Download Understanding DC Motor Basics

DC Current Electricity
and
Magnetism
in
Electrical Conductors
Electric Field
An Electric Field or Force Surrounding a Charged Particle
An electric field radiates outward from a positive charge and
radiates in toward a negative point charge.
Current Electricity
•The movement of Electric Charges is called Current.
• Current is measured by the amount of charge
(Coulombs) passing through the cross-sectional area of
a conductor in a given period of time (Seconds).
•A Conventional Current flows from a positive battery
terminal to a negative battery terminal.
Electric Fields Drive Current Electricity
Conventional Current
Anion
Cation
Assumes Charge Flows from Positive to Negative
Current Electricity
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Batteries use
electrochemical
reactions to
produce
dissimilar
charges used to
create current
in DC motors
and circuits.
Ions contain CHARGES that create
electric fields
Current Electricity
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The electric
field produced
in a battery
forces current
through an
electric circuit
or conductor
connected
across the
battery poles,
Ions contain CHARGES that create electric fields. These
opposite electric fields produce imbalanced forces necessary
to move the charges through the circuit.
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A current created by the unidirectional movement of
charge(s) through a conductor is called a direct current.
This current is produced by all batteries
Positive Battery
Terminal
Negative Battery
Terminal
Magnetic Field Lines
When current moves through a conductor a circular
magnetic field is induced around the conductor
The Right Hand Rule
The direction of the magnetic field
surrounding the conductor can
be found using your
right hand
Position the thumb of your right hand
pointing in the direction of
conventional current (Positive to
Negative) and your fingers will wrap
around the conductor in the direction
of the induced magnetic field.
The Direction and Motion of an Induced
Magnetic Field in a Conductor
X
Current Coming
Towards You
Current Moving
Away From You
Current and Magnetism in a Coil
When current moves through a coiled conductor a
circular magnetic field is induced about the coil
Motor (armature) rotation is caused by the simultaneous
attraction and repulsion between the electromagnetic
field in the armature and a fixed magnetic field
Armature
Fixed Magnets
A Conductor in a Fixed
Magnetic Field
A Current Carrying Conductor
in a Fixed Magnetic Field
Force
Fixed Magnetic Field
Induced Magnetic Field
(Due to current)
A Motor Armature in a Fixed
Magnetic Field
S
N
Direction of Force (Torque) acting
to turn the Armature (Conductor)
The magnetic field surrounding a current
carrying conductor interacts with an
existing magnetic field.
Fleming's Left Hand (Motor) Rule
Thumb = Direction of
Conductor Motion
Fore Finger = Direction of
Fixed Magnetic Field (N to S)
Middle Finger =
Conventional
Current Direction
Determines the direction of DC current
carrying conductor in a fixed magnetic field
Fleming's Left Hand (Motor) Rule
Direction of Rotation
Fixed Magnetic Field Direction
Conventional
Current Direction
N
S
A
S
N
Use the Left Hand Rule to
Determine the Rotation
Direction of the Armatures
in A and B
Hint: You will have to turn
your left hand upside down
for example A
B
Notice that when the
current through the
armature is reversed,
it moves (Rotates) in
the opposite direction
S
N
Magnetic Forces Acting on Parallel
Current Carrying Conductors
Two parallel conductors carrying current
in the same direction will attract each
other
Magnetic Forces Acting on Parallel
Current Carrying Conductors
North
Two parallel
conductors
carrying currents
in opposite
directions will
repel each other,
and they will set
up a polarized
magnetic field
between
themselves.
X
South
Magnetic Forces Acting on Parallel
Current Carrying Conductors
South
South
X
North
North
Wrapping current carrying conductors around
an iron core creates an electro magnet
The Armature of a Brush Commutated DC
Motor is made up of Current Carrying
Conductors Wrapped Around an Iron Core
The Motor Armature is an electro Magnet and
Operates according to the Principles Described in
this Slide Show
The
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