Universal motor

Universal Motor principle, working and applications

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Universal Motor

2. UNIVERSAL MOTOR
Series-connected
Rotor and Stator are
connected in series
Operates on either
ac or dc
NEMA ratings
0.01hp – 1.0hp @
5000r/min or above
Universal Motor 2

3. EQUIVALENT CIRCUIT
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4. A CLOSER LOOK
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Armature
(Rotor)
Field Winding
Field
(Stator)

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The Commutator Bar and Brushes are a switch that
reverses the current in the armature coil as it rotates

6. CHECK THE DIRECTION OF
ROTATION
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Force on conductor B is
upwards, rotation is
counter-clockwise (CCW)
Flux
“Bunching”
+Positive Half-Cycle+

7. OPPOSITE HALF-CYCLE
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Force on Conductor B is
upwards, rotation is
counter-clockwise (CCW)
Flux
“Bunching”
-Negative Half-Cycle-

8. CONCLUSIONS
The direction of
rotation (and Torque)
is independent of the
polarity of the AC
source!
Universal Motor 8
2
D p a
p a
D a
T B I
B I
T I
m
m
m
T
D
= Developed Torque
B
p
= flux density due to current in field
I
a
= armature current

9. OTHER CONSIDERATIONS
How do you reverse the direction of rotation?
Reverse the direction of the current in either the field or in
the armature, but not both!
How do you control the speed of the motor?
Reduce the voltage applied to the motor
Use an autotransformer or SCR/Triac
This reduces the armature current, reducing the torque, reducing
the speed
Applications
Portable power tools
Small appliances

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10. OTHER CONSIDERATIONS
How do you reverse the direction of rotation?
Reverse the direction of the current in either the field or in
the armature, but not both!
How do you control the speed of the motor?
Reduce the voltage applied to the motor
Use an autotransformer or SCR/Triac
This reduces the armature current, reducing the torque, reducing
the speed
Applications
Portable power tools
Small appliances

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