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Brushless DC Motor Specifications

measuring a brushless DC motor specifications
measuring a brushless DC motor specifications
Resource: https://www.youtube.com

There are different brushless DC motor specifications. These are usually indicated in the specs sheet that the motor comes with. Some are also printed or stamped on the motor. When seeking to buy a brushless DC motor, it’s crucial that you are conversant with these specs. The different types of the motor, too, and their benefits. We already covered that in the previous chapters.

In this last section, I will go over BLDC motor specs as used by manufacturers. I will also be highlighting considerations when choosing a BLDC motor for a specific use. This will help you find the right EC motor for your project based on application and other requirements. Keep reading.

Common Brushless Motor Specifications

Brushless DC motor manufacturers use a range of parameters to describe their products. These include voltage and current rating, torque, speed, and others. Below is a list of brushless DC motor specifications, their symbols, and meaning (note that the list is in no way comprehensive and only includes the most important parameters)

  • Reference Voltage (V)- means the motor’s rated terminal voltage
  • Current (It)- the current that the motor will draw when operating within the rated torque
  • Peak current (IpK)- the maximum amount of current that the motor should draw
  • No load current ( INL) – amount of current that the motor draws when there’s no load to overcome
  • Resistance (R)- used to denote the resistance of a winding on the motor
  • Inductance (L)- used to calculate the total winding impedance
  • Speed (N)- used to indicate the motor’s rated speed or rpm
  • Temperature (T)- used to indicate the motor’s operating temperature
  • Continuous torque (Tc)- torque for a given speed
  • Motor constant (Km)- used to show the power to torque ratio of the motor

When choosing a BLDC motor, the specs listed above help you determine the motor’s operating characteristics or, in other words, the expected performance. There are other aspects to take into account, of course, such as the size of the motor and more, as explained next.

different types of brushless DC motors to choose from
different types of brushless DC motors to choose from
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Factors to Consider When Buying a Brushless DC Motor

There are many reasons to buy brushless motor such as the motor’s high efficiency, excellent torque, durability, and low maintenance requirements. But the motor has to fit its intended use, which calls for a careful approach when choosing one. We recommend checking brushless DC motor specifications before making your choice as well as other factors mentioned below.

Type of Motor

There are different brushless DC motor types out there. Each one of them offers benefits and drawbacks when used in specific environments. Based on the information contained in the preceding chapters, choose the one that best fits your requirements. In-runner BLDC motors, for example, are suitable for high speed applications but lack torque. Out-runners, on the other hand, are not as fast, but provide higher torque levels.

Motor Size

Different applications require motors of different sizes. Most of the time, BLDC motor manufacturers use a naming system that consists of 4-digit numbers. In this system, the first two digits indicate the size of the motor in terms of stator diameter in millimeters. The higher the number, the larger the stator and the more powerful the motor. But that also means a bulkier motor. Based on your specific project requirements, buy a brushless DC motor that fits planned use.

Type of Controller

A brushless motor uses an electronic controller to cover its operation. The controller can be a simple on/off system, sinusoidal or trapezoidal. An on/off controller generates audible noise and does not produce a smooth torque. However it provides for a cheaper control method. A trapezoidal controller is smoother, but not as smooth as the sinusoidal type. Consider the options carefully especially if buying your brushless DC motor online.


Just like it is the case with other products, the price of a BLDC motor plays a big role in your selecting process. You do not want to spend more than is necessary or too little and end up with a low-quality device. The brushless DC motor price is usually dictated by the number and type of components. A sensored BLDC motor, for example, costs more than the sensorless type.

Small brushless motors cost between $100 and $300. Bigger ones with complex constructions and high-end electronics are higher prices than that, going for up to several hundred or even higher. These are normally used in industrial settings. Remember, a cheap brushless DC motor is less likely to offer the best performance. However, a high price does not guarantee better performance either. Go for moderately priced brands.

Motor Ratings

These are brushless DC motor specifications that indicate the operating characteristics for power, voltage, speed, torque, and more. The ratings are usually written in the specs sheet, indicated on the motor itself, or mentioned online on the manufacturer’s website. The most important are:

  • Torque- brushless DC motor torque levels vary based on the operating condition. The torque specs include peak torque and continuous torque. Peak torque usually denotes the highest value for a short period such as when starting, while continuous torque means the rated torque for any given speed. It’s advisable to choose a motor whose torque suits the needs of the application, or it will struggle to move loads.
  • Rated Voltage- this value refers to the rated terminal voltage that the motor requires to operate. This will usually be indicated by the manufacturer. Common portions include 12V 24V and 48V. A 12V brushless DC motor runs off a 12 volt source while a 48V motor requires a 48V source. Using the wrong voltage source can mean a motor that will not build enough torque or one that gets ruined completely.
  • Power Rating- the power rating is usually expressed in watts. A higher power rating means a more powerful motor, and vice versa. It’s important to select a motor whose power rating is high enough for your needs, but not too high to surpass the needs of the application. A brushless DC motor for RC car, for example, needs to maintain high torque at low power consumption.
  • RPM rating (speed) – high speed applications require a BLDC motor with higher RPM and the other way round. Usually, the speed will be indicated by the Kv and included in the specs sheet. A higher number means a higher level of RPM. To find a brushless DC motor highest speed, multiply the Kv rating by the voltage.
  • Stator Winding Size- the size of winding is directly related to the amount of torque, with larger size producing a more powerful motor. However, happens at the expense of speed, and such a motor would only attain a low peak rpm. The amount of this magnetic fix is proportional to the number of coil turns. For the right choice, consider balancing the two.


Buying a BLDC motor requires a careful attention to several details. These include the parameters that describe the motor’s working characteristics, or the brushless DC motor specifications. Matching these with your project needs, you can be sure to buy a BLDC motor that perfectly suits the intended purpose or use. That’s because BLDC motors come in many different types and making the wrong choice can mean a failed project.

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