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Can a brushless DC motor work without a BLDC motor controller?

Introduction

Recently, we have received a lot of customer inquiries, and they have some questions about whether brushless DC motors can work without BLDC motor controllers. Before discussing this issue, let us first briefly analyze the differences between brushed DC motors and brushless DC motors.

Difference between brushed DC motors and brushless DC motors

Friends who have asked this question, I think you may have used DC brush motors before and do not need a driver to drive them. They only need to connect the positive and negative poles. With electricity, a brushed DC motor can run normally. We must admit that the brushed DC motor is the earliest invention and the most classic type of DC motor.

However, due to the structure of the brushes and commutator, during the rotation of the motor, the brushes will wear due to friction, and over time, they will produce dust.

The brushes need to be replaced, or even the motor needs to be replaced, which pollutes the environment and increases maintenance costs.

At the same time, the working principle and working methods of brushed DC motor determine the low efficiency, high energy consumption, and large size of brushed DC motors. Smart humans don’t want this something happened, so the brushless motor was designed.

First, let’s talk about the most apparent differences between brushed DC motors and brushless DC motors on the application side.

1) In terms of working principle:

DC brush motor: Adopts mechanical commutation. The magnetic pole does not move, and the coil rotates. The main structure of the brush motor includes stator, rotor, brushes, and commutator. The brushes and the commutator are in constant contact and friction and play a role in conduction and phase commutation during rotation.

The sensored brushless motor adopts electronic commutation; the coil does not move, and the magnetic pole rotates. A brushless DC motor consists of a motor body and a driver.

It is composed of an actuator and is a typical electromechanical integration product. Brushless motors sense the position of the permanent magnet poles through Hall elements.

Timely switch the direction of the current in the coil to ensure that the magnetic force is generated in the correct direction to drive the motor.

2) Noise:

The two working principles and internal structures determine that the brushed DC motor will have a larger noise. In comparison, the brushless DC motor will have less noise because there are no internal brushes to wear each other, the noise can reach less than 50dB, and the operation is quiet.

3) Efficiency & Energy Saving:

At present, the highest system efficiency of the brushless DC motor we make can reach 95%. According to different motor parameters, the average efficiency of bldc motor can be reached to 85%, which is very important for energy saving. It plays a vital role in saving battery energy consumption and extending the working time of the device. However, the average efficiency of DC brushes can only reach between 50% and 70%.

4) Size:

Due to efficiency, motor density, and internal structure, with the same power and speed, such as a 500w brushless motor, we use an ordinary 8 pole bldc motor, and the diameter of the motor can be kept within 86mm, and motor length is 105mm.

Moreover, a 10 pole brushless dc servo motor, the diameter of the motor can be kept within 60mm, motor length can be controlled within 170mm.  However, the diameter of the 500W brushed DC motor should reach to be130mm. So, if the applications and equipment have some limitation for size and weight, bldc brushless motor would be a good choice. 

5) High-speed Operation:

DC brushed motor will produce sparks and dust when running at high speed, so the maximum rated speed can only reach to 3000 rpm/min on the normal market based on high power. But the highest speed of a brushless DC motor can reach 10,000 rpm or even 20,000 rpm/min. It makes brushless DC motors much more suitable for high-speed equipment such as power tools, hedge trimmers, juice machines etc.

6) High Power:

Also, based on the working principle of brushed DC motors, It will be hard for motor supplier to make very high power dc brushed motor. The highest rated power for dc brushed motor is about 5KW, However, the rated power of brushless DC motors can reach up to 37KW, or even higher.

7) Life-Time:

The life of a DC brush motor is usually determined by the life of the brush, which is normally within 2000 hours. However, the lifespan of brushless DC motors can reach 6,000 to 10,000 hours. The quality and lifespan of the motor’s bearings have a significant impact on this.

 8) Control Method:

The control of brushed DC motors is quite simple. Connecting the positive and negative terminals of the power supply allows the motor to operate normally. If you need to change the direction of the motor’s rotation, you just need to reverse the positive and negative terminals of the power supply. It can also adjust the speed, a simple version of a brushed DC motor speed regulator on the market can achieve this.

The control method of Brushless DC motor will be much more complicated, and they can achieve more functions. Next, in the following sections, an in-depth analysis of this topic is provided.

9) Price:

The price of brushed DC motors is very competitive. Due to differences in motor structure, materials, working principles, lifespan etc, the price of brushless DC motors is about 1.5 to 2 times higher than that of brushed motors, depending on different motor parameters. In fact, the price difference in the motor itself is not significant, but brushless DC motors need to be matched with a BLDC motor controller to work together, which makes the cost of brushless DC motors a bit higher.

What’s kind of DC motor should we choose?

