Chapter 8Power Supplies

MELJUN CORTESMELJUN CORTES

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OverviewIn this chapter, you will learn to

Explain the basics of electricityDescribe the details about powering the PCInstall, maintain, and troubleshoot power

supplies

Understanding Electricity

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Measuring ElectricityVoltage—pressure of electrons in a wire

Unit of measurement: Volts (V)Current— flow (or amount) of electrons in a wire

Unit of measurement: Ampere (A)When voltage is applied to a wire, electrons flow,

producing current

Wattage—measure of power consumed or needed Unit of measurement: Watt (W) W = V * A

Resistance—impedance or opposition to the flowUnit of measurement: Ohm (Ω)

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Measuring ElectricityWire has amperage rating

Defines how much amperage it can handle i.e., 20 amp, 30 amp

If you exceed amperage Wires heat up—may break

Circuit breakers are heat sensitiveSense when amperage exceeds thresholdBreaks the circuit to stop the flow of

electricity

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Two Types of CurrentAlternating Current (AC)—electrical

current flows in both directionsElectricity provided at wall socketFrequency of alternations measured in

cycles per second, or hertz (Hz)

Direct Current (DC)—electrical current flows in one directionElectricity provided by batteries

Powering the PCCompTIA A+Essentials

Essentials

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Types of PowerPCs use DC voltage

Power companies supply AC voltage

The power supply in a computer converts high-voltage AC to low-voltage DC

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Supplying ACIn the U.S., 115 VAC is standardOther countries use 230 VAC

Many PCs may have a small switch on the back to choose 115 or 230 V (used in other countries)

Pay attention to this switch, especially when traveling overseas

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Outlet VoltagesHot and neutral provide

path for ACHot has 115 V

Neutral carries no voltage

Ground used for safetyReturns excess electricity

to ground Wall outlet

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Multimeter BasicsA multimeter (or Volt-

Ohm meter: VOM) measures:VoltageResistanceContinuity

WarningSet it properly before

measuringIf not, damage can occur

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Testing AC VoltageVerifies wiring of outlet

Hot should be 115 VAC

Neutral completes the circuit

Ground should go to ground

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Surge Suppressors Surge suppressors provide protection against power

surges Insert between the power supply and the outlet Joule is a unit of electrical energy

Surge suppressor rated by joulesHigher joules = better protection

Some protect more than AC surgesPhone lines for traditional modemsCable connections for cable modems

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Uninterruptible Power Supply

An uninterruptible power supply (UPS) provides protection against a power dip or power outage

Contains a battery that provides continuous AC power

Provides surge protection and power conditioning Constantly charges battery

All UPSs measured in watts and volts-amps

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Supplying DCThe power supply acts as a step-down

transformer Converting AC into 5, 12, and 3.3 V DC

PCs use a 12 V current to power motors on devices such as hard drives and CD-ROM drives

PCs use a 5-volt/3.3-volt current to support onboard electronics

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Power ConnectorsMotherboard

20- or 24-pin P14-, 6-, 8-pin

PeripheralsMolex

Mini

SATA

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Power ConnectorsConnectors are keyed

Can plug in only one way

Splitters and adapters

Can create two power connectors from one

Can convert Molex to SATA

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Soft PowerATX power supplies first to use

P1 power connector

Always on when plugged in5 V supplied to motherboard when plugged

in

Configured in CMOS

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Power Supply VersionsATX 12 V 1.3

First widespread update to ATX PS

EPS 12 VIntroduced for server motherboards

ATX 12 V 2.0Overcame problem overloading 12 V railProvides multiple 12 V rails

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P4 ConnectorMany motherboards require a

second, four-wire connector Provides more 12 V power Can be MolexCan be PCI-E

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IT TechnicianCompTIA A+Technician

Niche MarketPower Supply Form Factors

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Form FactorsNiche market power supply form factors

TFX12V, SFX12V, CFX12V, LFX12V

Active PFCPower Factor CorrectionCommon in quality power suppliesEliminates harmonics

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Wattage RequirementsEvery device requires some wattage

Often starting requirements are higher than running requirements

Power supplies don’t run at 100% efficiencyATX 12 V requires power supplies to be at

least 70% efficient

General recommendationUse at least a 400 W power supplyEnough extra for starting and future growth

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Installing, Maintaining, and Troubleshooting Power Supplies

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InstallingRemoving

Disconnect wiresRemove 4 standard screwsRemove PS

To install Place PS in caseReplace screwsConnect wires

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ATX Soft Power and CMOS

An ATX power supply never turns offContinues to supply 5V to the

motherboard as long as it is connected to the power outlet

Always unplug an ATX power supply before working on it

Some ATX power supplies provide a real on/off switch on the back

Can use a screwdriver or car keys to short the two power jumpers to turn the system on or off in special circumstances

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Cooling The power supply fan provides basic cooling

for the PC

Fan keeps the voltage regulators cool and provides a constant flow of cool air through the computer

If power supply fan stops, replace power supply

Many fans have sensors to detect when they should run quicker

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Cooling Case fan provides extra cooling for PC

Most modern computers have case fans

Often plug into Molex connector

Connector adapters can be used

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Maintaining Airflow Keep case closed

Keep covers on case

If an expansion card is removed from the PC, be sure to cover the hole with a slot cover

Without proper airflow, the CPU can overheat and destroy itself

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Reducing Fan NoiseSome fans can be adjusted

Manually adjustable with knobSoftware adjustable by sensing heat

Larger fans that spin slower are quieter

Higher-end fans are quieterUse better bearings

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CMOS Fan OptionsCan monitor PC’s health by showing

temperaturesDoesn’t control fansCan set fan thresholds for alarms

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Freeware ToolSpeedfan

Allows monitoring of fan speeds

Can set fan speeds

Hundreds of chipsetssupported

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When Power Supplies DiePower supplies fail in two ways:

Sudden deathWhen the fan doesn’t turn and no voltage is presentComputer simply stops working

Slowly over time Intermittent errorsOutput voltages may exceed specs (± 10%)

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Power Supply TestPut the black lead onto

any black wire connection

Put the red lead onto colored wire

• 12 V ± 10%– 10.8 to 13.2 V– If readings are outside

tolerance and symptoms exist, replace power supply

• 5V ± 10%– 4.5 to 5.5 V

• 3.3 V ± 10%– 2.97 to 3.63 V

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Power Supply TestPower supplies need a load

Plug into motherboardPlug into tester

Check power switchesIf faulty, can turn on

with motherboard jumper

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When Power Supplies Die Slowly

Intermittent problemsSometimes occur, sometimes don’tYou could measure voltage now and it’s good;

10 minutes later, system crashes

A dying power supply can causeRandom lockups and rebootsSporadic boot-up difficulties

When you encounter intermittent symptoms, consider replacing the power supply

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Fuses and FireCircuit breakers are heat-sensitive

Sense when amperage exceeds thresholdBreaks the circuit to stop flow of electricity

Fuses blow for a reasonPower supply is malfunctioningAs a designed safety precaution, fuses

blow (break) to stop circuit

Alternative is a possible fire

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Fire ExtinguishersClass A

Ordinary combustibles such as paper and wood

Class BFlammable liquids such as gasoline

Class CLive electrical equipment

Use only Class C extinguishers on electrical fires

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Beyond A+ It glows

Fancy colors, light up, and have extra fans

Module power suppliesReduced cables

Rail powerLook for power supplies that

offer 16 to 18 A per 12 V rail

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