An Uninterruptible Power Supply (UPS) is a device that provides battery backup when the electrical power fails or drops to an unacceptable voltage level. Small Uninterruptible Power Supply systems provide power for a few minutes; enough to power down the computer in an orderly manner, while larger systems have enough battery for several hours. In mission critical datacenters, systems are used for just a few minutes until electrical generators take over.
UPS systems can be set up to alert file servers to shut down in an orderly manner when an outage has occurred, and the batteries are running out.
A surge protector filters out surges and spikes, and a voltage regulator maintains uniform voltage during a brownout, but a UPS keeps a computer running when there is no electrical power. Uninterruptible Power Supply systems typically provide surge suppression and may provide voltage regulation.
A standby uninterruptible power supply, also called an "offline uninterruptible power supply," is the most common type of UPS found in a computer or office supply store. It draws current from the AC outlet and switches to battery within a few milliseconds after detecting a power failure.
The line interactive Uninterruptible Power Supply "interacts" with the AC power line to smooth out the waveforms and correct the rise and fall of the voltage.
The online Uninterruptible Power Supply is the most advanced and most costly Systems. The inverter is continuously providing clean power from the battery, and the computer equipment is never receiving power directly from the AC outlet. However, online units contain cooling fans, which do make noise and may require some location planning for the home user or small office.
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