Brushless DC motors and brush DC motors occupy a large share of their respective markets due to their different characteristics.

The motor selection for our daily work should be determined based on the actual needs of our application and equipment, such as motor lifetime, motor size, motor parameters, control requirements, accuracy requirements, product selling price on the end market etc. We need to comprehensively consider various factors in order to select the most suitable motor power solution for our equipment.

What control functions can we achieve through brushless motor controller?

So, what functions can we achieve in daily applications through brushless motor controller? Let’s start with the following

1) Functions of motor’s start, stop and direction change:

That is to say, a brushless DC motors require a controller to achieve the functions of motor startup, shutdown, and direction change. The brushless DC motor itself is not connected to the power supply. It only needs to connect to the controller according to the wire definition. By opening and closing the COM and EN interfaces on the brushless dc motor controller, the motor’s start and stop functions can be achieved. In practical applications, it is crucial to ensure the stability and reliability of the interface signals, and to follow the relevant documentation and instructions for operation.

The direction change function of a brushless DC motor is achieved by connecting and disconnecting the F/R (Forward/Reverse) interface with the COM interface on the motor controller. By altering the connection status between the F/R interface and the COM interface, the rotation direction of the motor can be switched. 

For simplicity and convenience of control, we can also use a three-position switch to externally connect the start/stop and direction change signals, allowing for manual and simplified control of the motor’s start/stop and direction change. This requires prior communication and confirmation with the motor driver manufacturer to ensure specific requirements are met.

2) Function of motor’s speed adjustment

Brushless DC motors can realize speed adjustment in a variety of ways. The most commonly used ones are generally the following four ways.

a. Speed Control by 0-5V Analog Voltage

In terms of hardware connections, first, the output terminal of a 0-5V analog input device (such as a microcontroller, PLC, or analog potentiometer) is connected to the analog input port of the brushless motor driver.This typically requires the use of appropriate cables and connectors, ensuring correct and safe connections. Once the motor driver receives the 0-5V analog signal, it interprets the speed control request represented by this signal. Typically, this signal is treated as a proportional value, where 0V represents the lowest speed or stopped state of the motor, and 5V represents the highest speed.

When using 0-5V analog speed control, it is crucial to ensure that the output range of the analog input device matches the input requirements of the brushless motor driver. Additionally, based on the actual needs and characteristics of the motor, it is necessary to set appropriate minimum and maximum speed limits to prevent motor overload or damage.

Speed control of brushless DC motors through 0-5V analog signals is an efficient and precise method. It relies on the motor driver’s ability to interpret and convert analog signals, as well as its internal control algorithms and PWM technology. By adjusting the magnitude of the analog signal, continuous and smooth regulation of the motor speed can be achieved, satisfying the requirements of various application scenarios.

b. Speed Control by 10K manual potentiometer

 Using an external 10KΩ speed control potentiometer relies primarily on the interaction between the analog signal output by the potentiometer and the motor driver. Firstly, a 10KΩ speed control potentiometer needs to be selected to ensure that its output range matches the input requirements of the motor controller.

Connect the three pins of the potentiometer (typically labeled A, B, C, or 1, 2, 3) to the corresponding interfaces of the motor controller. Among them, pins A and B (or 1 and 2) are the two ends of the potentiometer, and pin C (or 3) is the sliding contact point used to output a varying voltage signal.

As the knob of the potentiometer is rotated, the sliding contact point moves between A and B, thus changing the voltage value output by pin C. This voltage value is an analog signal, typically ranging from 0V to 5V (depending on the design of the potentiometer and the requirements of the driver).

Upon receiving this analog signal, the BLDC motor controller interprets it as a proportional value. This proportional value represents the motor speed requirement, with 0V corresponding to the lowest speed or stopped state and 5V corresponding to the highest speed.

It is important to ensure that the output range of the potentiometer matches the input requirements of the motor controller. If the output range of the potentiometer is too large or too small, it may lead to the driver being unable to interpret the signal correctly or the motor being unable to operate normally.

Connecting a 10KΩ speed control potentiometer to a BLDC motor controller for speed control is a simple and convenient method. By adjusting the knob of the potentiometer, its output voltage can be changed, thereby achieving continuous and smooth regulation of the motor speed. This method relies on the correct connection and signal conversion between the potentiometer and the motor controller, so attention should be paid to issues such as compatibility, accuracy, and stability in practical applications.

c. Speed Control by RS485 

How to Adjust the Speed of a Brushless DC Motor Driver via RS485 Communication?

The adjustment of the speed of a brushless DC motor driver through RS485 communication primarily relies on proper configuration and the execution of communication protocols. Here is a detailed step-by-step explanation:

Communication Protocol and Connection Preparation:

First, ensure the correct connection of the RS485 communication line. RS485 communication utilizes differential signaling, typically requiring only two signal wires (A+ and B-) for normal communication.

