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Introduction
Electromechanical device that converts electrical energy to mechanical energy
Mechanical energy used to e.g.
Rotate pump impeller, fan, blower
Drive compressors
Lift materials
DC Motors – Components
Field pole
North pole and south pole
Receive electricity to formmagnetic field
Armature
Cylinder between the poles
Electromagnet when current goes through it
Linked to drive shaft to drive the load
Commutator
Overturns current direction in armature
AC Motors – Synchronous motor
Constant speed fixed by system frequency
DC for excitation and low starting torque: suited for low load applications
Can improve power factor: suited for high electricity use systems
Synchronous speed (Ns):

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ELECTRIC MOTORS
An Introduction to DC and Stepper Motors
Electric Motors
Electric motors are everywhere!
In your house, almost every mechanical movement that you see around you is caused by an AC or DC electric motor.
Direct Current Motors
overall plan of a simple 2-pole DC electric motor
A simple motor has 6 parts, as shown in the diagram
Direct Current Motors
Direct Current Motors
Brushed DC Motor
The brushed DC motor is one of the earliest electric motor designs
Easy to understand design
Easy to control speed
DC STEPPER MOTORS
Stepping motors are electric motors without commutators
Commutation is handled externally by the motor controller
Controller charges opposite coils attracting the center rotor magnets
DC STEPPER MOTORS
DC STEPPER MOTORS
Voltage Rating
provides desired torque
Resistance-per-winding determines
the current draw of the motor
Maximum operating speed
Degrees per Step
Sets the number of degrees the shaft will rotate for each full step
UNIPOLAR STEPPER MOTOR
Relatively easy to control
simple 1-of-'n' counter circuit can generate the proper stepping sequence
1 transistor per winding
UNIPOLAR STEPPER MOTOR
two center-tapped coils
represents the connection of a 4 -phase unipolar stepper motor
UNIPOLAR STEPPER MOTOR
6 wires with a center tap on each of two coils
IDENTIFYING WIRES
Check make and model to see if wire colour code is available
Observe the wires to see if you can identify groups of 3 wires
Measure resistance between wires
Wire with lowest resistance is power wire
IDENTIFYING WIRES
6 wire motors
Groups of 3 wires
1 power & 2 signal
5 wire motors
1 power & 4 signal wires
CONTROL PROGRAM
Once wires identified and connected to the circuit: a program is needed to run the motor
Example Turing Program:
loop
parallelput (1)
delay (500)
parallelput (2)
delay (500)
parallelput (4)
delay (500)
parallelput (8)
delay (500)
end loop
STEPPER MOTOR CONTROL
4 signal wires fired in the correct sequence will turn the motor

Electric Motors

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Magnetic Force On A Current – Carrying Conductor


The magnetic force (F) the conductor experiences is equal to the product of its length (L) within the field, the current I in the conductor, the external magnetic field B and the sine of the angle between the conductor and the magnetic field. In short
F= BIL (sin)


The force on a current-carrying conductor in a magnetic field:


When a current-carrying conductor is placed in a magnetic field, there is an interaction between the magnetic field produced by the current and the permanent field, which leads to a force being experienced by the conductor:


The magnitude of the force on the conductor depends on the magnitude of the current which it carries. The force is a maximum when the current flows perpendicular to the field (as shown in diagram A on the left below), and it is zero when it flows parallel to the field (as in diagram B, on the right):


The directional relationship of I in the conductor, the external magnetic field and the force the conductor experiences


Electric Motor


An electromagnet is the basis of an electric motor

An electric motor is all about magnets and magnetism: A motor uses magnets to create motion.

Opposites attract and likes repel. Inside an electric motor, these attracting and repelling forces create rotational motion.

A motor is consist of two magnets.

Electric Motors

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Induction motors
These motors are probably the simplest and most rugged of all electric motors. They consist of two basic
electrical assemblies: the wound stator and the rotor assembly.
The rotor consists of laminated, cylindrical iron cores with slots for receiving the conductors. On early motors,
the conductors were copper bars with ends welded to copper rings known as end rings. Viewed from the end,
the rotor assembly resembles a squirrel cage, hence the name squirrel- cage motor is used to refer to induction
motors. In modern induction motors, the most common type of rotor has cast-aluminum conductors and shortcircuiting
end rings. The rotor turns when the moving magnetic field induces a current in the shorted
conductors. The speed at which the magnetic field rotates is the synchronous speed of the motor and is
determined by the number of poles in the stator and the frequency of the power supply.


Wound-rotor motors — Although the squirrel-cage induction motor is relatively inflexible with regard to
speed and torque characteristics, a special wound-rotor version has controllable speed and torque. Application
of wound-rotor motors is markedly different from squirrel-cage motors because of the accessibility of the rotor
circuit. Various performance characteristics can be obtained by inserting different values of resistance in the
rotor circuit.



Single-phase motors — These motors are commonly fractional-horsepower types, though integral sizes are
generally available to 10 hp. The most common single phase motor types are shaded pole, split phase,
capacitorstart, and permanent split capacitor.
Figure 4 - Typical speed-torque
characteristics for Design A, B, C, and
D motors.
• Shaded pole motors have a continuous copper loop wound
around a small portion of each pole, Figure 5. The loop causes
the magnetic field through the ringed portion to lag behind the
field in the unringed portion. This produces a slightly rotating
field in each pole face sufficient to turn the rotor. As the rotor
accelerates, its torque increases and rated speed is reached.
Shaded pole motors have low starting torque and are available
only in fractional and subfractional horsepower sizes. Slip is
about 10%, or more at rated load.
• Split phase motors, Figure 6, use both a starting and running
winding. The starting winding is displaced 90 electrical degrees
from the running winding. The running winding has many turns
of large diameter wire wound in the bottom of the stator slots to
get high reactance. Therefore, the current in the starting winding
leads the current in the running winding, causing a rotating field.
During startup, both windings are connected to the line, Figure
7. As the motor comes up to speed (at about 25% of full-load
speed), a centrifugal switch actuated by the rotor, or an
electronic switch, disconnects the starting winding. Split phase
motors are considered low or moderate starting torque motors
and are limited to about 1/3 hp.
• Capacitor-start motors are similar to split phase motors. The
main difference is that a capacitor is placed in series with the
auxiliary winding, Figure 8. This type of motor produces greater
locked rotor and accelerating torque per ampere than does the
split phase motor. Sizes range from fractional to 10 hp at 900 to
3600 rpm.
• Split-capacitor motors also have an auxiliary winding with a
capacitor, but they remain continuously energized and aid in
producing a higher power factor than other capacitor designs.
This makes them well suited to variable speed applications.