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NI SMD-7613/7614/7615/7616 User Manual
Figure 54.
SMD-7614/7616 Torque Curve for ST34-1/4/7, 60V Power Supply
Motor Heating
Step motors convert electrical power from the driver into mechanical power to move a load.
Because step motors are not perfectly efficient, some of the electrical power turns into heat on
its way through the motor. This heating is not so much dependent on the load being driven but
rather the motor speed and power supply voltage. There are certain combinations of speed and
voltage at which a motor cannot be continuously operated without damage.
The following table and figures show the maximum duty cycle versus speed for each motor at
commonly used power supply voltages. Please refer to this information when planning your
application.
A step motor typically reaches maximum temperature after 30 to 45 minutes of operation. If
you run the motor for one minute then let it sit idle for one minute, that is a 50% duty cycle.
Five minutes on and five minutes off is also 50% duty. However, one hour on and one hour off
has the effect of 100% duty because during the first hour the motor will reach full (and possibly
excessive) temperature.
The actual temperature of the motor depends on how much heat is conducted, convected, or
radiated out of it. Our measurements were made in a 40 °C (104 °F) environment with the motor
mounted to an aluminum plate sized to provide a surface area consistent with the motor power
dissipation. Your results may vary.
Oz-in
S
T
3
4-1/4/7 with
S
MD-7614/7616
60 VDC Power
Su
pply, 20000
S
tep
s
/Rev, All Motor
s
Connected in P
a
r
a
llel
Rev/
S
ec
200
100
400
600
800
5
10
15
20
3
0
3
5
25
40
1000
900
700
500
3
00
0
0
S
T
3
4-7 (6.72 A/Ph
as
e)
S
T
3
4-4 (7.56 A/Ph
as
e)
S
T
3
4-1 (7.56 A/Ph
as
e)