Check that the 485 address selection on the driver matches the communication address set on the host computer.

The communication protocol parameters (such as baud rate, data bits, stop bits, etc.) must be consistent between the host computer and the brushless motor controller.

Setting RS-485 Function to Active:

Before sending any control instructions, the RS-485 function must first be set to an active state. This is because the driver typically defaults to having the 485 function inactive and does not retain this setting after power loss, so it must be set every time after power-on.

The setting instruction is typically sent as a specific hexadecimal code.

Sending Speed Control Instructions:

Once the RS-485 function is set to active, speed control instructions can be sent. This often involves converting the desired speed value (e.g., 1000 rpm) to a hexadecimal format (e.g., 1000 rpm corresponds to hexadecimal 3E8).
When sending instructions, ensure that all data is sent in the correct format and order.

Checksum and Error Handling:

After ending instructions, you can use a serial port debugging assistant or other tool to check if the sent data is correct.
If there are issues with communication or inaccurate speed control, check the data format, baud rate settings, line connections, and other possible problems.

Considerations:

When sending instructions, pay attention to delays between instructions. For example, there may be a delay of approximately 30ms between setting the RS-485 function to active, setting the speed, and sending a forward rotation instruction.

Also, be mindful of data conversion and formatting. Since decimal points cannot be sent in data communication, the received data may need to be divided by a coefficient (e.g., current data divided by 100) to obtain the actual value.

Adjusting Data Transmission Rate:

If the data transmission rate needs to be adjusted, it can be achieved by configuring the baud rate settings on the driver and the host computer. Considering the stability and reliability of the system, an appropriate baud rate should be selected.
By following these steps and considerations, you can effectively use RS485 communication to adjust the speed of a brushless motor controller.

d. Speed Control by PWM

The speed control of a brushless motor controller using PWM (Pulse Width Modulation) relies primarily on the characteristics of PWM technology, which modulates a constant DC power supply voltage to produce a voltage sequence with a fixed frequency but variable pulse width, thereby changing the average output voltage and regulating the motor speed.

In PWM speed control, the frequency is typically fixed, while the pulse width is adjusted according to needs. By altering the high-level duration of the pulse width, the average voltage within the entire PWM cycle changes. A wider pulse width results in a higher average voltage received by the motor, leading to a corresponding increase in motor speed. Conversely, a narrower pulse width decreases the motor speed.

It is important to note that when using PWM speed control, it is essential to ensure that the PWM function of the driver is properly configured and matches the motor parameters (such as rated voltage and rated current).

Additionally, attention should be paid to the frequency and duty cycle range of the PWM signal to ensure they fall within the acceptable range for the motor.

When selecting a model, we need to confirm with brushless motor and controller manufacturers for what kind of adjustment way the driver and controller supports.

3) Functions of motor emergency start, emergency stop, slow start, and slow stop:

Some brushless dc motor controllers can also be set according to the application and equipment requirements. The customer desires the start and stop times. For example, some tapping machines have relatively high requirements for emergency start and stop, while for some equipment the starting time from 0 to rated speed needs to be extended, and the stop time from rated speed to 0 may also need to be extended.

Some drives are devices that adjust start and stop times according to customer application requirements, but this function is unavailable for all brushless dc motor controller

It is recommended that you confirm with the brushless motor controller supplier in advance whether the brushless dc motor controller you purchased supports this function.  Or carefully check the user manual provided by the supplier to see if the controller you want to buy has this feature.

4) Functions of communication control:

Most brushless DC motors on the market support RS232 or RS485, or even CAN bus communication. The function of signal control means that you can use the PC software on your computer to adjust and monitor various data of the motor. For remote speed regulation and control, DC brushless motors are indeed an excellent choice. Because many DC brushless motor manufacturers are on the market, each brushless motor driver may have some differences in performance and control.

In addition, not all brushless motor driver has communication functions because not all customers will require communication functions. In order to save costs, some brushless motor driver only have the simplest start, stop, and speed adjustment functions and are not equipped with communication functions. It depends on the different needs of customers.

5) Functions of protection and display:

Many engineers may have question about why brushed DC motors seem to have stronger overload capabilities compared to brushless DC motors. Because a brushed DC motor operates directly when connected to power, it is unable to identify whether it is being overloaded. If we do not monitor the motor’s load current, it will be hard for us to know if the motor is overloaded. We may only can realize that the motor was overloaded when the brushed dc motor is broken.  

But the brushless dc motor and controller has over-current, over-voltage, under-voltage, over-load, over-temperature protection, etc. The normal peak torque is about 2 times of the rated torque. But the peak torque is only allowed to be used for 1-3S, depends on different kind of controller. The motor driver may be powered off and protected if this time is exceeded.

