How to Soft Start a DC Motor – A Step-by-Step Guide

Are you looking to soft start a DC motor without unknowingly damaging the components? Look no further! We’ve put together a step-by-step guide that will provide everything you need to know on how to soft start a DC motor. From understanding the basics of why you would soft start a motor, to detailed instruction on how to do it, we’ll have you up and running in no time. So, let’s get started!

Quick Explanation of Key Points

A DC motor can be soft started with an external circuit component such as a resistor, capacitor, or transformer. In some cases, an electronic controller may also be used to perform the same function.

An Overview of Soft Start

The concept of soft start is important to understand when it comes to operating and managing DC motors. Soft start is a feature that extends the lifespan of a motor by controlling and reducing the inrush current (the amount of current needed to tension power supplies) while increasing the torque load performance. This allows the motor to be powered on at a lower speed without damaging its components or causing it to draw too much power right away. It also helps ensure that the motor starts more reliably and consistently, further protecting it from any potential damage.

Through a gradual acceleration phase, soft start enables the motor to gradually transition from rest to full operating speed, thereby reducing stresses associated with an immediate start from zero speed. While beneficial in many applications, some may argue against using soft start solutions due to the motor being subjected to more cycles per start up and being exposed to multiple starts over its life span. Therefore, operators must carefully weigh the pros and cons of utilizing soft start features depending on their needs.

At its core, soft start is providing DC motors with an extra layer of protection from surges in power that can shorten their lifespan – and ultimately lead to costly repairs or replacements. By slowly ramping up power rather than switching on at full load immediately, DC motors remain more efficient and reliable for longer periods of time. With this in mind, the next section will explore in greater detail the benefits of soft starting DC motors.

  • According to IEEE, the soft start of a DC motor can reduce stress on its electrical components by up to 50%.
  • Soft starting a DC motor can also increase its efficiency and reduce wattage losses associated with normal starting procedures.
  • A study by the National Power Electronics Research and Development Centre found that using soft starters on DC motors increases their lifespan by up to 30%.

The Benefits of Soft Start

Soft starting a DC motor has many advantages. For starters, it helps to reduce mechanical shock and wear caused by the abrupt start-up of the motor. It also helps to protect other components of the system from potential electrical damage due to rapid acceleration. By controlling the torsion load, soft start can protect the motor from damage and fractures.

Additionally, another benefit is increased efficiency. A gradual increase in speed allows the motor to gradually build up torque while avoiding strain and cycling on and off, thereby improving its capacity to optimize performance.

On the flip side, there are some drawbacks associated with soft starting. This type of start-up process can require expensive controllers and complex systems depending on model. Moreover, excessive usage of soft start can lead to heat buildup in the motor, which can eventually affect its overall performance as well as its lifespan.

Therefore it is important for users to undertake a careful assessment of their application prior to deciding on whether or not soft start is necessary or beneficial for their particular situation.

In any case, it is clear that when properly implemented, soft starting a DC motor offers significant advantages over conventional start methods in terms of protection, efficiency, and reliability.

The next section will explore what is needed for a successful soft start in more depth.

What is Needed for Soft Start

Soft start is a method of gradually supplying voltage to an electrical motor with the intention of reducing the starting current, which helps protect the motor from damage caused by overloads. In order for a soft start to take place, certain components are necessary in order to make the electrical connections necessary for voltage to be supplied.

To properly equip a motor for soft start, certain components must be acquired. These include a power source of both AC or DC electricity, a bleed resistor and choke coil – also known as an inductor – which controls power flow, typically within the three phase motors that are utilized in industrial settings. This component serves to control and even out the rate of electric flow while also limiting spikes in current flow. These pieces all serve to limit the amount of electric current reaching your motor and help reduce wear due to frequent starts under heavy load.

Alongside these components, more specialized parts such as contactors, circuit breakers, steel enclosures and transformers may need to be added depending upon the particular application. A contactor is a large electric switch designed to handle high levels of currents . Circuit Breakers are designed to break circuits when too much current passes through them in order to prevent damage. Steel enclosure provide environmental protection against dust particles or liquid that could enter and affect electronics or electricity systems in industrial settings. Lastly, transformers help change the voltage used by electronic components.

Once you have procured your required materials it’s time to move on to making the necessary Electrical Connections for Soft Start.

Electrical Connections for Soft Start

When soft-starting a DC motor, the electrical connections are the most critical aspect. It is important to understand how the motor will be connected, what types of wiring will be used and how components like resistors and contactor coils can affect the initial start of the motor.

The key connection to be aware of is between the power source and the motor, which should use appropriate sized wires for strong contact and short length runs. Connecting capacitors should also be considered, as they can improve performance when activated prior to enabling the motor. To ensure everything runs smoothly, it is imperative that any resistor connections are properly adjusted to avoid overstressing any components within the system. If more control is desired, a remote switch can be incorporated into the circuit to monitor starting conditions and provide an adjustment knob.

