# Chapter 4 Electricity and Power Supplies. You Will Learn…  How electricity is measured  How to protect your computer system against damaging changes.

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Chapter 4 Electricity and Power Supplies

You Will Learn…  How electricity is measured  How to protect your computer system against damaging changes in electrical power  About different form factors and computer cases  How to detect and correct power supply problems  About Energy Star specifications

Electricity: Basic Introduction

Measures of Electricity continued… Page 121

Measures of Electricity

Voltage  Measures potential differences  Electrical force created by the potential difference in electron charge flowing between 2 points  Measured in units called volts  Negative to positive flow  Measures when power is on Voltmeter: Page 122

Voltage

Amps  Ampere = unit of measurement for electrical current  Amps remain constant throughout electrical system  Current: volumn of electrons flowing through an electrical system Ammeter

Relationship Between Voltage and Current  Direct relationship As the electrical potential difference (voltage) increases, the electrical current increases As the voltage decreases, the current decreases

Ohms  Standard unit of measurement for electrical resistance  Resistors are devices used in electrical circuits to resist the flow of electricity  As resistance decreases, electricity increases Paragraph Page 124

Relationship Among Voltage, Current, and Resistance  Voltage and current have a direct relationship When voltage increases, current increases  Resistance has an inverse relationship with voltage and current As resistance increases, either current or voltage decreases As resistance decreases, either current or voltage increases (Ohm’s Law) V=I/R or Volts = Amps/Ohms  One volt drives a current of one amp through a resistance of one ohm

Wattage  Total amount of power needed to operate an electrical device  Measured in watts  Calculated by multiplying volts by amps in a system (W = V x A)

AC and DC  AC (alternating current) Means of sending power over extended distances Cycles back and forth rather than traveling in only one direction Most economical way to transmit electricity  DC (direct current) Travels in only one direction Type of current required by most electronic devices, including computers Computer power supplies function as both a transformer and a rectifier Device that changes ratio of current to voltage (reduces voltage to a usable level) Device that converts AC to DC

Computer Power Supply Hertz (Hz):

Power Supply Function Rectifier Chapter questions 2-6

Hot, Neutral, and Ground

 Hot: inbound current  Neutral: outbound current  Ground: protection for neutral line against short circuits  Short circuit Occurs when electricity is allowed to flow uncontrolled from hot line to neutral line or from hot line to the ground  Fuse Designed to prevent too much current from flowing through the circuit Rated in amps Paragraph 127

Hot, Neutral, and Ground 128

Hot, Neutral, and Ground Receptacle tester

Materials Used to Make Electronic Components  Conductors: easily conducts electricity (gold or copper)  Insulators: resists flow of electricity (glass or ceramic)  Semiconductors: falls between conductors & insulators—ability to conduct electricity when charge is applied (silicon) 129

Some Common Electronic Components Device serves as a gate or switch for electrical signal & can amplify the flow Device that can hold electrical charge for period of time & smooth the uneven flow through a circuit 130

Protecting Your Computer System  General safety precautions  Protecting against electricity  Protecting against electrostatic discharge (ESD or static electricity) and electromagnetic interference (EMI)  Surge protection and battery backup

Protecting Against Electricity  When working inside a computer Turn off the power Unplug the computer Use a ground bracelet 131

Static Electricity  Ground yourself and computer parts, using static control devices or methods Ground bracelet or static strap Ground mats Static shielding bags  Caution: Don’t wear a ground bracelet when working inside a monitor or with high-voltage equipment such as a laser printer

Using a Ground Bracelet

Using a Ground Bracelet and a Ground Mat

Using Static Shielding Bags

Electromagnetic Interference  Caused by the magnetic field produced as a side effect when electricity flows  Radio frequency interference (RFI) can cause problems with radio and TV reception  Use a line conditioner to filter electrical noise causing the EMI 135

Surge Protection and Battery Backup  Devices that filter AC input Surge suppressors (or surge protectors): protect against sudden changes in power level Power conditioners Uninterruptible power supply (UPS) Also provides backup power Tips on 136 Alters power to provide continuous voltage

Uninterruptible Power Supply  Benefits Condition line for brownouts and spikes Provide backup power during a blackout Protect against very high spikes that could damage equipment Spikes: temporary voltage surges Brownouts: temporary voltage reductions

Uninterruptible Power Supply

What to Consider When Buying a UPS  Cost  Rating should exceed your total VA or wattage output by at least 25%  Degree of line conditioning  Warranty, service policies, and guarantee

UPS Manufacturers 138

Computer Case and Form Factors  Form factor Describes the size, shape, and general makeup of a hardware component Must match for motherboard, power supply, and case

Case, Power Supply, and Motherboard Form Factors  AT  ATX (most popular)  LPX  NLX  Backplane systems  Most common form factors used on PCs: AT Baby AT ATX Mini-ATX

AT Form Factor

ATX Form Factor

NLX Form Factor

Types of Cases  Desktop cases  Tower cases Minitower Midsize (most popular) Full-size  Laptop cases

Desktop Cases

Minitower Cases

Tower and Desktop Cases

Case and Power Supply Vendors

Detecting and Correcting Power Supply Problems  Measuring the voltage of a power supply  Upgrading and installing power supplies  Troubleshooting the power system and power supply

Measuring the Voltage of a Power Supply  Use a multimeter Before using, tell it three things Whether to measure voltage, current, or resistance Whether the current is AC or DC What range of values it should expect How to measure voltage How to measure current How to measure continuity

A Multimeter

How to Measure the Voltage of a Power Supply  How to measure the power output for AT and ATX motherboards  Procedure for a secondary storage device

Measuring Voltage on an AT Motherboard

Measuring Voltage Output to an AT Motherboard

Measuring Voltage Output to an ATX Motherboard

Upgrading Your Power Supply  Sometimes necessary when you add new devices  Easiest way to fix a power supply you suspect is faulty is to replace it

Introduction to Troubleshooting  Categories of problems Problems that prevent the PC from booting Problems that occur after a successful boot  Learn as much as you can by asking questions of the user

Problem-Solving Flow Chart

Troubleshooting the Power System: Guidelines and Questions  Any burnt parts or odors?  Everything connected and turned on? Loose cable connections? Computer plugged in?  All switches turned on? Computer? Monitor? Surge protector? UPS? Separate circuit breaker? Wall outlet good?  If fan is not running, turn off computer: Connections to power supply secure? Cards securely seated?

Troubleshooting the Power System

 Troubleshooting the power supply itself  Troubleshooting the power supply fan  Power problems with the motherboard  Overheating

Energy Star Systems (The Green Star)  Satisfy energy-conserving standards of the U.S. EPA  Generally have a standby program that switches the device to sleep mode when it is not in use  Apply to computers, monitors, printers, copiers, and fax machines

Power Management Methods  Advanced Power Management (APM)  AT Attachment (ATA) for IDE drives  Display Power Management Signaling (DPMS) standards for monitors and video cards  Advanced Configuration and Power Interface (ACPI)

Power Management Features  Green timer on motherboard  Doze time  Standby time  Suspend time  Hard drive standby time

Power Management Features

Energy Star Monitors  Most adhere to DPMS specifications which allow for the video card and monitor to go into sleep mode simultaneously  View and change energy settings in Desktop Properties window (Windows 2000)

Changing Power Options in Windows 2000

Chapter Summary  How to measure electricity  The power supply and backup power sources  How to measure power supply output  How to change a defective power supply  Introduction to form factors  How Energy Star devices save energy

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