Part 9 – DC Machine Braking

Dynamic Braking

Dynamic braking is a braking technique that involves the conversion of mechanical energy into heat or electrical energy to decelerate or halt motion. This process is achieved by dissipating the energy through a large resistor, which serves as a load to slow down the system.

Dynamic braking is useful for limiting the speed of overhauling loads. For example, lowering heavy loads on elevators and winches or by electric trains going downgrade. This type of braking is sometimes called “resistive” or “short circuit” braking.

Electric Dynamic Brake

Electric dynamic brakes consist of an electric dynamo in which the mechanical energy is converted to electric form, and either converted to heat in a resistor or returned to the supply lines. Typically, electric braking is accomplished with the same machine that serves as the drive motor.

Regenerative Braking

Regenerative braking occurs when the energy of the rotating system is converted into electrical energy in the armature, which is then sent back to the supply lines. This process takes place when the counterelectromotive force (CEMF) surpasses the supply voltage, leading to a generator action.

Dynamic Versus Regenerative Braking

Dynamic braking

• The energy produced by generator action is dissipated in resistors.
• Must have a cool-down period or duty cycle to allow the resistors to get rid of the heat.

Regenerative braking

• Used if repetitive operation is required.
• Regenerative braking slows a motor faster from its base speed to a stop condition.