What is the difference between dynamic braking and free coasting?
In dynamic braking the motor terminals are short-circuited by the two lower switches of the bridge; the back-EMF drives current through the winding, an opposing torque forms and the motor stops quickly. In free coasting all switches are off and the motor slows down only through friction and load drag. The first is the fastest stop, the second the gentlest mechanically.
The two modes differ in where you send the motor's stopping energy.
Dynamic braking (slow decay): The motor forms a closed circuit with the back-EMF it generates itself; the current turns into heat in the winding resistance and produces torque against the direction of rotation. The stopping distance shortens and position repeatability improves. The price is increased heat in the motor and driver and a sudden load on the transmission components.
Free coasting: The motor is electrically isolated and coasts freely. No shock is applied to the transmission and no heat is produced, but the stopping point varies with the load's inertia and is not repeatable.
Selection guide:
- In applications that must stop at a definite point, such as doors, barriers and shutters, dynamic braking is preferred.
- On loads where free coasting is harmless, such as conveyors and fans, free coasting protects the mechanics.
- In lifting applications neither holds the load in the air; a mechanical brake is required for that.
The KS250 description states that an active brake circuit is present; in addition, the soft stop function softens the deceleration ramp. The right approach is to observe the braking behaviour under real conditions during commissioning with a heavy load and set the ramp accordingly.
The full topic: DC Motor Driver Selection Guide