The advantage of using the second type Of PWM
input would be for small DC motors, stepper motors, and
servo motors that require very little or no braking at all
before changing motoring directions. The first method
would be useful for larger motor applications that require
braking and more sensitive speed control to prevent high
surge currents.
2.5 Surge Current Measurements
One important consideration when designing the
system program was the surge current that results while
changing motoring directions. The speed of the motor at
the time of reversal directly affects the amount of surge
current. Not all applications allow the motor to completely
stop before starting in the opposite direction. Therefore,
depending on the size of the DC motor being driven, surge
currents must be considered when designing the system
program. The program shown in Fig. 6 is designed with a
variable braking delay. This delay was calculated from 42
V motor test measurements.