How to Choose an Electric Motor

Simply put, an electric motor converts electrical energy into mechanical energy. This is achieved by the principle of electromagnetic induction. Electromagnetic induction is the principle that a current carrying conductor, when placed in a magnetic field will have a force exerted on the conductor proportional to the current flowing and the strength of the magnetic field. The basic principles of electromagnetic induction were discovered in the early 1800's by Oersted, Gauss and Faraday. However, it was Tesla who was able to take motor technology to the next level in the late 1800's and revamped the manufacture of motors as well. Tesla was able to successfully garner 900 patents in the electrical field that had relevance for motor applications.

The working parts of a basic electric motor include:

• Fan
• Windings
• Commutator
• Field Poles
• Shaft
• Coils

Note: Please note that the larger the number of field coils used the smoother the motor will run.

AC Motors

There are various types of AC Motors, including single-phase and poly-phase. Poly-phase motors have phase winding groups that are placed in conjunction with the phase sequence of the power supply line. This produces a rotating field around the rotor surface. Single-phase electric motors do not produce a rotating field at a standstill, so a starter winding is added to give the effect of a ply-phase rotating field. Once the motor starts, the winding is eliminated from the circuit and the electric motor will continue to run on a rotating field that now exists due to the motion of the rotor interacting with the single-phase stator magnetic field.

DC Motors

DC Motors are ideal for converting direct current or electricity into mechanical energy. The advantages of a DC Electric Motor are: Speed Variation and Torque. Speed of the DC Motor can be controlled by varying the amount of current to the motor. And the turning power, or torque, of the DC Motor can be controlled by varying the amount of power coming from the power supply.

Fan Motors

There are many varieties of fan motors. Fan motors are electric motors that allow fans to run regularly over a long period of time. The type of fan motor necessary depends on its application.

• Single-Phase Fan Motor - Single-Phase motors are the most common electric fan motors, as they connect with most smaller sized fans and operate on existing (AC) power sources. Each cycle dips and tops as electrical power increases, making it an electric motor which runs off a reduced amount of electrical power. This process is low-cost and puts little pressure on the electric motor's mechanical functions.
• Single-Phase Electric Motor - Split-phase motors are used for big commercial fans, or fans in larger devices which run off of a medium amount of electricity. These motors have start and run windings, both of which are stimulated when the motor is activated. Split-Phase Electric motors have built-in safety features that allow them to automatically shut off to prevent burn-out.

Servo Motors

A Servo Motor allows for precise control of position. Feedback and angle of the motor is controlled via a control box in this type of motor. Servo Motor applications include laser cutting machines, robotics, CNC machinery or automated manufacturing.

How to Choose an Electric Motor

When you are attempting to choose the perfect motor, the following should always be considered:

1. Cross reference the manufacturer's part or model number from the motor itself. This information is usually on the nameplate of the motor.
2. If this information is not readily available, attempt to match the electrical specifications and physical dimensions of the defective motor.

The following questions should act as a guide through the electric motor selection process:

• What are the electrical specs? - (typically found on the nameplate of the motor)
  • HP, Volts, Amps, RPM's, Service Factor/SF (if applicable)
• What speeds do I need?
  • Rotation (CW, CCW, or Reversible)
  • Phase (1 or 3), in the case of appliance or industrial applications
• What are the physical dimensions?
  • Frame size (if provided) -or-
  • Length and Diameter of the Electric Motor, and
  • Length and Diameter of the Shaft
  • Number of Shafts (1 or 2)
• How should I mount this Motor?
  • What is the mounting style of the Electric Motor? (rigid base, belly band, thru-bolts, cradle base, etc...)
  • Vertical or Horizontal?
• What type of Enclosure do I need?
  • Is the Electric Motor open drip-proof (ODP), totally enclosed air over (TEAO), totally enclosed fan cooled (TEFC)?
  • Does it require special protection (i.e. hazardous location)?
• What additional specs are needed?
  • Ball or sleeve bearing?
  • Motor type (shaded pole, permanent split capacitor (PSC), capacitor start, etc...)
  • Motor application (to what is it attached?)