Why is a waiting period needed when changing direction?
A turning motor behaves like a generator; reversing the polarity while it is still moving adds the applied voltage to the back-EMF and creates a very high current pulse. In addition the torque reverses suddenly and a shock load hits transmission parts such as gears, couplings and chains. A short wait for the motor to slow down is essential.
While the motor turns forward there is a back-EMF on it close to the supply voltage. When you reverse the direction suddenly, the net voltage the motor sees becomes the sum of the applied voltage and the back-EMF; because the winding resistance is small, the current can rise even above the locked rotor value.
This pulse has three consequences:
- Sudden overcurrent and heating in the driver switches.
- Voltage collapse on the supply line; an RF receiver or control circuit on the same line can reset.
- Shock torque in the mechanics; broken gear teeth, coupling wear, chain throw.
The correct sequence: stop → wait → start in the reverse direction. The waiting time scales with the inertia of the load; a few hundred milliseconds is enough on small actuators, while heavy masses can need a few seconds.
In practice the ramp function does half of this job: the soft start/stop feature of the KS250 and the RMP pot of the PT500 smooth stopping and starting, reducing both the current pulse and the mechanical shock. Operators using a manual button or an RF remote control should also be trained in the habit of waiting for the motor to stop completely before changing direction.
The full topic: DC Motor Driver Selection Guide