MECP Basic Study Guide

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The Basic Installer Study Guide is based on carefully docu-mented material and research. Every attempt has been made to relay accurate and up-to-date information. This book is designed to assist Mobile Electronics Installers in passing the MECP Basic Installer Test and can also be used as a reference guide. MECP and/or the Consumer Electronics Association cannot be held responsible for discrepancies or inconsisten-cies contained in this publication.

All rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means - graphic, electronics, or mechanical, includ-ing photocopyinclud-ing, recordinclud-ing, tapinclud-ing or information storage and retrieval systems - without the written permission of the publisher.

MECP

Consumer Electronics Association 2500 Wilson Boulevard

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CONTRIBUTORS

WRITERS AND CONTRIBUTING EDITORS

Eric Abbiss Wayde Alfarone Paul Baird John Banse Ward Benjamin Bob Bentley Jim Boyte Kris Bulla Dennis Deck Tim Den Hartog Charlie Fox Mark Fukuda Joe Garruba Tom Gazda Doug Giddens Mary Ann Giorgio Lonnie Goddard Mark Gordon Jeff Halkin Homer Hawlins Scott Heidbrink Stan Hoffman Jim Jardin CONTRIBUTING COMPANIES Alpine Electronics ATX Research

Audio Comp Electronics, Inc. Audio Control

Audivox

Benjamin Consulting Bobit Publishing Car Audio Engineering

CMA School of Mobile Electronics Directed Electronics, Inc.

Installer Institute JBL Car Audio Listen Up

Luzerne County Community College, Advanced Technology Center

MANAGING EDITOR

Chris Cook ...MECP Dan Jobin Ed Kuehner Derek Lee David Long Martin Marino James Milton Ted Peterson Joe Petreau Todd Ramsey Rudy Sanders Allen Schultz Kerry Shrode Geoff Smith Kenny Snoddy Dave Sprosty Justin Stanley Jerry Sterling Gil Stroud Todd VanZandt Joe Walters Paul Wanders Ken Ward Mobile Dynamics Mobile One Auto Sound Mobilworks

Ora Electronics Pioneer Electronics Quality Auto Sound Robert Bentley Audio Sherwood

South Bay Cellular Telephone Company Stillwater Designs

Vehicle Security Electronics Traffic Jams

MECP would like to thank the following manufacturers: Alpine, Code Alarm, Directed Electronics, Kenwood, Metra Electronics Corporation, Pioneer Electronics, Scosche Industries, and Vehicle Security Electronics for their continued support of the program and contributions to this book.

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INTRODUCTION

The objective of the MECP Study Guide is to prepare you to become a Certified Installer in your area of expertise. Put simply, this book provides you with the answers to the questions that are asked in the Basic Installer Test and the related sections of the First Class test. The Basic Installer Study Guide will also give you the information needed to study for the Advanced Electrical and Installation Knowledge & Technique portions of the First Class test. Whether you’re trying to pass the Basic Installer, First Class, or Master Installer exam, this guide will provide you with a firm foundation to build on for your Mobile Electronics Education.

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UNDERSTANDING THE FORMAT

For some people, sitting down and reading a study guide is not very rewarding… or informative. In fact, it can be downright frustrating.

We realize that…but at the same time, we also recognize the importance for excel-lence in our industry. So in that vein, we have created a Study Guide that is infor-mative and educational – and above all, easy to use!

Why? Because we want to see you succeed – because your professional perfor-mance reflects positively on everyone in the industry. In addition, it also helps you and your company maintain a high level of customer satisfaction – and that can translate into repeat and referral business.

Here’s how we made this book easier to use:

For example, important facts or key terms are printed in bold type so they stand out on the page and are easy to locate. In addition, important notes are placed in the margins.

Here’s how this book is formatted:

■ Margin Notes with the

✍

symbol are key points taken directly from the

text. They emphasize material that you’ll find in the Installer and First Class tests.

■ Illustrations are included to reinforce important concepts.

■ Bold type alerts you to an important fact or key term. Many of these are included on the test, so make sure you clearly understand their meaning. ■ Glossary is located at the back of the book. This is essential study mate-rial for any of the test levels.

■ Sample Test Questions are at the end of the section. These sample ques-tions let you gauge your progress while preparing you for the test.

■ Key Formulas and equations are at the back of the text. They help you understand and memorize the equations included in the test.

Margin Notes

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WHAT IS MECP…AND WHAT DOES IT MEAN TO YOU?

MECP stands for the Mobile Electronics Certified Professional Program. It was designed and developed by the Education Committee and Certification Committee of CEA – the Consumer Electronics Association, which is a non-profit organization dedicated to the Consumer Electronics industry and is a sector of the Electronic Industries Alliance (EIA).

■ The purpose of this certification program is to foster a level of profession-alism and to achieve a level of knowledge.

■ MECP is also a learning and educational tool that allows installers of all levels – through continued study and daily experience – to grow to the next level of expertise.

■ MECP is a network of schools, manufacturers, retailers, installers, and concerned industry professionals from the U.S. and Canada whose primary goal is to help make this industry educationally sound with ongoing testing and training.

WHY CERTIFICATION IS ESSENTIAL: CUSTOMER PERCEPTIONS

When a customer makes a commitment to upgrade their car audio, security, nav-igation or wireless system, they’re looking to your company to provide them with the professionalism and service that accompanies their purchase decision. ■ Today’s customers are more demanding than ever before – they expect OEM quality on their installations. Accordingly, you need to keep pace with the latest techniques to ensure the “final product” lives up to your customer’s expectations. ■ _{In the automotive industry, there’s a statistic – a happy, satisfied customer tells 5} friends about their positive experience; but an unhappy, dissatisfied customer tells 15 - 20 people about their negative experience. A few dissatisfied customers can quickly wipe out the good reputation of a company

BOTTOM LINE BENEFITS MECP certification has its benefits:

■ Demonstrates your commitment, dedication and professionalism. ■ Assures consistent quality.

■ _{Qualifies the people who do the work.} ■ Demonstrates a “we care” attitude. ■ Reinforces the quality of your operation.

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MAKING THE MOST OF THIS STUDY GUIDE

First and foremost – this is not a “How To” book! It is a study guide – written specifically for installers who wish to become certified professionals.

Here’s how you can make the most of this information:

■ Take notes – write in the margins (that’s why they’re there).

■ Study additional sources of information to round out your knowledge. ■ This is not meant to be the definitive source for installation instructions; refer to the appropriate manufacturer’s publications for actual installation information.

