Power Supply Overview

Power Supply Overview

When expanding or upgrading your PC, ensure that your power supply is capable of providing sufficient current to power all the system’s internal devices. One way to see whether your system is capable of expansion is to calculate the levels of power consumption by the various system components in your system, and then compare that to the rating on the power supply to see if it is up to the job. This calculation can also help you decide whether you must upgrade the power supply to a more capable unit. Unfortunately, these calculations can be difficult to make accurately because many manufacturers do not publish detailed power consumption data for their products. In some cases, you can find the specs from a similar component and go by that data instead. Usually components of the same basic design, capability, and vintage have relatively the same power consumption characteristics. The following table shows the range of power usage for typical PC components I’ve observed over the past few years.

Power Consumption Calculation

Component 

Power Usage Comments

Motherboard 50 W–75 W Depends on the number of integrated components.

Processor 25 W–150 W For each physical processor (not cores). Most are 50 W–100 W.

RAM 5 W–15 W For each module (DIMM).

Integrated video 5 W–15 W Integrated into the North Bridge chip (Ed.: Though, increasingly on the CPU).

Discrete video card 25 W–300 W For each video card.

PCI card

5 W–15 W For each nonvideo card.

PCIe card 10 W–25 W For each nonvideo card.

Hard disk drive 15 W–30 W For each drive. Power use increased during startup.

Optical drive

15 W–35 W For each drive.

Cooling fan 3 W–5 W For each fan.

USB/FireWire 2 W–5 W For each used port.

Of course, power consumption can vary greatly for different devices such as processors and video cards, so if you want to be more informed, consult the data sheets or technical manuals for your specific components. Also, these overall wattage figures do not give the breakdown covering which of the rails (+3.3 V, +5 V, or +12 V) each device will use. In some cases, the combination of components used can exceed the available power on a single rail while still being under budget for the total wattage available from all the rails combined. That is in fact one reason that people end up purchasing a power supply with a much higher watt rating than might seem necessary.

After you’ve added up everything I recommend, multiply the total power consumed by all your components by 1.5 to estimate the size of power supply required. This allows some headroom for future expansion and accounts for the fact that at certain times some devices can draw much more than their nominal power.

If you want an easier way to calculate your estimated power requirements, Asus has a fairly good power supply wattage calculator that you can use online at the following URL: http://support.asus.com/PowerSupplyCalculator/PSCalculator.aspx. After you fill in all the fields with the components in the intended system, the calculator gives you an estimate of the minimum power supply rating you should choose to power the system.

Different types of bus slots can provide different levels of power for cards. Fortunately, it is rare for any cards other than video cards to use the maximum allowable power. The table below shows the maximum power available per slot for different bus types.

Maximum Available Power per Bus Slot

Bus Type +3.3 V Current (Amps) +5 V Current (Amps) +12 V Current (Amps) Total Power (Watts)

ISA N/A 2.0 0.175 12.1

EISA N/A 4,5 1.5,40.5

VL-bus N/A 2.0,N/A 10,16-bit MCA N/A 1.6, 0.175, 10.1

32-bit MCA N/A 2.0, 0.175, 12.1,PCI, 7.6 5,0.5, 56,AGP 6 2 1 42

PCI Express 4.8 N/A 4.8 75

The biggest cause of power supply overload problems has historically been filling up the expansion slots (especially with multiple video cards), using high-powered processors, and adding more drives. Multiple hard drives, optical drives, and floppy drives can create quite a drain on the system power supply. Be sure you have enough +12 V power to run all the drives you plan to install. Tower systems can be especially problematic because they have so many drive bays. Just because the case has room for the devices doesn’t mean the power supply can support them. Be sure you have enough power to run all your expansion cards, especially video cards. However, remember that most cards draw less than the maximum allowed. Today’s newest processors can have high current requirements for the +5 V or +3.3 V supplies. When you’re selecting a power supply for your system, it pays to be conservative, so be sure to take into account future upgrades or additions to the system.

Many people wait until an existing component fails to replace it with an upgraded version. If you are on a tight budget, this “if it ain’t broke, don’t fix it” attitude might be necessary. Power supplies, however, often do not fail completely all at once; they can fail in an intermittent fashion or allow fluctuating power levels to reach the system, which results in unstable operation. You might be blaming system lockups on software bugs when the culprit is an overloaded power supply. In addition, an inadequate or failing supply causing lockups can result in file system corruption, which causes even further system instabilities (which could remain even after you replace the power supply). If you use bus-powered USB devices, a failing power supply can also cause these devices to fail or malfunction. If you have been running your original power supply for a long time and have upgraded your system in other ways, you should expect some problems, and you might want to consider reloading the OS and applications fro

m scratch.

Although there is certainly an appropriate place for the exacting power-consumption calculations you’ve read about in this section, a great many experienced PC users prefer the “don’t worry about it” power calculation method. This technique consists of buying or building a system with a good-quality 500-watt or higher power supply (or upgrading to such a supply in an existing system) and then upgrading the system freely, without concern for power consumption.

Over the past few years, energy conservation has become a major focus for appliances, electronics, and especially for computers. Saving power can be accomplished through several means. One is to use more efficient components that simply use (or waste) less energy to do the job. The other is to properly manage the computer hardware so that components that are not being used are powered down or put into standby modes. By using more efficient components and turning off specific components of the PC when they are not in use, you can reduce the electric bill and avoid having to power the computer up and down manually. This not only saves energy, but it makes the system more convenient to use. The following sections discuss both of these approaches to saving power.

80 PLUS

When it comes to computers, one of the major factors in overall energy consumption is the efficiency of the power supply unit. In 2004, the Northwest Energy Efficiency Alliance (NEEA) funded the 80 PLUS Program to encourage computer manufacturers to improve the energy efficiency of their machines by installing highly efficient power supplies. Ecos Consulting, who manages the program, tests and certifies power supplies as being 80% (or higher) in efficiency. To help offset the cost of producing more efficient designs, the program also pays incentives to manufacturers producing PSUs and systems that are certified.

Systems with more efficient power supplies consume on average from 15% to 30% less power than conventional designs. This can result in a significant energy and cost savings over the life of a system. In addition, the resulting lower heat output both improves system reliability and saves additional energy in cooling the system as well as the surrounding environment.

The 80 PLUS program currently has five levels of certification, from 80 PLUS to 80 PLUS Platinum. Each level of certification signifies different minimum levels of efficiency, which are measured at three different loads (20%, 50%, and 100%). The following table shows the details of each of the certification levels.

80 PLUS Certification Levels

80 PLUS Rating Efficiency at 20% Rated Load Efficiency at 50% Rated Load Efficiency at 100% Rated Load

80 PLUS 80% 80% 80%

80 PLUS Bronze

82% 85%

82%

80 PLUS Silver 85%

88%

85%

80 PLUS Gold 87%/90%

87%

80 PLUS Platinum 90%,92%

89%

How is this efficiency determined, and what is the overall effect? The PSU in a PC converts the high voltage (120 V in the USA) AC wall current to 12 V and lower DC voltages for use in the PC. Unfortunately, no PSU is 100% efficient, meaning that some of the power is lost or used up during the conversion and ends up being dissipated as heat. Conventional PSUs are or were normally about 70% efficient, which means that 30% of the energy drawn from the wall socket is wasted and ends up as heat. As an example, let’s take a system that draws 250 watts total. The table below shows the resulting AC power draw and the amount of wasted energy if the PSU were 70%, 80%, or 90% efficient. 

The Effect of PSU Efficiency on AC Power Draw and Wasted Energy

Efficiency

70%

80%

90%

PSU Classification 

Conventional

80 PLUS 80 PLUS Gold

DC Power Draw (W) 250

250

250

AC Power Draw (W)

357

313

278

Wasted Energy (W) 107

63

28

As you can see, when supplying the same 250 watts of power to the system, the actual amount of power used, and consequently the amount of energy wasted, varies considerably. A more efficient PSU can save a tremendous amount of energy and money over the life of a system. Because of this, I highly recommend 80 PLUS certified power supplies, especially those earning the higher efficiency ratings.

