Temperature Effects On DC Motor Performance PDF
Temperature Effects On DC Motor Performance PDF
Temperature Effects On DC Motor Performance PDF
Authored By:
Dan Montone
Haydon Kerk Motion Solutions
/ Pittman Motors
Symbol
Description
Units
Temperature coefficient
/C
Current
I0
No load current
ILR
KE
Voltage constant
V/(rad/s)
KT
Torque constant
Nm/A
K(i)
KT or KE (initial cold)
Nm/A or V/(rad/s)
K( f )
KT or KE (final hot)
Nm/A or V/(rad/s)
Speed
RPM
n0
No load speed
RPM
Power
Pout
Output power
Pmax
Max power
Pmax(i)
Pmax( f )
Ploss
Dissipated power
Motor torque
Nm
TLR
Nm
Rm
Motor regulation
RPM/Nm
Rmt
Rmt(i)
Rmt( f )
VT
conductor( / C)
Silver
0.0038
Gold
0.0037
Angular velocity
rad/s
Copper
0.0040
rad/s
Aluminum
0.0043
Magnetic Material
magnet( / C)
Tmax(C)
Ceramic
-0.0020 / C
300 C
-0.0004 / C
300 C
-0.0002 / C
540 C
-0.0012 / C
150 C
In the case of using English units, KT and KE are expressed in oz-in/A (lb-in/A, lb-ft/A, etc.) and V/krpm.
One does not equal the other when using these units,
but both quantities will decrease in the same proportion
with elevated temperature.
Using
Motor Constants
Equation 4a.
Theoretical
Motor Regulation
R
Rm
= 9.5493 xx TT x EE
m 9.5493 K
KTT x K
KEE
Rm
=
m=
Rm
m
n00
n00
T
TLR
LR
T
TLR
LR
Terminal Voltage
VT
24
No Load Speed
n0
3160
RPM
No Load Current
I0
0.30
TLR
2.88
Nm
ILR
40.7
Terminal Resistance
Rmt
0.59
Voltage Constant
KE
0.071 V/(rad/s)
Torque Constant
KT
0.071
Nm/A
Motor Regulation
Rm
1111
RPM/Nm
25
125
100
Conditions:
Initial motor data was created using a rapid
dynamometer test at a room temperature of 25C
With a consistent load on the motor, the armature
temperature stabilized to 125C
No heat sink or forced air flow was used
The motor was operated open-loop
(no feedback to regulate shaft output power)
Power supply used regulated, 50A max output
with low output impedance
Copper motor windings
Strontium ferrite (ceramic) permanent magnets
conductor (f - i)]
magnet (f - i)]
ILR = VT / Rmt( f )
ILR = 24V / 0.83
ILR = 28.92A
Decreased Locked Rotor (Stall) Torque
TLR = ILR x KT( f )
TLR = 28.92A x 0.057Nm/A
TLR = 1.65Nm
Symbol
n0
@25C
@125C
3160 RPM
3979 RPM
331 rad/s
417 rad/s
ILR 40.7 A
28.9 A
TLR 2.88 Nm
1.65 Nm
Terminal Resistance
Rmt 0.59
0.83
Voltage Constant
KE
Torque Constant
KT
0.071 Nm/A
Motor Regulation
0.057 Nm/A
1) We assumed a stabilized 100C rise on all components of the motor. In practice, the various motor
components will stabilize at different temperatures, with
the wound motor armature being the highest.
2) The temperature coefficient for the magnetic material was an average used for that material. In reality,
different grades of a particular material class will have
values that deviate slightly from the average.
x TLR
x TLR
If the motors are tested at the maximum rated temperature, the user will better understand the motor capability when used in applications where motor temperature
will stabilize at a value significantly higher than room
temperature. The disadvantage is that there are many
other variables that can skew the test results such as
method of temperature measurement, motor mounting (causing a heat sinking effect), air flow around the
motor, etc. Some motor manufacturers will test their
motors under the worst case condition; a motor stabilized to full rated temperature with no heat sinking or
forced air flow. There are no strict guidelines dictating
how a manufacturer should present the performance
data. The important thing to remember when evaluating
the information is to ask the right questions.