If you’re taking the basic Installer test level, you need to study:

■ All of the sections on Basic and Advanced Electrical and Installation Knowledge and Technique (Study Guide 1 – Bronze level), as well as chapter 3 and the Glossary definitions. It is important that you know the basics, and have good knowledge of the technologies that you will be working with.

If you are taking the First Class test, you need to study:

■ All of the sections on Basic and advanced electrical, Installation Knowledge and Technique, and Chapter 3 on Basics of Autosound, Security, Wireless & Navigation (Study Guide 1 - Bronze level) as well as the entire First Class Study Guide (Silver level) and the related Glossary definitions. It is important that you know the basics, and have a good knowledge of the technologies that you will be working with.

If you are taking any of the Specialist test, you need to study:

■ All of the sections on Basic and Advanced Electrical and Installation Knowledge and Technique (Study Guide 1 – Bronze level).

■ The information that relates to your area of specialization –Autosound, or Security.

If you are taking the Master Installer test, you need to know the theory behind all these technologies:

■ This is the most challenging test; accordingly, you need to study all the MECP Study Guide levels (Study Guide 1,2, & 3 – Bronze, Silver, and Gold) including the Glossary of Terms, as well as the other books referenced in the back of the Master Installer Study Guide (Study Guide 3 – Gold level). Margin Notes

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UNDERSTANDING THE MECP TESTS Here’s a breakdown of the different tests:

Installer Level

■ Basic Installer test – 150 questions; allotted time: 3 hours

1 Basic Electrical

2 Installation Knowledge and Technique 3 Tools and Shop Safety

4 Definitions and application of core technologies

The Basic Installer level tests basic electronics and DC knowledge and their appli-cations to mobile electronics installations; basic knowledge pertaining to actual installations and troubleshooting; sound, music, and product; basic working knowledge and understanding of standard shop tools and safety procedures. The Basic Installer certification examination is a basic level, 150 question multiple choice and true/false examination broken down into three 50 question sections. The questions within the three sections can be further broken down into the nine categories listed below. The numbers in parentheses indicate the approximate per-centage of the 50 question sections devoted to each subject matter.

Electrical Section Questions

1 Ohms Law (25-30%) - These questions require the knowledge of Ohms Law formula and the math to solve a particular question. Many of these questions require computation.

2 Electronic Components (45-50%) - These questions pertain to the phys-ical electronic components such as capacitors, resistors, etc. This also includes related topics like “farads” and “henries”.

3 Measurements & Applications (25-30%) - This classifies all questions having to do with situations where knowledge needs to be applied and/or measured in some form. This also includes the application of units and scales such as dBs, amperes, etc..

Installation Knowledge and Technique Section Questions

4 Component Application and Usage (25-30%) - These questions pertain to the actual way a component is used or applied in an installation. An example is when (or when NOT to) install a noise filter or perhaps whether an open or closed circuit is appropriate.

5 Troubleshooting and Analysis (50-55%) - These questions deal with the

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6 Installation Techniques (15-20%) - This classifies all questions which deal directly with physical installation related procedures and/or concerns. Tools and Safety Section Questions

7 Measurement and Troubleshooting (50-55%) - This classifies all ques-tions which directly address the measurement and troubleshooting of 12volt systems. This includes both the techniques and tools.

8 Power and Hand Tools (25-30%) - This classifies all questions which deal with tools that ARE NOT considered measurement and trou-bleshooting tools.

9 Safety Practice and Safety Equipment (15-20%) - This classifies all ques-tions which deal with safety and proper use of safety equipment

Specialist Level

■ Autosound Specialist test – 150 questions (50 questions/section);

allotted time: 3 hours

1 Basic and Advanced Electrical 2 Autosound Section

3 General Installation Knowledge

The Autosound Specialist certification examination is a first class level, 150 ques-tion multiple choice examinaques-tion broken down into three 50 quesques-tion secques-tions. The questions within the three sections can be further broken down into the eight categories listed below. The numbers in parentheses indicate the approximate per-centage of the 50 question sections devoted to each subject matter.

1 Ohms Law (20-25%) - These questions ask for and/or require the knowledge of Ohms Law formula or math to solve a particular question. Many of these questions require computation.

2 Electronic Components (45-50%) - This classifies all questions having to do with the physical electronic components such as capacitors, resis-tors, etc.. This also includes related topics like “farads” and “henries”. 3 Measurements & Applications (30-35%) - These questions pertain to situations where the knowledge needs to be applied and/or measured in some form. This also includes the application of units and scales such as dB’s, amperes, etc..

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Autosound Section Questions

4 Audio Theory and Analysis (40-45%) - This classifies all questions which deal with both acoustic and electronic theory and analysis with relation to sound in the mobile environment.

5 Audio Components (30-35%) - These questions pertain to the physical audio components which make up a mobile audio system. This includes both passive and active electronic components as well as loudspeakers. 6 Installations and Testing (25-30%) - These questions deal directly with physical installation related procedures and/or testing of a mobile audio system. This includes subwoofer enclosure questions.

General Knowledge

7 Tools (45-50%) - This classifies all questions related to Tools. This includes hand tools, power tools, measurement tools, and troubleshoot-ing tools.

8 Safety and Installation Techniques (50-55%) - This classifies all ques-tions which deal with safety and proper use of safety equipment. This cat-egory also classifies all questions which deal directly with physical instal-lation related procedures and/or concerns.

■ Security Specialist test – 150 questions (50 questions/section);

allotted time: 3 hours:

1 Basic and Advanced Electrical 2 Security Section

3 General Installation Knowledge

The Security Specialist certification examination is a first class level, 150 question multiple choice examination broken down into three 50 question sections. The questions within the three sections can be further broken down into the eight cat-egories listed below. The numbers in parentheses indicate the approximate per-centage of the 50 question sections devoted to each subject matter.

2 Electronic Components (50-55%) - This classifies all questions having to do with the physical electronic components such as capacitors,

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3 Measurements & Applications (25-30%) - These questions deal with sit-uations where the knowledge needs to be applied and/or measured in some form. This also includes the application of units and scales such as dB’s, amperes, etc..

Security Section Questions

4 Security Components (20-25%) - This classifies all questions which pertain to the physical security components which make up a 12 volt mobile security system.

5 Relays and Semiconductors (45-50%) - This classifies all relay and semi-conductor questions as related to the installation of a 12 volt mobile secu-rity system.

6 Installations and Testing (35-30%) - These questions deal directly with physical installation related procedures and/or testing of a 12 volt mobile security system.

General Knowledge

7 Tools (65-70%) - This classifies all questions related to Tools. This includes hand tools, power tools, measurement tools, and troubleshoot-ing tools.

