Soft Start or VFD – Which is the Best Option for Your Motor?

If you’re trying to decide which control option for your motor is best, you’ve probably come across two power electronics devices — the soft starter and the Variable Frequency Drive (VFD). Since both provide a solution for controlling starting, speed, and torque of the connected motor, it can be a challenge to know which one is most suited for your application.

What’s important is to understand the differences between the two devices, and where it’s best to use one or the other. That’s what this blog post will look into, starting with descriptions of both the soft starter and VFD, then delving into the pros and cons of each, and finally comparing the two control options so you can make the best choice for your motor. Read on to learn whether a soft starter or variable frequency drive is the right control choice for your motor.

Quick Answer

A soft start is used to reduce the amount of inrush current when turning on an electric motor. A VFD on the other hand, is a device that can adjust the speed of an electric motor by changing its frequency.

Introduction to Electric Motors

Electric motors are powerful machines that convert electrical energy into mechanical energy. The common types of electric motors include AC and DC motors, induction motors, and synchronous motors.

AC Motors are powered by an alternating current and feature a highly efficient design. They are often used for low-power applications such as fans and pumps due to their relatively low cost. Advantages include self-starting capabilities, adjustable speed control, and torque limiting. On the other hand, AC motors have limited power outputs, require special wiring systems and are sensitive to high temperatures.

DC Motors are powered by a direct current from a battery or external source. They offer more power than AC motors but require more maintenance as there is more wear on parts like brushes and commutators which requires replacement over time. DC motors also suffer from reduced torque during startup compared to AC motors. However, they do provide superior speed control with fewer components making them ideal for higher power applications such as elevators and conveyor systems.

Induction Motors use an electromagnetic field to create motion in the rotor allowing it to turn without contacting the stator windings. These motors provide superior performance compared to DC or AC models while requiring little to no maintenance. The main disadvantages of induction motors are their increased cost, rated load limits, and less efficient operation at startup than a DC motor.

Synchronous Motors use permanent magnets or electromagnets to produce a rotating field once current is supplied to its stator windings. They offer superior performance due to their ability to run at constant speeds even when there is a large change in load on the motor. Synchronous motors are suitable for extremely precise applications, such as those found in manufacturing plants or robotics devices due to their high efficiency in both speed control and torque production. However, these types of motors require complex electronic controls with more costly components for operation and maintenance which can add up quickly over time.

Having weighed the pros and cons of different motor options available on the market, it’s important to determine which type of motor works best depending on application requirements and budget constraints. Factors like load torque requirements, speed range needed, coefficient of performance (COP), ambient environment factors, noise levels, power factor designs etc., all play a significant role in determining the most appropriate motor choice for any given task or project at hand.

In the next section we will look at two popular methods used for controlling electric motors: Soft Start and Variable Frequency Drive (VFD). We will examine their advantages as well as how they can help optimize any given electric motor system while delivering superior performance over conventional alternatives.

Advantages of Electric Motors

Electric motors are becoming increasingly popular due to their numerous advantages over other types of motors. Electric motors have high starting torque capabilities, meaning they can accelerate more quickly than other motor types, making them a great choice for applications where acceleration is important. Additionally, electric motors are comparatively small in size, making them easier to install and service than other motor types. Setting up an electric motor is also often quicker and simpler than other motor types since it does not require the additional steps of setting up gears or pulleys.

In addition, electric motors require little maintenance because they don’t rely on mechanical components like belts or chains. This makes them suitable for applications in areas with difficult conditions such as dusty or humid environments as it reduces the risk of failure from these weather conditions.

On the other hand, electric motors also produce less noise and vibration compared to larger motors with internal combustion systems. This makes them a desirable choice for noise-sensitive industries such as medical facilities and food processing plants. Furthermore, electric motors are very energy efficient and can save businesses considerable amounts of money in energy costs compared to other motor types.

Despite all of these advantages, there are still some drawbacks associated with choosing an electric motor. Electric motors are generally more expensive than their non-electric counterparts and require larger control systems which add to the expense of the system. Additionally, electric motors require a power supply which may be expensive or challenging to obtain in certain locations where it is unavailable or unreliable.

Regardless, the advantages offered by choosing an electric motor make it a popular choice across many different industries and applications. In the next section we will explore the two most commonly used methods for controlling an electric motor: Soft Starts vs Variable Frequency Drives (VFDs).

Soft Start vs VFD

Soft start and variable frequency drive (VFD) systems are two motor control technologies used to create consistent voltage and acceleration levels when starting electric motors. They are used in industrial applications where environmental conditions, mechanical wear, and energy efficiency are important factors. In addition, each system offers advantages that can be beneficial for specific types of operations or use cases.

