Motor Soft Starters

Results per Page:

How Does a Motor Soft Starter Work?

Curious about what a motor soft starter is and how it operates?

When an AC induction motor is at a standstill, it can draw an initial current that is three to five times higher than the normal load upon start up. As the motor approaches full speed, this current gradually decreases. However, these abnormally high currents can potentially harm the motor and electrical system due to heat stress. To combat this issue, oversized cables and components are typically used for start-up, but this can lead to high electricity costs.

Moreover, when full power is applied to the motor, it accelerates rapidly and generates up to three times the normal load torque. This can cause mechanical shock to the motor, drivetrain, and the load being driven. Consequences may include worn or failed bearings, belt drive slipping, gearbox and drivetrain wear and damage, water hammer in pumping systems, and damage to the driven machinery.

To address these problems, it is highly recommended to install a soft starter. This device allows the voltage supplied to the motor to gradually increase during start-up, preventing the current and torque from building up too quickly. By slowly ramping up the voltage, the motor's current and torque smoothly build up.

Most commonly, a soft starter includes two thyristors (also known as silicon-controlled rectifiers) connected back-to-back for each phase. These components work together to regulate the voltage supplied to the motor. The AC voltage rapidly alternates between positive and negative at the line frequency, allowing the supply voltage to be controlled by switching the power on and off at specific points in the AC voltage waveform. Thyristors, functioning as electrical switches, are perfectly suited for this task.

Soft starters for motors are equipped with a logic controller that determines the timing of the power supply to the motor. This controller can be either open-loop or closed-loop. Open-loop devices do not have a feedback system and do not modify their output based on the motor's behavior. Instead, they gradually increase the voltage according to a predetermined set of values. On the other hand, closed-loop devices closely monitor the motor's current build-up through a feedback loop, enabling them to effectively manage the motor's start-up for maximum efficiency.

Common applications for soft starters include pumps, rock crushers, and fans.

Soft Starter or VFD

When deciding whether to purchase a VFD or a soft starter for your AC motor, there are two key factors to consider. Soft starters are frequently the more cost-effective option (compared to VFDs) for applications that necessitate speed and torque regulation solely during motor initiation. Furthermore, they frequently serve as the perfect solution for applications where limited space is a concern, as they typically occupy less space compared to variable frequency drives.

Both options will:

  • Save on energy consumption
  • Mitigate the chances of power surges
  • Provide customizable acceleration duration
  • Minimize the risk of overheating
  • Enhance operational efficiency
  • Prolong the motor's lifespan

TECO Westinghouse Soft Starters

TECO Westinghouse’s VMX Series is low voltage soft starter, made specifically for use with motors. Our selection is a chassis mount and ranges from 3 horsepower to 900 horsepower. The input and output voltages range from 200 volt - 575volt.

Where to Buy Soft Starters in Canada

eMotors Direct’s stock of soft starters are designed to reduce load and torque temporarily during startup, helping to mitigate a current surge that could cause catastrophic damage to your electric motor and related equipment. They can be applied to water pump situations to avoid pressure surges at startup, conveyor belt systems to prevent jerking and other stresses, belt-driven systems to help prevent belt slippage, and any other application where you require a smooth and steady power ramp-up. By improving the power supply stability, soft starters help lower power costs and prevent mechanical stress on the driving components.

Our soft starter category covers products from a top soft starter manufacturer, TECO-Westinghouse. All available with three-phase input and chassis enclosures. With convenient filtering options, you can easily find the motor starter you’re searching for.

Need a hand finding the right motor starter for your application or legacy replacement? Contact our motor experts today. They have extensive knowledge, backed by over 45 years of experience, to help you with your electric motor project.

Related Articles