Energy Star

Energy Star is an international standard for energy-efficient consumer products, including computers and power supplies. The U.S. Environmental Protection Agency (EPA) introduced Energy Star as a voluntary labeling program designed to identify and promote energy-efficient products. The first products labeled in the program were computers and monitors. In the years since, Energy Star has become an international standard, and the label can be found on new homes, commercial and industrial buildings, appliances, office equipment, lighting, electronics, and more. Devices carrying the Energy Star logo generally use 20%–30% less energy than required by federal standards. In addition to Energy Star, many European-targeted products are labeled with TCO Certification, a combined energy usage and ergonomics rating from the Swedish Confederation of Professional Employees (TCO).

Starting in 2007, the Energy Star computer 4.0 specification required the use of a power supply that meets the 80 PLUS standard. In 2009 the 5.0 specification was released and now requires a power supply meeting the 80 Plus Bronze standard, for a minimum of 85% efficiency (at a 50% load).

Advanced Power Management

Advanced Power Management (APM) is a specification jointly developed by Intel and Microsoft that defines a series of interfaces between power management–capable hardware and a computer’s OS. When it is fully activated, APM can automatically switch a computer between five states, depending on the system’s current activity. Each state represents a further reduction in power use, accomplished by placing unused components into a low-power mode. The five system states are as follows:

    Full On—The system is completely operational, with no power management occurring.

    APM Enabled—The system is operational, with some devices being power managed. Unused devices can be powered down and the CPU clock slowed or stopped.

    APM Standby—The system is not operational, with most devices in a low-power state. The CPU clock can be slowed or stopped, but operational parameters are retained in memory. When triggered by a specific user or system activity, the system can return to the APM Enabled state almost instantaneously.

    APM Suspend—The system is not operational, with most devices unpowered. The CPU clock is stopped, and operational parameters are saved to disk for later restoration. When triggered by a wakeup event, the system returns to the APM Enabled state relatively slowly.

    Off—The system is not operational. The power supply is off.

APM requires support from both hardware and software to function. In this chapter, you’ve already seen how ATX-style power supplies can be controlled by software commands using the Power_On signal and the six-pin optional power connector. Manufacturers are also integrating the same type of control features into other system components, such as motherboards, monitors, and disk drives.

OSs that support APM trigger power management events by monitoring the activities performed by the computer user and the applications running on the system. However, the OS does not directly address the power management capabilities of the hardware. All versions of Windows from 3.1 up include APM support.

A system can have many hardware devices and many software functions participating in APM functions, which makes communication difficult. To address this problem, both the OS and the hardware have an abstraction layer that facilitates communication between the various elements of the APM architecture.

The OS runs an APM driver that communicates with the various applications and software functions that trigger power management activities, while the system’s APM-capable hardware devices communicate with the system basic input/output system (BIOS). The APM driver and the BIOS communicate directly, completing the link between the OS and the hardware.

Thus, for APM to function, support for the standard must be built into the system’s individual hardware devices, the system BIOS, and the OS (which includes the APM driver). Without all these components, APM activities can’t occur.

Power Savings: Advanced Configuration And Power interface

As power-management techniques continued to develop, maintaining the complex information states necessary to implement more advanced functions became increasingly difficult for the BIOS. Therefore, another standard was developed by Intel, Microsoft, and Toshiba. Called Advanced Configuration and Power Interface (ACPI), this standard was designed to implement power-management functions in the OS. Microsoft Windows 98 and later automatically use ACPI if ACPI functions are found in the system BIOS. The need to update system BIOSs for ACPI support is one reason many computer vendors have recommended performing a BIOS update before installing Windows 98 or later on older systems.

ACPI was initially released in 1996 and first appeared in the Phoenix BIOS around that time. ACPI became a requirement for the Intel/Microsoft “PC’97” logo certification in 1996, which caused developers to work on integrating ACPI into system designs around that time. Intel included ACPI support in chipsets starting with the PIIX4E South Bridge in April 1998, and ACPI support was included in Windows starting with the release of Windows 98 (June 25, 1998) as part of what Microsoft called its “OnNow” initiative. By the time Windows 2000 came out (February 17, 2000), ACPI had universally replaced APM on new systems. ACPI 4.0a was released in April 2010, and the ACPI 5.0 Specification is currently under development. The official ACPI specifications can be downloaded from www.acpi.info.

Placing power management under the control of the OS enables a greater interaction with applications. For example, a program can indicate to the OS which of its activities are crucial, forcing an immediate activation of the hard drive, and which can be delayed until the next time the drive is activated for some other reason. For example, a word processor may be set to automatically save files in the background, which an OS using ACPI can then delay until the drive is activated for some other reason, resulting in fewer random spin-ups of the drive.

ACPI goes far beyond the previous standard, APM, which consisted mainly of processor, hard disk, and display control. ACPI controls not only power but also all the Plug and Play (PnP) hardware configuration throughout the system. With ACPI, system configuration (PnP) and power-management configuration are no longer controlled via the BIOS Setup; they are instead controlled entirely within the OS.

ACPI enables the system to automatically turn internal peripherals on and off (such as CD-ROM drives, network cards, hard disk drives, and modems) as well as external devices such as printers, monitors, or any devices connected to serial, parallel, USB, video, or other ports in the system. ACPI technology also enables peripherals to turn on or wake up the system. For example, a telephone answering machine application can request that it be able to respond to answer the telephone within 1 second. Not only is this possible, but if the user subsequently presses the power or sleep button, the system only goes into the deepest sleep state that is consistent with the ability to meet the telephone answering application’s request.

ACPI enables system designers to implement a range of power-management features that are compatible with various hardware designs while using the same OS driver. ACPI also uses the Plug and Play BIOS data structures and takes control over the Plug and Play interface, providing an OS–independent interface for configuration and control.

ACPI defines several system states and substates. There are four Global System states, labeled from G0 through G3, with G0 being the fully operational state and G3 being mechanically turned off. Global System states are immediately obvious to the user of the system and apply to the entire system as a whole. Within the G0 state, there are four CPU Power states (C0–C3) and four Device Power states (D0–D3) for each device. Within the C0 CPU Power state, there are up to 16 CPU Performance states (P0–P15).

Device Power states are states for individual devices when the system is in the G0 (Working) state. The device states may or may not be visible to the user. For example, it may be obvious when a hard disk has stopped or when the monitor is off; however, it may not be obvious that a modem or other device has been shut down. The Device Power states are somewhat generic; many devices do not have all four Power states defined.

Within the G1 Global Sleep state are four Sleep states (S1–S4). The G2 Global Soft Off state is also known as the S5 Sleep state, in which case the system is powered off but still has standby power. Finally, G3 is the Mechanical Off state, where all power is disconnected from the system.

The following list shows the definitions and nested relationship of the various Global, CPU/Device Power, and Sleep states:

G0 Working—This is the normal working state in which the system is running and fully operational. Within this state, the Processor and Device Power states apply. The Device Power states are defined as follows:

    G0/D0 Fully-On—The device is fully active.

    G0/D1—Depends on the device; uses less power than D0.

    G0/D2—Depends on the device; uses less power than D1.

    G0/D3 Off—The device is powered off (except for wakeup logic).

The Processor Power states are defined as follows:

    G0/C0 CPU On—Normal processor operation.

    G0/C1 CPU Halted—The processor is halted.

    G0/C2 CPU Stopped—The clock has been stopped.

    G0/C3 CPU/Cache Stopped—The clock has been stopped and cache snoops are ignored.

G1 Sleeping—The system appears to be off but is actually in one of four Sleep states—up to full hibernation. How quickly the system can return to G0 depends on which of the Sleep states the system has selected. In any of these Sleep states, system context and status are saved such that they can be fully restored. The Sleep states available in the Global G1 state are defined as follows:

    G1/S1 Halt—A low-latency idle state. The CPU is halted; however, system context and status are fully retained.

    G1/S2 Halt-Reset—Similar to the S1 sleeping state except that the CPU and cache context is lost, and the CPU is reset upon wakeup.

    G1/S3 Suspend to RAM—All system context is lost except memory. The hardware maintains memory context. The CPU is reset and restores some CPU and L2 context upon wakeup.

    G1/S4 Suspend to Disk (Hibernation)—The system context and status (RAM contents) have been saved to nonvolatile storage—usually the hard disk. This is also known as Hibernation. To return to G0 (Working) state, you must press the power button, and the system will restart, loading the saved context and status from where they were previously saved (normally the hard disk). Returning from G2/S5 to G0 requires a considerable amount of latency (time).

