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From Awardline.com General Somewhere in the list of the Top Ten Things We Take for Granted, you'd have to include electricity. But the time to think about electricity is before you have a problem. How do you protect your computer from damage or data loss when good power goes bad?
ELECTRICITY BASICS Most of us are aware that there's a difference between alternating current (A0 and direct current (DO. AC is what you get from a wall socket, and DC is what you get from a battery. DC is easier to use for certain applications, including electronic circuits. Computers have power supplies that convert AC electricity to DC. So why don't we use DC for everything? The answer is a matter of moving electrons. It takes energy to move electrons from one atom to another in a wire, and some of this energy can be recovered at the other end of the wire to do useful work: to make a light glow, spin a motor, or switch a transistor on or off. If the circuit is relatively short, the electrons can be pushed from one end continuously with out much loss of efficiency. But a lot of power can get lost if you just push from one end over a long circuit. If you alternately push and pull from both ends instead, then each electron only rushes back and forth over a relatively short expanse, much like an ocean moving back and forth on a beach. With AC, the voltage rapidly alternates between positive and negative pushing and pulling the electrons in the wire, which is more efficient for transporting power over a distance. In the United States, this back-and-forth happens 60 times a second, or 60 Hz. The frequency of the alternating current is one factor; another is voltage. This refers to the force used to push the electrons along the wire. A typical U.S. electrical supply provides 120 Volts AC, which means that the voltage varies from 120 volts positive to 120 volts negative. The third factor to consider is how much electricity is available to be used (the current). This is measured in amperes (or amps for short) and refers to the rate of flow of electrons. The more electrons flowing through a wire over a given period of time (and at a given voltage), the more work that can be done. The amount of power available is a combination of the voltage (how hard the electrons are being pushed) and amps (how many of these electrons are available). Power is measured in watts, which are calculated by multiplying the voltage by the current. Assuming a 120?volt power supply, a device rated at I amp will consume approximately 120 watts of power. TOO MUCH POWER Although ideal electricity comes in at 120 volts with a clean, 60 Hz waveform, what you get from your outlet may be different. Most users are aware of the danger of power transients. These are extremely short lived Surges in voltage, but the increase can be in the thousands of volts. Lightning strikes are perhaps the most common source, and without sufficient protection, the extra voltage can find its way into sensitive components and damage or destroy them. The best way to protect against such damage is to put a surge protector between the electrical source and your electronics. This acts as a shock absorber and dissipates the extra voltage before it can be passed along. There are different types of designs available. The least expensive devices often rely on metal-oxide varistors (MOV’s) that have a finite ability to absorb extra voltage. Each incident uses up some of this capacity, and eventually, the device will not offer any further surge protection. More expensive devices use other components, such as gas-discharge capacitors, that are not used up by absorbing transients. Note that transients need not enter solely through your electrical supply. Telephone lines are also susceptible, and for good protection, consider placing surge-protection devices on the lines where they enter your home or business. DIRTY POWER Even without lightning, your electricity may be far from ideal. Other devices on the same electrical service can cause voltage spikes and surges. If you have an appliance with a large electrical load that turns on and off such as an air conditioner or refrigerator the voltage can "bounce" after the device turns off. The voltage increase is not usually as great as with a lightning induced transient, but it can be damaging nonetheless. Interference from other devices can create noise additional wave patterns on top of the normal 60?Hz waveform which can cause problems for electronics and for mechanical devices such as the motors in printers. The easiest way to avoid difficulties from surges, spikes, and noise generated by other devices in your building is to keep your computer equipment on a dedicated circuit connected to the main electrical service distribution box. Another way is to get a device called a power line conditioner. POWER INTERRUPTIONS Perhaps the best-known problem is no power at all. Blackouts are a part of life in many parts of the country, and often result from damage to the electric supply system caused by severe weather. Other, less obvious causes may include traffic accidents knocking down poles, or the electric company switching off or reducing power briefly for maintenance purposes. A sudden loss of power to your computer and peripherals can result in data loss and even permanent damage to your hardware. The easiest way to guard against such problems is to place a standby power supply between your equipment and the electrical source. A standby power supply contains a storage battery and circuitry (called an inverter) that can convert the battery's DC into the AC your computer expects. It also contains monitoring circuitry that measures the incoming voltage; when the voltage drops below a certain level, the standby power supply switches to its battery for power. Three well-known manufacturers of such devices are American Power Conversion Corp. (www.apcc.com), Best Power (www.bestpower.com), and Tripp Lite (www. tripplite.com). Standby power supplies are typically rated in terms of volt or amps, which describes the load that they can handle. You can usually find the power load rating printed on plates on the backs of most peripherals. Add up the amps required for all your devices, multiply by 120 (for the voltage), and pick a standby power supply with a rating greater than your total. The greater the difference between your system's demands and the standby supply's capacity, the longer you'll keep running after the lights go out. Some devices such as laser printers draw a great deal of power and can overload your standby system. A printer can be rated at 7 to 10 amps, which amounts to 840 to 1,200 volt for that device alone. Don't try to provide backup power for such devices; in most cases the additional cost isn't justified. TOO LITTLE POWER As many parts of the Northeast discovered during last summer's heat wave, the electric company may sometimes deliver substantially less than the standard 120 volts to your outlet. During such brownouts, your system may not receive sufficient power to operate. Fortunately, most standby power supplies also include voltage regulation capabilities, which allow them to pull up low voltages to the proper levels. If the supplied voltage drops too low, the unit will simply behave as if the power has been cut off completely and will provide all the power from its battery. Most standby power supplies provide a combination of power features: battery backup, voltage regulation, surge suppression, and in some cases, line conditioning to remove stray noise. GOING TO GROUND As mentioned above, keeping your computer equipment on a separate circuit is a good idea. This is most likely to provide you with clean power, but there are other advantages. You can monitor the loads of the devices plugged into the circuit, which helps avoid an overload that might cause the circuit breaker or fuse to blow. A separate circuit can also give you confidence about the ground connection. The third, round plug on a standard power cord is for the ground, which is intended to provide a safe route for stray current to be dissipated harmlessly. The problem is that the presence of a third hole in a wall socket does not mean that the ground is functional, especially in older homes. And in some cases, the circuits may not be wired correctly, which can result in power flowing into a device along the ground contact. This can result in dangerous shocks for you, or permanent damage for the device. If you have any doubts about how your wall sockets are wired, pick up a circuit checker at your local hardware store (for about $10 or less). This has indicator lights that show whether all three wires in the circuit are connected correctly. There's one more reason to consider a separate circuit for your computer equipment. Rather than buying separate standby power supplies for each computer, you might be better off buying a single, larger one, and installing it next to the electrical service. Taking electricity for granted is easy, and with a little preparation, you can work right through brownouts and blackouts with little risk to your equipment or data. Article reprinted from PC Magazine Mar 7 2000. (The best general computer magazine around) www.pcmag.com © Copyright 2001 by YourSITE.com |