8 Safety and Installation Techniques (30-35%) - These questions deal with safety and proper use of safety equipment. This category also classifies all questions which deal directly with physical installation related proce-dures and/or concerns.

Specialist level exams are designed to test advanced electronics knowledge and installation applications; and in-depth knowledge, understanding, application, and troubleshooting in either autosound, or security. Note: To take this exam, MECP requires notarized proof of one year’s work experience in mobile electronics.

■ First Class test – 150 questions total; allotted time: 3 hours

1 Autosound

2 Basic and Advanced Electrical 3 Security

First Class level exam is designed to test advanced electronics knowledge and instal-lation applications; and in-depth knowledge, understanding, application, and troubleshooting in autosound, wireless, security. Note: To take this exam, MECP requires notarized proof of one year’s work experience in mobile electronics. Margin Notes

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The First Class certification examination is a 150 question multiple choice exam-ination broken down into three 50 question sections. The questions within the three sections can be further broken down into the nine categories listed below. The numbers in parentheses indicate the approximate percentage of the 50 ques-tion secques-tions devoted to each subject matter.

1 Audio Theory and Analysis (20-25%) - This classifies all questions which deal with both acoustic and electronic theory and analysis with relation to sound in the mobile environment.

2 Audio Components (15-20%) - These questions pertain to the physical audio components which make up a mobile audio system. This includes both passive and active electronic components as well as loudspeakers. 3 Installations and Testing (55-60%) - These questions pertain directly to the physical installation related procedures and/or testing of a mobile audio system. This includes subwoofer enclosure questions.

5 Electronic Components (40-45%) - These questions pertain to the phys-ical electronic components such as capacitors, resistors, etc.. This also includes related topics like “farads” and “henries”.

6 Measurements & Applications (35-40%) - These questions cover situa-tions where knowledge needs to be applied and/or measured in some form. This also includes the application of units and scales such as dB’s, amperes, etc..

7 Security Components (10-15%) - This classifies all questions which pertain to the physical security components which make up a 12 volt mobile security system.

8 Relays and Semiconductors (25-30%) - This classification includes all relay and semiconductor questions as related to the installation of a 12 volt mobile security system.

9 Installations and Testing (55-60%) - These questions deal directly with

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■ Master test – 180 questions total; allotted time: 3 hours

1 Advanced Electrical

2 Installation Knowledge and Technique 3 Advanced Autosound

4 Advanced Security 5 Troubleshooting 6 Glossary of Terms

Master Installer Level exam is the most advanced level test and is designed to test installers in advanced electrical, autosound, security and troubleshooting. In order to qualify to take the Master Installer exam, you will need a score of 70% or better on all sections of the First Class test. Note: To take this exam, MECP requires notarized proof of three year’s work experience in mobile electronics. The Master Installer certification examination is MECP’s most advanced level. This is 180 question multiple choice and true/false examination broken down into four sections. The Electrical, Autosound and Security sections are each 50 questions, and the Troubleshooting section contains 30 questions. The questions within the four sections can be further broken down into the twelve categories listed below. The numbers in parentheses indicate the approximate percentage of the question sections devoted to each subject matter.

2 Electronic Components (35-40%) - This questions pertain to the phys-ical electronic components such as capacitors, resistors, etc.. This also includes related topics like “farads” and “henries”.

3 Measurements & Applications (35-40%) - This classifies all questions having to do with situations where the knowledge needs to be applied and/or measured in some form. This also includes the application of units and scales such as dB’s, amperes, etc..

4 Security Components (10-15%) - These questions pertain to the physi-cal security components which make up a 12volt mobile security system. 5 Relays and Semiconductors (30-35%) - This classifies ALL relay and semiconductor questions as related to the installation of a 12 volt mobile security system.

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6 Installations and Testing (50-55%) - This classifies all questions which deal directly with physical installation related procedures and/or testing of a 12volt mobile security system.

7 Audio Theory and Analysis (25-30%) - These questions pertain to both acoustic and electronic theory and analysis with relation to sound in the mobile environment.

8 Audio Components (40-45%) - This classifies all questions which per-tain to the physical audio components which make up a mobile audio system. This includes both passive and active electronic components as well as loudspeakers.

9 Installations and Testing (25-30%) - These questions deal directly with physical installation related procedures and/or testing of a mobile audio system. This includes subwoofer enclosure questions.

Troubleshooting Section Questions

10 Audio Related Troubleshooting (30-35%) - These questions pertain to troubleshooting the AUDIO part of the system installation.

11 Security Related Troubleshooting (20-25%) - This classifies all questions which pertain to troubleshooting the security and/or convenience items in an installation.

12 General 12volt Electrical System Troubleshooting (40-45%) - This classi-fies all questions which deal with the vehicle troubleshooting including audio and/or security components which may be causing problems or interference with the vehicle electrical systems.

HOW THE TESTS ARE CREATED

The test questions are written and developed by: ■ A Committee of Master Installers.

■ Manufacturers’ trainers and subject matter experts. ■ Industry educators from schools and community colleges.

■ Testing and certification industry experts are used for content writing and validation of each test.

The questions are designed to test your daily working knowledge of installation technologies. Hands-on applications can only be tested and proven in a school or work environment.

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Most questions are multiple choice and some True/ False:

■ Multiple choice questions have four or five possible answers. Only one answer is correct in every question.

PREPARING FOR THE EXAM

Some people get “test anxiety” and while they know all of the answers, they freeze-up during the test.

That can be frustrating – but if you’re thoroughly prepared, the odds are on your side that rather than feeling anxious…you’ll be ready to “ace” the exam.

Here are some easy steps that will help you to be fully prepared when you take your exam:

■ Read the Table of Contents to find the sections you need to focus your studies. ■ _{Scan through the appropriate sections to get a “feeling” for how the} infor-mation is organized.

■ Read each section – preferably three to four times.

■ Choose a time when you’re rested and fresh to study.

■ Note important topics or areas where you are weak in the margin. ■ Re-read each section a few days later until you feel you know the

information.

■ A week before the exam: re-read or review the chapter one more time to refresh your memory.

■ In between reading the chapters, review the Glossary so you’re

familiar with the key terms and definitions.

■ Take the sample tests a few times:

■ You can take the sample test provided in the Study Guide or log on

to www.ce.org and select the Tech education and Services Section.

■ The first time “tests” your knowledge of the material.

■ Subsequent reviews familiarize yourself with the type of test you’ll

be taking.

THE DAY BEFORE THE TEST

■ Review each chapter and the sample questions.

