How to Select the best Motors in Five Steps
Electric motors are found everywhere. From the common appliances such as the washing machines and pumps to advanced industrial machines such as driers, the common thing about them is electric motors. To pick the best motor, it is important to ensure you understand how they work, their loading capacities and types. This post provides you insights on how to select the best motors in five steps.
Types of Motors
There are many types of electric motors in the market. However, the commonest are brushless and brushed. Others include the stepper motors, servo motors, and vibrating motors.
Types of Electric Motors
- Brushed Motors: These are the simplest motors that are largely found in toys, automobiles, and home appliances. They are inexpensive to manufacture and generate good torque at low speeds. The downside of the brushed motors is that they require constant maintenance and are noisy.
- Brushless Motors: These motors utilize permanent magnets in their rotors. They have become the preferred choice in the aircraft industry as well as ground-vehicle appliances. Unlike the brushed models, the brushless designs are more efficient and do not require a lot of maintenance. The main shortcoming of this model is that the motors are difficult to control unless you are using a specialized regulator.
- Vibrating Motors: These motors are considered ideal for applications that need vibrations. Good examples are game controllers and cell phones. The vibrations are generated by electric motors with an unbalanced mass on a drive shaft.
- Stepper Motors: This model is common in printers, process control systems, and machine tools. They are designed for holding high torque that allows the user to move from one step to another. Though they are easy to make and control, they draw a lot of constant current.
- Servo Motors: This motor is largely preferred for the hobby market products such as RV toys and robotics.
In order to achieve optimal performance from your machine or appliance, you need to select and install the right motor. Here are five steps to follow:
Understand the Load Characteristics
If you are looking for a line operated a type of motor, it is prudent to understand the load characteristics. These motors are classified into three: those with constant torque, the models whose torque changes abruptly, and the ones that torque change progressively over time. For example, most bulk material conveyors used in industries, compressors, and positive displacement pumps require torque that is relatively steady.
Loads from unloaders, compressors, fans and similar equipment vary over time. Therefore, you should consider the motors that deliver the highest continuous loading points. This is typically the loads that occur at the highest speed.
Know the Horsepower Requirements
When selecting an electric motor, it is important to follow the rule of the thumb: “Pick only what you need”. The target is using the right motor that delivers the right, not excess or lower power, to your appliance. To know the right horsepower of the motor under consideration, here is the formula to use :
Horsepower = Torque x Speed / 5260
Consider Inertia Required when Getting Started
This is another crucial factor that plays a great role, especially during startup. Every motor has some type of inertia. However, gearboxes, bar mills, and punch presses have higher starting torques because of the large mass of their rotating elements.
A good sized motor should be able to start load from a dead stop, push it to the operating speed, and maintain the operating speed. This is important to allow constant production/ output.
Adjust the Motor for Duty Cycle
Duty cycle is the load that an electric motor is required to handle when it starts, runs, and stops. The duty can be continuous or intermittent. Continuous duty is the simplest because it starts at startup and then shifts to steady operations where heat stabilizes as the machine runs.
Intermittent duty, unlike the continuous type, is more complex. In this case, frequent starts end up shortening the life of a motor because inrush current heats the conductor rapidly. Because of the generated heat, the motors can make only a few starts and stops in an hour.
If your motor will run at an altitude that is relatively high above sea-level, then you should know that it will be impossible to operate at full potential. At a high elevation above sea level, air is less dense and does not cool appropriately. Therefore, to make your motor operate within the right temperature rise you need to derate it on the following sliding scale.
At about 3,300 feet, SF=1.15, AT 9,000 ft, it will decline to 1.0
The Final Take
When your electric motor fails, it is important to ask the main question: “Do you buy a new one or repair the current one” If you decide to buy a new motor, the first step should be to understand its design and how it works. Then, you should follow the outlined five steps to pick the perfect fit for your appliance.