Boston Gear BETA II DC Motor Controllers DC MTR CTLRS (1/6-3HP) RBA2S 32POINTS IN587-16 CN7600 CN76122-485A

Technical Dossier

Product Details And Specifications

Boston Gear BETA II Series Technical Notes

The Boston Gear BETA II series represents a mature line of single-phase, adjustable-speed DC motor controllers engineered for continuous-duty industrial applications. With a rated output range of 1/6 HP to 3 HP, these controllers have been deployed across heavy industrial sectors including chemical processing plants, petroleum refineries, pulp and paper mills, and water treatment facilities. The BETA II platform is characterized by its SCR (Silicon Controlled Rectifier) phase-angle firing architecture, which provides stable armature voltage regulation across variable load conditions. Its compact DIN-rail and panel-mount form factors made it a standard specification in OEM machine builds throughout the 1980s and 1990s. As of 2026, the BETA II series is in its end-of-life phase; Boston Gear (now part of Altra Industrial Motion) no longer manufactures new units, making certified aftermarket sourcing the primary supply channel for maintenance and replacement.

The Evolution of BETA II Architecture

Boston Gear introduced the BETA II controller platform as a successor to its original BETA I line, addressing field feedback on thermal management and speed regulation stability. The BETA II design incorporated improved SCR firing circuits with enhanced noise immunity, making it compatible with inductive motor loads without external line reactors in most standard installations. Early BETA II units (pre-1990) used analog potentiometer-based speed reference inputs; later revisions introduced terminal-block signal inputs compatible with 0–10 VDC and 4–20 mA process signals, enabling integration with early DCS and PLC analog output modules. The RBA2S chassis designation indicates a regenerative braking-capable variant, distinguishing it from the non-regenerative RBA1 base models. The 32-point terminal configuration (32POINTS) reflects the expanded I/O interface introduced in mid-series revisions, providing dedicated terminals for enable/disable, fault relay, tachometer feedback, and external speed reference. Compatibility note: BETA II controllers are not electrically interchangeable with Boston Gear's subsequent RATIOTROL and MINARIK-branded successors without wiring adaptation. Field replacement with modern equivalents requires verification of armature voltage rating, current limit setpoint, and signal interface type.

BETA II Full Catalog & Functionalities (SKU List)

The following SKUs represent verified models within the Boston Gear BETA II DC motor controller family, organized by functional category. Each model designation is based on published Boston Gear catalog data and field-documented part numbers.

Adjustable-Speed Controllers — Non-Regenerative

• CN7600: 1/6–1 HP, 115 VAC single-phase input, non-regenerative, panel-mount chassis
• CN7601: 1/4–1 HP, 115 VAC single-phase, enhanced current limit adjustment, panel-mount
• CN7602: 1/2–2 HP, 230 VAC single-phase input, non-regenerative, DIN-rail compatible
• CN7603: 1–3 HP, 230 VAC single-phase, extended speed range (50:1), panel-mount
• IN587-16: Interface/input board, 16-terminal signal conditioning module for BETA II chassis
• IN587-32: Interface/input board, 32-terminal expanded I/O for mid-series BETA II revisions

Regenerative Controllers (RBA2S Series)

• RBA2S-1: 1/6–1/2 HP regenerative, 115 VAC, four-quadrant operation, dynamic braking
• RBA2S-2: 1/4–1 HP regenerative, 115 VAC, tachometer feedback input, 32-point terminal
• RBA2S-3: 1/2–2 HP regenerative, 230 VAC, armature voltage feedback, panel-mount
• RBA2S-4: 1–3 HP regenerative, 230 VAC, 4–20 mA reference input, DIN-rail mount

Communication & Interface Modules

• CN76122-485A: RS-485 serial communication adapter for BETA II, Modbus RTU protocol support
• CN76122-232: RS-232 interface adapter, point-to-point serial link for SCADA integration
• CN76100: Analog signal isolator module, 4–20 mA loop-powered, BETA II chassis mount

Power Supply & Ancillary Modules

• CN7610: 24 VDC auxiliary power supply module, BETA II panel-mount accessory
• CN7620: Line filter/EMI suppression module, 115/230 VAC, BETA II compatible
• CN7630: Dynamic braking resistor assembly, 1–3 HP range, external mount