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…

Measures of Electricity

Voltage

Electrical force created by the potential difference in charge

Measured in units called volts

Voltage

Amps

Ampere = unit of measurement for electrical current

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

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)

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)• 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

Computer Power Supply

Hot, Neutral, and Ground

Hot, Neutral, and Ground

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

Hot, Neutral, and Ground

Hot, Neutral, and Ground

Some Common Electronic Components

Materials Used to Make Electronic Components

Conductors Insulators Semiconductors

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

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

Surge Protection andBattery Backup

Devices that filter AC input• Surge suppressors (or surge protectors)

• Power conditioners

• Uninterruptible power supply (UPS)• Also provides backup power

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

Uninterruptible Power Supply

What to Consider WhenBuying 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

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 AT Motherboard

Measuring Voltage Output to an ATX 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 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