G2/S5 Soft Off—This is the normal power-off state that occurs after you select Shutdown or press the power button to turn the system off. The system and all devices are essentially powered off; however, the system is still plugged in and standby power is coming from the power supply to the motherboard, allowing the system to wake up (power on) if commanded by an external device. No hardware context or status is saved. The system must be fully rebooted to return to the G0 (working) state.

G3 Mechanical Off—Power is completely removed from the system. In most cases this means the system must be unplugged or the power turned off via a power strip. This is the only state in which it is safe to disassemble the system. Except for the CMOS/clock circuitry, power consumption is completely zero.

In normal use, a system alternates between the G0 (Working) and G1 (Sleeping) states. In the G1 (Working) state, individual devices and processors can be power-managed via the Device Power (D1–D3) and Processor Power (C1–C3) states. Any device that is selectively turned off can be quickly powered on in a short amount of time, from virtually instantaneous to only a few seconds (such as a hard disk spinning up).

When the system is idle (no keyboard or mouse input) for a preset period, the system enters the Global G1 (Sleeping) state, which means also selecting one of the S1–S4 sleep states. In these states, the system appears to be off, but all system context and status are saved, enabling the system to return to exactly where it left off, with varying amounts of latency. For example, returning to the G0 (Working) state from the G1/S4 (Hibernation) state requires more time than when returning from the G1/S3 (Suspend) state.

When the user presses the power button to turn the system off or selects Shutdown via the OS, the system enters the G2/S5 (Soft Off) state. In this state, no context is saved, and the system is completely off except for standby power. Fully disconnecting AC or battery power causes the system to be in the Global G3 (Mechanical Off) state, which is the only state in which the system should be disassembled.

During the system setup and boot process, ACPI performs a series of checks and tests to see whether the system hardware and BIOS support ACPI. If support is not detected or is found to be faulty, the system typically reverts to standard Advanced Power Management control, which is referred to as legacy power management under ACPI. Virtually all ACPI problems are the result of partial or incomplete ACPI implementations or incompatibilities in either the BIOS or device drivers. If you encounter any of these errors, contact your motherboard manufacturer for an updated BIOS or the device manufacturers for updated drivers.

Power Cycling

Should you turn off a system when it is not in use? To answer this frequent question, you should understand some facts about electrical components and what makes them fail. Combine this knowledge with information on power consumption, cost, and safety to come to your own conclusion. Because circumstances can vary, the best answer for your own situation might be different from the answer for others, depending on your particular needs and applications.

Frequently powering a system on and off does cause deterioration and damage to the components. This seems logical, but the simple reason is not obvious to most people. Many believe that flipping system power on and off frequently is harmful because it electrically “shocks” the system. The real problem, however, is temperature or thermal shock. As the system warms up, the components expand; as it cools off, the components contract. In addition, various materials in the system have different thermal expansion coefficients, so they expand and contract at different rates. Over time, thermal shock causes deterioration in many areas of a system.

From a pure system-reliability viewpoint, you should insulate the system from thermal shock as much as possible. When a system is turned on, the components go from ambient (room) temperature to as high as 185°F (85°C) within 30 minutes or less. When you turn off the system, the same thing happens in reverse, and the components cool back to ambient temperature in a short period.

Thermal expansion and contraction remains the single largest cause of component failure. Chip cases can split, allowing moisture to enter and contaminate them. Delicate internal wires and contacts can break, and circuit boards can develop stress cracks. Surface-mounted components expand and contract at rates different from the circuit boards on which they are mounted, causing enormous stress at the solder joints. Solder joints can fail due to the metal hardening from the repeated stress, resulting in cracks in the joint. Components that use heatsinks, such as processors, transistors, or voltage regulators, can overheat and fail because the thermal cycling causes heatsink adhesives to deteriorate and break the thermally conductive bond between the device and the heatsink. Thermal cycling also causes socketed devices and connections to loosen, or creep, which can cause a variety of intermittent contact failures.

Thermal expansion and contraction affect not only chips and circuit boards, but also things such as hard disk drives. Most hard drives today have sophisticated thermal compensation routines that make adjustments in head position relative to the expanding and contracting platters. Most drives perform this thermal compensation routine once every five minutes for the first 30 minutes the drive is running and then every 30 minutes thereafter. In older drives, this procedure can be heard as a rapid “tick-tick-tick-tick” sound.

In essence, anything you can do to keep the system at a constant temperature prolongs the life of the system, and the best way to accomplish this is to leave the system either permanently on or permanently off. Of course, if the system is never turned on in the first place, it should last a long time indeed!

Now, I am not saying that you should leave all systems fully powered on 24 hours a day. A system powered on when not necessary can waste a tremendous amount of power. An unattended system that is fully powered on can also be a fire hazard. (I have witnessed at least two CRT monitors spontaneously catch fire—luckily, I was there at the time.)

The biggest problem with keeping systems on 24/7 is the wasted energy. Typical rates are 10 cents for a kilowatt-hour of electricity. Using this figure, combined with information about what a typical PC might consume, we can determine how much it will cost to run the system annually and what effect we can have on the operating cost by judiciously powering off or taking advantage of the various ACPI Sleep modes that are available. ACPI is described in more detail later in this chapter.

A typical desktop-style PC consumes anywhere from 75 W to 300 W when idling and from 150 W to 600 W under a load, depending on the configuration, age, and design of the system. This does not include monitors, which for LCDs range from 25 W to 50 W while active, whereas CRTs range from 75 W to 150 W or more. One PC and LCD display combination I tested consumed an average of 250 W (0.25 kilowatts) of electricity during normal operation. The same system drew 200 W when in ACPI S1 Sleep mode, only 8 W while in ACPI S3 Sleep mode, and 7 W of power while either turned off or hibernating (ACPI S4 mode).

Using those figures, here are some calculations for annual power costs:

Electricity Cost:    $0.10 Dollars per KWh

PC/Display Power:    0.250 KW avg. while running

PC/Display Power:    0.200 KW avg. while in ACPI S1 Sleep

     PC/Display Power:    0.008 KW avg. while in ACPI S3 Sleep

    PC/Display Power:    0.007 KW avg. while in ACPI S4 Sleep

    PC/Display Power:    0.007 KW avg. while OFF

Work Hours:     2080 Per year

Non-Work Hours:     6656 Per year

     Total Hours:     8736 Per year

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Annual Operating Cost:  $218.40 Left ON continuously

Annual Operating Cost:  $185.12 In S1 Sleep during non-work hours

Annual Operating Cost:   $57.32 In S3 Sleep during non-work hours

Annual Operating Cost:   $56.66 In S4 Sleep during non-work hours

Annual Operating Cost:   $56.66 Turned OFF during non-work hours

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       Annual Savings:    $0.00 Left ON continuously

       Annual Savings:   $33.28 In S1 Sleep during non-work hours

   Annual Savings:  $161.08 In S3 Sleep during non-work hours

   Annual Savings:  $161.74 In S4 Sleep during non-work hours

Annual Savings:  $161.74 Turned OFF during non-work hours

This means it would cost more than $218 annually to run the system if it were left on continuously. However, if it were turned off during nonwork hours, the annual operating cost would be reduced to $56, for an annual savings of more than $161! As you can see, turning systems off when they are not in use can amount to a huge savings over time.

But even more interesting is that you don’t have to turn a system all the way off to achieve this type of savings. When properly configured, most PCs will enter ACPI S3 Sleep mode either manually or after a preset period of inactivity, dropping to a power consumption level of 8W or less. In other words, if you configure the PC to enter S3 Sleep mode when it’s not active, you can achieve nearly the same savings as if you were to turn it off completely. In the preceding example, it would only cost an additional $0.66 to keep the system in Stand By mode during nonwork hours versus turned completely off, still resulting in an annual savings of more than $161.

With the improved power management capabilities of modern hardware, combined with the stability and control features built into modern OSs, systems can Sleep and Resume almost instantly, without having to go through the lengthy shutdown and cold boot startup procedures over and over again. I’m frankly surprised at how few people I see taking advantage of this because it offers both cost savings and convenience.

Many people perform a full shutdown procedure when turning off their computer, closing all open applications, shutting down the OS and system completely. Then when powering back on, they do a cold boot and reload the OS, drivers, and applications from scratch.