However, the stall time can be customized according to customer’s needs, and the maximum value does not exceed 10 seconds. Therefore, DC brushless motors cannot provide the same overload torque as DC brushed motors. But from the perspective of long-term use, DC brushless motors are safer and more stable because of the protective function of the motor driver.

It is recommended that structural engineers conduct in-depth communication with DC brushless motor manufacturers and controller supplier before selecting a suitable motor power solution for the equipment. Make sure whether the controller they provided supports communication?What types of communications are supported? What speed adjustment methods are supported? Whether it can monitor the motor’s inside temperature?

For high-speed and high-current motors, we’d better add a temperature sensor inside of the motor and choose the type of controller which can support to monitor the motor temperature. The brushless dc motor controller will cut off the power supply immediately when the internal operating temperature of the motor reaches 100-130 degrees, which can effectively avoid the occurrence of motor burnout due to overheating

Before purchasing a motor and driver, you discuss the above issues with the DC brushless motor manufacturer and controller supplier. In that case, we can avoid the situation that the purchased motor and controller fail to meet the equipment’s requirements.

From a technical point of view, the working principle of the brushless DC motor determines that it must rely on the driver to control its commutation and operation. The motor will not work properly.

Due to the installation space limitation and easy control request of some equipment, if the rated power and rated current of the motor are relatively low, we can customize the controller to be a built-in driver. Put the motor driver control board inside the motor casing, and the signal lines, such as start, stop, and commutation, led out to the outside of the motor.

From the appearance of the motor, it will be little hard for people to whether it is a brushed DC motor or a brushless DC motor.

What should we pay attention to when using a brushless motor controllers?

1) First of all, there will be wire definition for size drawing gave by brushless motor manufacturers. There will be eight wires if it is an sensored brushless motor with a Hall sensor, three phase wires (U V W) and five Hall wires (5V Hu Hv Hw 0V).

We need to follow the motor control manual’s wiring instructions to connect the wires between the motor and the controller. Wrong wiring will cause the motor to operate abnormally.

2) The positive and negative poles of the current cannot be connected reversely. DC+ is the positive pole, and DC- is the negative pole. Follow the text instructions on the driver.

3) Regarding the rated voltage and rated current of the motor controller, as well as the rated voltage and rated current of the motor, there may  have some misunderstandings sometimes . Generally speaking, brushless motor controllers have an input voltage range which the controller itself can accept, such as 15V to 50V.

However, the voltage which supplied by power supply or battery need to match the rated voltage of the BLDC motor, but not the voltage range that the motor controller can accept. The normal voltage for power supply or battery should be kept with ±10% of the rated voltage of the brushless motor.

If the voltage is too high, it may cause the controller to give an over-voltage alarm, and too low voltage may cause an low-voltage warning of controller. The most common voltage for brushless DC motors is 12v, 24v, 36v, 48v, 72v, 96v, and 310v (when the voltage of power supply is AC220V). That is to say, if the motor’s rated voltage is DC48V, it means that we need to choose a 48v brushless motor controller.

Different-sized controller for brushless motor can bear different continuous operating currents. The higher current a controller can bear, the size will be larger, and cost will be higher too. When we choose a BLDC motor with controller, it’s better for us to give about 30% margin for it if you have high request for over-load ability for the motor and controller. Different requirements for overload torque are determined according to different applications.

How to choose a suitable BLDC motor controller

1) Select a brushless dc motor controller with matching parameters according to the motor ‘s specification

2) Pay attention to matching voltage, current, power, and other parameters with your application.

3) Consider the stability and reliability of the motor controller.

4) Choose dc motor controller with well-known brands, reliable quality, and technical support.

5) In-depth communication with motor driver brushless motor manufacturers to select driver functions for your application.

6) If your application need to achieve high-precision control request, such as position mode, speed mode, torque mode, etc. You’d better choose a brushless servo motor with encoder and matching controller. Sensored brushless motor with hall sensors and sensorless brushless motor and controller are difficult to meet this kind of high precision control request.

Conclusion

To sum up, the brushless DC motor cannot work without the BLDC motor controller. The brushless motor controller is the core components to control the start, stop, speed and other functions. Therefore, when selecting brushless dc motor, controller selection and configuration must be considered also.

During the operation of a DC brushless motor, a DC brushless driver is indispensable. In the process of industrial automation and intelligence development, it plays an important role together with the DC brushless motor, which is the key to ensure the motor’s high-efficiency and stable operation.

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Hey,I‘m Jack.

Because of my work, my customers may know more about how to choose suitable motor power solution for their application. lf you have any questions about this, please feel free to contact with me!

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