The UPS VA Rating you require will depend on the load current of the equipment you intend plugging into the UPS.
To calculate the VA Rating : multiply the Amps of the equipment (normally indicated on a label on the rear of the equipment or in the technical
manual or ask the supplier) you will use with the mains voltage you require and divide by the Power Factor (PF) of the equipment.
Sizing a UPS System
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 UPSdoes 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.
The backup time is proportional to the load that is connected to the UPS. The higher the load, the less the backup time. You can have
backup time as little as 5 minutes which will enable you to shut down the equipment connected to the UPS before the power fails;
or 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.
UPS Topologies and Protection Offered
OFFLINE (BACKUP, STANDBY)
Standby- is the most basic UPS topology. A standby UPS resorts to battery backup power in the event of common power problems
such as a blackout, voltage sag, or voltage surge. When incoming utility power drops below or surges above safe voltage levels,
the UPS switches to DC battery power and then inverts it to AC power to run connected equipment. These models are designed for consumer
electronics, entry-level computers, POS systems, security systems, and other basic electronic equipment.
A line interactive- UPS incorporates technology which allows it to correct minor power fluctuations (under-voltages and over voltages)
without switching to battery. This type of UPS has an autotransformer that regulates low voltages (e.g., brownouts) and over voltages
(e.g., swells) without having to switch to battery. Line interactive UPS models are typically used for consumer electronics, PCs, gaming systems,
home theater electronics, network equipment, and entry-to-mid-range servers. They provide power during such events as a blackout,
voltage sag, voltage surge, or over-voltage. A double-conversion (online) -UPS provides consistent, clean, and near perfect power regardless
of the condition of incoming power. This UPS converts incoming AC power to DC, and then back to AC. UPS systems with this technology operate
on isolated DC power 100 percent of the time and have a zero transfer time because they never need to switch to DC power.
Double-conversion UPS systems are designed to protect mission-critical IT equipment, data center installations, high-end servers,
large telecom installations and storage applications, and advanced network equipment from damage caused by a power
blackout, voltage sag, voltage surge, over voltage, voltage spike, frequency noise, frequency variation, or harmonic distortion.