Absolute Beginners Guide to A+ Certification. Covers the Hardware and Operating Systems Exam

Question : How well can a power supply work if it has poor-quality AC power to work with?

Answer : Not very well.

Because computers and many popular computer peripherals run on DC power that has been converted from AC power, it's essential to make sure that proper levels of AC power flow to the computer and its peripherals. There are four problems you might run into:

• Overvoltages (spikes and surges)

• Undervoltages (brownouts)

• Power failure (blackouts)

• Noisy power (interference)

Extremely high levels of transient or sustained overvoltages can damage the power supply of the computer and peripherals, and voltage that is significantly lower than required will cause the computer and peripherals to shut down. Shutdowns happen immediately when all power fails. A fourth problem with power is interference; "noisy" electrical power can cause subtle damage, and all four types of problems put the most valuable property of any computer, the data stored on the computer, at risk. Protect your computer's power supply and other components with appropriate devices:

• Surge suppressors , which are also referred to as surge protectors

• Battery backup systems, which are also referred to as UPS or SPS systems

• Power conditioning devices

Surge Suppressors

Stop that surge! While properly designed surge suppressors can prevent power surges (chronic overvoltage) and spikes (brief extremely high voltage) from damaging your computer, low-cost ones are often useless because they lack sufficient components to absorb dangerous surges. Surge suppressors range in price from under $10 to close to $100 per unit.

Both spikes and surges are overvoltages: voltage levels higher than the normal voltage levels that come out of the wall socket. Spikes are momentary overvoltages, whereas surges last longer. Both can damage or destroy equipment and can come through data lines (such as RJ-11 phone or RJ-45 network cables) as well as through power lines. In other words, if you think of your PC as a house, spikes and surges can come in through the back door or the garage as well as through the front door. Better "lock" (protect) all the doors. Many vendors sell data-line surge suppressors.

How can you tell the real surge suppressors from the phonies? A surge suppressor must have a UL -1449 rating to be considered a "true" surge protector. Many low-cost units labeled "surge suppressors" actually have a different UL rating (UL-1363) for a multioutlet strip ("transient voltage tap"). Although UL-1363 units can provide a minimal level of protection against modest overvoltages, UL-1449 “rated units are recommended for significant protection. An alternative rating to look for is the IEEE-587 Category A rating; high-quality surge suppressors will normally have both UL-1449 and IEEE-587 Category A ratings (IEEE-587 Category B applies to major feeders and local branch circuits, and Category A applies to outlets and long branch circuits).

Beyond the UL-1449 rating, look for the following features to be useful in preventing power problems:

• A low UL-1449 let-through voltage level (400V AC or less). This might seem high compared to the 115V standard, but power supplies have been tested to handle up to 800V AC themselves without damage.

• IEEE-587A let-through voltage rating of under 100V.

• A covered-equipment warranty that includes lightning strikes (one of the biggest causes of surges and spikes).

• A high joule rating. Joules measure electrical energy, and surge suppressors with higher joule ratings can dissipate greater levels of surges or spikes.

• Fusing that will prevent fatal surges from getting through.

• Telephone, fax, and modem protection if your system has a modem or is connected to a telephone or fax.

• EMI / RFI noise filtration (a form of line conditioning).

• Site fault wiring indicator (no ground, reversed polarity warnings).

• Fast response time to surges. If the surge suppressor doesn't clamp fast enough, the surge can get through.

• Protection against surges on hot, neutral, and ground lines.

caution

If you use surge protectors with these features, you will minimize power problems. The site-fault wiring indicator will alert you to wiring problems that can negate ground and can cause serious damage in ordinary use.

In preparing for the A+ Certification Exam, you should pay particular attention to the UL and IEEE standards for surge suppressors and the major protection features just listed.

UPSs and SPSs

A UPS (uninterruptible power supply ) is another name for a battery backup unit. A UPS provides emergency power when a power failure strikes (a blackout ) or when power falls below minimum levels (a brownout ).

There are two different types of UPS systems: true UPS and SPS systems. A true UPS runs your computer from its battery at all times, isolating the computer and monitor from AC power. There is no switchover time with a true UPS when AC power fails because the battery is already running the computer. A true UPS inherently provides power conditioning (preventing spikes, surges, and brownouts from reaching the computer) because the computer receives only battery power, not the AC power coming from the wall outlet. True UPS units are sometimes referred to as line-interactive battery backup units because the battery backup unit interacts with the AC line, rather than the AC line going directly to the computer and other components.