■ Do not try to “cram” for the test the day before the test (it didn’t work in high school…it doesn’t work here, either).

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■ If you have properly read this Study Guide, the information should already be in your head and the correct answers will come to you quickly during the test.

■ Last-minute cramming can confuse you and make you even more

anxious about the test.

■ Review each area you feel you may be weak in and review your notes in the margins.

THE DAY OF THE TEST

■ Get plenty of rest the night before.

■ If you are coming straight from work, allow some extra time to relax and unwind before you start the test (at least 15 - 20 minutes).

■ During that time, “clear” your head of the day’s activities.

■ Do not try to re-read the Study Guide at any time.

■ Stay relaxed and confident that you will do well on the test.

AT THE TEST SITE Bring the following:

■ Two sharpened #2 pencils. ■ Your acceptance letter (if needed). ■ One form of photo identification. Arrive at the test site on time or a little early:

■ Look in the lobby or front office for MECP signs or an events board that directs you to the test location.

■ _{Check in at the room or designated testing area.}

■ Have all of your information available to give to the proctor.

■ Take your test packet, sit down, relax, and wait for the proctor’s instructions.

■ Seating will be arranged every other seat, or at least an arm’s length

apart.

■ Each test is different from the person sitting next to you.

■ Listen carefully to the proctor’s instructions.

■ He or she will explain any last minute changes. ■ They will tell you how to fill out the scantron sheet.

■ They will also instruct you on how to hand the materials back to the

proctor when you are finished.

■ DO NOT MARK IN THE TEST BOOKLETS.

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■ Any marks in the booklets cannot be permanently erased.

■ A mark, circled answers (right or wrong), or notes, will confuse the

next test applicant and could disqualify your score. ■ Do not talk during the test.

■ The appearance of cheating will immediately disqualify you from the test, so make sure you follow the proctors directions in all areas.

■ No smoking is allowed in the test room.

■ If you must leave the room, do so quietly, leaving all your test materials on the table.

■ If you have a question or there is a problem with your test booklet, raise your hand or wait for the proctor to come to you.

■ Please be courteous to others taking the test, as you would expect them to be with you.

■ Everyone wants to do well on the test and does not need

unnecessary distractions.

HOW TO TAKE THE TEST

It’s common to be anxious when taking a test – most people are. That can lead to unnecessary, sloppy mistakes.

Here are some tips that will help you improve your performance:

■ Make sure that you neatly write your name on the scantron sheet – as you would like it to appear on your certificate.

■ Read each questions twice before you look at the answers. ■ Do not attempt to “read into” a question.

■ There are no “hidden meanings” – so don’t ask the question, “What if?”

■ Answer the question as stated – leave all preconceived notions at home…or in the install bay…on the day of the test.

■ Don’t skip around – answer the questions in sequence. (Can you imagine if you tried to perform an installation out of sequence? You get the idea.)

■ If you come to a question that you cannot answer, mark the

ques-tion number down on your scratch paper and come back to it after you finish that section.

■ Be careful to keep your answers in numerical order – if you skip a

question, make sure you skip the answer on the scantron sheet or your answers will be in the wrong place.

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Marking the scantron sheet:

■ Refer to the box on the front of the sheet on how to properly mark each answer block.

■ Use two or three hard strokes to darken the block.

■ Do not draw a circle, a dot, or make one soft line.

■ If the answer blocks are not marked properly, the scantron machine

will score improper marks as wrong answers.

■ Once you get into the rhythm of marking the answer blocks, you’ll find that it’s easy to do correctly.

■ Be sure to erase all mistakes completely or the scoring machine could mark your answer as wrong.

AFTER THE TEST When you are finished:

■ Follow the instructions on page one of the test booklet and take your test materials up to the proctor.

■ Leave the room quietly.

■ If you’re waiting for someone else to finish the test, wait in the lobby

or somewhere away from the test room.

■ Looking in the room to see if someone has finished, or waiting in

the hall outside the room, talking to other applicants, will only disturb the others still taking the test.

You will receive your test results in four or six weeks of the test date.

Congratulations and Continued Success!

MECP

For testing dates and locations, call MECP: (703) 907-7689, or visit our web site at www.ce.org and select Tech education and services.

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CHAPTER 1 BASIC AND ADVANCED ELECTRICAL

1

No matter your desires – whether professional or personal – before you can start on any project, you need a solid grasp of “the basics.” Accordingly, Chapter 1 forms the foundation of your entire MECP training. This chapter introduces some basic principles of electronics, as well as some of the more advanced formulas and laws.

Both the Basic Installer level and the First Class level Electrical section of the MECP certification tests are included here. You should have a thorough understanding of each topic before moving on to the next topic. For the First Class level test you will need to study the complete First Class Study Guide available from MECP.

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It’s hard to imagine life without electricity. And while internal combustion engines power our vehicles, it’s electricity that lights the stoplamp when you put your foot on the brakes. And it’s electricity that powers the audio system.

The computer may be fueling today’s technological growth, but it was electricity that started the revolution.

Therefore, before you can move into more specific areas of expertise, you first need a solid foundation in electrical theory and application.

Section 1

Electrical Laws and Formulas for the Mobile Electronics Environment

What do “electrical laws and formulas” have to do with you - an installer? Good question.

On the surface, it may seem like a plumber studying hydrodynamic physics - sure, they both deal with the motion of fluids, but one is a little overkill.

The same theory does not hold true here.

Today’s installations are increasingly more complex - and the vehicles you are working on are equally sophisticated. It is no longer just about hooking up the components.

Being a mobile electronics installer truly is a profession - it requires skill and training, and there’s always something new to learn. But before you can learn the “new stuff,” you need to have a solid understanding of the basic electrical theories. That way, when you encounter a particular challenge, you’ll know where to start troubleshooting. After all, you can easily figure out when you’ve used the wrong size wire gauge or have a bad connection without all that math cluttering your mind. But while hands-on experience is essential; understanding why a wire gauge is too small or what caus-es a bad ground will help you through many practical situations. A firm grasp of electronics knowledge can guide you logically to the source of almost any problem. Before getting to the mathematical relationships involved in electronics, you need to know about the two types of electrical current you will be working with in the mobile electronics environment - AC and DC.

■ “AC” stands for Alternating Current, which is current that alternates polarity between positive and negative. AC has both an amplitude compo-nent (how much) and a frequency compocompo-nent (how often).

Margin Notes

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■ “DC” stands for Direct Current, and it is current which supplies power to electronic components and is EITHER positive OR negative in polarity, but not both. DC has only an amplitude component (called potential) and a fre-quency of zero.

