DC Dynamic Braking

Carlo B. DeLuca, PE (Ret.), MBA

Course Outline

Definition of Dynamic Braking and its relationship to energy is explained.  Energy is expressed in mechanical and electrical terms, comparing horsepower and watt-secs.  Advantages and disadvantages of electrical braking as compared to mechanical devices is discussed.

This course will deal with DC motors.  The difference between DC and AC motor dynamic braking is explained.  We first define the task to be accomplished and the parameters.  Once task and parameters are defined, we shall consider the components available to perform the task.  Samples of applications using dynamic braking are mentioned.

The task is to stop rotation of a model airplane propellor being driven by a DC motor after power is removed.  The purpose of the task and the manner in controlling the device is explained.  Electrical parameters of the motor are established.  Attention is directed to the energy and time in overcoming inertia to reach steady state condition.  Assumptions are made to determine the amount of energy required to stop the motor.  A capacitor is considered as an energy source.  A circuit (Circuit 1) is developed.  The schematic is shown and explained in detail.  An equation is expressed representing the amount of energy to be stored by employing the timed discharge of a charged capacitor.  Equations are presented to determine timing and energy required.  This reveals that the size of the capacitor will be too large for this application.  A second approach is proposed, using the prime power for braking.  A second circuit (Circuit 2) is developed.  The schematic is shown and explained in detail.  This concept uses a relay to direct energy to the proper components for braking action.  It is actuated and timed by discharge of a small capacitor.  Equations and mathematical calculations determine component values and timing.  The device is assembled and successfully tested.

This course includes a multiple choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

Major learning objectives of this course are offered, but not limited, to the following:

• A working knowledge of “Dynamic Braking”;
• Application of electrical dynamic braking in the solutions of tasks;
• An understanding of circuit schematics;
• Steps in creating electrical circuits;
• Insight in defining the task and parameters of an electrical device;
• Determining total resistance of resistors in parallel;
• Use of the number “e” (2.713....) in capacitor analysis;
• A refreshment in mathematical integration to determine total values in a non-linear equation;
• The use of mathematical analysis in determining component values;
• Evaluation of final results;
• Decisions in approaching alternate solutions; and
• Conducting a program of task definition, parameter identification, design and evaluation of a solution.

Intended Audience

The engineer subscribing to this course should have a working knowledge of electrical circuitry, although some review is included in the course.  An understanding of the physics of energy will help to better appreciate dynamic braking.  Familiarity with mathematical integration and the tools it contributes to mathematical analysis is helpful.

The course is particularly intended for the engineer frequently called upon to resolve a technical need, whether it be electrical or mechanical.  The concept of dynamic braking will be of particular interest to designers in the automation and robotic fields.

Benefit to Attendees

The audience will be made aware of a most interesting solution to a problem involving mechanical needs.  In developing the solutions, mathematical analysis is applied in a simple but descriptive manner.  The reader can view the steps in developing the circuits as a guideline for steps to create solutions for other needs and programs.

Course Introduction

Technical needs are often viewed as an electrical or mechanical problems.  Many times a solution seems more efficient and effective using mechanics to solve a mechanical need and electrical  solutions for an electrical need.  My first experience with Dynamic Braking was a solution to a mechanical need that was best provided electrically.  A long range zoom lens was used in concert with a telescope.  Control of the focus was very sensitive, thus the lens assembly movement had to be stopped quickly to achieve best focus settings.  Dynamic Braking provided the best solution.  It is a concept that uses magnetic force, usually applied to motors, for braking rather than propelling the device.  In the presentation of the course, an alternate application was pursued.  A different approach to the solution became evident due to the differences in application.  Perhaps the most effective and interesting lessons in this course are the procedures and techniques used to achieve a final solution.  However, the use of dynamic braking and variations of the design details can prove to be valuable in surprising applications.

Course Content

The course content is in a PDF file (100 KB):

DC Dynamic Braking.