An SPS (standby power supply ) is also referred to as a UPS, but its design is quite different. Its battery is used only when AC power fails. A momentary gap in power (about 1ms or less) occurs between the loss of AC power and the start of standby battery power; however, this switchover time is far faster than is required to avoid system shutdown because computers can coast for several milliseconds before shutting down. SPS-type battery backup units are far less expensive than true UPSs, but work just as well as true UPSs when properly equipped with power-conditioning features.

Battery backup units can be distinguished from each other by differences in

• Runtimes ” The amount of time a computer will keep running on power from the UPS. A longer runtime unit uses a bigger battery and usually will cost more than a unit with a shorter runtime. Fifteen minutes is a minimum recommendation for a UPS for an individual workstation; much larger systems are recommended for servers that might need to complete a lengthy shutdown procedure.

• Network support ” Battery backup units made for use on networks are shipped with software that broadcasts a message to users about a server shutdown and shuts down the server automatically before the battery runs down.

• Automatic shutdown ” Some low-cost UPS units lack this feature, but it is essential for servers or other unattended units. The automatic shutdown feature requires an open RS-232 serial port or USB port and appropriate software from the UPS maker. If you change operating systems, you will need to update the software for your UPS to be supported by the new operating system.

• Surge suppression features ” Virtually all UPS units today have integrated surge suppression, but the efficiency of integrated surge suppression can vary as much as separate units. Look for UL-1449 and IEEE-587 Category A ratings to find reliable surge suppression in UPS units.

Always plug a UPS directly into a wall outlet, not into a power strip or surge suppressor.

Buying the Correct-Sized Battery Backup System

Battery backups can't run forever. But then, they're not supposed to. How can you make sure you get enough time to save your files and shut down your computer?

UPS units are rated in VA (volt-amps ), and their manufacturers have interactive buying guides you can use online or download to help you select a model with adequate capacity. If you use a UPS with an inadequate VA rating for your equipment, your runtime will be substantially shorter than it should be.

Here's how to do the math: You can calculate the correct VA rating for your equipment by adding up the wattage ratings of your computer and monitor and multiplying the result by 1.4. If your equipment is rated in amperage (amps), multiply the amp rating by 120 ( volts ) to get the VA rating.

For example, my computer has a 300W power supply, which would require a 420VA-rated UPS (300x1.4) and a 17-inch monitor that is rated in amps, not watts. The monitor draws 0.9A, which would require a 108VA-rated UPS (0.9x120). Add the VA ratings together, and my computer needs a 528VA-rated battery backup unit or larger. Specifying a UPS with a VA rating at least twice what is required by the equipment attached to the UPS will greatly improve the runtime of the battery.

In the previous example, a typical 600VA battery backup unit would provide about seven minutes of runtime when used with my equipment. However, if I used a 1050VA battery backup, I could increase my runtime to more than 20 minutes because my equipment would use only about half the rated capacity of the UPS unit.

caution

Power Conditioning Devices

Although power supplies are designed to work with voltages that do not exactly meet the 120V or 240V standards, power that is substantially higher or lower than what the computer is designed for can damage the system. Electrical noise on the power line, even with power at the correct voltage, also causes problems because it disrupts the correct sinewave alternating-current pattern the computer, monitor, and other devices are designed to use.

Better-quality surge protectors often provide power filtration to handle EMI/RFI noise problems from laser printers and other devices that generate a lot of electrical interference. However, to deal with voltage that is too high or too low, you need a true power conditioner.

These units take substandard or overstandard power levels and adjust them to the correct range needed by your equipment. Some units also include high-quality surge protection features.

To determine whether you need a power-conditioning unit, you can contact your local electric utility to see if it loans or rents power-monitoring devices. Alternatively, you can rent them from power consultants . These units track power level and quality over a set period of time (such as overnight or longer) and provide reports to help you see the overall quality of power on a given line.

Moving surge- and interference- causing devices such as microwaves , vacuum cleaners, refrigerators, freezers, and furnaces to circuits away from the computer circuits will help minimize power problems. However, in older buildings, or during times of peak demand, power conditioning might still be necessary. A true (line-interactive) UPS provides built-in power conditioning by its very nature (see the previous discussion).