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Navigation: Home > Hardware Info Library and Tips
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This page has been provided to help shed some light on the importance of each type of device that is commonly installed in or available for today's computers.
Courtesy Rick Russell Why Provide Back-up Power? Well, by now you've come out of the Y2K bunker and found that the power is still on. But providing clean electrical power to your computer is a year-round concern. Sudden power loss can cause all sorts of problems, especially with modern computers and operating systems which write to the hard disk almost constantly. An interrupted hard disk write can trash your operating system installation or damage files and applications. The solution is an uninterruptible power supply, or UPS. Put simply, the UPS is a big backup battery which provides the precious minutes required to save your work and shut down your computer in an orderly fashion when the power goes out. The circuitry inside the unit keeps the battery in a constant state of charge, and when there's a power glitch the circuits switch over to the battery. A UPS can do more than just provide backup power, too. Today's UPSes include surge & spike protection and interference filtering. Some UPSes have enough plugs to completely replace a power strip, and some come with telephone or ethernet passthrough plugs that isolate your modem and network card from surges carried over those lines. Cleverly designed UPS boxes can sit under the monitor, providing a power console and backup power. Choosing a UPS, the Traditional Way There are a lot of UPS choices, and choosing a UPS is easier than you might think. UPSes have two important performance numbers -- maximum power and run-time. The maximum power is usually represented in VA, or Volts times Amps. The UPS power must exceed the total power consumption of all devices attached to it, or the UPS will fail when the AC power goes out. The traditional way to compute maximum power is to multiply the operating voltage times the maximum current for each device on your computer system, then add them up. Looking at the back of a monitor, for example, you might find that it's rated at 110 volts and 1.5 amps, for a total of 110 * 1.5 = 165 VA. The computer itself might draw 2 amps at 110 volts, for 220 VA. If those were the only devices on your computer system, you would look for a UPS rated at 165 + 220 = 385 VA or more. Choosing a UPS, the New Way Although you'll always be safe if you choose a UPS based on the traditional calculation, you can do a more accurate calculation and save yourself some money by using a utility like those provided by APC, Tripp-Lite and Sutton Designs. APC and Sutton use a web form, and Tripp-Lite uses a downloadable caculator. Both utilities will help you profile the power use of your system and provide a more accurate value for the appropriate VA rating. Typically, this value will be lower than the traditional calculation. Run-Times Once you've settled on a maximum power rating for your UPS, look at the listed capacities or "run-times". The run-time determines how long the UPS will provide safe power. Normally, UPS companies provide two run-times -- the run-time at half maximum power, and the run time at maximum power. So if a UPS is rated at 450VA and has a listed full-power capacity of 6 six minutes, that means you can expect 6 minutes worth of safe power if you're draining the UPS at the full rated power of 450VA. Typically, the half-power run-time will be longer than twice the full-power run-time, because the backup batteries work much more efficiently when they are not fully loaded. In general, UPSes with higher maximum power capacity will provide longer run-times when attached to the same computer system, so you can get longer run times by picking a higher-rated UPS. An even better way to report run-times is to provide an extensive table matching power consumptions (in VA) to run-times in minutes, such as this chart for NetSaver WebUPS systems from Sutton Designs. I'm not sure why the more popular UPS companies like APC and Tripp-Lite don't report similar information. Extra Features Some UPSes come with extra convenience features which may be of value. The most popular extra feature is a serial or USB cable which connects to the back of your computer, and allows the UPS to signal a system shutdown in the event of power loss. Other nice extra features include surge protection for your telephone, 10BT ethernet or coaxial cable lines, or individual power switches to control the individual outlets. UPS Dos and Don'ts When you buy a UPS, you need to treat it right. Remember that it's got a large chemical battery in it, and you'll wear your UPS out before its time if you run it beyond its specifications.
Like any chemical battery, the battery in your UPS will eventually wear out. But if you treat it well, it should last for at least 4 to 5 years. Related: | |||||||
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