Applied Motion STR2 - Manual (Page 18)

18
STR2 Hardware Manual 920-0059B
1/30/2014
Step 2: Fine Tuning the Motor Current
The maximum current for the motor you have selected was set automatically when you selected
the motor in Step1. But you may want to reduce the current to save power or lower motor
temperature. This is important if the motor is not mounted to a surface that will help it dissipate
heat or if the ambient temperature is expected to be high.
Step motors produce torque in direct proportion to current, but the amount of heat generated
is roughly proportional to the square of the current. If you operate the motor at 90% of rated
current, you’ll get 90% of the rated torque. But the motor will produce approximately 81% as
much heat. At 70% current, the torque is reduced to 70% and the heating to about 50%.
Switches A4 and A5 on the front of the STR2 drive are used to set the percent of rated current
that will be applied to the motor. Please set them according to the illustration below.
Step 3: Setting Idle Current
Motor heating and power consumption can also be reduced by lowering the motor current
when it is not moving. The STR2 will automatically lower the motor current when it is idle to
either 50% or 90% of the running current. The 50% idle current setting will lower the holding
torque to 50%, which is enough to prevent the load from moving in most applications. This
reduces motor heating by 75%. In some applications, such as those supporting a vertical load, it
is necessary to provide a high holding torque. In such cases, the idle current can be set to 90%
as shown below. The idle current switch is located in switch bank A, on the front of the STR2.
3
50%
3
90%
4 5
100%
4 5
90%
4 5
80%
4 5
70%