Soft Start Motor Starters – How to Choose the Right One for Your Application

When it comes to keeping industrial machinery operational, motor starters are an important piece of the puzzle. Soft start motor starters come in many shapes and sizes with various features and benefits. With so many choices, understanding how to choose the right one for your application can be challenging. In this blog post, we’ll go over the key factors to consider when selecting soft start motor starters, the different types available, and why they’re important for optimal operation. Armed with this knowledge, selecting the perfect soft start motor starter for your industrial machinery just became easier!

Quick Response

A soft start motor starter is an electronic device used to reduce current surge and torque during the startup of an Electric Motor. It gradually builds up voltage over time, allowing for smoother startups with less strain on the motor.

Introduction to Soft-Start Motor Starters

Soft-start motor starters are devices used to ramp up the power applied to electric motors. This gradual ramp up, known as soft starting, reduces drive train and electrical system stress by reducing the inrush current at startup. In certain applications, this reduction in the current can reduce mechanical wear and tear of drivetrain components such as belts, pulleys, and chains.

When using a soft start motor starter, the user can adjust the ramp up speed and duration to meet their application’s needs. There are two primary methods of implementing this type of soft start—using a capacitor bank or an adjustable voltage controller. Both of these systems provide similar benefits with slightly different implementations and maintenance requirements.

Proponents of soft-start motors argue that they reduce wear and tear on drivetrain components and allow for improved handling during cold weather conditions, when electric motors tend to be particularly sluggish due to low temperatures. A softer start also allows for smoother integration with automated systems where a sudden surge in voltage could cause issues with the equipment using the motor.

Critics are quick to point out that because soft starts employs an increased quantity of electrical components meant to regulate the voltage, there is a higher risk of failure than with traditional motor starters due to repeated use or aging components. Additionally, these units tend to cost more than traditional starters because of their additional components making them less suitable for lower budget applications.

Fortunately, careful consideration while choosing the right starter and diligent maintenance can help ensure that these issues are kept to a minimum so as to truly benefit from the advantages offered by a soft start motor starter. With that understood, let’s move on to an overview of what makes a soft-start motor starter unique.

  • According to the Department of Energy, soft starter motors are capable of saving up to 55% of energy consumption compared to direct on-line starters.
  • A recent survey suggests that more than 65% of industrial motors now use soft starters.
  • Studies have shown that most conventional starters exhibit an inrush current at start up which can be 5 – 10 times higher than the steady state current. Soft starters are designed with inrush current limits that are well below the conventional starter inrush for reduced power loss and increased efficiency.

Overview of Soft-Start Motors

Soft-start motors are increasingly popular as they provide a convenient, cost-effective starting solution for motors. They are designed to slowly and progressively accelerate the motor speed to eliminate shock loading and reduce potential damage to equipment, components, and electrical systems. Although soft-start motors can provide many benefits, there are also some drawbacks that should be considered before making a decision to use them in an application.

Advantages of Soft-Start Motors: Soft-start motors can help extend the life of equipment and devices by reducing the risk of damage associated with starting current surges. Additionally, they can help address problems related to harmful harmonic content as well as line voltage interference. Finally, since they can be incorporated into many existing systems without significant costly modifications, soft-start motors will often represent a lower overall cost of ownership solutions compared to other solutions such as variable frequency drives.

Disadvantages of Soft-Start Motors: One potential issue with using soft-start motors is the time lag required for acceleration when the motor starts up. If there is a pressing need for quick starts, then this technology might not be the most appropriate choice for the given application. Additionally, for applications where constant speed control is necessary (such as conveyor belts or cranes), soft-start motors may be inefficient choices without sophisticated added controls or torque feedback provisions.

Overall, while soft-start motors come with both advantages and disadvantages, they remain an important option worth considering when evaluating potential starting solutions. In the next section, we will explore how the design and function of soft-start motors contributes to their ability to limit inrush current surges during startup operations.

Design and Function of Soft-Start Motors

Design and function of Soft-Start Motors.

Soft-start motors are specialized motor starters that are designed to create a smooth start-up for electric motors. They employ three main methods to achieve this: voltage, frequency, and current ramping. These technologies ensure that the starting current is lower than with traditional contactors or breakers, resulting in reduced peak currents, no shocks or surges, and smoother acceleration.

This can help to extend motor life by reducing mechanical stress on the motor’s internals, as well as reduce stress on the power system since it won’t need peak starting currents which may otherwise be many times higher than continuous running current. Additionally, applied loads such as pumps or conveyors attached to the motor will have their starting energy needs moderated when using a soft-start motor starter, further helping to reduce the risk of damage from high current spikes or thermal overloads.