Alternating Current is an electronic current that periodically changes polarity

(i.e., it alternates from positive to negative).

■ In an alternating current circuit, the current flow reverses its direction on each alternation. The voltage alternates from positive to negative and back again to positive.

■ The rate of alternation (how often) is called frequency, which is measured in cycles per second, or Hertz (Hz).

■ The number of times the AC signal cycles in one second is its specific fre-quency. Multiple frequencies blended together is how music is sometimes clas-sified as AC.

On an oscilloscope, AC looks like this:

The other form of AC at work in the vehicle is the charging system. A key com-ponent of this system is the alternator. The alternator creates AC that is changed into DC by a process called rectification, which allows the battery to charge. When it comes to the audio signal, we are concerned with the “AC” that flows from the head unit through the signal processors, which is then amplified to drive the loudspeakers. That audio signal contains many varied frequencies and amplitudes which make up the tempo and pitch of individual sounds in music.

■ _{Alternating Current and music signals are covered in detail in the} AUTOSOUND chapter of the First Class Study Guide.

For now, most of our applications will focus on DC.

Margin Notes

✍

Alternating Current is an electronic current that periodically changes polarity.

+

0

— 1 Cycle Amplitude Time

✍

The alternator creates AC that is changed into DC by a process called rectification.

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Direct Current is defined as a current that travels in one direction only. One

ter-minal is always positive, and the other is always negative.

■ All things that rely on the vehicle battery as their source of power operate with DC. This includes amplifiers, head units, security systems, radar detec-tors, car phones, and other electronic accessories. Sometimes a component, though powered by DC, may output AC. This is the case with car amplifiers. On an oscilloscope, positive DC looks like this:

When analyzing electronic circuits, you’ll encounter the relationships between these four electronic properties:

1 Voltage (E)

2 Current (I)

3 Resistance (R)

4 Power (P)

Ohm’s Law is the electrical formula that defines the relationship of these proper-ties to each other.

UNDERSTANDING OHM’S LAW

Ohm’s Law is one of the most basic laws of electricity. Using mathematical

for-mulas, Ohm’s Law describes a specific and measurable relationship between cur-rent, voltage, resistance and power.

Let’s look at these parameters and see how they apply to mobile electronics: The properties that you need to understand are Voltage, Current, Resistance, and Power. Power will be discussed later in this chapter.

Margin Notes

✍

Direct Current is defined as current that travels in one direction only.

+

ø

✍

Ohm’s Law describes a specific and measurable relationship between current, voltage, resistance and power.

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Ohm’s Law mathematically describes the interaction among these parameters. Understanding the relationship among current, voltage resistance, and power can help you figure out many different installation problems and answer many instal-lation questions (even before the instalinstal-lation begins). For Example, Ohm’s Law will tell you how much power an amplifier really puts out, if the voltage supplied to an amplifier is too low, or if a higher power alternator should be considered. So lets take a look at Ohm’s law and discover how it effects our work environment.

■ Current is the rate of electron flow through a given point, and is mea-sured in Amperes or Amps. If you marked a point on a main road in a city and counted the cars that pass that point in a specific window of time, you could gain an understanding of the traffic flow on that road. A wider road with more lanes would allow more cars to pass in a given window of time, while a narrower road with fewer lanes would allow a smaller number of cars to pass in that window of time. This illustrates the concept of current flow in a wire or circuit.

■ Voltage is the electrical pressure that moves charged particles in a circuit, and is measured in Volts. Voltage can be considered as the force of electrici-ty. Voltage is also sometimes called difference of potential (potential differ-ence) and, like the force of electricity, can be thought of as electrical pressure that moves the current.

Just as the width of the road and number of lanes would effect traffic as we described with current, a vehicle’s natural ability or potential to movement would also affect traffic flow. A vehicle moving downhill could start and move much more quickly than the same vehicle moving uphill. The natural force of gravity assists that. Electrically, the natural force, (determined by potential) that moves the charged particles through the circuit is much the same concept. More electri-cal pressure means more potential for electronic traffic flow.

■ What is the pressure exactly? How does it move the charged particles? Let’s start to answer these questions by first defining some terms that relate

Margin Notes

✍

Current is the rate of elec-tron flow through a given point.

✍

Voltage is the electrical pressure that moves charged particles in a circuit.

I Current Amps or Amperes

E Voltage Volts

R Resistance Ohms

P Power Watts

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■ Charge — or electrical charge is the fundamental unit for an amount of electricity. Symbolized (Q).

■ Polarity — in an electrical circuit there are two different polarities: elec-trons posses a negative charge while protons posses a positive charge. It can also be said that an electron has a negative polarity and a proton has a pos-itive polarity.

■ Potential - refers to the ability to do work. Now with these definitions let’s discuss some actions.

■ Like charges repel - two negatively charged particles held together will repel or want to move away from one another. Likewise, two positively charged particles held together will repel or want to move away from one another.

■ Unlike charges attract - when two unlike charges are brought close together they will attract or try to move toward each other.

These two reactions are proof of an electric field. Since potential is the ability of the charges to do work, it’s the difference of potential (using the natural ability to attract and repel) that allows the current to move and do work.

■ Resistance is the opposition to current flow. To understand Resistance think of anything that limits or blocks the flow of electrical traffic. Electrical Resistance describes the property that various materials possess to restrict or inhibit the flow of electricity. Electrical resistance is measured in Ohms (Ω). Electrical resistance is relatively low in most metals and relatively high in most non-metallic substances.

The basic formulas used by Ohm’s Law to find current, voltage, or resistance are as follows: I = E R E = I x R R = E I Margin Notes

✍

Electrical Resistance describes the property that various materials possess to restrict or inhibit the flow of electricity. P I E R I•_R P E P I2 E R E2 R P I E I E2 P P•_R I•_E I2 •_R P = Watts I = Amps P/R E = Volts R = Resistance

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According to Ohm’s Law:

If you want to find… and you know… then the math is…

Current (I) Resistance (R) and Voltage (E) E ÷ R = I

Current (I) Power (P) and Voltage (E) P ÷ E = I

Current (I) Power (P) and Resistance (R) (Sq.Rt.) √P ÷ R = I Voltage (E) Power (P) and Resistance (R) (Sq.Rt.) √P x R = E Voltage (E) Current (I) and Resistance (R) I x R = E

Voltage (E) Current (I) and Power (P) P ÷ I = E

Resistance (R) Current (I) and Voltage (E) E ÷ I = R Resistance (R) Current (I) and Power (P) P ÷ I2= R Resistance (R) Voltage (E) and Power (P) E2÷ P = R

Power (P) Current (I) and Voltage (E) E x I = P

Power (P) Current (I) and Resistance (R) R x I2 = P Power (P) Resistance (R) and Voltage (E) E2÷ R = P

Let’s take a less scientific approach to understanding the relationship between cur-rent, voltage, and resistance by comparing electrical characteristics to hydraulics. Suppose you have a container of water. The pressure at the bottom of the contain-er caused by the volume of watcontain-er above it is similar to voltage. The more watcontain-er, the more pressure, the more voltage, the higher the difference of potential (voltage).