There is an alternative that is much better. Instead of shutting down completely, put the system to Sleep instead. When in Sleep mode the system saves the full system context (state of the system, contents of RAM, and so on) in RAM before powering off everything but the RAM. Unfortunately, many systems aren’t configured to take advantage of Sleep mode, especially older ones. Note that Sleep was called Standby (or Stand by) in Windows XP and earlier.

The key is in the system configuration, starting with one important setting in the BIOS Setup. The setting is called ACPI suspend mode, and ideally you want it set so that the system will enter what is called the S3 state. S3 is sometimes called STR for Suspend to RAM. That has traditionally been the default setting for laptops; however, many if not most desktops unfortunately have ACPI suspend mode set to the S1 state by default. ACPI S1 is sometimes called POS for Power on Suspend, a state in which the screen blanks and CPU throttles down; however, almost everything else remains fully powered on. As an example, a system and LCD display that consumes 250W will generally drop to about 200W while in S1 Sleep; however, the same system will drop to only 8W of power consumption in the S3 (Suspend to RAM) state.

When the system is set to suspend in the S3 state, upon entering Sleep (either automatically or manually), the current system context is saved in RAM and all the system hardware (CPU, motherboard, fans, display, and so on) except RAM is powered off. In this mode, the system looks as if it is off and consumes virtually the same amount of power as if it were truly off. To resume, you merely press the power button just as if you were turning the system on normally. You can configure most systems to resume on a key press or mouse click as well. Then, instead of performing a normal cold boot and full restart, the system almost instantly powers on and resumes from Sleep, restoring the previously saved context. Your OS, drivers, all open applications, and so on, appear fully loaded just as they were when you “powered off.”

As mentioned, many people have been using this capability on laptops, but few seem to be aware that you can use it on desktop systems also. To enable this deeper sleep capability, there are only two main steps:

    Enter the BIOS Setup, select the Power menu, locate the ACPI suspend setting, and set it to enter the S3 state (sometimes called STR for Suspend to RAM). Save, exit, and restart.

    In Windows, open the Power Options tool in the Control Panel, locate the setting for the Power button and change it to Sleep or Stand by.

You can also take advantage of hibernation, which allows you to use the ACPI S4 (STD = Suspend to Disk) state in addition to S3. ACPI S4 is a lot like S3, except the system context is saved to disk (in a file called hiberfil.sys) instead of RAM, after which the system enters the G2/S5 state. The G2/S5 state is also known as Soft-Off, which is exactly the same as if the system were powered off normally. When you power on from Hibernation (S4), the system still cold boots; however, rather than reloading from scratch, Windows restores the system context from disk (hiberfil.sys) instead of rebooting normally. Although hibernating isn’t nearly as fast as S3 (Suspend to RAM), it is still much faster than a full shutdown and restart and works even if the system loses power completely while suspended. Windows XP and earlier allows you to place a system in Standby (Sleep) or Hibernate modes, while Windows Vista and later has Sleep, Hibernate, and Hybrid Sleep modes. Hybrid Sleep is a combination of sleep and hibernate, where the system state is saved both in RAM and to the hard disk as a backup. Hybrid Sleep is the default Sleep function setting for desktop systems, and because of the extra time to create the hiberfil.sys file it unfortunately makes the system take just as long to Sleep as it does to Hibernate. To speed up the Sleep mode functionality in Windows 7/Vista you can disable

Hybrid Sleep.

Finally, to make the system Sleep automatically, you can change the Windows Power Scheme settings to put the system in Sleep mode after a time duration of your choice. This allows the system to automatically enter Sleep mode after the preset period of inactivity (I usually set it for 30 minutes to an hour) has elapsed.

By using S3 Sleep mode, you can effectively leave the system running all the time yet still achieve nearly the same savings as if you turned it off completely. Servers, of course, should be left on continuously; however, if you set the system to Wake on LAN (WOL) in both the BIOS Setup and in Windows, the system can automatically wake up anytime it is being accessed. The bottom line is that taking advantage of Sleep mode can save a significant amount of energy (and money) over time.

Power Supply Troubleshooting: Basics, Overloading, coling

Troubleshooting the power supply basically means isolating the supply as the cause of problems within a system and, if necessary, replacing it.

Caution: It is rarely recommended that an inexperienced user open a power supply to make repairs because of the dangerous high voltages present. Even when unplugged, power supplies can retain dangerous voltage and must be discharged (like a monitor) before service. Such internal repairs are beyond the scope of this book and are specifically not recommended unless the technician knows what she is doing.

Many symptoms lead me to suspect that the power supply in a system is failing. This can sometimes be difficult for an inexperienced technician to see because at times little connection seems to exist between the symptom and the cause: the power supply.

For example, in many cases a parity check error message can indicate a problem with the power supply. This might seem strange because the parity check message specifically refers to memory that has failed. The connection is that the power supply powers the memory, and memory with inadequate power fails.

It takes some experience to know when this type of failure is power related and not caused by the memory. One clue is the repeatability of the problem. If the parity check message (or other problem) appears frequently and identifies the same memory location each time, I would suspect that defective memory is the problem. However, if the problem seems random, or if the memory location the error message cites as having failed seems random, I would suspect improper power as the culprit. The following is a list of PC problems that often are related to the power supply:

    Any power-on or system startup failures or lockups

    Spontaneous rebooting or intermittent lockups during normal operation

    Intermittent parity check or other memory-type errors

    Hard disk and fan simultaneously failing to spin (no +12 V)

    Overheating due to fan failure

    Small brownouts that cause the system to reset

    Electric shocks felt on the system case or connectors

    Slight static discharges that disrupt system operation

    Erratic recognition of bus-powered USB peripherals

In fact, just about any intermittent system problem can be caused by the power supply. I always suspect the supply when flaky system operation is a symptom. Of course, the following fairly obvious symptoms point right to the power supply as a possible cause:

    System that is completely dead (no fan, no cursor)

    Smoke

    Blown circuit breakers

If you suspect a power supply problem, some of the simple measurements and the more sophisticated tests outlined in this section can help you determine whether the power supply is at fault. Because these measurements might not detect some intermittent failures, you might have to use a spare power supply for a long-term evaluation. If the symptoms and problems disappear when a known-good spare unit is installed, you have found the source of your problem.

Following is a simple flowchart to help you zero in on common power supply–related problems:

    Check the AC power input. Make sure the cord is firmly seated in the wall socket and in the power supply socket. Try a different cord.

    Check the DC power connections. Make sure the motherboard and disk drive power connectors are firmly seated and making good contact. Check for loose screws.

    Check the DC power output. Use a digital multimeter to check for proper voltages. If it’s below spec, replace the power supply.

    Check the installed peripherals. Remove all boards and drives and retest the system. If it works, add items back in one at a time until the system fails again. The last item added before the failure returns is likely defective.

Many types of symptoms can indicate problems with the power supply. Because the power supply literally powers everything else in the system, everything from disk drive problems to memory problems to motherboard problems can often be traced back to the power supply as the root cause.

Overloaded Power Supplies

A weak or inadequate power supply can put a damper on your ideas for system expansion. Some systems are designed with beefy power supplies, as if to anticipate a great deal of system add-ons and expansion components. Most desktop or tower systems are built in this manner. Some systems have inadequate power supplies from the start, however, and can’t adequately service the power-hungry options you might want to add.

The wattage rating can sometimes be misleading. Not all 500-watt supplies are created the same. People familiar with high-end audio systems know that some watts are better than others. This is true for power supplies, too. Cheap power supplies might in fact put out the rated power, but at what temperature? Many cheap power supplies are rated at ridiculously low temperatures that will never be encountered in actual use. As the temperature goes up, the power output capability goes down, meaning that in some cases these supplies will only be capable of 50% less than their rating under normal use.

Also, what about noise and distortion? Some of the supplies are under-engineered to just barely meet their specifications, whereas others might greatly exceed their specifications. Many of the cheaper supplies provide noisy or unstable power, which can cause numerous problems with the system. Another problem with under-engineered power supplies is that they can run hot and force the system to do so as well. The repeated heating and cooling of solid-state components eventually causes a computer system to fail, and engineering principles dictate that the hotter a PC’s temperature, the shorter its life. Many people recommend replacing the original supply in a system with a heavier-duty model, which solves the problem. Because power supplies come in common form factors, finding a heavy-duty replacement for most systems is easy, as is the installation process.