Soft-start motors are particularly useful for applications where high inrush currents could cause system instability or short circuit faults, such as centrifugal fans and blowers typically found in HVAC systems. In these scenarios, the soft-start motor limits inrush current by slowly ramping up prior to reaching full speed thus avoiding any sudden jolting or impacts to the mechanical components. Though they may cost more initially than a traditional contactor motor starter, they will likely pay off over time with saved costs due to reduced maintenance and increased resource efficiency in many applications.

While there are clear advantages to using a soft-start motor starter, it isn’t always necessary depending on the application. Examples of cases where a soft start may not be an asset include variable frequency drives (VFDs) used with long lead machines such as belt driven compressors—in these scenarios VFDs are often better suited and provide flexible control while maintaining protection features suitable for starting inrush conditions. Furthermore, permanent magnet motors such as those found on some pump models already limit inrush current by design and therefore may not require a soft-start installed along with them for their own protection needs.

Overall, soft-start motors offer improved safety measures and operational performance by allowing for smoother startup at lower peak currents. When properly applied they can prove beneficial in terms of protecting both beginning resources 1and ensuring long term usage with lessened maintenance concerns due to stress reduction on the system’s mechanical components. After reviewing all these considerations properly associated with a particular application then an informed decision may be made as whether or not a soft-start motor starter is required which brings us now into our next section focused upon understanding the components of a soft-start motor starter.

Components of a Soft-Start Motor

Soft start motor starters are designed to limit the torque and current generated by an electric motor during start-up. They work by releasing a gradually increasing amount of voltage and current over a specified period of time. To achieve this, they consist of three main components: a power semiconductor, control electronics, and soft start circuitry.

The power semiconductor is designed to handle the large amount of current required for starting an electric motor. Typical power semiconductors used in soft start systems include triacs, thyristors and IGBTs (Insulated Gate Bipolar Transistors). These components are capable of switching large amounts of power while preventing excessive inrush currents.

Control electronics monitor incoming signals from external devices, such as automation controllers and sensors, to provide control of the soft start system. They contain memory chips that store parameters related to the speed and voltage requirements of the motor, and use this data to determine the timing of electric pulses sent to the power semiconductor.

Soft start circuitry applies varying voltages or currents over time to slowly increase the speed at which electric motors reach their set speed. This circuitry typically consists of inductors, timer components, resistors, and capacitors which work together to provide an adjustable rise time for motor turn-on . Soft start capacitor banks can also be used to quickly bring motors up to speed using a large but immediate burst of energy.

Both types of motor starter systems have their merits; however, it is important to consider the application before choosing one. Soft start systems can reduce mechanical stress on equipment as well as prevent inrush currents from overloading circuits, but can also cause unwanted surges in noise or voltage levels when used improperly.

Now that we have discussed the components of a soft-start motor starter system, let’s discuss how electric current, voltage levels and protection all factor into selecting a system that meets your needs.

Electric Current, Voltage and Protection

Electric current, voltage and protection are three important considerations when choosing a soft start motor starter. The electric current rating must be sufficient to meet the needs of your specific application. A lower current rating may put too much strain on the motor and can cause it to overheat or even fail, while a higher rating may lead to expensive underemployment of power. Voltage also matters as it affects power input and can cause overheating or failure if too high or insufficient power output if too low.

Protection is essential for any motor starter. Overcurrent protection prevents the motor from being overloaded and ensures that the temperature of the windings does not exceed their safe operating limits. Undervoltage protection prevents damage due to insufficient or fluctuating incoming power. Additionally, short circuit protection should be included, which isolates any direct short and shuts down the system until a protected condition is established.

Protection systems help protect motors from overloads, outages, surges, shorts and other conditions that can cause damage to the machine and its components. Finding the right combination of protection features and degree of protection will ensure that the motor is adequately protected while still meeting performance requirements. With this in mind, an effective protection system for soft-start motors should include protective features such as overload relays, motor starters with built-in thermal overloads, surge suppressors, fuses and protective relays. The next section will discuss these protection systems for soft-start motors in more detail.

Protection System for Soft-Start Motors

When it comes to soft-start motors, a reliable protection system is essential. Without one, the motor can be damaged or even destroyed by overloading, poor voltage supply, temperature changes, and sudden power interruptions. Thus, it is important to ensure that the protection system chosen provides the necessary safeguards for the motor.

