Intelligent Three-Phase AC Motor Soft Starter (380V/660V, Bypass & Online Series)

Independently developed and manufactured in China by Yongfan Electric Co., Ltd. (YOF®)—an ISO9001 & CCC-certified manufacturer, factory, and global B2B supplier—the Intelligent Soft Starter uses a high-performance microprocessor as its control core. It integrates SCR (thyristor) power drive technology, hardware and software protection, a menu-driven LCD screen, keypad operation, torque control, and a fuzzy PID closed-loop control algorithm into an advanced intelligent motor starting device.

Combining smooth motor soft start, soft stop, light-load energy saving, and comprehensive motor protection functions with stable performance, this series is widely deployed across industrial and commercial transmission equipment, ventilation fans, water pumps, compressors, and heavy loads. All units strictly comply with national and international standards GB14048.6-2008 (and IEC60947-2-2: 2002) and are available for bulk wholesale, custom OEM, and ODM engineering projects.

Model Description & Nomenclature

Product Features

Technical Parameter Specification

Parameter Setting & Description (Menu Codes F0 – FN)

1. Setting code F6 (Maximum operating current) refers to the maximum continuous operating current calculated from the FP motor rated current class; exceeding this value initiates inverse-time thermal overload protection.
2. In the parameter setting state, if no key is pressed within 2 minutes, the controller automatically exits the setting mode.
3. Parameters cannot be modified during active soft start or soft stop processes, but can be modified in standby or other operating states.
4. Pressing and holding the confirm key (YES) while powering on restores all parameters (except FE) to their factory default values.

Working Principle & Soft-Start Characteristic Curves

1. Torque and Current Characteristics of Three-Phase AC Induction Motors

Three-phase AC induction motors are widely used in agriculture, commercial buildings, and industrial plants due to their rugged durability, simple structure, and maintenance-free operation. However, during direct-on-line (DOL) starting, a three-phase AC induction motor draws a severe inrush starting current—typically 6 to 8 times its rated working current (I_N)—while generating starting torque and breakdown (pull-out) torque reaching 2 to 4 times its rated torque (M_N).

For driven machinery sized according to rated motor torque, direct starting creates severe mechanical shock loads and results in three major engineering drawbacks:

• Severe Mechanical Stress: High starting torque shocks couplings, belts, gearboxes, and driven transmission mechanisms;
• Increased Maintenance Costs: Accelerated mechanical wear and water-hammer effects in piping systems raise maintenance downtime and repair costs;
• Oversized Power Grid Requirement: The upstream transformer and distribution network must be oversized to withstand the 6–8× starting current surge. Deploying a motor soft starter smoothly tailors both starting current and starting torque to match the exact load curve of the equipment.

Figure 1: Direct-On-Line (DOL) Motor Current (I) and Motor Torque (M) vs. Speed (n) Curves

2. Soft-Start Working Principle (Anti-Parallel Thyristor Phase Control)

Each phase of the soft starter employs two anti-parallel thyristors (SCRs)—one conducting during the positive half-wave and the other during the negative half-wave. Using phase-angle triggering control within a selectable start-up ramp time, the controller continuously increases the effective RMS motor voltage from a selectable initial starting voltage up to the full rated line voltage. Because motor starting current is directly proportional to the applied voltage, the starting current is reduced linearly by the voltage reduction factor. Meanwhile, because motor torque is proportional to the square of the applied voltage, the starting torque decreases quadratically with voltage reduction—eliminating mechanical shock and current surges.

Figure 2: Torque and Current Characteristics of Three-Phase AC Asynchronous Motor During Soft Start

① Voltage ramp during soft start

② Regulated starting torque via soft starter

③ Typical load torque curve (e.g., centrifugal pump)