Inadequate Cooling

Some replacement power supplies have higher-capacity cooling fans, which can minimize overheating problems—especially for hotter-running processors. If system noise is a problem, models with special fans can run more quietly than the standard models. These power supplies often use larger-diameter fans that spin more slowly, so they run more quietly but move the same amount of air as the smaller fans. There are even fanless power supplies, although these are more expensive and are generally available only in lower output ratings.

Ventilation in a system is also important. In most prebuilt systems, this is not much of a concern because most reputable manufacturers ensure that their systems have adequate ventilation to avoid overheating. If you are building or upgrading a system your own system, then the responsibility for proper cooling falls on you. In that situation it’s critical that your processor is cooled by an active heatsink and that the case include one or more cooling fans for additional ventilation. If you have free expansion slots, I recommend spacing out any expansion cards in the system to permit airflow between them. Place the hottest-running boards nearest the fan or the ventilation holes in the system. Make sure that adequate airflow exists around the hard disk drives, especially for those that spin at high rates of speed. Some hard disks can generate quite a bit of heat during operation. If the hard disks overheat, data can be lost.

Always be sure you run your computer with the case cover on, especially if you have an older, loaded system using passive heatsinks. Removing the cover in that situation can actually cause the system to overheat. With the cover off, the power supply and chassis fans no longer draw air through the system. Instead, the fans end up cooling only the supply, and the rest of the system must be cooled by simple convection. Systems that use an active heatsink on the processor aren’t as prone to this type of problem; in fact, the cooler air from outside the normally closed chassis can help them to run cooler.

In addition, be sure that any empty slot positions have the filler brackets installed. If you leave these brackets off after removing a card, the resultant hole in the case disrupts the internal airflow and can cause higher internal temperatures.

Finally, the location of the system can have an effect on cooling. I don’t recommend placing a system on a carpeted floor, as most chassis are designed to draw in air at the bottom of the front bezel, which can easily be blocked or become clogged with carpet fibers. Another problem is that a system sitting directly on a floor will ingest a large amount of dust and debris, even more so if the floor is carpeted. If you must place a system on the floor, whether it is carpeted or not I recommend elevating it at least an inch or so via some sort of platform.

If you experience intermittent problems that you suspect are related to overheating, upgraded chassis fans and/or a higher-capacity replacement power supply are usually the best cures.

Power Supply Troubleshooting: Test Equipment

Using Digital Multimeters

One simple test you can perform on a power supply is to check the output voltages. This shows whether a power supply is operating correctly and whether the output voltages are within the correct tolerance range. Note that you must measure all voltages with the power supply connected to a proper load, which usually means testing while the power supply is still installed in the system and connected to the motherboard and peripheral devices.

Selecting a Meter

You need a simple digital multimeter (DMM) or digital volt-ohm meter (DVOM) to perform voltage and resistance checks on electronic circuits (see below). Only use a DMM instead of the older needle-type multimeters because the older meters work by injecting 9 V into the circuit when measuring resistance, which damages most computer circuits.

A DMM uses a much lower voltage (usually 1.5 V) when making resistance measurements, which is safe for electronic equipment. You can get a good DMM with many features from several sources. I prefer the small, pocket-size meters for computer work because they are easy to carry around.

Some features to look for in a good DMM are as follows:

    Pocket size—This is self-explanatory, but small meters that have many, if not all, of the features of larger ones are available. The elaborate features found on some of the larger meters are not really necessary for computer work.

     Overload protection—If you plug the meter into a voltage or current beyond the meter’s capability to measure, the meter protects itself from damage. Cheaper meters lack this protection and can be easily damaged by reading current or voltage values that are too high.

    Autoranging—The meter automatically selects the proper voltage or resistance range when making measurements. This is preferable to the manual range selection; however, really good meters offer both autoranging capability and a manual range override.

    Detachable probe leads—The leads can be damaged easily, and sometimes a variety of differently shaped probes are required for different tests. Cheaper meters have the leads permanently attached, which means you can’t easily replace them. Look for a meter with detachable leads that plug into the meter.

    Audible continuity test—Although you can use the ohm scale for testing continuity (0 ohms indicates continuity), a continuity test function causes the meter to produce a beep noise when continuity exists between the meter test leads. By using the sound, you quickly can test cable assemblies and other items for continuity. After you use this feature, you will never want to use the ohms display for this purpose again.

    Automatic power-off—These meters run on batteries, and the batteries can easily be worn down if the meter is accidentally left on. Good meters have an automatic shutoff that turns off the unit when it senses no readings for a predetermined period of time.

    Automatic display hold—This feature enables you to hold the last stable reading on the display even after the reading is taken. This is especially useful if you are trying to work in a difficult-to-reach area single-handedly.

    Minimum and maximum trap—This feature enables the meter to trap the lowest and highest readings in memory and hold them for later display, which is especially useful if you have readings that are fluctuating too quickly to see on the display.

Although you can get a basic pocket DMM for as little as $20, one with all these features is priced closer to $100, and some can be much higher. RadioShack carries some nice inexpensive units, and you can purchase the high-end models from electronics supply houses, such as Newark or Digi-Key.

Measuring Voltage

To measure voltages on a system that is operating, you must use a technique called back probing on the connectors. You can’t disconnect any of the connectors while the system is running, so you must measure with everything connected. Nearly all the connectors you need to probe have openings in the back where the wires enter the connector. The meter probes are narrow enough to fit into the connector alongside the wire and make contact with the metal terminal inside. The technique is called back probing because you are probing the connector from the back. You must use this back-probing technique to perform virtually all the following measurements.

To test a power supply for proper output, check the voltage at the Power_Good pin (P8-1 on AT, Baby-AT, and LPX supplies; pin eight on the ATX-type connector) for +3 V to +6 V of power. If the measurement is not within this range, the system never sees the Power_Good signal and therefore does not start or run properly. In most cases, the power supply is bad and must be replaced.

Continue by measuring the voltage ranges of the pins on the motherboard and drive power connectors. If you are measuring voltages for testing purposes, any reading within 10% of the specified voltage is considered acceptable, although most manufacturers of high-quality power supplies specify a tighter 5% tolerance. For ATX power supplies, the specification requires that voltages must be within 5% of the rating, except for the 3.3 V current, which must be within 4%. The table below shows the voltage ranges within these tolerances.

Voltage Ranges

Loose Tolerance Tight Tolerance

Desired Voltage Min. –10% Max. (+8%) Min. (–5%) Max. (+5%)

+3.3 V

2.97 V 3.63 V

3.135 V 3.465 V

+/–5.0 V 4.5 V 5.4 V 4.75 V 5.25 V

+/–12.0 V 10.8 V 12.9 V 11.4 V 12.6 V

The Power_Good signal has tolerances that are different from the other voltages, although it is nominally +5 V in most systems. The trigger point for Power_Good is about +2.4 V, but most systems require the signal voltage to be within the tolerances listed here.

Signal  Minimum

Maximum

Power_Good (+5 V) 3.0 V 6.0 V

Replace the power supply if the voltages you measure are out of these ranges. Again, it is worth noting that any and all power-supply tests and measurements must be made with the power supply properly loaded, which usually means it must be installed in a system and the system must be running.

Specialized Test Equipment

You can use several types of specialized test gear to test power supplies more effectively. Because the power supply is one of the most failure-prone items in PCs today, you should have these specialized items if you service many PC systems.

Digital Infrared Thermometer

One of the greatest additions to my toolbox is a digital infrared thermometer. This is also are called a noncontact thermometer because it measures by sensing infrared energy without having to touch the item it is reading. This enables me to make instant spot checks of the temperature of a chip, a board, or the system chassis. They are available from companies such as Raytek (www.raytek.com) for less than $100. To use these handheld items, you point at an object and then pull the trigger. Within seconds, the display shows a temperature readout accurate to +/–3°F (2°C). These devices are invaluable in checking to ensure the components in your system are adequately cooled.

Variable Voltage Transformer

When you’re testing power supplies, it is sometimes desirable to simulate different AC voltage conditions at the wall socket to observe how the supply reacts. A variable voltage transformer is a useful test device for checking power supplies because it enables you to exercise control over the AC line voltage used as input for the power supply. This device consists of a large transformer mounted in a housing with a dial indicator that controls the output voltage. You plug the line cord from the transformer into the wall socket and plug the PC power cord into the socket provided on the transformer. The knob on the transformer can be used to adjust the AC line voltage the PC receives.