In choosing the right protection system for soft-start motors, there are two main options: mechanical protection systems and electronic protection systems. Mechanical protection systems typically employ various sensors such as temperature sensors and current sensors to detect any potential issues with the motor and its environment. Once an issue is detected, the system will shut off the power supply automatically to prevent further damage. The benefit of these systems is that they are relatively easy to install and require minimal maintenance.

Electronic protection systems use complex algorithms in combination with various sensors to monitor signals from the motor and operating conditions in real-time. This type of system can detect subtle shifts in performance before larger issues occur such as overheating or voltage inconsistencies thus providing more advanced protections. Furthermore, many electronic protection systems are designed in modular form, which allows for quick repairs in case of failure as opposed to having to replace the entire system.

Overall both types of protection systems have merits and drawbacks depending on your specific application needs. It is important to consider all factors of your unique situation when determining which method best suits your needs.

Now that we understand the different kinds of protection system used with soft-start motors, let’s delve into the advantages and disadvantages of using these motors in our next section.

Advantages and Disadvantages of Soft-Start Motors

Soft-start motor starters offer a number of advantages and disadvantages. These considerations should be taken into account when deciding whether to choose a soft-start motor starter for your application.


The primary advantage to using soft-start motors is decreased wear on the motor itself and its associated systems. By providing a slow start and stop to the motor, it puts less strain on the electric system, reducing the potential for premature failure and costly repairs. Also, by allowing the current to ramp up slowly, it helps tame the inrush of electricity that typically occurs when a motor is started up. This can reduce electrical bill costs due to decreased demand charges.

Another advantage of soft-start motors is that they are much quieter than normal starting methods. The gradual ramping up of current reduces any jerky movements in the machinery, which can create unnecessary noise. Furthermore, they also offer improved control over machines as they come up to full speed, meaning that production processes can be optimized with more accuracy and precision.


The primary disadvantage of soft-start motors is the added cost for installation and operation. The added complexity of these systems requires additional controls and components, resulting in increased cost for purchase, installation, maintenance, and operation. Additionally, since soft-start motors run at lower currents than typical ‘hard’ starts, there will be an associated efficiency penalty; this equates to higher running costs over time compared with conventional motor starters.

Overall then, soft-start motor starters can provide a range of benefits to users depending on their application needs. However, care should be taken to weigh up all factors such as initial cost versus saved wear-and-tear on motors; potential power savings versus the extra cost associated with having a more complex system; and so on.

With careful consideration of all relevant factors then, soft-start motor starters can be chosen for maximum benefit in specific situations – and now it’s important to consider how best to install them and make sure that your switchgear needs are met appropriately.

Must-Know Points to Remember

Soft-start motor starters offer decreased wear on the motor and electricity system, lower electrical costs due to the gradual ramp up of current, increased control over machines and quieter operation. The primary disadvantage of soft-start motors is their higher cost of installation and operation as well as efficiency penalty. Care should be taken when selecting a soft-start motor starter to ensure it is right for the application.

Installation and Switchgear

Installation and switchgear is a critical part of proper operation for a soft starter motor system. When installing a soft starter, there are important safety considerations to be aware of in order for the equipment to function properly. First, the installer should make sure that proper grounding is provided for the starter by connecting it to the frame ground on motors with speeds over 1200 RPM. Additionally, it’s important to install circuit breakers that are properly sized for the soft starter motor so that they do not exceed their ratings.

Switchgear can also play an influential role when dealing with soft starters. To operate correctly, low-voltage protection systems need to be integrated in order to protect against overloads and short circuits. A circuit breaker should always be used when a line disconnection is required. Also, if excess energy is expected to flow during operations, then surge suppressors or limiters should be added. These additional parts may add cost and time to installation but will ultimately save money in repairs or replacements if something were to fail without them.

After completing the installation and switchgear components of a soft starter system, operation cost and time can greatly affect the efficiency and reliability of this equipment. The next section will discuss these factors in more detail.

Operation Cost and Time

When deciding between use of soft start motor starters, operation costs and the time associated with their implementation should be taken into consideration. The decision will ultimately have an impact on efficiency, productivity and cost savings related to overall equipment expenses.

Soft start motor starters can help reduce energy costs associated with operating a motor since it allows for more control over its starting conditions. With more precise initial settings, power draw is reduced thereby significantly lowering the total amount of energy consumed.

In addition, mechanical strain on parts used during each startup is also lower when a soft start starter is used. This helps reduce wear and tear and increases the total operating life of the motor by helping to prevent premature failure. As a result, fewer repairs are necessary, which reduces the cost associated with downtime due to maintenance or replacements.

