Enter the supply voltage, current at full load, and current at no load into the calculator to estimate the BLDC motor power. (Brushless Motor Power) The RPM per volt (Kv) is optional and is used only for torque/speed estimates in the calculation steps.

BLDC Motor Power Calculator

Enter any 3 of the 4 power values, or use the Kv tab for motor estimates.

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BLDC Motor Power Formula

The following equation estimates BLDC motor power using supply voltage and the “torque-producing” current (full-load current minus no-load current). This is an idealized estimate; real output power is lower due to losses and depends on the operating speed/torque point.

P \approx V\,(I - I_0)
  • Where P is the estimated BLDC motor power (watts, W)
  • V is the supply voltage (volts, V)
  • I is the current at full load (amps, A)
  • I0 is the current at no load (amps, A)

What is a BLDC Motor Power?

Definition:

BLDC motor power is the power delivered by a brushless DC motor at a specific operating point. Electrical input power is Pin = V·I, while mechanical output power is lower due to losses (copper loss, iron loss, friction, windage, and controller losses).

How to Calculate BLDC Motor Power?

Example Problem:

The following example outlines the steps and information needed to estimate BLDC Motor Power.

First, determine the motor’s RPM per volt (Kv). In this example, Kv is 350 RPM/V (optional for the power estimate).

Next, determine the supply voltage. In this example, the voltage is 48 V.

Next, determine the current at full load. This is measured to be 50 A.

Next, determine the current at no load. This is measured to be 10 A.

Finally, calculate the estimated BLDC motor power using the formula above:

P ≈ V·(I − I0)

P ≈ 48·(50 − 10)

P ≈ 1,920 W = 1.92 kW