There are many different types and sizes of electric motors. Electric motors are everywhere now. There are likely even some in the computer you are using to read this article. The fans, disk drives, and DVD or CD-ROM player all use electric motors.

Electric motors can be divided into two types: alternating current (AC) electric motors and direct current (DC) electric motors. A DC electric motor will not run when supplied with AC current, nor will an AC motor run with DC current. AC electric motors are further subdivided into single phase and three phase motors. Single phase AC electrical supply is what is typically supplied in a home. Three phase electrical power is commonly only available in a factory setting.

DC electric motors are also split into types. These include brush motors, brushless motors, and stepper motors. Of these types, brush electric motors are by far the most common. They are easy to build and very cost effective. Their major drawback is that they use carbon brushes to transfer electrical current to the rotating part, and these brushes wear over time and eventually result in the failure of the electric motor. The DC brushless motor eliminates the brushes, but is more costly and requires much more complicated drive electronics to operate.

A stepper motor is a special type of brushless motor that is used primarily in automation systems. A stepper motor uses a special type of construction that allows a computerized control system to “step” the rotation of the motor. This is very important when controlling a robotic arm. For instance, when you wish to move a specific distance as directed by a procedure in a program on the computer, a stepper motor may be the best choice.

Electric motors are usually sized in horsepower. The most common sizes are what are called fractional horsepower motors, i.e. ½ horse power or ¼ horsepower. Larger motors are typically only found in factories, where they can range in size to thousands of horsepower.

Electric motors also come with various speed ratings. Speed is usually specified as rotations per minute (RPM) at no load condition. As the motor is loaded down, the speed will slow down. If the electric motor is loaded too heavily, the motor shaft will stop. This is known as the stall speed and should be avoided.

Finally, before you order an electric motor, you should determine the mounting type you require, the start up torque, the type of enclosure required, and the type of shaft output required. There are many choices in each of these categories. Hopefully, you just need to replace an existing motor that has failed and the salesperson can help you find a direct replacement. Otherwise, specifying the correct electric motor can be a daunting task.