrity, connector condition, housing for mechanical damage, and date-code legibility. Units that do not meet acceptance criteria are quarantined and not dispatched.

All products carry a 12-month warranty from the date of shipment. In the event of a confirmed defect, replacement or credit is arranged without requiring return of the defective unit for low-value components, subject to photographic evidence of the fault condition.

Dispatch is handled from Xiamen, China, with access to DHL Express, FedEx International Priority, and UPS Worldwide Expedited services. Standard in-stock orders are processed and handed to the carrier within 1–3 business days. For time-critical requirements, same-day dispatch can be arranged for orders confirmed before 14:00 CST. Full export documentation — commercial invoice, packing list, and certificate of origin — is provided with every international shipment. Bulk orders are eligible for sea freight consolidation with competitive transit times to major ports in Southeast Asia, Europe, and North America.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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