Selecting a proper Uninterruptible Power Supply (UPS) for power protection of your personal computer or small office can be easily accomplished based on specifying the right UPS and implementing a smart shopping method.



UPS systems solve three basic problems:



Firstly they protect your computer from utility voltage deviations beyond permitted margin, and from hazardous phenomena associated by high voltage surges occurring during lightning, Power Transformers failures and grid distribution failures.



Secondly they allow you to continue operation from UPS backup batteries upon mains outage.

Thirdly the UPS allows graceful shut down, by storing current information on computer's hard disk, and turning your computer off in an orderly manner, in case mains outage persists, and battery capacity is too small to continue operation.



To specify a proper UPS you need to decide its Size, Type and Battery Backup (Autonomy) Time.



Size of a UPS is defined by Volt-Ampere (VA) or kVA units and Watt or kWatt units. A UPS rated higher than 350VA and 245Watt covers most home and small office computers. You should however check computer power from its label, literature or supplier.



The VA and Watt figures of the individual computers should be added up if more than a single computer is protected. You need a UPS grater than 1050VA, (1.05 kVA) and 735W, for three 350VA/ 245W computers.



Three main UPS types are generally used:



A Standby (Battery Backup) UPS, protects against voltage surges, as well as utility outages, and voltage deviation beyond set limits, transferring to battery operation. Backup UPS frequently used for home computers in stable grid environments.



A line Interactive UPS, in addition to the functions of Standby UPS, acts also as Power Conditioner, achieved by means of an Automatic Voltage Regulator (AVR), able to correct also mains deviation without transferring to batteries, thus enabling continuous operation at low or high mains voltage without switching to batteries. Line Interactive UPS is considered to be a cost effective solution for office and small professional installations.


An Online UPS, supplies power from internal Inverter correcting all grid disturbances. It forms the preferred solution for business in mission critical application which need UPS redundancy for achieving high reliability or extended back up times for providing critical on line services.



All UPS system types are normally supplied with batteries able to supply about five minutes backup time at full load and 14 minutes half load, thus covering above 90%-95 % of expected utility fail durations. Generally longer backup times can be provided by extended battery banks, if needed for service supplying applications.



After specifying the needed UPS characteristics, you can contact UPS suppliers or seek a proper UPS on the internet, just by entering the type of the UPS in Google or other search engine, and browsing in the displayed results for systems that meet your requirements.



You can do however better by implementing a "window shopping" procedure. Before making a decision, check prices of UPS type you need, in sizes you need as well as one and two sizes bigger than needed. Afterwards, repeat the procedure for the next UPS type.



Then make your decision taking in account the following factors:



Prefer a Line Interactive UPS over Battery Backup and Online UPS over Line Interactive UPS if the difference in price is not significant. The better type provides better protection and is generally more reliable.



Prefer bigger UPS size if the added cost is not proportionally higher. The bigger UPS enables to increase future loads and provides un-proportionally higher battery backup time, sometimes at lower cost than extended Power Battery if needed. Bigger systems also offer better UPS reliability, considerably increasing battery lifetime.



When making final selection prefer brand names, such as GE, APC, Eaton, Powercom, Minutemen, MGE and Chloride Power, considering also as such issues as power battery swapping ability, type and quantity of outlets, warranty period and local service availability.