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.