Soft Start operates by progressively ramping up the current going to the motor over a fixed amount of time. This helps reduce current draw from the power supply which effectively reduces strain on the electrical network. As the name implies, Soft Starts also provide a smoother transition from no load to full operating speed allowing for quieter, vibration free operation. However, Soft Starts cannot adjust speed after startup and are therefore limited in their utility as speed control devices.

VFD are more sophisticated than Soft Starts as they allow precise adjustments to voltage and frequency throughout runtime, thus enabling precise control over motor speed. This allows better optimization at both low and high speeds while maintaining high efficiency. Furthermore, VFDs offer advanced features such as built-in sensors which can detect changes in motor torque or current and then automatically adjust output parameters accordingly. This is especially beneficial when dealing with machinery that is subject to shock loading or other external forces during operation.

Soft Start and Variable Frequency Drive systems both offer different benefits that make them ideal solutions in certain scenarios. During periods of short duration, soft start may be most suited due to its low complexity and fast installation time whereas for long duration operations with changing loads VFD provides more features and greater flexibility making it the preferred choice. Before deciding which system is most suitable for a particular application it’s important to consider cost, performance requirements, and any special considerations or capabilities needed from the solution itself. To gain a better understanding of these two technologies it’s vital to compare the differences between Soft Start and VFD side-by-side which will be discussed in detail in the next section.

Comparison of Soft Start and Variable Frequency Drive

The two main methods for controlling motor speed and ramping up a motor from a standstill are soft start technology and variable frequency drives (VFDs). Although both systems can eventually achieve the same outcome – efficient motor control – the techniques used to accomplish this result differ significantly. To determine which option is best for an application, understanding the differences between soft start and VFD is paramount.

Soft starts accomplish steady-state acceleration to full-load speed by controlling a motor’s voltage during ramp up. During startup, a soft starter provides power to the motor in short bursts or waves, slowly bringing the motor up to speed over time with minimal electrical stress. Soft starters are known for their ability to reduce current draw, maintain more constant temperature rise throughout, and limit starting current compared with traditional starter switches. On the other hand, VFDs use variable-frequency AC power to physically adjust incoming current to control motor speed. When a VFD is programmed properly, it can almost instantaneously bring a motor up to speed in an electronically smooth manner, all while reducing energy consumption.

In terms of cost efficiency and practicality, soft starters often appear as the better option due to their low upfront investment and ease of installation. But they have limited capacity when combined with large motors, meaning they are not suitable for high-power applications. VFDs provide more versatile features at a higher cost but provide precision control and energy savings across multiple applications and environments.

Advocates of both technologies point out that each has unique advantages based on individual application requirements and user preference: Soft starters utilize burst energy waveforms to reduce inrush currents while minimizing high start torques; whereas, VFDs allow overall machine efficiency improvements and dynamic operation while promoting reliability in extreme conditions. Ultimately, the best option will largely depend on specific operational needs such as available power supplies and surge protection capabilities.

To explore these options further, the following subsection will focus on the key benefits of soft start and VFD technology.

Top Highlights

Soft starters and variable frequency drives (VFDs) are two methods of controlling motor speed and ramping up a motor, although they function differently. Soft starts use power in short bursts to slowly bring a motor up, while VFDs offer quicker, electronically smooth movement but cost more. Depending on the application and operational need, soft starters may be seen as the better option for low-power systems due to their low upfront costs and easy installation, but VFDs provide greater versatility and better energy savings across multiple settings. The best option will depend on available power supplies, surge protection, and the individual requirements of the user.

Benefits of Soft Start & VFD

Soft start and variable frequency drive (VFD) systems both offer distinct advantages for motor applications. Understanding these benefits can help you determine whether soft start or VFD is best suited for your motor needs.

Soft start applications offer quick starting of motors, eliminating the sudden in-rush current often associated with direct-on-line motor starters. Due to its ability to reduce in-rush current and to provide a gentle ramp up to full power, soft start systems are often used in applications where very high starting torque is not required. The time it takes for a motor to reach full speed is reduced by a soft-start system, which helps extend the life of the motor’s internal components. Also, installation costs are usually lower than with conventional methods since fewer components are required.

On the other hand, Variable Frequency Drive (VFD) systems allow precise control of a motor’s speed and torque output. VFDs can be used over a long period of time since they do not apply force directly to the starter contacts. This reduces wear on the starter contacts and ensures that more consistent performance is achieved over extended periods of operation. In addition, VFDs allow for precise speed control and can result in quieter operation as well as energy savings from reduced power consumption during slowdown periods. Many applications benefit from VFD’s ability to adjust operating speed without altering motor pulley sizes or gearing ratios which would be necessary with conventional methods.