When the valve is opened, pressure forces the water through the pipe.

■ Voltage is like that “pressure” - only it is electrical pressure that is forcing charged particles through a circuit.

■ If you were to open the valve wider, more water would flow through

the pipe.

If you were to make the valve opening smaller, less water would flow

Margin Notes

Container of Water

Valve

On Tube

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This increase and decrease in the rate of water flow is comparable to the idea of current, but remember that current is the rate of electrons that flow through a conductor.

In addition, if you were to decrease the size of the pipe or bend it slightly, the rate of water flow would decrease because you would be increasing the resistance.

■ This limitation in flow volume is similar to electrical resistance,

which restricts the flow of electrons.

The relationship between current, voltage, and resistance is similar to the con-tainer of water - change one parameter while leaving another alone and the third has to change. It will always change according to Ohm’s law, which is the real beauty in knowing this concept.

Understanding the relationship between current, voltage, and resistance can help you figure out many different installation problems.

■ Ohm’s Law will tell you things such as:

■ How much power an amplifier really puts out. ■ If the voltage supplied to an amplifier is too low. ■ If a higher output alternator should be considered.

Let’s say, for example, that you’re powering up a high wattage audio system, but you choose a wire that’s too small to supply the current required by the system. The resistance in the wire will develop an unwanted voltage drop across it (E = I x R) when the amplifiers draw power. Amplifiers operating with low volt-age may overheat, motorboat, or fail.

An easy way to memorize Ohm’s Law is to use the Ohm’s Law Pie Chart. Simply “cover up” the letter you wish to find the value of and carry out the remaining formula. Here’s another example of how useful Ohm’s Law can be in every day installations:

■ Suppose you have a resistor with a known value of 8 Ohms (R = 8), and you know the current value that flows through the resistor is 1 Amp (I = 2). What is the voltage across the resistor?

Simply apply Ohm’s Law:

R = 8 I = 2 E = I x R E = 2 x 8 E = 16 Volts Margin Notes

E

I R

■ Figure 5. OHM’s Law Pie Chart.

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The following circuits show examples of how these formulas can be applied to installations. Use what you’ve learned so far about Ohm’s Law to calculate the cur-rent, resistance, and voltage.

1 How much CURRENT will flow through this circuit?

2 What is the RESISTANCE of an alarm siren when 12 Volts causes 11/2

Amperes to flow?

3 How much VOLTAGE is supplying this circuit?

The answers are: 1 2 Amperes

2 8 Ohms

3 4.8 Volts

Margin Notes

■ Figure 7. Resistance Circuit.

■ Figure 8. Voltage Circuit.

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Ohm’s Law is also very practical to know when you’re trying to calculate effective resistance.

■ _{Effective resistance is the “calculated” resistance that a device presents to a} circuit while it is operating.

Knowing how to apply Ohm’s Law to determine resistance is practical because it’s fairly easy to use a VOM (Volt Ohm Meter) to measure current and voltage, but you cannot directly measure resistance in a live circuit.

For example, if you have an amplifier that draws 50 Amps, with an applied volt-age of 12 Volts, for full power output with both channels driven into a 4 Ohm load. How would you determine the effective resistance of the amplifier by apply-ing Ohm’s Law?

Since we know that I = 50 Amps, and E = 12 Volts, we can manipulate Ohm’s Law so that R is the isolated variable.

■ Simply divide both sides of the equation by I:

E = I x R E = I x R I I R = E

I

Now, insert the known values into the formula: R eff = 12V

50A

R eff = 0.24 Ohms

ELECTRICAL POWER

Ohm’s Law relates a fourth circuit parameter - Power.

■ Electrical POWER is the conversion of energy into work over a certain period of time, and a watt represents the rate over time that the energy is converted. It’s the result of the collective work of current, voltage, and resis-tance. The last parameter, “P”, allows you to determine how much a system can produce, how many amps it will draw, and therefore what gauge wire Margin Notes

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Power is the conversion of energy into work over a certain period of time.

✍

Effective resistance is the “calculated” resistance that a device presents to a circuit while it is operating.

✍

A watt represents the rate over time that the energy is

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There are four basic forms of power:

■ Mechanical power, usually measured in horsepower. ■ _{Heat, measured in BTU’s (British Thermal Units).} ■ Nuclear power, measured in Roentgens.

■ Electrical power, which is measured in Watts.

The law of conservation of energy states that energy cannot be created or destroyed, only changed into some other form of energy. The same law is valid in audio cir-cuits, where electrical energy is being converted into heat and sound.

In more advanced studies of electronics, you’ll come across the terms coulomb and joule.

■ _{A coulomb (pronounced koo-loam) is an electrical charge which contains} 6.24 x 1018of electrons.

■ A joule (pronounced jew-el) is the energy required to move 6.24 x 1018 electrons (one coulomb of charge) past a point in a circuit.

■ If one coulomb of charge moves past the point every second, the

flow rate (current) is one ampere.

■ Since a watt represents the rate over time that energy (joules) is converted into work (heat, sound, light, etc.), then a watt represents the conversion of one joule per second into light, heat, sound, or some other form of work. These definitions are not really necessary to know in every day installations; how-ever, they help define the relationship between energy, power, and time.

Getting back to Ohm’s Law, electrical power is equal to volts times amperes, or

P = E x I.

■ _{One volt will move one amp through one ohm of resistance at a work rate} of one watt.

■ Resistors convert electrical energy into heat.

Margin Notes

✍

Coulomb is an electrical charge which contains 6.24 x 1018of electrons.

P Power Watts

SYMBOL PARAMETER UNIT OF MEASURE

✍

Joule is the energy required to move 6.24 x 1018electrons (one coulomb of charge) past a point in a circuit.

✍

A watt represents the conversion of one joule per second into light, heat, sound, or some other form of work.

✍

The law of Conservation of energy states that energy cannot be created or destroyed, only changed into some other form of energy.

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Remember that amperage is current flow per second, and therefore, a watt is rated in seconds.

