The backup time is proportional to the load that is connected to the UPS. Backup time can be as little as 5-10 minutes, this will provide you with sufficient time to shutdown the equipment that is connected to the UPS before the power fails; or else you may require many hours of backup time so you can keep your equipment running until mains power returns.
Longer backup time and higher protection levels cost more than short backup times and lower protection levels.
A UPS system is often used to provide uninterrupted power after mains fail until a generator starts up.
The Watt rating must always be smaller than or equal to the V-A rating
AC power measurements are related as follows:
VA = Volts X Amps only if PF = 1
If PF is smaller than 1 then Volts X Amps = Watts, Watts รท PF = VA
Volts = 230 typical
Amps = Load Current
Power Factor = between 0 and
SIZING A UPS SYSTEM :
For example :
Computer equipment requires : 2 Amps (current)
Mains voltage used : 230VAC (AC voltage)
Power factor of computer equipment : 0.6 (typical for computer equipment)
2A x 230V = 460W / 0.6 PF = 766 VA
You will require a 800VA but to cater for your future expansions and to not stress the UPS by running on 100% load all the time, you always add 20-25% capacity. Therefore a 1000VA UPS (1KVA) should be used in this case.When choosing a UPS system it is a good idea to also plan ahead to cater for expansion so that your investment in a UPS does not outgrow your future needs.If several computers or pieces of equipment are involved, add all the Amps together and do the calculation as shown.