When considering whether to employ soft start or VFD technology, it is important to understand the specific requirements and benefits desired for each application. Soft starts may be suitable for some applications, while VFDs may be more advantageous in others depending on factors such as power supply availability and pulsation requirements. Furthermore, when opting for either option total cost of ownership must also be weighed against performance gain in order to select the most optimal decision.

So while both soft start and VFD systems have their own associated advantages, determining which one offers the better value depends on many factors related to the specific application under consideration. In our next section we will explore common applications of both technologies in further detail and provide insight into how each can offer certain operational benefits over more traditional ideals.

Common Applications of Soft Start & VFD

Soft Start and Variable Frequency Drives (VFDs) are two of the most commonly used motor controllers for applications in numerous industries. As both have potential advantages and disadvantages, it is often difficult to determine which option is best for a particular application. It is important to understand the unique capabilities of each type of controllers so that their specific strengths can be harnessed for the benefit of a given project or process.

Soft Starts provide functionality by providing smooth starting, reduced in-rush current, and peak current limit protection features, as well as torque control during acceleration. This makes them ideal for use in hoisting, pumping, or cooling systems as these applications require precise and consistent operation with minimal energy loss. Furthermore, Soft Starts can reduce noise pollution in motors that are subjected to frequent starting and stopping, such as HVAC systems, conveyors, winches, and compressors.

On the other hand, VFDs offer some advantages over Soft Starts in applications involving large motors and higher motor speeds. By giving users finite control over the motor speed they are able to regulate power output more precisely than with a Soft Start. This feature makes them well-suited for applications such as fans, pumps, elevators and cranes where torque output needs to be controlled efficiently to meet operational requirements. VFDs also offer variable accelerations rates which allows faster starts and stops , an important feature for operations requiring precision timing or rapid changes in speed like pumps or cooling systems .

Clearly, there are benefits to using either soft start or variable frequency drives in a variety of applications from hoisting to cooling systems. To better understand which solution would work best for your motor system it is important to consider not only the power requirements but also dynamics related to start up times, torque control, operational costs and other factors unique to your specific application. In the following section we will discuss how these considerations apply when considering pumps or cooling systems for your motor system.

Pumps and Cooling Systems

Pumps and cooling systems are used to move liquid or gas through a system, allowing them to keep temperatures steady. This can be important in processes such as chemical, industrial, medical, construction, and more. The choice between using a soft start or VFD (Variable Frequency Drive) for the power supply to pumps and cooling systems depends on certain factors, which will be discussed in this section.

Both soft start and VFD provide energy savings for pumps and cooling systems by preventing water hammering (pressure shock waves), eliminating the need for motor protection devices, and reducing both flow capacity requirements and power surges. Soft start systems limit current flow rate by ramping up electrical currents over time. This prevents major spikes in current when starting up a pump or cooling system. VFDs use frequency modulation to control the speed of a motor with an AC voltage by changing its frequency output. This also helps minimize current spikes when starting up a motor because it eliminates large jumps in torque during acceleration.

Soft starts are generally recommended as the best option for small motors because they are highly reliable, relatively inexpensive compared to VFDs, and have become increasingly sophisticated over time. However larger pumps or cooling systems that require more dynamic control may benefit from a VFD power source due to their greater speed range and higher accuracy in controlling torque over a great range of frequencies. With that being said, soft starts should not be ruled out for larger applications as some new models offer built-in adjustable switching times along with advanced control methods such as bump-less transfer between operating modes for better load matching performance.

Overall, there is no single answer to this question as each application must be evaluated individually to decide on the best power source option for the application at hand. Understanding what each technology offers is critical when making an informed decision on whether to utilize a soft start or VFD system for pumps and cooling systems.

The next section will discuss how to make an informed decision on choosing between soft start vs VFD when looking at applications that involve pumps and cooling systems.

How to Choose Between Soft Start and VFD

When deciding whether to choose a soft start system or variable frequency drive (VFD) for powering a motor, there are several considerations to take into account. One of the most important is cost. Generally speaking, a VFD solution offers greater flexibility and control, but can also be more expensive than a soft start system. On the other hand, a soft start system may be simpler to install and requires fewer components than a VFD system, offering potential cost savings that may outweigh the added flexibility of the VFD system.

The application itself should also be taken into account when deciding between these two options. A soft start system is ideal for most standard applications because it provides adequate protection from current inrush at the time of starting and can limit energy use. In contrast, a VFD has greater flexibility compared with a soft start system since it offers adjustable speed settings, allowing for more precise operations with fewer disruptions to the overall process/system. If a motor needs to operate in variable speed conditions, then a VFD might be preferable over soft start systems due to its advanced features and increased flexibility.