■ _{Since power equals: E x I, we know from Ohm’s Law that} E = I x R, P = I x R x I.

■ This is the formula we will use to figure out the power (wattage) for most of our DC applications.

Here are some more ways Ohm’s Law can help you figure out different situations (in addition, see the full Ohm’s Law pie chart in the back of this book):

■ How would you find the total current (I) of an amplifier at the electrical system’s idle voltage?

■ Simply divide the amplifier’s total root mean square (rms) wattage (P) by the vehicle’s idle voltage (E).

■ In a system with 250 Watts rms total audio output power,

(125 Watts rms/channel into 4 Ohms) and an electrical system with a 12.6VDC, the equation would look like this:

250 = 19.84 Amps 12.6

This can appear to be complicated - but if you focus on each element in the equa-tion, then it’s easy to understand.

Here’s why it is important that you understand this equation:

■ It “tells” you what size wire to run from the battery to the amplifiers.

■ If the amplifiers are in the trunk. ■ You have a 15-foot cable run.

■ According to Figure 9, a #10 American Wire Gauge (AWG) cable is

necessary to adequately power up this system. Ohm’s Law is indeed a very helpful tool to have in the bay. Margin Notes

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Using the same example and applying it to IASCA rules - an international sanc-tioning body for sound-off events - you derive a much different answer.

■ The first formula is perfectly adequate for a system to operate safely.

■ In an effort to compensate for the power wasted by the amplifier,

Margin Notes 1.5 15 20 30 ₄₀ 50 10 300 400 20 18 16 14 12 10 8 6 4 2 1 1/0 2/0 3/0 4/0 100 75 50 45 40 35 30 25 20 15 12 10 Wire Size Amperes 175 150 125 100 90 80 70 60 200

POWER CABLE CALCULATOR

Total Amperage Up to 4 to 7 to 10 to 13 to 16 to 19 to 22 to Draw of System 4 Ft. 7 Ft. 10 Ft. 13 Ft. 16 Ft. 19 Ft. 22 Ft. 28 Ft. 0-20 14 12 12 10 10 8 8 8 20-35 12 10 8 8 6 6 6 4 35-50 10 8 8 6 4 4 4 4 50-65 8 8 6 4 4 4 4 2 65-85 6 6 4 4 2 2 2 0 85-105 6 6 4 2 2 2 2 0 105-125 4 4 4 2 0 0 0 0 125-150 2 2 2 0 0 0 0 00

The above chart shows wire gauges to be used, if no less than a .5 volt drop is accepted. If aluminum wire or tinned wire is used, the gauges should be of an even larger size to com-pensate. Cable gauge size calculation takes into account terminal connection resistance. ■ Figure 9. Electrical Wire Chart.

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IASCA uses the following formula: 250 x 2 = 500 (Watts) 500 (Watts) = 39.68 Amps

12.6(Volts)

According to the IASCA wire table, this would require a #4 gauge AWG cable. For a 2 Ohm load, multiply by 2 again, as follows:

250 x 2 x 2 = 1,000 (Watts) 1,000 (Watts) = 79.37 Amps

12.6 (Volts)

This would require a #2 gauge AWG cable.

Whatever method you use, it is important to correctly identify the proper wire gauge to use in the installation.

As a Mobile Electronics Installer, it is important for you to understand not only Ohm’s Law as a concept, but also its applications to everyday installation. Ohm’s law can figure out complex answers to installation questions by using the build-ing blocks of current, voltage, resistance, and power. The facts don’t lie. Ohm’s Law can provide real answers to many mobile electronics questions. Now that we have covered Ohm’s Law, its time to move to more advanced formulas.

SERIES AND PARALLEL TOTAL RESISTANCE FORMULAS

One of the more important calculations you’ll make is to figure out how much of a load speakers will present to an amplifier.

When designing a system, it is sometimes necessary to connect circuit components - such as speakers, inductors and capacitors - in series or parallel combinations.

■ There are occasions when combinations of multiple subwoofers in single or dual voice coil models could be optimum or be potentially damaged depending on the method of connection.

■ Series and parallel combinations will have an effect not only on the source which they are connected to, but on one another as well.

■ It’s common practice to connect two loudspeakers in parallel. ■ When these “paralleled” speakers are connected to the amplifier, the

combined speaker load will have a significant effect on how that ampli-fier performs.

Margin Notes

✍

Series and parallel combinations will have an effect not only on the source, which they are connected to, but on another as well.

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Therefore, understanding how series and parallel circuit relationships work is another useful tool, especially when you’re building crossover networks, installing multiple subwoofers, or performing system analysis.

The drawing below shows resistors wired in parallel:

A series circuit is established when circuit components are connected in a string - end to end - so only one common terminal is shared between two components. Series circuits share current and divide voltage.

■ _{When resistors are connected in a series, the total resistance is the sum of} the resistance of each component.

■ For example, when you’re trying to figure out the total resistance

(Rt) of a series circuit, simply add up the numbers.

Resistance in a series circuit is additive, and the formula looks like this:

Rt = R1 + R2 + R3…etc.

In schematic form, it looks like this:

Margin Notes

✍

A series circuit is estab-lished when circuit components are connected in a string, end to end, so that only one common terminal is shared between two components and they share the same current.

+

Resistor #1

-#2 #3 Rt =Total Resistance Rt =R1 + R2 + R3

■ Figure 10. Resistors wired in parallel.

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Figuring parallel-total resistance formulas is a little more difficult.

A parallel connection exists when circuit elements are connected so that two ter-minals are shared and voltage is common across the shared terter-minals. Parallel cir-cuits share voltage and divide current.

When two devices (resistors, for example) are connected in parallel, the formula is as follows:

Rt = R1 x R2 R1 + R2

In schematic form, it looks like this:

Assuming that we have a 4 Ohm and an 8 Ohm resistance (similar to common speakers resistance): Rt = R1 x R2 R1 + R2 Rt = 4 x 8 4 + 8 Rt = 32 12 Rt = 2.67 Ohms Margin Notes

+

-Resistor #1 Resistor #2 Rt = R1 X R2 R1 + R2 R2 R1

✍

A parallel connection exists when circuit elements are connected so that two terminals are shared and voltage is common across the shared terminals.

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Schematically, a parallel circuit with more than two resistances looks like this:

If more than two resistances are wired in parallel circuit and need to be figured into the total resistance, use the following formula:

1 R =

1 1 1

+ … 1

R1 R2 R3 RN

This formula can look complicated, but is easily accomplished with a calculator. Let’s say we are trying to solve a parallel circuit with three resistors: a 4 ohm, a 6 ohm, and an 8 ohm. Using the calculator’s 1/X function we can solve the equation in this manner.

