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Faith and Works

Faith and Works. James 2:17-18  17 Even so faith , if it hath not work , is dead, being alone. 18 Yea, a man may say, Thou hast faith , and I have works: shew me thy faith without they works , and I will shew thee my faith by my works . Lecture 27 – Motors & Transformers.

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Faith and Works

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  1. Faith and Works James 2:17-18  17 Even so faith, if it hath not work, is dead, being alone. 18 Yea, a man may say, Thou hast faith, and I have works: shew me thy faith without they works, and I will shew thee my faith by my works. Discussion #27 – Motors

  2. Lecture 27 – Motors & Transformers Discussion #27 – Motors

  3. Solenoids – a simple motor • Use coil to pull (or push) plunger – a “solenoid” • Current-induced magnetic field is concentrated in core • Field attempts to “center” the core, which can pull or push plunger • Other configurations such as a rotary solenoid are common • Relays (electrically operated mechanical switch) Rotary Pull/push solenoid

  4. Electro-mechanical Relay Solenoid used to close a switch AC or DC can be used to energize coils Energized coil pulls plunger or lever which closes switch contacts Adding a permanent magnet can make a “holding” relay Toggle by energizing Rotary relays Relay logic Solid-state relays Ladder logic w/relays Electromechanical Relay

  5. Loudspeakers • Moving “voice coil” is attached to a diagram • Creates high frequency air movement (vibration) to couple electrical energy to acoustic energy • Diaphragm size/shape optimized for frequency range • Woofer, mid-range, tweeter • Cross-over (filter) networks

  6. Transformer – two coupled inductors • An electric transformer converts an AC voltage from one value to another • Can step up or step down voltage/current • Also used for signal isolation

  7. Power distribution • Generated at medium voltage • Stepped up for long-distance distribution to minimize line losses • Stepped down locally for consumers • Lower voltages “safer” • Long-distance > 138 kV • Residential distribution typically 13.8 kV • House wiring 120/220 V • Computer chips 1.2-1.5 VDC 120/240 V

  8. Typical house wiring diagram • “hot” (two) • “neutral” • “ground” • Grounding & Safety

  9. Types of electric motors • Electric motors • Convert electrical energy to rotary motion • (some linear motors) • Changing electric field produces a changing magnetic field • DC machines • Motor/generator • Stepper • AC machines • Synchronous • Induction

  10. DC Motor Fixed pole DC machine • Coil (inductor) rotates between magnetic poles • Commutator acts as switch to reverse field polarity to keep rotor turning • Motor/generator

  11. “Universal” AC Motor (Ch 20) • Conceptually similar to a DC machine except that the commutator “switch” is replaced by the alternating voltage/current from AC power source • Motors can have multiple poles to change the rotation rate • AC motors typically run at fixed rotation rates, i.e. fixed RPM • Will stall (and burn out) if overloaded

  12. Variable speed drive and Pulse width modulation • Variable speed motors are DC with a variable supply voltage/ current or an AC motor with a “variable frequency” (non-60 Hz) controller • DC systems often use “pulse width modulation”

  13. Stepper Motors • Stepper motors use EXTERNAL switching to rotate • Use an electronic controller • Motor moves or “cogs” one step for each input change • Multiple coils are “phased” to create rotation • Can be used as a break with fixed DC current • Small, low-torque • Commonly used in mechtronic systems

  14. Actuator Summary • All sorts of motors • Electric controllers provide additional capability for motors and feedback • “Mechtronics” • Combination of electronics and mechanical/electrical systems • Interdisciplinary • EE, ME, AE • Future is now..

  15. Motor Performance (last of Ch. 20) • (Conventional motors) • How do you select a motor? • Determine requirements • Needed torque and rotation rate • Don’t forget startup! • Optimize motor size/power input/stall torque • Chapter 20 has a nice summary of the design procedure • Get help from an expert

  16. 3-phase power • High power is more efficiently transferred using a scheme known as “3-phase” power • One “leg” is conventional “single-phase” 60 Hz power

  17. i Ideal Diode V-i diagram V AC to DC Conversion • Diode – a Semi-conductor switch • Allows current to flow one way but not the other Half-wave Bridge Full-wave Bridge Capacitor across load acts as a low-pass filter to reduce ripple applied to load

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