What is UPS efficiency and how is it calculated?

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The efficiency of a UPS (uninterruptible power supply) is defined as the ratio between the output electrical power and the input electrical power. For example, in a UPS with 97% efficiency, 97% of the input electrical power is used to power the load (at the UPS output) while 3% is absorbed by the UPS and lost in thermal dissipation.

As a UPS runs 24/7/365, efficiency is one of the key criteria when selecting a UPS because it strongly impacts the TCO (total cost of ownership). A low-efficiency UPS will add hidden costs such as electricity and air conditioning fees. For instance, for larger UPSs such as 3-phase systems, the cost of electricity over the lifetime of the unit (typically 10 to 15 years) can vary from 2 to 5 times the initial price of the UPS.

Efficiency also varies a lot, depending on the load. Efficiency ratio is usually optimal when the system is loaded at 30-90% of the total capacity, so it’s important to consider the actual efficiency rate (usually provided by the UPS manufacturer) at the real load that the system will run. One simple way of estimating the impact of 3-phase UPS efficiency on the electricity consumption is to use the 3-phase UPS efficiency calculator.

For customers concerned with electricity costs, Schneider Electric has developed a unique high-efficiency mode that achieves 99% efficiency while keeping the protection of critical loads at the maximum level (Class 1 UPS performance per IEC 62040-3). It is called eConversion. This patented mode drastically reduces electricity waste and heat generation during UPS operation, which saves electricity, money, and reduces CO2 emissions. Learn more on the eConversion page.