Most variable transformers can adjust their AC outputs from 0 V to 140 V no matter what the AC input (wall socket) voltage is. Some can cover a range from 0 V to 280 V as well. You can use the transformer to simulate brownout conditions, enabling you to observe the PC’s response. Thus, you can check a power supply for proper Power_Good signal operation, among other things.

By running the PC and dropping the voltage until the PC shuts down, you can see how much reserve is in the power supply for handling a brownout or other voltage fluctuations. If your transformer can output voltages in the 200 V range, you can test the capability of the power supply to run on foreign voltage levels. A properly functioning supply should operate between 90 V and 135 V but should shut down cleanly if the voltage is outside that range.

One indication of a problem is seeing parity check-type error messages when you drop the voltage to 80 V. This indicates that the Power_Good signal is not being withdrawn before the power supply output to the PC fails. The PC should simply stop operating as the Power_Good signal is withdrawn, causing the system to enter a continuous reset loop.

Variable voltage transformers are sold by a number of electronic parts supply houses, such as Newark and Digi-Key.

Power Supply Recommendations 

When you are shopping for a new power supply, take several factors into account. First, consider the power supply’s shape, or form factor. Power supply form factors can differ in their physical sizes, shapes, screw-hole positions, connector types, and fan locations. When ordering a replacement supply, you need to know which form factor your system requires.

Some systems use proprietary power supply designs, which makes replacement more difficult. If a system uses one of the industry-standard form factor power supplies, replacement units with a variety of output levels and performance are available from hundreds of vendors. An unfortunate user of a system with a nonstandard form factor supply does not have this kind of choice and must get a replacement from the original manufacturer of the system—and usually must pay a much higher price for the unit. PC buyers often overlook this and discover too late the consequences of having nonstandard components in a system.

Name-brand systems on both the low and high end of the price scale are notorious for using proprietary form factor power supplies. For example, Dell has used proprietary supplies in many of its systems. Be sure you consider this if you intend to own or use these types of systems out of warranty or plan significant upgrades during the life of the system. Where possible, I always insist on systems that use industry-standard power supplies, such as the ATX12V form factor supply found in most systems today.

With backward compatibility ensuring that the new 24-pin ATX power connector will plug into older 20-pin motherboard sockets, when purchasing a new power supply, I now recommend only those units that include 24-pin main power connectors, which are usually sold as ATX12V 2.x, EPS12V, or “PCI Express” models. For the most flexible and future-proof supply, also ensure that the power supply includes two or more PCI Express graphics connectors as well as multiple integrated SATA drive power connectors. Choosing a power supply with these features provides flexibility that allows it to work not only in newer systems, but also in virtually all older ATX systems—and with no adapters required.

As a guide, here are some of the features I recommend looking for in a PSU:

    Adequate power connectors (24-pin main, 4/8-pin +12 V CPU, 6/8-pin PCIe Graphics, SATA, and so on) for the intended system

    Adequate power output (watts) for the intended system

    80 PLUS certification

    Active Power Factor Correction (required with 80 PLUS)

    SLI and/or Crossfire certification

    Single +12 V rail design

There are other variables to consider, depending on your specific needs or desires. One feature that many people like is modular cables, which minimize the clutter in a system. Another feature to consider is noise, which is mostly related to cooling. The type and arrangement of cooling fans has a great effect on how quiet (or noisy) the unit will be. There are even some fanless units that are completely silent, but these usually come at a premium price and with a lower overall power output capability.

When building systems with case windows, some people also like to look for PSUs with appearance-related features like colored cases.

Modular Cables

One feature often discussed in relation to PSUs is the use of modular cables. This means cables with connectors at both ends that are detachable from the power supply. Modular cables allow you to attach only the cables you need—in some cases greatly reducing the congestion inside the system.

The main argument against modular cables is that additional resistance is introduced via another set of connector contacts. This is true, but how much resistance exactly, and is it enough that it really matters? Fortunately, this can easily be calculated.

The connectors used in modern power supplies are mostly Molex Mini-Fit Jr. types, which have a contact resistance of 10 milli-ohms (0.01 ohms). Most power supply cables use 18 AWG (American Wire Gauge) copper wire, which has a resistance of about 0.0064 ohms per foot. This means that adding an extra connector at the PSU end is equal to about 1.5 feet of wire in additional resistance.

To put it another way, in a maximum load situation, each terminal normally carries a maximum of about four amps, at which point the additional resistance equals about 0.16 watts of power loss. In an eight-pin power connector, this only adds up to around a watt, a loss I consider negligible.

Finally, when you consider that a typical PSU cable already consists of 1.5 feet of wire with a connector on the end, adding another connector to make the cable modular only adds about one-third more overall resistance to what is already there, which was negligible to begin with.

If modular cables aren’t much of a problem technically, why don’t more PSU manufacturers include them? Well, besides the (negligible in my opinion) extra resistance, they do add to the cost of making a power supply, and that is reflected in a higher final price. They can also create clearance issues with other components in the system, depending on exactly where the connectors attach to the PSU. In addition, modular cables can easily become lost or misplaced. Think of opening a system to add another internal drive or upgraded video card several years after it was initially built, finding that the PSU uses modular cables, and discovering the extra cables needed are nowhere to be found. One solution to this problem is to place any unused cables inside the case when building a system. For example, you could place them in a small plastic bag and tape them inside, so that if or when you need them in the future, they are easy to find. Besides these issues, perhaps the biggest drawback to modular cables is that modular PSU cables using standard connectors are patented (www.google.com/

patents/about?id=w0ehAAAAEBAJ), and the patent is owned by Systemax (aka TigerDirect and Ultra Products). There is another patent on modular PSUs that use nonstandard connectors at the PSU end (www.google.com/patents/about?id=iOGqAAAAEBAJ). If there was no legal “baggage” against using them, I suspect we would see more modular cable equipped PSUs on the market today.

Power-Protection Systems: Surge Protectors And Line Condition

Power-protection systems do just what the name implies: They protect your equipment from the effects of power surges and power failures. In particular, power surges and spikes can damage computer equipment, and a loss of power can result in lost data. In this section, you learn about the four primary types of power-protection devices available and when you should use them.

Before considering any further levels of power protection, you should know that a quality power supply already affords you a substantial amount of protection. High-end power supplies from the vendors I recommend are designed to provide protection from higher-than-normal voltages and currents, and they provide a limited amount of power-line noise filtering. Some of the inexpensive aftermarket power supplies probably do not have this sort of protection. If you have an inexpensive computer, further protecting your system might be wise.

Caution: All the power-protection features in this chapter and the protection features in the power supply inside your computer require that the computer’s AC power cable be connected to a ground.

Many older homes do not have three-prong (grounded) outlets to accommodate grounded devices.

Do not use a three-pronged adapter (that bypasses the three-prong requirement and enables you to connect to a two-prong socket) to plug a surge suppressor, computer, or UPS into a two-pronged outlet. They often don’t provide a good ground and can inhibit the capabilities of your power-protection devices.

You also should test your power sockets to ensure they are grounded. Sometimes outlets, despite having three-prong sockets, are not connected to a ground wire; an inexpensive socket tester (available at most hardware stores) can detect this condition.

Of course, the easiest form of protection is to turn off and unplug your computer equipment (including your modem) when a thunderstorm is imminent. However, when this is not possible, other alternatives are available.

Power supplies should stay within operating specifications and continue to run a system even if any of these power line disturbances occur:

    Voltage drop to 80 V for up to 2 seconds

    Voltage drop to 70 V for up to .5 seconds

    Voltage surge of up to 143 V for up to 1 second

Most high-quality power supplies (or the attached systems) will not be damaged by the following occurrences:

    Full power outage

    Any voltage drop (brownout)

    A spike of up to 2500 V

To verify the levels of protection built into the existing power supply in a computer system, an independent laboratory subjected several unprotected PC systems to various spikes and surges of up to 6000 V—considered the maximum level of surge that can be transmitted to a system through an electrical outlet. Any higher voltage would cause the power to arc to the ground within the outlet. None of the systems sustained permanent damage in these tests. The worst thing that happened was that some of the systems rebooted or shut down when the surge was more than 2000 V. Each system restarted when the power switch was toggled after a shutdown.