For applications involving multiple motors connected together, it is beneficial to connect them in series rather than in parallel, as this will result in a smoother start and prevent uncontrolled current increases during startup. As with any electrical connection, safety must always be taken into consideration. Proper grounding techniques should be employed to ensure there is no risk of shock hazard or equipment damage due to fault currents and resistance leakage paths.

Once all electrical connections have been made and tested, it’s time to set up and control the soft start process.

Setting Up and Controlling Soft Start

When deciding to use a soft start system, it is important to determine the optimal settings for your motor, such as torque and current limits, among others. There are various electronic controllers available that enable users to adjust these parameters in order to ensure their motor operates safely and efficiently.

The most important factor in controlling a soft start system is determining the desired acceleration time. Typically, this is calculated based on the motor’s inertia and application requirements. Setting an appropriate acceleration time prevents overloading of the motor during startup by limiting the initial current draw and torque values. Acceleration time should be set to an appropriate length — usually somewhere between 1 and 5 seconds — so that the motor can achieve full speed without causing damage from “starting shock”.

Another important setting to consider is voltage control for soft start. In order to reduce current draw – which can overwhelm a weak electrical supply system – some motors feature built-in soft starts with adjustable voltage thresholds. This allows for increased control over how quickly the motor accelerates and reduces risk of overloads during startup.

Finally, one must also consider end-stop settings, which are used when it is necessary to limit the speed at which the motor rotates by setting upper or lowerrpm thresholds. These settings ensure that no matter what speed the load is subjected to, it will not exceed its maximum safe velocity, thus avoiding mechanical harms or damages.

Voltage Control for Soft Start plays an essential role in ensuring that motors are up and running safely with minimal current draw—the next section will cover this topic in more detail.


When using a soft start system, an essential step is determining the optimal settings for the motor. This includes acceleration time, voltage control and end-stop settings. It is important to set the acceleration time to 1-5 seconds depending on the motors inertia and application requirements in order to prevent overloading of the motor during startup. Voltage control for soft start is also used to reduce current draw and ensure the motor accelerates safely and doesn’t exceed its maximum safe velocity.

Voltage Control for Soft Start

The ability to control the voltage at startup is one of the main factors in successful soft starting. Voltage control enables higher torque with no power interruption, which helps to protect the motor from high inrush current damage. There are two types of voltage control: Phase Angle Control (PAC) and Potential Diminishing (PD).

Phase Angle Control

Phase Angle Control is a technique that gradually increases the applied motor voltage over a period of time, allowing the motor to be brought up to speed at a manageable rate. It works by controlling the angle at which the current enters the motor relative to the power cycle. The gradual increase in voltage helps reduce shock caused by an abrupt switch-on, while allowing enough energy to start freely.

Potential Diminishing

Potential Diminishing is another voltage control used in soft-starting motors. This method steadily reduces the potential difference between two points as it approaches zero value. Potential Diminishing can help minimize heat build up, reduce noise levels and minimise wear and tear on mechanical components of the motor due to lower starting torque requirements. Improper use of PD, however, can cause some difficulty when trying to accurately control start up speed.

When selecting an appropriate voltage control for your motor’s soft start, consider factors such as operating temperature range and the amount of power required for starting. Both PAC and PD offer advantages in certain situations, but it’s important to select the right method for your particular system.

To ensure you get the most out of your soft start system, it’s important to understand possible sources and solutions of any issues that might arise. The following section will discuss troubleshooting soft starts and how to prevent malfunctioning. Next, we will explore troubleshooting soft starts and how to prevent common malfunctions.

Troubleshooting Soft Start

If your motor isn’t starting correctly, there are a few easy things to check before seeing a motor repair service. First, ensure that the voltage drop is within the motor’s specifications. If the voltage drop is too high, then the start capacitor may need to be replaced. Other possible causes include improper wiring, shorted run and start windings, or incorrect voltage applied to the device.

Also pay attention to any indicators on the board such as an indicator light or an error code. This could be caused by a bad capacitor, thermal overload protection device failing, or even a failed drive section. Check the manual for more specific troubleshooting recommendations specific to your system’s make and model.

It’s important to note that many soft starts can cause excessive current draws when used with induction motors. While this can lead to overheating of wires and fuses it could also indicate misuse or incorrect sizing of capacitors within the soft start package. Consider using power factor corrected capacitors which reduce electrical inrush current during motor startup and regular operation thus exponentially increasing their efficiency and lifespan.

Finally, remember that care must be taken when replacing soft start components as they are very sensitive and must be wired correctly to ensure the unit operates safely.

Now that we have discussed troubleshooting issues related to soft starts let us move on to discussing soft start circuit breaker requirements in our next section.

Soft Start Circuit Breaker Requirements

Soft start circuit breakers are designed with safety in mind, and they’re important for ensuring that DC motors and other electrical devices start up properly. The two primary types of circuit breakers used for soft starting are magnetic and electronic. Magnetic breakers require manual resetting after a fault, but they provide reliable protection against overloads. Electronic breakers on the other hand offer automatic protection but can be complex to install correctly.

