An electric motor is a device using electrical energy to produce mechanical energy, nearly always by the interaction of magnetic fields and current-carrying conductors.
Although electric motors range in size from that of powering a simple wrist watch to the propulsion of large ships, the most widely known electric motors are medium-sized and provide convenient mechanical power for industrial applications.
Electric motors may be classified by the source of electric power, by their internal construction, and by application.
When choosing an electric motor, there are four key components to consider: Horsepower, RPM, Voltage, and Frame.
Horsepower (HP) - Horsepower is used to measure the energy produced by an electric motor while doing work. A horsepower is a unit of power equal to 746 watts or 33,0000 lb-ft per minute (550 lb-ft per second).
Unfortunately, not all motors are rated the same. Some are rated under load, while others are rated at peak horsepower. A quick general calculation when looking at an electric motor is 1 HP = 10 amps on 110 volts and 1 HP = 5 amps on 220 volts.
Revolutions per Minute (RPM) - RPM is a unit of frequency of rotation: the number of full rotations completed in one minute around a fixed axis. It is used as a measure of rotational speed of a mechanical component.
The shaft on a typical shop motor will rotate at either 1725 or 3450 RPM (revolutions per minute).
Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the unit is operated with no significant load.
Voltage - Voltage is electric potential energy per unit charge, measured in joules per coulomb ( = volts).
Voltage is listed on the electric motor specs for a reason. The best life and most efficient operation occurs when you operate motors at voltages very close to the nameplate ratings. When supplying voltage to motors, stay away from the "outer limits."
Motors are available for both AC and DC currents, and voltage will vary for each.
Frame Size - Motors are built to standard specifications, such as shaft height, shaft diameter, and style of mounting.
A key part of motor interchangeability has been the standardization of frame sizes from the National Electric Manufacturers Association (NEMA). The same horsepower, speed, and enclosure will normally have the same frame size from different motor manufacturers. This means that a motor from one manufacturer can be replaced with a similar motor from another company, provided they are both in standard frame sizes.