(4) (1/X) + (6) (1/X) + (8) (1/X) = (1/X) = Answer

(The 1/X function takes 1 and divides it by the value of the resistor or answer. Your cal-culator might use the X-1 function instead, it does the same thing as 1/X.)

To figure the parallel resistance of two speakers when both are the same imped-ance, simply divide one of the speaker’s resistances by two.

■ Remember, when devices are wired in parallel, the total resistance is always less than the resistance of the component with the smallest value. Always keep this in mind: The wiring of automobile, audio, cellular, and security systems are in parallel with the car’s battery, and they are powered by the battery.

■ Current flows through the system from the positive battery terminal to the power input of the system, through the system, through the body of the car, then it goes back to the negative terminal of the battery.

■ Each of these systems also has a power switch that is wired in series ulti-mately from the battery’s positive source to the equipment.

Margin Notes

✍

Remember, when devices are wired in parallel, the total resistance is always less than the resistance of the compo-nent with the smallest value.

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Series and Parallel Capacitors (to clarify the one exception to the rule)

■ Series Inductors and Resistors use the above formula for SERIES WIRING. The same SERIES FORMULA applies to PARALLEL CAPACITORS. ■ Parallel Inductors and Resistors use the above formula for PARALLEL WIRING. The same PARALLEL FORMULA applies to SERIES CAPACITORS.

KIRCHOFF’S VOLTAGE LAW

We’ve seen from some of the previous examples that single resistor circuit analy-sis can be figured out by using Ohm’s Law. More complicated circuit analyanaly-sis, however, requires an understanding of another important electrical law -Kirchoff’s Voltage Law (KVL).

Kirchoff’s Voltage Law (KVL) states that the voltage applied to a DC series

cir-cuit must equal the sum of the voltage drops within the circir-cuit.

Vt = VR1+ VR2+ VR3...( + Vn)

Where: Vt is the applied voltage, VR1is the voltage drop across resistor #1, VR2is the voltage

drop across resistor #2, etc. and Vn is the remaining voltage after all of the measured drops. In other words, if you add up all the voltage drops across each individual com-ponent, the total equals the applied voltage.

■ This means that one volt dropped through wiring or connectors in a sys-tem will reduce the voltage to the equipment by one volt.

This is especially true in practical applications, for example in multiple speaker or subwoofer (single and dual voice coil) installations.

■ Each speaker wired down the line to the same power cable would get a little less power to it than the one before it.

■ Often overlooked, even in the simplest of installations, is that one bad connection or poorly crimped terminal can affect the voltage for that series section, but not for the whole system. That could explain all kinds of other-wise mysterious speaker behavior.

KIRCHOFF’S CURRENT LAW

Kirchoff’s Voltage Law will help you determine single loop circuits; however, solv-ing parallel circuits which have multiple loops requires the use of Kirchoff’s Current Law (KCL):

Margin Notes

✍

Kirchoff’s Voltage Law (KVL) states that the voltage applied to a DC series circuit must equal the sum of the voltage drops within the circuit.

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■ This law states that the total current entering a point or junction in a cir-cuit must equal the sum of the currents leaving that point or junction.

It = IR1+ IR2+ IR3...( + In)

Where: It is the total current, IR1is the sum of current #1, IR2is the sum of current #2,

etc. and In is the remaining current after all of the other measured currents.

Think of your power and ground connections as one big loop from and to the battery. ■ A heavy gauge ground wire is just as important, if not more so, as the power wire gauge.

■ Too small a gauge ground wire will develop a voltage drop which

may also cause the amplifiers to overheat, motorboat, or fail.

CURRENT FLOW

In the front part of this section, we covered many of the basic and advanced elec-trical laws you will need to know. Before we continue on to elecelec-trical components, we need to clarify current flow.

There are two schools of thought on which direction current flows:

1 Conventional current flow - current flows from positive to negative

in the direction voltage drops across a resistor.

2 Electron flow current flows in the direction that electrons flow

-from negative to positive.

Which theory is correct? Even the “experts” disagree:

■ Scientists generally analyze circuits with the scientifically accurate, but harder to understand “electron flow” theory, which states that electrons

trav-Margin Notes

✍

Kirchoff’s Current Law states that the total current entering a point or junction in a circuit must equal the sum of the currents leaving that point or junction.

✍

According to convention-al current flow, current flows from positive to negative in the direction voltage drops across a resistor.

✍

According to electron flow, current flows in the direction that electrons flow from negative to positive.

Conventional

Current Flow

Electron Flow

Current + -+ -Resistive Load Battery Current + -+ -Resistive Load Battery

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■ Engineers analyze circuits with “conventional current flow” theory, where current flows from higher voltage potential to lower voltage potential. Either method - when properly applied - will result in the same answer when ana-lyzing a circuit.

Section 2

Electrical Components

With those formulas in mind, let’s look at some of the electrical components you’ll be using to improve system design and performance.

RESISTORS

For installers, the actual definition of a resistor is not as important as the concept behind resistance. For test purposes, however, a resistor is defined as an electri-cal component designed to have a specific resistance (or opposition) to the flow of electrons, measured in ohms.

The concept of resistance was introduced in Section 1. It describes the property that some materials posses to restrict the flow of current.

■ Resistance is generally an undesirable characteristic in mobile electronics wiring.

■ _{There are instances where an installer will use a resistor to introduce a} specific resistance.

■ Resistance can be added to a signal cable to reduce the input signal

voltage to an amplifier.

■ Power resistors can be used to reduce the amount of power to a

speaker (essentially changing the speakers sensitivity) to connect left and right amplifier outputs into one speaker (center channel, rear mono speakers), or to change the ohm load that a passive crossover sees. Resistors come in all values and power ratings:

■ The most common values are between .1 and 10 million Ohms, with power ratings of 1/8, 1/4, & 1/2 Watts for signal work, or 5, 10, 25 and up to 1,000 Watts and higher for power work.

■ A resistor’s wattage rating indicates how much electrical energy can

be safely converted to heat.

CAUTION: All resistors can produce heat, and you want be sure that this heat does not create a fire hazard.

Margin Notes

✍

A resistor is an electrical component designed to have a specific resistance (or opposition) to the flow of electrons, measured in ohms.

MECP Basic Study Guide

CONTRIBUTORS

TABLE OF CONTENTS

INTRODUCTION

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Installer Level

Specialist Level

CHAPTER 1

BASIC AND ADVANCED ELECTRICAL

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Conventional

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