Despite these benefits, there may still be added cost or increased amount of time needed for software installations or different adjustments associated with new usage depending on application requirements. If regular maintenance or inspections are required in order to maintain performance of the machine or equipment utilizing a soft start motor starter, additional time must be taken into account as well.

Employees must also be trained to correctly operate machines with these starters correctly to ensure safety and optimal results. If unfamiliarity exists among workers, instruction must first be provided about how to properly operate the equipment; this too has time implications as part of the overall operation cost to consider.

To summarize, when controlling operation cost and time associated with choosing a soft start motor starter, it is important to weigh both the advantages and possible drawbacks related to its usage in order maximize efficiency while minimizing expense.

Finally, given all aspects discussed above regarding the cost and time considerations tied to soft start motor starters – now is the ideal opportunity to move into our conclusion section in order to better decide if they are right for your application needs or not.


Soft starters provide a cost effective and efficient means of controlling the starting torque on an electric motor so as to protect both your equipment, wiring, and power supply. This can often be achieved with a simple upgrade from a standard IM (induction motor) starter, or even by replacing a totally worn out variable frequency drive. The most common type of soft starters is the three-phase, current-limited adjustable voltage soft start motor controller, which provides quick and easy control of the power delivered to any three-phase motor.

When it comes to selecting the right soft start motor starter for your application, there are many variables to consider such as the voltage requirements, size limitations, and protection requirements. You must also be aware of the potential impact that any adjustment made could have on the motor in terms of acceleration time and ability to withstand inrush current. It’s therefore important to research potential components before making any decisions.

Ultimately, ratings, types of components used, costs, and installation instructions should all factor into the selection process; however these all must remain secondary considerations to choosing a solution that will not only meet your immediate performance needs but also offer long-term return on investment. A professional engineer or experienced electrician or contractor can assist you in accurately evaluating your specific application needs and proposing the best overall solution.

From simple repairs on existing systems to installing brand new motors and soft starters from scratch – understanding all aspects of this process is essential for ensuring successful deployment and reliable operation for years to come. The key takeaway is that soft starters provide a cost effective way to reduce wear on equipment and extend its lifespan over time – something every business wants to achieve safely and efficiently!

Answers to Common Questions

What are the benefits of using a soft start motor starter?

A soft start motor starter provides many benefits to an application. Firstly, it minimizes the inrush current on starting which helps with power grid stability. Secondly, it reduces the mechanical shock that can occur on motor start-up due to sudden torque, ensuring a longer life for equipment such as bearings and couplings. Thirdly, it can give smoother acceleration and deceleration of the motor which may help reduce vibration and noise levels. Finally, it can potentially improve the efficiency of a system by eliminating the need for other components such as separate starters or contactors which take up more space, as well as cost savings due to less power consumption.

How does a soft start motor starter work?

A soft start motor starter works by gradually increasing the torque applied to the motor so that it can start up with minimal wear on the motor, as well as reducing electric current impact on the power system. To accomplish this, a soft starter uses three programming functions: acceleration, deceleration and ramp up speed.

The acceleration function allows users to configure the amount of time between when voltage is first applied and when the full voltage is applied. This means that rather than having an immediate full-voltage application, the initial voltage is slowly increased until reaching full-voltage. This prevents spikes in current which cause a sudden spike in heat and mechanical stress on the motor.

The deceleration function allows users to program the reduction of radiated reactive power from the motor and counteracts any overloads from high inertia loads such as conveyor belts or fans. Similarly, users can adjust ramp-up speed so that instead of an abrupt increase in speed that can damage the motor, there is a gradual increase allowing for longer life and stability of performance.

Are there any potential disadvantages to using a soft start motor starter?

Yes, there are potential disadvantages to using a soft start motor starter. These include:

1. Increased Cost: Soft start motor starters tend to be more expensive than other types of motor starter due to their complexity. Additionally, they also require an additional power supply to drive the soft start circuitry, which can further increase the cost.

2. Reduced Performance: Soft starts can reduce the overall performance of the motor as they limit the starting current and increase the inrush current time when compared with other starters. This can reduce rapid acceleration and deceleration speeds, reducing overall machine cycle times.

3. Vibration and Noise: Since soft starts control acceleration and deceleration of motors, they can produce higher levels of vibration and noise during operation than traditional motor starters. This can lead to increased maintenance costs due to component wear and tear.

Overall, these potential disadvantages should be considered when determining if a soft start motor starter is the best choice for a particular application. If cost or performance is of paramount importance then a different type of starter may be more suitable for the application in question.