DCC Impulses Column - 3
PWM is where full voltage is always applied. The voltage to
the motor is turned on and off in repetitive pulses. The lon-
ger the pulses, the faster the motor runs. If you want the
motor to run at half speed, the full voltage is applied for
about half the time and zero voltage the rest of the time.
Thus, you control the motor speed, not by changing the
applied voltage but by varying the time that it is applied
(that is, the Width of the Pulses).
When DCC was created, PWM was selected for many reasons
as the motor control method. Also, part of the basic DCC design
was the ability to adjust the amount of power provided to the
motor at the starting speed step (CV 2), at the middle (CV 6) and
at the top (CV 5). See figure 2.
2
2: PWM – full voltage, variable time driving a motor at
30% and 70%.
MRH-Dec 2013
