1. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Unit 36 Electric Motors, Drives, and Controls

2. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Electric Motors Important to select the proper type, size, and capacity motor for the job Motors larger than ½ horsepower run more efficiently Typically run at 1150, 1750, or 3450 rpm

3. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Reasons for Electric Motors –Adaptable –Automatic –Compact –Dependable –Economical –Efficient –Endurance –Low-maintenance –Quiet –Safe –Simple

4. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Characteristics Generally connected directly to the load (no clutch in the drive train) Need sufficient torque in order to start Motor type: refers to the way current flows in the motor and the accessories it has to help it start or run –Motor type will include a name for starting and a name for running (for example—a capacitor-start, induction-run motor)

5. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Nameplate The motor’s nameplate provides vital information –Model –Serial number –Type –Horsepower –Rpm –Duty ratio

6. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Motor Drives Can be coupled directly to the equipment the motors drive, but the two must have matching speed Direct drives –Flexible-hose –Flange –Cushion-flange –Flexible shaft couplings

7. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Belts Belts, chains, and gear boxes allow the motor to run at one speed while the machine runs at another Belts are flexible and quiet Reinforced with nylon or wire cords Classified according to shape and size

8. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Pulleys Device attached to a shaft to carry a belt Types –single –step –adjustable –variable speed As the diameter of a motor pulley turning at a given rpm is increased, the belt speed and the speed of the driven machine increases proportionally Formula: S x D = S' x D'

9. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Circuits for Motors May be an independent circuit directly from the distribution panel, or power cord plugged into an outlet Fuses can be either cartridge or plug type Circuit must be properly grounded Protected by fuses or circuit breakers

10. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Motor Protection Overload devices use a bimetallic strip that bends when overheated and opens the circuit; the motor switch is then tripped Switches –toggle –rotary –push-button –trigger –magnetic

11. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Controls Most motors do not operate independently Most motors are part of a system that contributes to a larger operation

12. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Maintenance Require a few drops of motor oil periodically Keep free of dust, dirt, and moisture Periodically grease or oil shafts Keep belts clean and dry

13. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Important Terms Ball bearings: set of hardened steel balls in a container or cage that keeps a shaft centered in a frame Needle bearings: steel rollers in a cage to keep a shaft centered; useful when extreme pressure is involved Bushing: sleeve in a frame that keeps a shaft centered Frame: housing or case Clutch: disengages a power source from its load

14. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Important Terms (continued) Drive train: collective components that transfer mechanical power from a power source to a load Induction: type of motor where electricity from the power source does not flow directly to the armature Centrifugal: the outward force created by a spinning object Horsepower: force needed to lift 33,000 pounds, one foot high, in one minute Duty Rating: the percent of time a motor may run without overheating

15. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Important Terms (continued) Temperature rise: how warm the motor can get without causing internal damage Step pulley: several sizes of pulleys fused together Adjustable pulley: pulley with a movable side that gets locked in place Variable speed pulley: pulley with a movable side that can be moved while the equipment is running Sprockets: wheels with spokelike teeth Transmission: a gear box that permits two or more choices of speed

16. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Important Terms (continued) Gear: wheel with teeth that mesh with teeth on another wheel to transfer power Sensor: device that receives and responds to a signal Fustat: a fuse with threads in its base that permit the fuse to be used only in circuits that match its capacity Actuator: device responsible for placing another device in motion Float switch: turned on and off by the action of a float

17. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Important Terms (continued) Sump: hole where unwanted water drains and is removed by a pump Manual: by hand Override: to take precedence over Pilot light: glows when a circuit is energized Timer: device that activates a switch after a preset time lapse Heat sensor: a switch that responds to temperature changes

18. Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Important Terms (continued) Flow switch: reacts to the movement of a gas or liquid Pressure switch: responds to changes in liquid, gas, or mechanical pressure Gas analyzer: device that determines the content of gases present in an atmosphere Air pollution detector: type of gas analyzer that senses and presents a warning when air has unacceptable amounts of pollutants