Allen-Bradley 1391B AC Servo Controller Modules

Technical Dossier

Product Details And Specifications

Allen-Bradley 1391B Series: Comprehensive Module Range and Technical Overview

The Allen-Bradley 1391B is a dedicated AC servo drive series engineered by Rockwell Automation for closed-loop motion control in high-demand industrial environments. Deployed extensively across petrochemical refineries, nuclear power auxiliary systems, offshore drilling platforms, and continuous-process manufacturing lines, the 1391B occupies a critical position in legacy servo infrastructure worldwide. Its architecture supports brushless AC servo motors and integrates directly with Allen-Bradley PLC platforms—including the PLC-5 and SLC 500 families—via analog command interfaces, making it a foundational component in plants where control system replacement is cost-prohibitive. Installed base estimates place the 1391B in active service at thousands of facilities across North America, Europe, and Asia-Pacific, with many sites operating units manufactured between 1988 and 2005.

The Evolution of 1391B Architecture

The 1391B series succeeded the earlier 1391 and 1391-DES analog servo drives, introducing improved current-loop bandwidth, enhanced fault diagnostics via front-panel LED arrays, and a modular power structure that separated the control board from the power bridge. Early production units (circa 1988–1993) used discrete IGBT gate driver circuits and required external shunt resistors for regenerative braking. Mid-generation units (1994–1999) incorporated integrated regenerative clamp circuits and expanded parameter DIP-switch configurability. Late-production units (2000–2005) added improved EMI filtering and UL 508C compliance markings.

The 1391B is not compatible with EtherNet/IP or DeviceNet natively; communication with upstream PLCs is achieved via ±10 VDC analog velocity reference or pulse-direction inputs. This architecture places the 1391B firmly in the analog servo generation, predating the Kinetix 300, Kinetix 350, and Kinetix 5500 families that Rockwell Automation positions as direct functional successors. Facilities migrating from 1391B to Kinetix platforms must account for motor re-commissioning, feedback device replacement (resolver-to-encoder conversion), and PLC motion instruction rewrites—a scope that frequently justifies continued 1391B maintenance over full replacement.

1391B Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly sourced models within the Allen-Bradley 1391B product family. Units are classified by output current rating and enclosure type.

1391B-AA08: 8A continuous output, 230 VAC input, open chassis, analog velocity command
1391B-AA15: 15A continuous output, 230 VAC input, open chassis, ±10 VDC reference interface
1391B-AA20: 20A continuous output, 230 VAC input, open chassis, integrated regen clamp
1391B-AA30: 30A continuous output, 230 VAC input, open chassis, expanded fault LED diagnostics
1391B-AA45: 45A continuous output, 230 VAC input, open chassis, high-inertia load compensation
1391B-AA60: 60A continuous output, 230 VAC input, open chassis, dual current-loop bandwidth setting
1391B-BA08: 8A continuous output, 460 VAC input, open chassis, three-phase power stage
1391B-BA15: 15A continuous output, 460 VAC input, open chassis, resolver feedback compatible
1391B-BA20: 20A continuous output, 460 VAC input, open chassis, DIP-switch parameter configuration
1391B-BA30: 30A continuous output, 460 VAC input, open chassis, regenerative braking module
1391B-BA45: 45A continuous output, 460 VAC input, open chassis, high-power servo axis control
1391B-BA60: 60A continuous output, 460 VAC input, open chassis, heavy-duty continuous duty cycle
1391B-BA75: 75A continuous output, 460 VAC input, open chassis, large-frame servo applications
1391B-BA100: 100A continuous output, 460 VAC input, open chassis, multi-axis coordinated motion
1391B-ES: Enhanced diagnostics control board retrofit, compatible with AA and BA power frames
1391B-SB: Shunt brake resistor assembly, external regenerative energy dissipation module
1391B-RM: Resolver-to-digital converter module, feedback signal conditioning board

Sourcing Hard-to-Find & Obsolete 1391B Parts

Rockwell Automation formally discontinued the 1391B series, and the product line has been in end-of-life status for over a decade. OEM replacement parts, including control boards, IGBT power modules, gate driver cards, and resolver interface assemblies, are no longer available through authorized distribution channels. DriveKNMS maintains a dedicated inventory of new-surplus, refurbished, and tested-functional 1391B units and sub-assemblies sourced from decommissioned plant equipment, authorized liquidations, and long-term storage stock.

For facilities operating under long-term maintenance agreements or regulated asset replacement schedules—common in nuclear auxiliary systems, chemical processing, and water treatment infrastructure—DriveKNMS provides condition-verified units with full functional test documentation. Each unit is cross-referenced against the original catalog number to confirm frame size, voltage class, and current rating compatibility before shipment. Emergency same-day quotation is available for critical production-down situations.

Quality Control for the 1391B Range

The 1391B power bridge and control board assembly requires a structured test protocol that differs from standard VFD bench testing. DriveKNMS applies the following verification sequence to all 1391B units processed through its facility:

DC bus capacitor ESR and capacitance measurement against OEM specification tolerances. IGBT gate drive signal integrity verification under no-load switching conditions. Current loop response test using a calibrated resistive load bank at 25%, 50%, and 100% of rated output. Resolver feedback signal simulation to verify the control board's velocity feedback processing chain. Fault code injection test to confirm all diagnostic LED indicators and protection circuits respond correctly. Final run test under motor load at rated speed and torque for a minimum 30-minute continuous cycle.

Units that do not pass all stages are either repaired to specification or quarantined and listed as parts-only. Test records are retained and available upon request for regulated-industry customers.