BLDC Efficiency Analyzer

This calculator breaks down BLDC motor losses into copper, iron, and mechanical components to determine efficiency across the operating range. Drone designers, EV engineers, and robotics developers use it to find the optimal current for maximum flight time or minimum thermal stress.

Total motor loss has three components. Copper loss $P_{Cu} = I^2 R_{phase} \times n_{phases}$ dominates at high current and scales quadratically. Iron loss follows the Steinmetz equation: $P_{Fe} = k_h f B^{\alpha} + k_e f^2 B^2$, where hysteresis loss ($k_h$ term) dominates below 500 Hz and eddy current loss ($k_e$ term) dominates above. For typical silicon steel laminations, $\alpha \approx 1.6$ and iron loss is roughly proportional to RPM$^{1.5}$. Mechanical loss $P_{mech}$ from bearing friction and windage is approximately constant for a given speed.

The efficiency curve $\eta = P_{out}/(P_{out} + P_{Cu} + P_{Fe} + P_{mech})$ peaks at a specific current. Per Krishnan (2010), the optimal current for maximum efficiency is $I_{opt} = \sqrt{P_0 / R}$, where $P_0 = P_{Fe} + P_{mech}$ is the speed-dependent no-load loss and $R$ is phase resistance. This occurs when copper loss equals the sum of iron and mechanical losses -- the equal-loss principle.

No-load current $I_0$ measured at operating voltage directly gives $P_0 \approx V \times I_0$ (since copper loss at no-load is negligible). This single measurement anchors the entire efficiency model. Per IEC 60034-2-1, the preferred method for small motors is loss segregation from no-load and locked-rotor tests.