Single phase uninterruptible power supplies (UPS) sit between an AC outlet (i.e., a wall outlet or power strip) and an electronic device (such as a computer, server, or phone equipment) to provide power conditioning, back-up protection and distribution for electronic equipment loads and to prevent power disturbances (outages, sags, surges, spikes, noise, etc.) from affecting the performance and life of the electronic device and vital data.
The most important capacity specifications to consider when specifying uninterruptible power supply (UPS), single phase include the volt-amp rating, watt rating, and input voltage range. UPS units are rated in volt-amperes (VA) or kilo-VA (kVA). The VA rating is the maximum number of Volts * Amps a unit can deliver. The VA rating is not the same as the power drain (in Watts) of the equipment. The easiest way to find out how many VA is needed is to look at the back of the equipment that is to be protected and note the total number of amps listed for each device. Take the total and multiply it by the nominal voltage (120V) to get the number of VA. For example, a computer and monitor which are both rated at two (2) amps would require 480VA (2A+2A=4A 4Ax120V=480VA). With this rating, at least a 500VA UPS is recommended. The watt rating is specified only if VA Rating is not known (the Watt Rating is less than or equal to VA Rating). The input voltage range is the precise identification of the electrical system is critical in the proper selection and application of a UPS device.
In an uninterruptible power supply (UPS), single phase the unit type can be on-line or double conversion, line-interactive, hybrid or ferroresonant, and off-line or standby. In an on-line unit the load is supplied from a power converter that always operates and takes its input from a DC supply. The DC supply consists of a battery and a large battery charger, which are connected in parallel. In a line-interactive unit the inverter works in parallel with conditioned input AC power to supply power to the load (boosting or bucking), and only handles the full load power when the AC input power fails. With a hybrid unit the supply conditions power using a ferroresonant transformer. This transformer maintains a constant output voltage even with a varying input voltage and provides good protection against line noise. With an off-line unit the power is usually derived directly from the power line, until power fails. After power failure, a battery-powered inverter turns on to continue supplying power. Mounting options for uninterruptible power supply (UPS), single phase include tower type, rack or tray, strip type or plug strip, and mounts on or in device protected.
Important runtime specifications for uninterruptible power supply (UPS), single phase include runtime at half load, runtime at full load, and switchover time. Runtimes refer to the length of time the UPS will run at half load, full load, and the amount of time for switchover. On line or double conversion units do not have a switchover time. Important output specifications include output voltage in battery mode, number of "backed-up" electrical outlets, and outlet options. Outlet options include additional electrical outlets, RJ type connectors, and coaxial cable connectors.
Other important parameters to take into consideration when specifying uninterruptible power supply (UPS), single phase include performance features, interfaces, surge suppression options, general features, and environmental operating conditions. Common performance features include self-diagnostics, automatic shutdown, automated saving, and application software. Interface choices include serial, parallel, other digital, modem, Ethernet, and PC card. Surge suppression options include UL 1449 rated surge protection, rated AC energy absorption, and maximum surge current. Additional features to consider include LCD or LED display, expandable battery jacks, integral audible alarms, manual bypass switches, and hot-swappable batteries. An important environmental operating parameter to consider is operating temperature.