UPS is the abbreviation of Uninterruptible Power Supply, in the name, the unit would supply the power generated from the batteries in very short time to maintain the system or appliances without break when the AC mains got off. Besides the main function to support the continuous power supply, UPS is also built-in protection circuit to protect the connected devices or data when the AC mains is in bad condition such as SAGS, spikes, surges, noise or transient high/low voltage happened. So, what the UPS do is to supply the steady and clean power to the connected devices and applied widely for the computer systems, surveillance or test instruments, medical equipments, home appliances etc.
When mains fault, The UPS offers power to load depend on battery. A standard type UPS with battery(ies) inside. When mains fault, the UPS can continuous offer uninterruptible power for about several minutes or even several ten minutes. But the long backup type UPS collocates battery(ies) bank outside, is able to offer power for a long time, meet the user demand. Commonly, a long backup type UPS, with full load, can offer several hours.
And the battery is affected by the load, battery capacity, ambient temperature, battery discharge cut-off voltage, and so on. Commonly, after calculated the UPS backup time, you can calculate out the discharge current, and then understand the discharge time according to the battery discharge curve. What’s more, you can calculate the discharge power current by the following formula:
Discharge Current=UPS Capacity(VA)*Power Factor/UPS DC Voltage(VA)*Efficiency
This discharge current can be regard as this UPS, with full load, needed battery capacity for back up time is one hour.
For example, a UPS: power factor is 0.75, efficiency is 0.8, built in DC Current is 48V, so this UPS discharge one hour will need about: 48V-58.59Ah battery capacity, and if require back up for 2 hours, that is 59.59*2, can choice one bank batterie 48V100Ah or two banks 48V65Ah.
According to the back up time, UPS has Standard Type and Long Backup Type.
Standard type with battery(ies) inside, and its power offing time is short, mainly about 5 to 15 minutes.
Long Backup type is depending on customer need, adding the capacity of battery(ies) collocation, extending back up time.