Calculate transformer efficiency across load levels, including no-load and copper losses.
Iron loss is constant while copper loss rises with the square of load, so efficiency peaks where the two are equal. That optimum is usually between 40 and 60 per cent of rating, which is why transformers are rarely sized for continuous full load. A transformer left energised at light load still burns its full iron loss, which over a year is often the larger part of the total.
Transformer Efficiency
η = output ÷ (output + iron loss + copper loss × load²); maximum efficiency at load = √(iron ÷ copper)
η = output ÷ (output + iron loss + copper loss × load²); maximum efficiency at load = √(iron ÷ copper) Iron loss is constant while copper loss rises with the square of load, so efficiency peaks where the two are equal. That optimum is usually between 40 and 60 per cent of rating, which is why transformers are rarely sized for continuous full load.
A transformer left energised at light load still burns its full iron loss, which over a year is often the larger part of the total.
This calculator takes 5 inputs: Transformer rating, Loading, No-load (iron) loss, Full-load copper loss, Load power factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.