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An introduction to UPS Battery Backup

This guide should give anyone interested in protecting their equipment with an UPS the basic grounding to make the right purchase

What is the point in a UPS?

It is important to protect sensitive electronic equipment such as computers from fluctuations and cuts in the power as unexpected loss of power can cause permanent damage to components and data loss. A UPS will act as a surge protector, battery backup and generally “smooth” out the power your computer receives and ensure maximum stability. UPS devices are normally found attached to expensive mission critical workstations (such as graphical workstations or CAD machines) or servers where any downtime is unacceptable.

How do UPS devices work?

UPS systems work by detecting decreases in the amount of electricity coming from the wall circuit and then boosting power to maintain a constant flow of electricity to the connected equipment. This power boost is achieved either from an internal transformer than enhances the electricity supply or from an internal battery that substitutes for the normal power source in the event of power failure.

What types of UPS are available?

There are three major types of UPS available in the market, each with their own advantages and cost.

Off-Line Units: Off-line units switch from the regular power source to an internal battery when there is a power drop. There is a brief delay between the time the power drops and the time the battery starts supplying power. However this downtime should be brief enough to avoid causing the computer to shut down. On-Line units are normally the cheapest UPS products available.

Line-Interactive Units: Line-interactive units add a transformer to minimise the need for an internal battery to be used with every power fluctuation. These units monitor the line voltage at all times and active the power transformer when the voltage falls below certain parameters. The battery is only ever activate when lower voltages are recorded. There is a brief delay between the time the power drops and the time the battery starts supplying power. However just like the Off-line units this downtime should be brief enough to avoid causing the computer to shut down.

On-Line Units: On-line units constantly supply power to the connected PC from their internal battery; the battery is constantly charged and depleted on an ongoing basis. There is no lag time between power failure and battery backup as these units constantly server as the primary power source for the connected computer. In the case of a power cut the On-line UPS will continue to generate power keeping the PC running, but will be unable to recharge.

How do I choose the right UPS?

When deciding what type of UPS to purchase, you should determine how much an unexpected power failure would impact you or your business.

On-line units offer the most protection, since they run constantly. The additional cost of these systems is often deemed worthwhile for key equipment where a shutdown is unacceptable. They are usually recommended for mission critical applications such as phone systems or a computer server.

Standby and line-interactive UPS are more appropriate when an unexpected power outage, and the resulting loss of data or other information, would be more of an inconvenience than a major problem. These systems should be able to keep equipment going during most power fluctuations, but there may be the occasional situation where they do not quite work as expected. They can be a more cost-effective solution for equipment such as standalone computers or a fax machine.

Line-interactive UPS are best suited for situations where power fluctuations are common occurrences. Power fluctuations occur when "power-hungry" equipment such as an air conditioner is frequently turned on and off, causing brownouts and surges. With line-interactive UPS, these fluctuations can be handled by the transformer instead of the internal battery.

How big a UPS do I need?

To add up all the power requirements of protected equipment and make sure that the UPS has a protection capacity that is equal to or greater. If your equipment is measured in Amps, just multiply it by the number of volts it requires and that will give you the VA rating. It is recommended to use a UPS that has a protection rating that is greater than the total power needed for the protected equipment, by at least 25%. For most multiple computer setups, units that offer a power protection capacity of 500 - 1000VA tend to suffice. However, this should not be a substitute to calculating your equipment's "true" power requirements.

How long will my UPS last for?

UPS units are designed to provide about ten minutes of backup power. This should be enough time to appropriately shut down the connected equipment and avoid data loss. Since power cuts typically last no more than two minutes, this should also be enough time to work right through most power failures.

Manufacturers report how long a battery will last under full-load or half-load conditions. Running under full load signifies that a UPS is working at its maximum capacity. A typical UPS should report a full-load time duration of about ten minutes. Under half-load conditions, when the UPS provides only half the power it is capable of generating, the time duration is often more than three times as long.

If ten minutes is not enough security for you or your company's needs, there are also units that can last as long as a day on backup power. This is ideal if you need a system to operate overnight. While this amount of backup may seem much more desirable, it can cost significantly more.

Another option is to purchase extra battery attachments. Expect these extra batteries to cost about one-fourth to half the price of the UPS itself.