Motor Soft Starter 5.5–22 kW | Intelligent Reduced-Voltage Soft Starter (YCQR7)

Starting a large motor direct-on-line throws up to six or seven times its running current at the supply and snaps the shaft straight to full torque. On pumps that means water hammer; on conveyors and compressors it means jerked belts and stressed gearboxes; across the site it means a voltage dip that can trip other equipment. A soft starter solves all of that by ramping the voltage up gradually over a few seconds, so the motor accelerates smoothly and the inrush is held in check.

What the YCQR7 soft starter does

The YCQR7 sits between the supply and the motor and controls thyristors to raise the voltage on a set ramp, bringing the motor up to speed gently before handing over to a run state. It also soft-stops — easing the motor down rather than letting it coast or slam off, which is important on pumps to avoid water hammer. Throughout, it continuously protects the motor, and it can be commanded and monitored remotely over RS485 (Modbus RTU) with a 4-line LCD and keypad on the front.

Model range and frame sizes

The YCQR7 covers 5.5–450 kW on an AC 380 V supply. CNC publishes the range by power band and frame size — send your exact motor rating and we'll confirm the model:

Units up to 115 kW share one construction; from 132 kW up the wiring changes. A cabinet version, the YCQR7-G soft-start control cabinet, is also available in 5.5–30 kW, 37–45 kW and 55–115 kW bands for panel-ready installation.

Key specifications

Built-in protections

The YCQR7 protects the motor and itself against short circuit (instantaneous quick-break), over-current, overheating, inverse-time overload (class 1–5 selectable), input phase loss, current imbalance, under-voltage, over-voltage, underload, start failure and phase-sequence error — so a fault stops the motor instead of burning it out.

What the YCQR7 does not do

A soft starter controls the start and stop of a fixed-speed motor — it does not vary the motor's speed once it's running. If you need ongoing speed control, use a variable frequency drive like the CNC YCB600 instead. It also isn't a substitute for the upstream breaker and contactor around the motor. For a single unit that combines switching and protection, see the CNC YCKB7 integrated motor starter.

Downloads

• YCQR7 soft starter catalogue (PDF)
• YCQR7-G control cabinet catalogue (PDF)
• YCQR7 operation manual — English (PDF)

Frequently asked questions

What is a soft starter and why use one?

A soft starter gradually raises the voltage to a motor at start-up so it accelerates smoothly instead of jumping to full torque. That reduces the mechanical shock on belts, couplings and gearboxes, avoids water hammer on pumps, and limits the start-up inrush current that dips your supply and trips other equipment.

What is the difference between a soft starter and a VFD?

A soft starter only controls the start and stop; once the motor is running it turns at normal mains speed. A VFD (variable frequency drive) controls speed continuously. If you just need gentle starts on a fixed-speed motor, a soft starter is more economical; if you need to vary speed, use a VFD like the YCB600.

Soft starter vs star-delta starting?

Star-delta cuts starting current in fixed steps and jolts the motor at the star-to-delta changeover. A soft starter ramps voltage smoothly with no changeover jolt, gives an adjustable start, adds soft-stop, and protects the motor — a cleaner result for most modern installations.

What size YCQR7 do I need?

Match it to your motor kW and supply. The range runs 5.5–450 kW at 380 V. Send us the motor nameplate (kW and full-load current) and we will confirm the exact model and frame.

Can it soft-stop a pump to prevent water hammer?

Yes. The adjustable soft-stop (0–60 s) eases the pump down gradually rather than cutting power abruptly, which prevents the pressure surge that damages pipework and check valves.

Can it be controlled from a PLC?

Yes — built-in RS485 with Modbus RTU lets the YCQR7 be started, stopped and monitored from a PLC or control system, and the front LCD gives local status and settings.