The document discusses the basics of electric motors including their advantages, factors to consider when selecting a motor such as power requirements and nameplate information, different types of motor drives including pulleys and belts, examples of calculations for determining pulley speeds and diameters, determining belt length, step pulleys, and types of motor switches. The document provides information on electric motors to help with proper selection and understanding of their operation.

1. MAGM 225
Electric Motor Basics
Mr. Conrado

2. Why use electric motors?
• Adaptable – can be used anywhere
• Automatic – can be controlled with
automatic devices.
• Compact – large power in small unit.
• Dependable – if chosen properly they
give little trouble.
• Economical – can replace many man
hours.
• Efficient – can be up to 95% efficient.
• Low-maintenance – require little or no
maintenance.
• Quiet
• Safe
• Simple to operate

3. Selecting the proper motor
• Power supply
– What power is available 120v, 240,
single phase, three phase? Most
motors larger than ½ HP are run on
240v for greater efficiency and three
phase for even more efficiency.
• Power Requirements
– How much HP is required?
– Is machine easy to start?
• If not a high torque motor may be
needed.
– What speed is needed?
– Generally when replacing motors the
replacement should match as closely
as possible to the old motor.

4. Selecting the proper motor
• Base, Bearings, & Frame
– Generally the motor base or the
mounting frame are slotted to
accommodate bolts for mounting.
– Often rubber mounts are used to
reduce vibration.
• Ball Bearing vs. Bushing
– Ball/Needle bearings are a set of
hardened balls or needles set in a
metal frame. They are usually
permanently lubricated, have a higher
initial cost, but last longer. They can be
mounted in any position, create less
friction, withstand greater shaft
pressure, and rarely need replacing.
– Bushings is a sleeve in a frame that
keeps the shaft centered. Bushing are
cheaper but require lubrication, wear
out faster, and withstand less shaft
pressure.

5. Selecting the proper motor
• Starting and running
Characteristics
– Generally electric motors
are connected directly to
the load with no clutch or
drive train. Therefore
must have sufficient
torque to start.

6. Interpreting nameplate information
• Model and serial number
– Enable the manufacture to identify the
motor and useful for warranty and
replacement
• Type, Horsepower, RPM, and duty
ratios all indicate the capabilities of the
motor.
– Horsepower
• 1HP = 33,000lbs lifted one foot in
minute.
• Calculated HP = lbs. lifted x Distance in
feet x time in seconds ÷ 550
• W(LBS) X D(FT) X T(SEC) ÷ 550
• An efficient motor will generate one HP
while using about 800 watts.
– Duty Rating refers to the percent time
a motor may run without overheating.
– Temperature rise indicates how hot a
motor can get without internal damage.

7. Motor Drives
• Motor Drives
– Direct drive couplers
• Flexible-hose, Flange, Cushion Flange, and Flexible shaft
– Belts
• Permit the motor and machine to run at different speeds.
• Flexible and quiet
• Classified by shape and size

8. Motor Drives
• Pulley replacement
– To change desired output speed
– Lost or destroyed pulleys
• Formula
– The formula can be rearranged to find the needed
component.
Formula:

9. Example 1
Find Driven Pulley Speed
• Example
– What is the speed of an 8” driven
pulley if the diameter of the drive pulley
is 12” and a speed of 150 RPM?
?
150 rpm
12” 8”

10. Example 2
Find Drive Pulley Diameter
• Calculating drive pulley diameter is based on
knowing the speed of the driven pulley and the
diameter of the drive pulley. The formula:
• Example
– What is the diameter of a driven pulley rotating at 225
rpm if the diameter of the drive is 12” and its speed is
150 rpm?
225 rpm
150 rpm
12” ?

11. Example 3
Find Drive Pulley Speed
• Calculating drive pulley speed is based on knowing the
diameters of the drive and driven pulleys and the driven
pulley speed. The formula:
• Example
– What is the speed of a 12” drive pulley if the diameter of the
driven pulley is 8” and its speed is 225 RPM?
225 rpm
?
12”
8”

12. Example 4
Find Drive Pulley Diameter
• Calculating drive pulley diameter is based on
knowing the speed of the drive pulley and the speed
and diameter of the driven pulley.
– The formula:
• Example
– What is the speed of a 12” drive pulley if the diameter of
the driven pulley is 8” and its speed is 225 RPM?
225 rpm
150 rpm
12”
? 8”

13. Belt Length
• Belt length can be determined by using
the pulley diameters and the proper
formula.
•Example:
•What is the belt length for two
pulleys 5” and 10” in diameter and
30” apart at center?
5”
30” 10”

14. Step Pulley Determination
• Given: A motor speed of 1725rpm and a step pulley of 2”,3”,4”, & 5”
inverted pulleys.
• Find the speed at a given belt location.
• Calculation:
1. Divide the diameter of the motor pulley by the size of the corresponding driven
pulley. In example below 3” ÷ 4” = 0.75.
2. Then multiply the motor speed by the result of the above calculation to get the
spindle speed. 1725 x .75 + 1293 rpm.

15. Motor Switches
• Types of switches
– Toggle, rotary, Push-button, trigger, or magnetic.
– Magnetic switches are recommended for motors 1hp or more.
• Reversing switches
– Allows the machine to run in either direction.