How to calculate the load capacity of a DC brushed small motor?
Nov 24, 2025
Calculating the load capacity of a DC brushed small motor is crucial for ensuring its optimal performance and longevity. As a supplier of DC brushed small motors, I've encountered numerous customers who are often unsure about this process. In this blog, I'll break down the steps to calculate the load capacity of these motors, so you can make informed decisions when choosing the right motor for your application.
Understanding the Basics
Before we dive into the calculations, let's quickly go over some basic concepts related to DC brushed small motors. These motors work on the principle of electromagnetism. When an electric current passes through the motor's coils, a magnetic field is created, which interacts with the permanent magnets in the motor to produce rotational motion.
The load capacity of a motor refers to the maximum amount of mechanical load it can handle without overheating or stalling. This capacity is influenced by several factors, including the motor's power rating, torque, speed, and efficiency.
Factors Affecting Load Capacity
Power Rating
The power rating of a motor, usually measured in watts (W), indicates the amount of electrical power it consumes. It's a fundamental parameter that gives you an idea of the motor's overall performance capabilities. A higher power rating generally means the motor can handle heavier loads. However, it's important to note that the power rating alone doesn't tell you the exact load capacity.
Torque
Torque is the rotational force produced by the motor. It's measured in Newton - meters (N·m) and is a critical factor in determining the motor's ability to start and maintain rotation under load. There are two types of torque to consider: starting torque and running torque. Starting torque is the torque required to start the motor from a standstill, while running torque is the torque needed to keep the motor running at a constant speed.
Speed
The speed of a motor, typically measured in revolutions per minute (RPM), also affects its load capacity. Generally, as the load on the motor increases, its speed decreases. So, you need to find a balance between the required speed and the load the motor can handle.
Efficiency
Efficiency is the ratio of the mechanical power output to the electrical power input. A more efficient motor will convert a higher percentage of the electrical energy into mechanical energy, which means it can handle more load with the same amount of power input.
Calculating the Load Capacity
Step 1: Determine the Required Torque
The first step in calculating the load capacity is to determine the required torque for your application. This depends on the type of load you're dealing with. For example, if you're using the motor to lift a weight, you can calculate the torque using the following formula:
[T = F \times r]
where (T) is the torque (N·m), (F) is the force (N) exerted by the weight, and (r) is the radius (m) of the pulley or lever arm.
Let's say you want to lift a weight of 10 kg using a pulley with a radius of 0.1 m. The force exerted by the weight is (F = m \times g), where (m = 10\space kg) and (g = 9.81\space m/s^{2}). So, (F=10\times9.81 = 98.1\space N).
The required torque is (T = F\times r=98.1\times0.1 = 9.81\space N·m)
Step 2: Consider the Starting and Running Torque
As mentioned earlier, you need to account for both starting and running torque. In most cases, the starting torque is higher than the running torque. You should choose a motor whose starting torque is sufficient to overcome the initial resistance of the load.
Some motors have a torque - speed curve that shows how the torque varies with speed. You can use this curve to determine the motor's torque capabilities at different operating points.
Step 3: Check the Power Requirements
Once you've determined the required torque, you can calculate the power required to drive the load. The power ((P)) can be calculated using the following formula:
[P=\frac{T\times\omega}{1000}]
where (P) is the power in kilowatts (kW), (T) is the torque in N·m, and (\omega) is the angular velocity in radians per second. To convert RPM to radians per second, use the formula (\omega=\frac{2\pi\times RPM}{60})
Let's assume the required torque is (T = 9.81\space N·m) and the desired speed is (RPM = 1000). First, calculate the angular velocity:
(\omega=\frac{2\pi\times1000}{60}\approx104.72\space rad/s)
Then, calculate the power:
(P=\frac{9.81\times104.72}{1000}\approx1.027\space kW)
Step 4: Account for Efficiency
Since no motor is 100% efficient, you need to account for the motor's efficiency when calculating the power input. Let's say the motor has an efficiency of 80% or 0.8. The actual power input ((P_{in})) required is:
[P_{in}=\frac{P}{\eta}]
where (\eta) is the efficiency. So, (P_{in}=\frac{1.027}{0.8}\approx1.284\space kW)
Choosing the Right Motor
After calculating the required torque and power, you can choose a motor that meets or exceeds these requirements. At our company, we offer a wide range of DC brushed small motors, including Braked DC Brushless Motor, Low RPM DC Brushed Motor, and DC Carbon Brushed Motor. Each motor has its own specifications and capabilities, so you can select the one that best suits your application.
Conclusion
Calculating the load capacity of a DC brushed small motor is a multi - step process that involves understanding the motor's basic parameters, determining the required torque and power, and accounting for efficiency. By following these steps, you can ensure that you choose the right motor for your application, which will lead to better performance and longer motor life.
If you're still unsure about which motor to choose or need further assistance with load capacity calculations, don't hesitate to reach out. We're here to help you make the best decision for your project. Contact us to start a procurement discussion and find the perfect DC brushed small motor for your needs.
References
- "Electric Motors and Drives: Fundamentals, Types and Applications" by Austin Hughes and Bill Drury
- "Motor Handbook" by Arnold Tustin