Soft starter for an electric motor: when to use it, when a VFD is the better call
We install a soft starter when the customer needs to remove the inrush hit. Speed regulation is not required. Typical scenario in our shop: conveyor, crusher, compressor. Or a constant-speed fan. Direct-on-line motor start draws 6-8x rated current for 1-3 seconds. That means voltage sag across the site. A shock load on the coupling. Accelerated bearing wear. A soft starter ramps the voltage over 5-30 seconds, inrush drops to 2-3x rated. If you need to control speed or save energy on a variable load, we ship a VFD instead.
The difference vs pump applications: a motor on a conveyor or crusher runs constant-torque. Starting torque needs to be close to rated from the first second. So the ramp profile is short, 5-15 seconds, and we often enable boost (a brief voltage kick at start to overcome inertia). For pumps it is the opposite: torque is quadratic (squared with speed). Ramp profile is long, 15-30 seconds, no boost. Pick the wrong type and you get either a no-start motor or a water hammer in the pipe.
How we size a soft starter for a motor
First question we ask: rated motor current from the nameplate. The soft starter must match or exceed it. For a normal start (fan, pump) +10% headroom is enough. For a heavy start (loaded conveyor, crusher with material) we add 30-50%. In stock we ship Schneider Electric ATS22D47Q (47 A, ATS22 with built-in bypass, we install it on 22 kW conveyors). Next to it ships ATS22D32Q (32 A, for compressors up to 15 kW). Budget: ATS01N222QN (22 A, for fans up to 11 kW). Small units: Siemens 3RW3016-1BB14 (9 A, small drives). For heavy 50+ kW motors see Schneider ATS480/ATS490 or Danfoss MCD500.
What else we ask before ordering. First: load type (constant torque or quadratic), this drives the ramp profile. Second: starts per hour. More than 6-10, we look at series with reinforced internal bypass. Without it the thyristors heat up from running current after ramp-up. Third: any communication requirements (Modbus RTU, Profinet) for higher ATS22 or ATS480 variants. Warranty 12-24 months depending on the manufacturer, delivery nationwide from our Kyiv warehouse.
| Model | Series | Rated Current | Application |
|---|---|---|---|
| Schneider Electric ATS22D47Q | ATS22 | 47 A | Conveyors, crushers |
| Schneider Electric ATS22D32Q | ATS22 | 32 A | Compressors, mixers |
| Schneider Electric ATS01N222QN | ATS01 | 22 A | Fans, pumps |
| Schneider Electric ATS130N2C11LT | ATS130 | 105 A (55 kW) | Industrial lines, large pumps |
| Siemens 3RW3016-1BB14 | SIRIUS 3RW30 | 9 A | Small fans, drive mechanisms |
Soft Starter Manufacturers for Motors
Our catalog features soft starters from leading industrial automation manufacturers:
- Schneider Electric — Altistart series ATS01, ATS22, ATS130. Sales leader: wide range from 6A to 480A, built-in motor protection, bypass relay in ATS22/ATS130.
- Danfoss — MCD200 series. Compact soft starters with an extended voltage range of 200-575V.
- Siemens — SIRIUS 3RW30/3RW40 series. Reliable devices for industrial motors with IP20 protection class.
Soft Starters by Application
- All soft starters — complete soft starter catalog
- Soft starter for pump — soft starters for pump applications with soft stop function
Warranty and Delivery
All soft starters come with an official manufacturer warranty of 12 to 24 months. Delivery across Ukraine — Kyiv, Kharkiv, Odesa, Dnipro, Lviv, and other cities. Bank transfer for businesses or cash on delivery for individuals.
