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Replacing or Upgrading a Power Supply
151
Disassembly
and Power
4
Replacing or Upgrading a Power Supply
Power supplies are rated in watts. Today’s typical computers have power supplies with rat-
ings ranging from 250 to 500 watts, although powerful computers, such as network servers or
higher-end gaming systems, can have power supplies rated 600 watts or higher. Each device
inside a computer uses a certain amount of power, and
the power supply must provide enough to run all the
devices. The power each device or adapter requires is
usually defined in the documentation for the device
or adapter or on the manufacturer’s website. The
computer uses the wattage needed, not the total
capacity of a power supply. The efficiency (more AC is
converted to DC) is what changes the electricity bill.
Some power supplies are listed as being dual
or triple (or tri) rail. A dual-rail power supply
has two +12V output lines. A triple-rail power supply simply has three +12V output lines for
devices. Keep in mind that most manufacturers do not have two or more independent 12V
sources; they all derive from the same 12V source but have independent output lines. Figure
4.30 shows how the +12V rails might be used.
Look on top of the power supply for the various voltage levels and
maximum current output in amps.
+12V
CPU
Dual
rail
+12 volts
Triple
rail
+12 volts
Drive motors
and video card
CPU
Video card
Drive motors
Figure 4.30 12V rails
Power supplies can be auto-switching or have a fixed input. An auto-switching power
supply monitors the incoming voltage from the wall outlet and automatically switches itself
accordingly. Auto-switching power supplies accept voltages from 100 to 240VAC at 50 to 60Hz.
These power supplies are popular in mobile devices and are great for international travel.
A power supply might also allow adjusting the input value by manually selecting the value
through a voltage selector switch on the power supply. A fixed-input power supply is rated for a
specific voltage and frequency for a country, such as 120VAC 60Hz for the United States.
Some people are interested in exactly how much power their system is consuming.
Every device in a computer consumes power, and each device could use one or more
different voltage levels (+5V, –5V, +12V, –12V, +3.3V). A power supply has a maximum
amperage for each voltage level (for example, 30 amps at +5 volts and 41 amps at +12V).
To determine the maximum power being used, in watts, multiply the amps and volts. If
you add all the maximum power levels, the amount will be greater than the power supply’s
rating. This means that you cannot use the maximum power at every single voltage level
(but since the –5V and –12V are not used very often, normally this is not a problem).
In order to determine the power being consumed, you must research every device to
determine how much current it uses at a specific voltage level. Internet power calculators
are available to help with this task. Table 4.6 lists sample computer components’ power
requirements.
Watch the wattage
Many manufacturers overstate the wattage. The
wattage advertised is not the wattage available at
higher temperatures, such as when mounted inside
a computer. Research a model before purchasing.
Tech
Tip
- Guide to PCs 2
- Complete CompTIA 3
- Contents at a Glance 4
- Contents 10
- Contents 11
- About the Author 19
- Dedication 20
- Acknowledgments 20
- We Want to Hear from You! 21
- Reader Services 21
- It Pays to Get Certified 22
- CompTIA Career Pathway 23
- Steps to Certication 23
- Content Seal of Quality 24
- Why CompTIA? 24
- Introduction 25
- Organization of the Text 26
- Features of This Book 27
- IT work 31
- CompTIA A+ Exam Objectives 32
- CompTIA Exam Objectives 33
- Disassembly 36
- Disassembly Overview 37
- Electrostatic Discharge (ESD) 37
- Opening the Case 41
- Cables and Connectors 41
- Snug connections 43
- Storage Devices 45
- Motherboards 46
- Mobile Device Issues 47
- Reassembly 49
- Preventive Maintenance 49
- Basic Electronics Overview 51
- Electronics Terms 51
- Good connection Broken wire 53
- Power Supply Overview 54
- Power Supply Form Factors 55
- Tech Tip 56
- Purposes of a Power Supply 58
- Power Supply Voltages 60
- Mobile Device Power 61
- Keep Li-ion batteries cool 63
- Power Interface) 64
- Windows power management 65
- Watch the wattage 68
- Solving Power Supply Problems 70
- Adverse Power Conditions 71
- Adverse Power Protection 72
- Surge Protectors 72
- Line Conditioners 74
- Figure 4.32 Line conditioner 75
- Figure 4.33 Sine wave and 75
- Standby Power Supply (SPS) 77
- Electrical Fires 78
- Computer Disposal/Recycling 79
- Chapter Summary 81
- Review Questions 82
- Exercises 85
- External Cables 86
- Computer Case Removal 86
- Adapter Placement 86
- Motherboard 88
- Lab 4.3 Amps and Wattage 89
- Lab 4.4 Continuity Check 89
- Lab 4.5 Pin-Out Diagramming 90
- Lab 4.6 Fuse Check 91
- Lab 4.7 Using a Multimeter 91
- Figure 4.38 AC outlet 93
- GND to hot 120VAC 93
- GND to neutral 0VAC 93
- Hot to neutral 120VAC 93
- +5 volts 95
- +12 volts 95
- Activities 97
- Critical Thinking Skills 99
- A+ Certification Exam Tips 99
- Complete PC Restore tool 107
- FireWire 114
- IRQs (Interrupt Requests) 120
- PBs (petabytes) 129
- Setup program 136
- SSDs (solid state drives) 138
- SSDs (solid state drives) 139
- TBs (terabytes) 140
- troubleshooting 143
- video 145
- Windows 147
- Windows Vista 148
- Windows Vista 149
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