What Are Motor Soft Starters and How They Work?

soft starter motor
Source: bpa.ru

Electricity and its infrastructure are everywhere. A lot of machinery nowadays, such as hoists and cranes, rely on electricity. From cables and conduits to switches and motors, you can find every piece of this power source in every commercial facility and household. When it comes to motors though, things can be a bit different. An electric motor, unlike other electrical infrastructure, can vary depending on where and what’s it used for. Although all electric motors work the same way in order to power machinery and devices, they don’t always have the same capabilities.
Be it AC or DC motors, they all rely on copper wires inside them and the power of electromagnetic forces. Sometimes though, an electric motor isn’t able to do its best when it comes to powering machinery safely. This is where a motor soft starter is used. Soft starters are an electrical device that sits between the power supply and motor and helps regulate the amount of current being sent to the motor.

How Does a Motor Soft Starter Work?

soft starter motor
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Soft starters for motors reduce the current supplied to the motor by making use of rectifiers and thyristors. A quality soft starter motor uses both of these components to reduce the incoming voltage and they allow operators to keep it at a constant rate until they achieve full speed. It’s much more complicated than this, but this is a simple explanation to help you understand how soft starters keep your electric motor safe.  

Applications of a Soft Starter

Water Supply

When using a pump, like in the case of water supply systems, you do need to implement a soft starter device. This is because the system needs to make the pressure change start off gradually, just like the motor. Otherwise, there can be pressure surges which could lead to all kinds of hazards.

Dust Collector

A motor soft starter is also commonly used in industrial applications, such as dust collection systems. With this kind of system, there is a high inertia load and a large inrush of current, soft starters are definitely needed. These systems usually have large fans inside and it takes some time to get them moving. Once the fan is moving fast enough, the current and torque on the motor need to be reduced. As a result, a slow start is definitely needed with these systems.

Conveyor System

Heavy load conveyor systems are one of those systems that can be optimised with the help of a soft starter motor. This is because a soft stater placed inside the control panel in these systems can easily supply three-phase power without the risk of damage caused by quick surges.

Types of Soft Starters

soft starter motor
Source: dmebservice.com

Auto Transformer

One of the most effective soft starters is the auto transformer starter, since it relies on taps on the transformer windings to control the power input to the motor. This is not your conventional soft starter, as it can provide 50%, 65%, and even 80% line voltage with each tap.

Primary Resistor

Primary resistor starters have been around since the early 1900s. Primary resistors are simple devices that have a resistor for each phase. Resistors keep the flow of current down and thus, help reduce the voltage, which results in approximately 70% of line voltage coming through. This provides smooth starts and two-point acceleration for even smoother starts.

Part Winding

With a part winding motor, you have the motor windings divided into two or even more sets. When starting up the motor, power is sent to only one set, and as the motor comes up to speed, power is sent to the other sets. Part winding starters are intended for parallel operation.

Solid State

soft starter motor

If you want to get your hands on the latest type of soft starting technology, then you should be on the lookout for sold state starters. These replace any mechanical components found in other starters with electrical ones. The main component of solid state soft starters is called SCR (a type of thyristor) or silicon control rectifier. This component is what controls the motor voltage, torque, and current during acceleration. The taps solid state starters rely on offer a lot of flexibility, as activating any of the three available enables the device to allow different amounts of current flow to the motor.


Using a wye-delta starter means that the startup of your electric motor will rely on connection points on every coil winding. There are three of these windings, which give the starter its name, as they’re positioned in a way that looks similar to the letter “Y”. But when the starter switches the windings, it puts them in different positions which form the Greek letter “delta” (Δ). A wye-delta starter is most commonly used as an open transition starter which has a momentary hitch that lets it perform a momentary current inrush. There are also closed transition wye-delta starters that use an added contractor and a set of resistors to keep the motor running during the transition.

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