Motor Controls

Deceleration Methods 380

This class describes the various methods used to cause motor deceleration. It explains the situations where braking is needed and shows how braking is accomplished.

  • Difficulty Advanced

  • Format Online

  • Number of Lessons 14

  • Language English


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Course Outline
  • Objectives
  • What Is Deceleration?
  • Coasting
  • Reasons to Brake a Motor
  • Deceleration Methods
  • Friction Braking
  • Friction Braking Methods
  • Electric Braking
  • Electric Braking Methods
  • Dynamic Braking
  • Dynamic Braking Methods
  • Plugging
  • Brake Maintenance
  • Summary
  • Define deceleration.
  • Describe coasting.
  • Describe the reasons to brake a motor.
  • Identify common deceleration methods.
  • Describe friction braking.
  • Describe common friction braking methods.
  • Describe electric braking.
  • Describe electric braking methods.
  • Describe dynamic braking.
  • Describe dynamic braking methods.
  • Describe plugging.
  • Describe common brake maintenance practices.
Vocabulary Term


To increase the rate of speed.

brake fade

A reduction in braking effectiveness caused by excessive heat and wearing of components.

brake fluid

Hydraulic fluid used in some brake designs. When disk brakes are applied, the hydraulic fluid is sent through the brake lines to the pressure plate or caliper to apply pressure to the rotor and slow or stop motion.

brake pad

The anti-friction material that lines plates and calipers used in disk brakes. Brake pads help to reduce heat and increase the life span of braking elements.

brake shoe

Anti-friction material that lines metal plates in brakes. Shoes help to reduce heat and increase the life span of braking elements.


Applying some force to cause deceleration.

bridge rectifier

A type of full-wave rectifier with four diodes that converts both the positive and negative cycles of AC voltage to DC.


Sliding electrical contacts used to provide a connection between the armature and the external circuit.


A component in disk brakes that holds brake pads and straddles the rotor, pressing against it when the brake is applied to slow and stop motion. Disk brakes with calipers do not create as much heat as brakes with a friction plate.


The natural rate of deceleration of a motor when the power is removed. Coasting is the simplest deceleration method.


Damaging foreign material such as dirt or shop debris that causes wear to machine components.

counter emf

The voltage induced in the armature of a DC motor that opposes the applied voltage and limits armature current.

counter torque

A rotational force that opposes the directional force of torque. Plugging and dynamic braking apply counter torque to a rotor.

DC injection braking

Another name for electric braking. Direct current is injected into the system to create constant pole magnetic fields.


To decrease the rate of speed.

disk brake

A friction brake that stops motion when a stationary element is pressed against a rotating disk. Disk brakes are commonly used in automobiles and in some industrial machinery, especially in older machines.

dynamic brake

A type of brake that reconnects a motor as a generator. This converts the mechanical motion into electrical energy.

dynamic braking

A motor deceleration method that reconnects a motor as a generator. This converts the mechanical motion into electrical energy.

electric brake

A non-contact brake design actuated when an electric current charges a coil that acts as an electromagnet. Electric brakes are widely used in automated machinery and provide a high cycling rate.

electric braking

A motor deceleration method that uses DC to create a constant magnetic field.


The resistance to motion between the contact surfaces of two objects. Friction generates heat and increases the wear between components but is the key to providing mechanical braking force.

friction brake

A brake that engages when two surfaces press together and transfer energy through friction. Friction brakes are the most common type available.

friction plate

A stationary disk used in disk brakes to apply pressure to the rotor and slow and stop motion.


The tendency of an object to stay in its state of rest or motion until acted on by an external force. Torque and braking must overcome inertia to accelerate or decelerate a motor.

mechanical interlock

Arranging forward and reverse contacts so that it is physically impossible for both sets of contacts to close at the same time.

off delay timer

A delay timer that immediately closes contacts when the control coil is energized, then waits for a predetermined amount of time to open them after power is removed from the coil.


A piece of metal that moves up and down inside a hollow cylinder in response to a pressure change in pneumatic and hydraulic systems. Pistons may be used to transfer motion to brake components.


A motor deceleration method that reverses the motor connections so that the motor develops a strong counter torque.

plugging switch

A mechanical switch that opens and closes contacts when a motor reaches a set speed. Plugging switches keep the load from reversing once the counter torque has stopped the load.


The driven, rotating disk in a disk brake that is stopped when pressure is applied by a stationary friction plate or by a caliper.

service factor

A measure of the amount of overload a motor can reasonably handle. A service factor of 1.35, or 35% over the rated horsepower without overheating, is required for a motor to be plugged for regular braking.