DCmotor basics

1
DC-motor basics

• Thomas Vinz
• Thomas Junger

2
DC-motor basics DC-motor

• Rotor with commutator (armature)

3
Motor Review

• Armature
• Moving Part
• Develop Torque
• Electrical to Mechanical Torque

• Field
• Stationary Part
• Constant Field Flux

4
DC Motor
Ia
A1
ARMATURE
FIELD
If
F1
EMF
Va
Vf
Ra
F2
A2
1) Va EMF Ia Ra 2) EMF s K1 f , f If 3)
T Ia K1 f 4) Vf If Rf
EMF ElectroMagnetic Force T Torque Vf Field
Voltage K1 Motor Constant f Field Flux
5
Commutation
6
Speed Relationship
If armature current (constant load) and field
flux are in the steady state
The Speed relates to the Armature Voltage
If the armature current is in the steady state
and armature voltage is constant
The Speed is Inversely Proportional to Field
Current
S - Speed Va Armature Voltage Ia Armature
Current Ra Armature Circuit Resistance K1
Motor Constant f Field Flux
7
Torque Relationship
T K1 f Ia
If the field flux is constant
The Torque relates to the Armature Current
T Torque Output of Motor Ia Armature
Current K1 Motor Constant f Field Flux
8
1Q operation
T
n
T
n
9
4Q operation
T
Here the rotation time constant
of load is greater than acceleration
and deceleration time constants.
n

3.rd Q 2.nd Q
T
n
Change
CONS. SPEED
direction













I
a
lt
0
Ualt0
Ualt0
Ualt0
Ialt0
Ialt0
Iagt0
1
2
1
n
t






3







4
3
10
Torque - Speed - Horsepower
TORQUE
Constant Torque
Constant Horsepower
Torque
Horsepower
Base Speed
Top Speed
SPEED
Armature Range
Field Range
NOT TO SCALE
11
Motor Checklist
Horsepower or Kilowatt Speed - Base Speed - Max
Speed Voltage - Armature Voltage - Field Supply
Voltage Current - Armature Current - Field
Current Speed Feedback - Tach -
Encoder Options - Fan - Location of Conduit
Box - Thermostat - Bearings - Brake
Formula
T s
P HP T ft lb s rpm P kW M Nm n rpm
P
5250
M n
P
9550
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DC-motor basics Characteristics of sep.ex.
DC-motor
13
Motor insulation
Highest ambient temperature temperature
limit thermal reserve
H 180oC
Hotspot
F 155oC
15
B 130oC
E 120oC
125
10
A 105oC
105
10
5
80
5
75
60
40
40
40
40
40
0oC
14
Types of DC Motors

• Shunt Wound Motor
• Most common motor you will encounter
• Field Flux is constant
• Armature current is controlled

15
Types of DC Motors

• Series Wound Motor
• Field is connected in series with the armature
• Field must be disconnected before speed loop
  tuning is performed!!!

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Types of DC Motors

• Stab Shunt Motor
• Light field winding in series with armature
• Also has a shunt field
• Series winding can generally be disconnected
  permanently
• Field must be disconnected before speed loop
  tuning is performed!!!