Uninterruptible Power Supplies - 08 Mar 2000

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Power interruptions can cause severe repercussions for business computer systems. The problem is especially difficult in places where power outages and fluctuations frequently occur.

A UPS provides a backup battery and power inverter circuitry to insulate systems and data from power outages. In situations where momentary power fluctuations occur, a UPS provides constant power to keep your systems running. During extended power failures, a UPS provides backup power to keep your computers running long enough so that you can gracefully power down. The transfer time to backup is typically very short (usually rated in milliseconds) to maintain system and data integrity. Many UPSs provide filtration circuitry to eliminate voltage spikes, and some also deliver a constant voltage to your systems when the utility voltage surges or sags.

When choosing a UPS, match the unit's capacity to your needs. UPS vendors provide VA (volts * amperes) power ratings to indicate the maximum amount of power provided when AC power is present. Some UPSs might provide less power than their VA rating suggests because of losses incurred during the conversion from AC to DC, so it is also important to verify the UPS's output wattage. The wattage ratings listed on your computer equipment might not accurately represent the amount of power your system uses. You should either measure your equipment's actual power draw or select a UPS with a wattage rating that significantly exceeds the wattage rating on your equipment. The UPS's output wattage rating might not have any relevance to the unit's battery runtime under your projected power requirements. Carefully read the vendor's battery life specifications and consider the typical length of the power outages in your area.

After you address the electrical concerns, consider the optional hardware available or the features that the vendor's management software provides before you buy. For example, if the UPS must protect a group of servers, the management software's ability to vary the amount of time it takes to close each server's applications and shut down when power fails might be an essential feature. You might also want the UPS's software to alert the administrator and network users about an impending shutdown.

Finally, it's important to ask questions about the vendor's warranty and on-site service options. Remember that in a few years you'll have to replace the batteries, and replacement is quite labor-intensive if you plan to purchase numerous units. Securing on-site service options with the vendor before you purchase might free your IT staff from that labor in the future. Make sure you explore all the possible warranty alternatives with the vendor so that you receive the option that is most convenient for you.

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