Electric Motors

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Electric Motors
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Types of Motors

• Split-phase
• Cheapest electric motor
• Available in sizes up to 1/3 hp
• Works on a single-phase power
• Operates on 120 and/or 240 volt service
• Used on easy starting loads

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Types of Motors

• Repulsion-start
• Uses single-phase power
• Uses 120 and/or 240-volt service
• Available in sizes from 1/6 to 10hp
• Used on hard-to-start loads

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Types of Motors

• Capacitor-start, capacitor-run
• Uses single-phase power
• Has two capacitors
• One for starting
• One for running
• Available in sizes of 5, 7 ½, and 10 hp
• Used on hard-to-start loads

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Types of Motors

• Repulsion-start, capacitor-run
• Uses single-phase power
• A combination of the two motors
• Available in sizes of 1 to 15 hp

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Parts of Induction-run Motor

• Ventilated end bell or shield
• Stator and frame
• Thermal protection
• Centrifugal starting
• Switch sleeve bearing
• Rotor and fans
• Resiliant mounting
• Neopreme thrust washers

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Motor Requirements

• Must start the equipment loads
• Must drive the load once it is started
• Must survive the abuse of the surroundings

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Factors in Selecting Electric Motors

• Type of electric power available
• Type and size of load
• Condition under which motor must operate

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Thumb rules in estimating motor size

• If equipment can be continuously operated by
  hand, a ¼-hp electric motor will do the job
• A gas engine can be replaced with a electric
  motor of about 2/3 to ¾ as much horsepower as the
  engine
• To replace a 2-hp gasoline engine
• 2 x 2/3 4/3, select a 1 ½ hp electric motor

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Replacing Motors

• Horsepower rating must be the same or not more
  than one size larger
• Full-load speed, cycles, duty, and base must be
  the same
• Voltage 120 and/or 240
• Type should be the same

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Types of bearings

• Sleeve
• Oil lubrication
• Shaft must be mounted parallel to the floor
• Ball
• No problems of oil loss
• Installed in any position
• Requires no greasing

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Types of Motor Enclosures

• Open drip-proof- used on most farms where water
  is not sprayed
• Splash-proof- designed for either indoor or
  outdoor use such as milk barns or irrigation
  pumps
• Totally enclosed- used where dust and grit are a
  problem
• Totally enclosed explosion-proof- used around
  explosive materials such as oil and gasoline

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Reasons for having protective devices

• Protects excessive overcurrent
• Prevents short circuits

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Causes of excessive current

• Load too heavy
• Machine locked or jammed
• Belt too tight
• Bearings worn or needing lubrication
• Voltage lower than name plate indicated
• Motor and equipment pulley out of line

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Name Plate Information

• Type of current
• Type of overload protection
• Horsepower
• RPM
• Temperature the motor is to operate
• Hours the motor can operate

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Name Plate Information

• Volts
• Type of enclosure
• Motor type
• Type of frame
• Cycle
• Serial number