chapter 7 - dc motors

8/12/2019 Chapter 7 - Dc Motors

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DC Motor Theory

http://hyperphysics.phy-

astr.gsu.edu/HBASE/magnetic/motdc.html

DC Motor Java Applet

http://www.magnet.fsu.edu/education/tutorial

s/java/dcmotor/index.html

Flash of various motorshttp://www.st.com/stonline/products/support/

motor/tutorial/motor.swf
http://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/motdc.htmlhttp://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/motdc.htmlhttp://www.magnet.fsu.edu/education/tutorials/java/dcmotor/index.htmlhttp://www.magnet.fsu.edu/education/tutorials/java/dcmotor/index.htmlhttp://www.st.com/stonline/products/support/motor/tutorial/motor.swfhttp://www.st.com/stonline/products/support/motor/tutorial/motor.swfhttp://www.st.com/stonline/products/support/motor/tutorial/motor.swfhttp://www.st.com/stonline/products/support/motor/tutorial/motor.swfhttp://www.magnet.fsu.edu/education/tutorials/java/dcmotor/index.htmlhttp://www.magnet.fsu.edu/education/tutorials/java/dcmotor/index.htmlhttp://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/motdc.htmlhttp://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/motdc.htmlhttp://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/motdc.html


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DC Motor theory

http://www.youtube.com/watch?v=Xi7o8cMPI

0E

http://www.youtube.com/watch?v=FjNnRyLex

NM
http://www.youtube.com/watch?v=Xi7o8cMPI0Ehttp://www.youtube.com/watch?v=Xi7o8cMPI0Ehttp://www.youtube.com/watch?v=FjNnRyLexNMhttp://www.youtube.com/watch?v=FjNnRyLexNMhttp://www.youtube.com/watch?v=FjNnRyLexNMhttp://www.youtube.com/watch?v=FjNnRyLexNMhttp://www.youtube.com/watch?v=Xi7o8cMPI0Ehttp://www.youtube.com/watch?v=Xi7o8cMPI0E


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DC Motor cutaway

1. Bearing

2. Case/end bell

3. Brush holder4. Rotor Windings (Armature)

5. Brushes

6. Commutator

7. Stator windings (Field) (permanent magnets

in this motor)

8. Armature Bars


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Toque is based on Armature Current and

Magnetic Flux of the fieldT = kTIA

Generator Action: Moving a conductorthough a field produces a voltage (EMF) based on flux and speed:EMF = KES

In a motor this EMF is opposite appliedvoltage.


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Induced voltage counters applied voltage,

and is called counter EMF or CEMF

Va = Vin CEMF

Ia = (Vin

CEMF)/Ra

Speed therefore is:

S = CEMF/KE


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Speed Regulation: ability of a motor to

maintain rated speed under load. Based

on no-load and full-load speed.

%speed regulation = (SNL-SFL)/SFLX 100


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Series-Wound Motor

Initial current is very high until motor comes

up to speed.

Provides large starting torque Car

starters.

Under no-load can run-away (over speed)


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Stall Torque Maximum torque a motor

can supply without stalling

No-Load Speed Speed of motor with no

load. Any motor that is doing something

useful must be running at less than no-loadspeed.

Reversing applied voltage does NOT

change motors direction. Changing onlyarmature connections would.


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Shunt-Wound

Lower stall and no-load speeds.

Much less speed change from NL to FL

(15%)

Speed control via line voltage.

Reversing only shunt or armature will

reverse motor.


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Compound Motor

Combination of series and shunt.

Good starting torque and good speed

control.


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Permanent Magnet Motors

High flux permanent magnets provide flux.

Very good linear control

Low power use


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DC Motor Control

Adjusting voltage or using PWM


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Analog Drive


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Direction Control


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PWM Speed Control

By cycling the voltage fully on and off within

a small time, the speed can be controlled.

The higher the on-time, or duty cycle, the

more power that is received.


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Generating PWM


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Large Motor Control


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Braking

Braking: Since a motor generates voltage,

by applying a load when power is removed,the generated power is consumed by a

load resistor absorbing the power of the

generator and slowing it.Plugging: Monetarily reversing the supply

BUT - CEMF and Supply voltage will

combine potentially leading to damagingcurrents.


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Brushless DC Motor

Electronic Commutation to control which

magnet is on.

Uses Hall effect sensors to detect rotor

position and control field coils to control

speed.


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chapter 7 - dc motors

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