The most popular and reliable back up system for any load is the UPS or Uninterrupted Power Supply as it has a multi purpose protection system for the driven load. An Uninterruptible Power Supply or UPS is an electrical apparatus that sits between a primary source and a device (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, spikes, harmonic distortion etc.) from the supply from harmfully affecting the performance of the device. A back up UPS contains a battery that starts to act as a proxy of the primary source when the device senses a loss of power from the primary source.
If you are using the computer when the UPS warns you of the power loss, you have time to save any data you are working on and exit gracefully before the secondary power source (the battery) runs out. When power suddenly runs out any data in your computer’s random access memory (RAM) is wiped out so using a back up UPS will provide you some buffer time which will consequently enable you to save that data in the RAM. When power surges occur, a UPS intercepts the surge so that it does not damage your computer. A UPS is typically designed to protect computers, large telecom centers, servers and control panels or other electrical equipments where an unforeseen power interruption could cause injuries and mortal losses, hamper business productions or data loss.
A UPS differs from a back up or emergency power system or standby generator in that it will provide immediate protection from source power interruptions with practically nil switch over time by means of one or more attached batteries and associated electronic circuitry for low loads and by means of diesel generators and flywheels for higher loads. A typical back up UPS is designed to keep the machine alive through a 15 minutes power loss which would allow the operator to bring a supplementary power source on line or to properly shut down the protected equipment. The power that comes from the primary source is AC and all the modern devices use AC power. However batteries provide DC power so a circuitry is used in all UPS’s to convert the AC power to DC power to charge the battery.
There are two common systems in use today: standby UPS and continuous UPS. A standby back up UPS monitors the power line constantly and switches to battery power as soon as it detects a problem to keep the system running through short blackouts and allow enough time to safely shut down the equipment during longer power outages. An UPS avoids momentary power lapses by constantly providing power from its own inverter even when the power line is functioning properly. It is a combination of inverter/converter and is always connected to the output, powering the equipment thus allowing faster response to a power failure than a standby UPS.