FREE DELIVERY ON ORDERS OVER £50 IN THE UK & EU
FREE DELIVERY ON ORDERS OVER £50 IN THE UK & EU
FREE DELIVERY ON ORDERS OVER £50 IN THE UK & EU
FREE DELIVERY ON ORDERS OVER £50 IN THE UK & EU
Electric motors are at the heart of countless industrial processes, powering pumps, conveyors, compressors, fans, mixers, and manufacturing equipment. However, when a motor starts directly across the line (Direct-On-Line or DOL), it can draw six to ten times its normal operating current, placing significant stress on both the electrical supply and the mechanical equipment it drives.
Soft Start Controllers provide a smarter and more controlled method of starting electric motors. By gradually increasing the voltage supplied to the motor during start-up, they reduce inrush current, minimise mechanical shock, and improve the overall reliability of industrial systems.
Whether you’re designing new equipment or upgrading an existing installation, understanding how Soft Start Controllers work can help improve equipment life, reduce maintenance costs, and increase operational efficiency.
A Soft Start Controller, often referred to as a motor soft starter, is an electronic device that controls the voltage applied to an AC motor during start-up.
Instead of applying full voltage instantly, the controller gradually ramps up the voltage over a predetermined period. This allows the motor to accelerate smoothly until it reaches full operating speed.
Unlike a Variable Frequency Drive (VFD), which changes both voltage and frequency to continuously control motor speed, a Soft Start Controller is primarily designed to manage the starting and stopping process while the motor operates at its normal speed once fully started.
Soft Start Controllers are commonly used with:
£60.00 ex. VAT
£160.00 ex. VAT
Soft Start Controllers use thyristors (SCRs) connected in each motor phase to control the voltage supplied during start-up.
The controller gradually increases the conduction angle of the SCRs, allowing the motor to receive progressively more voltage until full voltage is reached.
The process typically follows these stages:
When the motor receives the start command, the controller supplies a reduced voltage instead of the full mains voltage.
This limits the inrush current while producing enough torque to begin rotating the motor.
The controller gradually increases the output voltage over a preset ramp time.
This allows the motor to accelerate smoothly without sudden mechanical shock.
Once the motor reaches full speed, many Soft Start Controllers automatically engage an internal bypass contactor.
This bypasses the SCRs, reducing heat generation and improving overall efficiency.
Some Soft Start Controllers also provide a controlled stopping function.
Instead of stopping abruptly, the controller gradually reduces voltage, preventing water hammer in pumping systems and reducing mechanical stress.
One of the biggest advantages is limiting the high current normally experienced during motor start-up.
Benefits include:
Abrupt motor starting can damage:
Soft Start Controllers reduce mechanical shock, significantly extending equipment life.
Reducing mechanical and electrical stress results in:
Smooth acceleration improves operator safety by preventing sudden equipment movement and reducing stress on driven machinery.
Although Soft Start Controllers are primarily designed for motor protection rather than speed control, they contribute to energy efficiency by:
Soft Start Controllers are widely used wherever controlled motor starting is required.
| Feature | Direct-On-Line (DOL) | Soft Start Controllers |
|---|---|---|
| Starting Current | Very High | Low |
| Mechanical Shock | High | Minimal |
| Motor Protection | Limited | Excellent |
| Equipment Life | Reduced | Extended |
| Maintenance Costs | Higher | Lower |
| Start-up Control | Instant | Smooth |
For most industrial applications, Soft Start Controllers offer a safer and more efficient method of motor starting.
Many engineers ask whether they should use a Soft Start Controller or a Variable Frequency Drive.
| Feature | Soft Start Controller | Variable Frequency Drive |
|---|---|---|
| Controls Motor Speed | No | Yes |
| Reduces Inrush Current | Yes | Yes |
| Continuous Speed Control | No | Yes |
| Cost | Lower | Higher |
| Ideal For | Motor starting | Speed control applications |
If the application requires the motor to run at a constant speed, a Soft Start Controller is often the most cost-effective solution.
If variable speed operation is required, a VFD is the better choice.
Soft Start Controllers are frequently used alongside other industrial power control products, including:
Together, these technologies help engineers design reliable, energy-efficient industrial automation systems.
Soft Start Controllers are an essential component in modern industrial automation, providing a reliable and cost-effective solution for protecting motors and reducing electrical and mechanical stress during start-up.
By gradually increasing motor voltage, they improve equipment lifespan, reduce maintenance costs, minimise inrush current, and enhance overall system reliability.
Whether you’re operating pumps, fans, conveyors, compressors, or manufacturing equipment, investing in the right Soft Start Controller can deliver long-term performance improvements and lower operational costs.
Explore United Automation’s range of Soft Start Controllers to find the ideal solution for your motor control application.
A Soft Start Controller gradually increases the voltage supplied to an electric motor during start-up, reducing inrush current and mechanical stress.
Their primary purpose is motor protection rather than energy savings. However, by reducing electrical peaks and improving system efficiency, they can contribute to lower operating costs.
They are most commonly used with three-phase AC induction motors, although some models are suitable for single-phase applications.
They are widely used in:
– Manufacturing
– Water treatment
– HVAC systems
– Food processing
– Mining
– Quarrying
– Agriculture
– Packaging
– Material handling
A Soft Start Controller controls only the motor starting and stopping process, whereas a Variable Frequency Drive continuously controls motor speed by varying both voltage and frequency.
Whether you need our proven standard products or a custom control system, United Automation delivers robust and reliable engineering solutions tailored to your industry.
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