Electric motors can be divided into AC, DC, and universal types. DC motors have brush, brushless, and stepper variations. Universal motors are used in household appliances, while larger motors are found in factories. Motors are rated by horsepower and speed, and selecting the correct motor requires consideration of mounting, torque, enclosure, and shaft output.
Electric motors can generally be divided into several types: alternating current (AC) motors, direct current (DC) motors and universal motors. A DC motor will not run on AC power, nor will an AC motor run on DC; a universal motor will run on AC or DC current. AC motors are further divided into single-phase and three-phase motors. Single phase AC power is what is normally supplied in a home. Three-phase electrical power is commonly only available in a factory setting.
DC motors are also divided into types. These include brush motors, brushless motors and stepper motors. Of these types, brush motors are by far the most common. They are easy to build and very affordable. Their main disadvantage is that they use carbon brushes to transfer electric current to the rotating part and these brushes wear out over time and eventually cause the electric motor to fail. The brushless DC motor eliminates brushes, but is more expensive and requires much more complicated drive electronics to operate.
A stepper motor is a special type of brushless motor that is mainly used in automation systems. A stepper motor uses a special type of construction that allows a computer control system to “push” the motor into rotation. This is very important when controlling a robotic arm. For example, when you want to travel a specific distance as directed by a procedure in a program on your computer, a stepper motor may be the best choice.
General purpose motors tend to have many characteristics in common with DC motors, especially brush motors. Also called series wound motors, they are most commonly found in household appliances that run very fast for a short period of time. Food processors, blenders and vacuum cleaners often work with universal motors.
Electric motors are usually rated in horsepower. The most common sizes are so-called fractional horsepower motors, i.e. 1/2 horsepower or 1/4 horsepower. The largest engines are typically only found in factories, where they can range in size up to thousands of horsepower.
Electric motors are also equipped with various speed ratings. Speed is usually specified as revolutions per minute (RPM) at no load. When the engine is loaded, the speed will slow down. If the motor is too heavily loaded, the motor shaft will stop. This is known as the stall speed and should be avoided.
Before ordering an electric motor, it is necessary to determine the type of mounting required, the starting 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 seller can help you find a direct replacement. Otherwise, specifying the correct electric motor can be a daunting task.
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