The automatic shutdown of a computer during power disturbances is a built-in function of most high-quality power supplies. You can reset the power supply by flipping the power switch from on to off and back on again. Some power supplies even have an auto-restart function. This type of power supply acts the same as others in a massive surge or spike situation: It shuts down the system. The difference is that after normal power resumes, the power supply waits for a specified delay of 3–6 seconds and then resets itself and powers the system back up. Because no manual switch resetting is required, this feature might be desirable in systems functioning as network servers or in those found in other unattended locations.

The first time I witnessed a large surge that caused an immediate shutdown of all my systems, I was extremely surprised. All the systems were silent, but the monitor and modem lights were still on. My first thought was that everything was blown, but a simple toggle of each system-unit power switch caused the power supplies to reset, and the units powered up with no problem. Since that first time, this type of shutdown has happened to me several times, always without further problems.

The following types of power-protection devices are explained in the sections that follow:

    Surge suppressors

    Phone-line surge protectors

    Line conditioners

    Standby power supplies (SPS)

    Uninterruptible power supplies (UPS)

Surge Suppressors (Protectors)

The simplest form of power protection is any one of the commercially available surge protectors—that is, devices inserted between the system and the power line. These devices, which cost between $20 and $200, can absorb the high-voltage transients produced by nearby lightning strikes and power equipment. Some surge protectors can be effective for certain types of power problems, but they offer only limited protection.

Surge protectors use several devices, usually metal-oxide varistors (MOVs), that can clamp and shunt away all voltages above a certain level. MOVs are designed to accept voltages as high as 6000 V and divert any power above 200 V to ground. MOVs can handle normal surges, but powerful surges such as direct lightning strikes can blow right through them. MOVs are not designed to handle a high level of power and self-destruct while shunting a large surge. These devices therefore cease to function after either a single large surge or a series of smaller ones. The real problem is that you can’t easily tell when they no longer are functional. The only way to test them is to subject the MOVs to a surge, which destroys them. Therefore, you never really know whether your so-called surge protector is protecting your system.

Some surge protectors have status lights that let you know when a surge large enough to blow the MOVs has occurred. A surge suppressor without this status indicator light is useless because you never know when it has stopped protecting.

Underwriters Laboratories has produced an excellent standard that governs surge suppressors, called UL 1449. Any surge suppressor that meets this standard is a good one and definitely offers a line of protection beyond what the power supply in your PC already offers. The only types of surge suppressors worth buying, therefore, should have two features:

    Conformance to the UL 1449 standard

    A status light indicating when the MOVs are blown

Units that meet the UL 1449 specification say so on the packaging or directly on the unit. If this standard is not mentioned, it does not conform. Therefore, you should avoid it.

Another good feature to have in a surge suppressor is a built-in circuit breaker that can be manually reset rather than a fuse. The breaker protects your system if it or a peripheral develops a short.

Network and Phone Line Surge Protectors

A far bigger problem than powerline surges are surges through network and/or phone cabling. I’ve personally experienced surges resulting from nearby lightning strikes damage multiple computers and other equipment via ethernet and telephone lines, while virtually nothing was damaged through the power lines. In systems with separate network cards the damage was often limited to just the card, while in systems with the network interface built-in to the motherboard, the motherboard itself was damaged. In many areas, the cable and phone lines are above ground, making them especially susceptible to lightning strikes.

Several companies manufacture or sell simple surge protectors that plug in between your modem and the network or phone lines. These inexpensive devices can be purchased from most electronics supply houses. Some of the standard power line surge protectors include connectors for network and/or phone line protection as well.

Line Conditioners

In addition to high-voltage and current conditions, other problems can occur with incoming power. The voltage might dip below the level needed to run the system, resulting in a brownout. Forms of electrical noise other than simple voltage surges or spikes might travel through the power line, such as radio-frequency interference or electrical noise caused by motors or other inductive loads.

Remember two things when you wire together digital devices (such as computers and their peripherals):

    Any wire can act as an antenna and have voltage induced in it by nearby electromagnetic fields, which can come from other wires, telephones, CRTs, motors, fluorescent fixtures, static discharge, and, of course, radio transmitters.

    Digital circuitry responds with surprising efficiency to noise of even a volt or two, making those induced voltages particularly troublesome. The electrical wiring in your building can act as an antenna, picking up all kinds of noise and disturbances.

A line conditioner can handle many of these types of problems. It filters the power, bridges brownouts, suppresses high-voltage and current conditions, and generally acts as a buffer between the power line and the system. A line conditioner does the job of a surge suppressor, and much more. It is more of an active device, functioning continuously, rather than a passive device that activates only when a surge is present. A line conditioner provides true power conditioning and can handle myriad problems. It contains transformers, capacitors, and other circuitry that can temporarily bridge a brownout or low-voltage situation. These units usually cost $100–$300, depending on the power-

handling capacity of the unit.

Power-Protection Systems: Backup Power Options

Backup Power

The next level of power protection includes backup power-protection devices. These units can provide power in case of a complete blackout, thereby providing the time necessary for an orderly system shutdown. Two types are available: the SPS and the uninterruptible power supply (UPS). The UPS is a special device because it does much more than just provide backup power; it is also the best kind of line conditioner you can buy.

Standby Power Supplies

A standby power supply is known as an offline device: It functions only when normal power is disrupted. An SPS system uses a special circuit that can sense the AC line current. If the sensor detects a loss of power on the line, the system quickly switches over to a standby battery and power inverter. The power inverter converts the battery power to 120 V AC power, which is then supplied to the system.

For a stand-by (switching) type UPS to work, the hold-up time of the power supply has to be longer than the switching time of the UPS. For example, I have a TrippLite SMART1000LCD, which is a stand-by type UPS with a 4ms switching time. Because this is well below the 16ms hold-up time called for in the official Power Supply Design Guide, it should switch well before any properly designed and functioning power supply allows the system to reset. Unfortunately if the power supply in a PC is poorly designed or overloaded, it may be disrupted by even a 4ms switch, causing the system to shut down or reset anyway, and all unsaved work to be lost.

A truly outstanding SPS adds to the circuit a ferroresonant transformer, which is a large transformer with the capability to store a small amount of power and deliver it during the switch time. This device functions as a buffer on the power line, giving the SPS almost uninterruptible capability.

Tip: Look for SPS systems with a switch-over time of less than 10 milliseconds (ms). This is shorter than the hold-up time of typical power supplies.

SPS units also might have internal line conditioning of their own. Under normal circumstances, most cheaper units place your system directly on the regular power line and offer no conditioning. The addition of a ferroresonant transformer to an SPS gives it extra regulation and protection capabilities because of the buffer effect of the transformer. SPS devices without the ferroresonant transformer still require the use of a line conditioner for full protection. SPS systems usually cost between a hundred and several thousand dollars, depending on the quality and power-output capacity.

UPSs

Perhaps the best overall solution to any power problem is to provide a power source that is conditioned and that can’t be interrupted—which is the definition of an uninterruptible power supply. UPSs are known as online systems because they continuously function and supply power to your computer systems. Because some companies advertise ferroresonant SPS devices as though they were UPS devices, many now use the term true UPS to describe a truly online system. A true UPS system is constructed in much the same way as an SPS system; however, because the computer is always operating from the battery, there is no switching circuit.

In a true UPS, your system always operates from the battery. A voltage inverter converts from +12 V DC to 120 V AC. You essentially have your own private power system that generates power independently of the AC line. A battery charger connected to the line or wall current keeps the battery charged at a rate equal to or greater than the rate at which power is consumed.

When the AC current supplying the battery charger fails, a true UPS continues functioning undisturbed because the battery-charging function is all that is lost. Because the computer was already running off the battery, no switch takes place and no power disruption is possible. The battery begins discharging at a rate dictated by the amount of load your system places on the unit, which (based on the size of the battery) gives you plenty of time to execute an orderly system shutdown. Based on an appropriately scaled storage battery, the UPS functions continuously, generating power and preventing unpleasant surprises. When the line power returns, the battery charger begins recharging the battery, again with no interruption.

Note: Occasionally, a UPS can accumulate too much storage and not enough discharge. When this occurs, the UPS emits a loud alarm, alerting you that it’s full. Simply unplugging the unit from the AC power source for a while can discharge the excess storage (as it powers your computer) and drain the UPS of the excess.

