A UPS is most efficient when it is 100% loaded, this is not an ideal condition in reality as it doesn't allow any overhead for increases in load. Depending on the type of UPS the full-load efficiency is normally between 85-95%.
How is UPS efficiency determined?
The efficiency is determined by two factors:-
- The amount of power lost during the conversion stage (if any) of the UPS
- The amount of power required to operated the UPS circuits and battery chargers
In a Standby UPS, the incoming power to flows straight through to the connected equipment, the only power required by the unit itself is to operate the electronics of the unit and keep the battery charged. This makes them very efficient but provides less protection than Online UPS.
In an Online or Double Coversion UPS, the device converts the incoming AC power to DC, and then back to AC to provide a clean sinewave out. Because there is energy lost in every conversion this 'double conversion' system has lower efficiency when compared to a stanby UPS, but this is the price you pay for better protection.