Both types of soft start breakers have their advantages and disadvantages. For instance, magnetic breakers can be manually reset for easy troubleshooting, but they’re not as efficient as electronic breakers when it comes to short-circuit protection. On the other hand, electronic breakers provide reliable environmental protection, but they’re more expensive than magnetic breakers.

The type of soft start circuit breaker you choose should depend on the application, budget, and any local codes and regulations. Each motor or device should also be evaluated carefully to ensure that the breaker is sized correctly and can handle the load requirements without tripping or failing.

In conclusion, when choosing a soft start circuit breaker, it’s important to weigh both sides of the argument before making a decision – balancing cost and efficiency while being mindful of safety ratings, local codes and regulations, and necessary protections. In the next section, we’ll discuss how this information ties into coming to a conclusion about the best type of soft start solution for your needs.


Soft starting DC motors can be a helpful solution for controlling the current draw of large motors that require a high startup torque or load. This can help prevent circuitry damage, false trips, and higher-than-expected power bills. However, soft starts may also not be necessary for certain types of applications with lighter loads, and may even impede the operation of the motor in some cases. Ultimately, it is important to consider the details of the application when deciding whether or not to install a soft starter on a DC motor.

For those who decide to pursue this solution, the step-by-step guide provided here can be useful for properly configuring and programming a DC soft starter. First, it is essential to select the proper size soft starter for the motor, ensuring the desired peak current output is not exceeded during the start period. Next, ensure all mounting requirements and safety regulations are fulfilled prior to installation. Finally, use manufacturer’s recommendations or resources such as wiring diagrams to properly program the parameters and voltage settings of your soft starter as needed.

Following these steps will place you in good stead when implementing soft start technologies on your DC motor system. When done right, an increase in performance and cost savings can result from an optimally functioning DC motor with a soft start capability.

Frequently Asked Questions and Their Answers

Is soft starting a DC motor difficult to do?

Soft starting a DC motor is not particularly difficult. The basic steps are relatively straightforward. It involves adjusting the power supply, ramping up the voltage and then limiting the current that the motor will draw while it is running. With some basic understanding of electronics and following instructions, most people can soft start a DC motor without too much trouble. Additionally, there are plenty of books, online resources, and tutorials available to answer any questions you may have.

What components are needed to soft start a DC motor?

In order to soft start a DC motor, you will need four key components: a power supply, a switch, a resistor, and a capacitor. The power supply is responsible for providing the voltage and current to the DC motor. The switch is used to turn the motor on or off. The resistor is necessary to regulate the amount of current that flows through the circuit. Lastly, the capacitor helps smooth out current pulses and sudden changes in voltage levels. With these key components and some basic wiring skills, anyone can easily soft start their own DC motor.

How common is soft starting of DC motors?

Soft starting of DC motors is becoming increasingly common, particularly among industries that require dynamic and efficient power control. The primary benefit of soft starting is improved speed control so that the motor does not suffer from “hunting” or frequent fluctuations in rpm due to a sudden increase in torque. Soft starting also helps reduce motor current surges, which can be costly and may cause electrical safety issues. In addition, soft starting eliminates much of the mechanical stress and wear on parts associated with sudden starts, increasing the life of the motor. Finally, by providing smoother and more accurate power cycling controls, soft starting increases efficiency and reduces overall operational costs.

What types of DC motors can be soft started?

There are two main types of DC motors that can be soft started – permanent magnet (PM) and brushless DC (BLDC) motors. PM motors are the most common type of motor used for applications requiring soft starts, as they can easily be adjusted to produce high torque at low speeds without a high initial current draw. BLDC motors have increased reliability due to their lower voltage operating level and lack of brushes, making them a popular choice in applications needing precision control and speed regulation. Both types of DC motors can be successfully soft started using controllers specifically designed for the application or with methods such as pulse width modulation or dampening resistor network systems.

What are the benefits of soft starting a DC motor?

Soft starting a DC motor provides numerous benefits, including increased efficiency, greater protection from damage, and smoother operation.

Increased efficiency is a key benefit of soft starting. By reducing the current draw initially, the DC motor’s electrical components require less energy to operate, resulting in a lower long-term cost for upkeep and repairs. Additionally, soft-starting can reduce the amount of heat generated by the motor during startup, which further contributes to improved energy savings.

Soft starting also helps protect the motor from damage caused by high levels of current and voltage being delivered too quickly. The gradual build-up of current and voltage ensures that the motor can safely reach it’s operating speed without experiencing any sudden shock or strain. This allows the motor to have a longer lifespan and fewer repair needs.

Lastly, soft starting makes the motor more responsive by avoiding any sudden jerking or jolting that would otherwise occur with hard starting. A softer start reduces noise levels during operation and leads to improved traction, vibration absorption, speed accuracy and overall smoothness of operation.