Many SPS systems are advertised as though they are true UPS systems. You can tell a Standby Power Supply from a true UPS by the unit’s switch time. If a specification for switch time exists, the unit can’t be a true UPS because UPS units never switch. However, true UPS systems are very expensive, and a good SPS with a ferroresonant transformer can virtually equal the performance of a true UPS at a much lower cost.

Note: Many UPSs and SPSs today come equipped with a cable and software that enables the protected computer to shut down in an orderly manner on receipt of a signal from the UPS. This way, the system can shut down properly even if the computer is unattended. Some OSs designed for server environments contain their own UPS software components.

UPS cost is a direct function of both the length of time it can continue to provide power after a line current failure and how much power it can provide. You therefore should purchase a UPS that provides enough power to run your system and peripherals and enough time to close files and provide an orderly shutdown. Remember, however, to manually perform a system shutdown procedure during a power outage. You will probably need your monitor plugged into the UPS and the computer. Be sure the UPS you purchase can provide sufficient power for all the devices you must connect to it.

Because of a true UPS’s almost total isolation from the line current, it is unmatched as a line conditioner and surge suppressor. The best UPS systems add a ferroresonant transformer for even greater power conditioning and protection capability. This type of UPS is the best form of power protection available. The price, however, can be high. To find out just how much power your computer system requires, look at the UL sticker on the back of the unit. This sticker lists the maximum power draw in watts, or sometimes in just volts and amperes. If only voltage and amperage are listed, multiply the two figures to calculate the wattage.

As an example, if the documentation for a system indicates that the computer can require as much as 120 V at a maximum current draw of five amps, the maximum power the system can draw is about 550 watts. The system should never draw any more power than that; if it does, a five-amp fuse in the power supply will blow. This type of system usually draws an average of 200 to 300 watts. However, to be safe when you make calculations for UPS capacity, be conservative; use the 550-watt figure. Adding an LCD monitor that draws 50 watts brings the total to 600 watts or more. Therefore, to run two fully loaded systems (including monitors), you’d need a 1200-watt UPS. A UPS of that capacity or greater normally costs several hundred dollars. Unfortunately, that is what the best level of protection costs. Most companies can justify this type of expense only for critical-use PCs, such as network servers.

Note: The highest-capacity UPS sold for use with a conventional 15-amp outlet is about 1400 watts. If it’s any higher, you risk tripping a 15-amp circuit when the battery is charging heavily and the inverter is drawing maximum current.

In addition to the total available output power (wattage), several other factors can distinguish one UPS from another. The addition of a ferroresonant transformer improves a unit’s power conditioning and buffering capabilities. Good units also have an inverter that produces a true sine wave output; the cheaper ones might generate a square wave. A square wave is an approximation of a sine wave with abrupt up-and-down voltage transitions. The abrupt transitions of a square wave are not compatible with some computer equipment power supplies. Be sure that the UPS you purchase produces power that is compatible with your computer equipment. Every unit has a specification for how long it can sustain output at the rated level. If your systems draw less than the rated level, you have some additional time.

Caution: Be careful! Most UPS systems are not designed for you to sit and compute for hours through an electrical blackout. They are designed to provide power only to essential components and to remain operating long enough to allow for an orderly shutdown. You pay a large amount for units that provide power for more than 15 minutes or so. At some point, it becomes more cost-effective to buy a generator than to keep investing in extended life for a UPS.

Some of the many sources of power protection equipment include American Power Conversion (APC) and Tripp Lite. These companies sell a variety of UPS, SPS, line protector, and surge protector products.

Caution: Don’t connect a laser printer to a backed-up socket in any SPS or UPS unit. Such printers are electrically noisy and have widely varying current draws. This can be hard on the inverter in an SPS or a UPS and frequently cause the inverter to fail or detect an overload and shut down. Either case means that your system will lose power, too.

Printers are normally noncritical because whatever is being printed can be reprinted. Don’t connect them to a UPS unless there’s a good business need to do so.

Some UPSs and SPSs have sockets that are conditioned but not backed up—that is, they do not draw power from the battery. In cases such as this, you can safely plug printers and other peripherals into these sockets.

Real-Time Clock/Nonvolatile RAM (CMOS RAM) Batteries

Most PCs have a special type of chip in them that combines a real-time clock (RTC) with at least 64 bytes (including 14 bytes of clock data) of nonvolatile RAM (NVRAM) memory. This chip is officially called the RTC/NVRAM chip, but it is often referred to as the CMOS or CMOS RAM chip because the type of chip used is produced using a CMOS Complementary Metal-Oxide Semiconductor (CMOS) process. CMOS design chips are known for low power consumption. This special RTC/NVRAM chip is designed to run off a battery for several years.

The original chip of this type was the Motorola MC146818, which was used in the IBM AT dating from August 1984. Although the chips used today have different manufacturers and part numbers, they all are designed to be compatible with this original Motorola part. Most modern motherboards have the RTC/NVRAM integrated in the motherboard chipset South Bridge or I/O Controller Hub (ICH) component, meaning no separate chip is required.

The clock enables software to read the date and time and preserves the date and time data even when the system is powered off or unplugged. The NVRAM portion of the chip has another function: It is designed to store the basic system configuration, including the amount of memory installed, types of disk drives installed, PnP device configuration, power-on passwords, and other information. Although some chips have been used that store up to 4KB or more of NVRAM, most motherboard chipsets with integrated RTC/NVRAM incorporate 256 bytes of NVRAM, of which the clock uses 14bytes. The system reads this information every time you power it on.

Modern CMOS Batteries

Motherboard NVRAM (CMOS RAM) batteries come in many forms. Most are of a lithium design because they last 2–5 years or more. I have seen systems with conventional alkaline batteries mounted in a holder; these are much less desirable because they fail more frequently and do not last as long. Also, they are prone to leak, and if a battery leaks on the motherboard, the motherboard can be severely damaged. By far, the most commonly used battery for motherboards today is the coin cell, mounted in a holder that is part of the motherboard. Two main types of coin cells are used, differing in their chemistry. Most use a manganese dioxide (Mn02) cathode, designated by a CR prefix in the part number; others use a carbon monoflouride (CF) cathode, designated by a BR prefix in the part number. The CR types are more plentiful (and thus easier to get) and offer slightly higher capacity. The BR types are useful for higher-temperature operation (above 60°C or 140°F).

Because the CR series is cheaper and easier to obtain, it is generally what you will find in a PC. The other digits in the battery part number indicate the physical size of the battery. For example, the most common type of lithium coin cell used in PCs is the CR2032, which is 20 mm in diameter (about the size of a quarter) and 3.2 mm thick and uses a manganese dioxide cathode. These are readily available at electronics supply stores, camera shops, and even drugstores. The following figure shows a cutaway view of a CR2032 lithium coin cell battery.

 Any site you go to will have their 'favorite' PSUs. Personally I am going to say that with power supplies you will get what you pay for, and the quality is generally in the weight of the PSU.

In my most humble (and relatively authoritative) opinion on the topic (though this is not my particular strong suit), I would say that anything over $1 per 10W (ie $40 for 400W, $75 for 750W) is a fairly safe bet. Spec wise PC Power and Cooling is the technical 'Best' when it comes to the cleanest power, and longevity; but you pay for that, and they are not the 'sexiest' looking PSUs as they are intended for business machines, not gamers. OCZ owns PCPnC, and has benefited in their quality from the purchase (they use to have terrible PSUs, but not anymore). Corsair, CoolerMaster, and other 'Big Name' brands are all quite good as well, and I would not shy away from any of them if they are at a good price.

When purchasing just remember 5 things:

1) weight is good

2) 120+mm fans are a requirement as silence is golden, and it is not hard to have your PS be the quietest device in the computer.

3) use a system power calculator and buy a PSU that matches your build. When too large a power supply dies it is more likely to take parts out with it, if too small then your system won't run properly.

4) Dont buy cheap; Your power supply is your last, and often best, line of defense between bad power and your parts. Many computers never run quite right because some silly teenager with too much money buys a crappy 1000W (hard to believe, but they do exist) power supply for a 500W system, instead of a smaller power supply to fit their needs of better quality.

5) A good power supply is no excuse to not invest in some form of line conditioner or UPS. If you live in an area prone to high winds or electrical storms then line conditioning is more important than a high end power supply (though both are quite important).