The environment and maintenance should also be considered when selecting between soft start systems and variable frequency drives. A variable frequency drive will typically require more frequent maintenance as well as careful environmental control due to its interaction with electrical wires and components. In contrast, soft-start systems can generally provide reliable service in industrial environments without needing specialist support or attention unless they are being used outside their recommended usage limits.

Given all of these different factors, there is no one-size-fits-all answer when it comes to choosing between soft starts or VFD systems and what would work best for each individual application will depend on the specific requirements. Ultimately, having an understanding of the differences between these two commonly used motor power solutions will help you decide which is best for your application.

Finally, each option must be evaluated on its own merits and costs—both initial purchase price and operating costs over time—in order to determine which option makes most financial sense in terms of return on investment (ROI). With an understanding of each option’s advantages and drawbacks along with full evaluation of both initial purchase costs as well as ongoing maintenance costs over time, customers can make an informed decision on how best to power their motor applications.

Conclusion: Now that we’ve looked at the options available in Soft Start vs VFD systems as well as how to choose between them based on your individual application requirements and budget, let’s move onto our conclusion in the next section where we will summarize our findings so far.


The goal of this article was to examine the differences between a VFD and soft starter system, while determining which option is best for your motor. To summarize, both system types are efficient, cost-effective solutions that can help reduce motor wear and tear. However, their specific applications may differ depending on the individual motor’s requirements.

In terms of general operational performance, a VFD offers superior speed control while a soft start requires less maintenance and has reduced current distortion. On the other hand, there are also some potential downsides. Soft starters are less energy-efficient than VFDs and may not provide as precise of speed calibration. Additionally, they have a slightly higher installation cost as well as higher harmonic distortion levels.

Ultimately, the choice between soft start or VFD will depend on your specific application and needs. If you’re looking for precision in operation with minimal maintenance required and acceptable harmonic distortion levels, then a VFD might be your best bet. Alternately, if you’re looking for more efficiency at lower installation costs but don’t need the exact precision provided by a VFD, then a soft start should do the job just fine. It’s important to consider all these factors when making an informed decision about which system type is right for you.

Responses to Common Questions

Are there any specific safety concerns I should be aware of when using either system?

Yes, there are some key safety considerations when using a Soft Start or VFD system for your motor. It is important to keep in mind that these systems are much more complex compared to conventional systems and require special attention.

Soft Starts can cause currents peaks and this can lead to equipment damages or even unexpected shutdowns if not properly attended to. Similarly, Variable Frequency Drives (VFDs) require careful setup configuration in order to avoid any electrical issues such as high voltage output levels, harmonic distortion, overcurrent voltage and grounding problems. Additionally, overheating on motors caused by the back-EMF must also be watched closely in order to avoid any damage due to prolonged exposure to high temperatures.

What are the main advantages and disadvantages of each system?

Soft Start:

Advantages: Soft start systems offer benefits to motor control, including smooth acceleration and deceleration which can reduce mechanical wear and stress on the motor. Additionally, soft start systems are very versatile, allowing for not only variable speed control but also overload protection, reduced starting current, as well as voltage regulation.

Disadvantages: The main disadvantage of a soft start system is the additional cost associated with them; they are more expensive than standard starters due to their increased complexity. Additionally, they may require more maintenance than other systems as they are more susceptible to environmental factors such as temperature and humidity.

VFD (Variable Frequency Drive):

Advantages: VFDs offer a number of advantages over traditional motor starters, including improved energy efficiency, greater operational flexibility, and softer starting characteristics. Additionally, VFDs are very versatile in terms of their programming capabilities, allowing for multiple parameters to be adjusted for a variety of applications.

Disadvantages: VFDs can be costly to install and maintain due to their complexity; in addition, their components may be prone to failure over time due to the high frequency switching involved. Additionally, some motors may require modifications or redesigns when operating with a VFD in order to ensure compatibility and correct operation.

What types of applications are best suited for a soft start vs a VFD?

Soft start applications are best suited for applications that require precise speed control, such as conveyor belts and printing presses. In these applications, the soft start helps to reduce the amount of wear and tear on the motor since it does not have to start up at full speed or full torque. Soft starts may also be necessary for motors with high inertia loads or high starting currents.

VFDs, on the other hand, are better suited for applications that require accurate control of speed and torque over a broad range of speeds. These applications include pumps, fans, blowers, and other equipment that benefits from better control of their start up speed. VFDs are also used in more advanced applications, such as CNC machining and robotics. They provide greater flexibility than a soft start by allowing users to adjust frequencies and voltages as needed to precisely throttle the motor’s output.