Softstarters
Controlled motor start and stop to reduce inrush current and mechanical stress on connected equipment.
About Softstarters
A soft starter brings an AC induction motor up to speed gradually by controlling the voltage applied to it through back-to-back thyristors. Rather than the sudden current surge and torque jolt of a direct-on-line or star-delta start, the motor accelerates along a set ramp. Once it reaches full speed, an internal bypass takes over so the thyristors stop dissipating heat during normal running.
Microtech supplies soft starters from the Amtech Electronics Axpert-OPTI Torque series, which covers motors from 3.7 kW to 1000 kW on 200–690 V three-phase supplies. Starting can follow a voltage, current or torque ramp, and stopping can be a controlled ramp — useful for preventing water hammer when a pump shuts down.
A soft starter is the right choice when a motor runs at fixed speed but its start is causing problems: voltage dips on a weak supply or DG set, belt slip, coupling wear or pipework surges. If the process actually needs variable speed, a VFD is the better fit, and we will tell you which one suits the load.
Key specifications
| Motor power range | 3.7 kW to 1000 kW (5 to 1340 HP) |
|---|---|
| Rated current | 15 A to 1065 A |
| Supply voltage | 200–690 V AC, 3-phase, 50/60 Hz |
| Starting modes | Voltage ramp, current ramp, torque ramp; kick start |
| Stopping modes | Voltage ramp, torque ramp, brake stop, coast to stop |
| Connection | In-line (3-wire) or inside-delta (6-wire) |
| Motor protection | Electronic overload (trip class 2–30), overcurrent, ground fault, PTC thermistor input |
| Communication | RS-485 Modbus |
| Enclosure | IP20 up to 110 A; digital operation panel IP65 |
Features & benefits
- Internal bypass that cuts running losses once the motor reaches full speed
- Torque-ramp starting and stopping for smoother acceleration on pumps
- Inside-delta wiring option that lets a smaller unit serve a delta-connected motor
- Motor protection built in, so a separate overload relay is often not needed
- Built-in energy meter and fault history for maintenance records
- Modbus link for remote monitoring from a PLC or SCADA
- Direct replacement for star-delta and DOL starters in existing MCCs
Where it’s used
- Centrifugal and borewell pumps
- Fans and blowers
- Compressors
- Conveyors and crushers
- Motors fed from DG sets or weak supplies
Standards & compliance
Softstarters — FAQs
What is the difference between a soft starter and a VFD?
A soft starter only controls the start and stop; once running, the motor runs at full fixed speed on bypass. A VFD controls speed throughout operation. If you do not need to vary speed, a soft starter is usually smaller and cheaper for the same motor.
Can a soft starter replace my star-delta starter?
In most cases, yes. The soft starter gives a smoother start than the star-to-delta changeover and adds motor protection. We check the motor connection and the existing control wiring before quoting a retrofit.
Does a soft stop help with water hammer?
A controlled ramp-down slows the pump gradually instead of letting it stop abruptly, which reduces pressure surges in the pipeline. The ramp time is set to suit the system during commissioning.
What size soft starter do I need?
It depends on the motor's full-load current, how heavy the load is to start and how many starts per hour it makes. Share the motor nameplate and the application and we will select the rating.
