UPS Sizing Calculator
Size a UPS for a control system, server or instrument panel. The UPS must cover both the real power (W) and apparent power (VA) of the load with a margin for growth.
- Design load = 2,400 × (1 + 0.25) = 3,000 W
- kVA needed = max(W ÷ load pf, W ÷ UPS pf) = 3.333 kVA
UPS Sizing Method
Required kVA = max(W ÷ load pf, W ÷ UPS output pf) ÷ 1000
Worked example
A 2,400 W control panel with pf 0.9 and 25 % margin needs 3,000 W and 3.33 kVA, so a 5 kVA UPS (4.5 kW at pf 0.9) is the next standard size.
Frequently Asked Questions
How do I size a UPS?
Add up the load in watts, add a growth margin, and check that both the kW and kVA ratings of the UPS exceed the load.
What is UPS output power factor?
The ratio of the UPS kW rating to its kVA rating. Modern units are typically 0.9 or 1.0.
Does UPS size affect backup time?
Backup time depends on the battery and the actual load, not on the UPS rating. Use the battery backup calculator for runtime.
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