Energy systems
Conversion efficiency and losses
- where
- power lost (W)
- useful output power (W)
- conversion efficiency
Explain this equation
Gives the power lost in a converter, such as an inverter, power supply or drive, from its useful output and efficiency. Use it to estimate heat to be removed from an enclosure, or the extra energy drawn.
P_out is the useful output power in watts. η is the conversion efficiency as a decimal. P_loss is the power wasted, nearly all as heat. The calculator also shows the input power, P_out / η.
Input is output divided by efficiency, and loss is input minus output. Putting those together gives P_out × (1/η − 1).
900 W out at 90% efficiency means 1000 W in and 100 W lost. At 95% the loss falls to about 47 W. Small changes in efficiency make a big difference to heat, because the loss rises quickly as η falls.
Watch out: enter efficiency as a decimal. Taking 10% of the output (90 W here) understates the loss; the correct figure is 100 W. Efficiency also varies with load.
Efficiency compares useful output with input. Divide the required output by efficiency to obtain input power, then subtract output to obtain the loss.
Loss appears mainly as heat and can affect enclosure cooling and energy use. Efficiency varies with operating point, so use data for the actual load.
Enter your values to see the result.
Common mistake
Subtracting the efficiency percentage directly from watts.
Limits
Steady-state supplied efficiency; not a full thermal design. Auxiliary loads must be accounted for consistently.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.