What Is the BLDC Motor Back-EMF & Torque Constant Calculator?
Kv and Kt are reciprocal fundamental constants governing electric motor performance.
A motor with higher Kv spins faster per volt but produces less torque per ampere of winding current.
How Does the BLDC Motor Back-EMF & Torque Constant Calculator Work?
Converts Kv in RPM/V into torque constant Kt in Newton-meters per Ampere.
Computes stall current based on terminal winding resistance and bus voltage.
Determines maximum theoretical mechanical power output at half stall speed.
BLDC Motor Back-EMF & Torque Constant Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Electromechanical conservation of energy linking voltage back-EMF and torque constant in SI units.
How to Use the BLDC Motor Back-EMF & Torque Constant Calculator
- Enter the Kv rating in RPM/V from the motor datasheet.
- Input the DC voltage supply and no-load current.
- Enter terminal phase-to-phase winding resistance in ohms.
Step-by-Step Example Calculation
Drone Propulsion Motor
Input Values:
Understanding Your Result
Kt in N*m/A indicates electromagnetic torque production capability.
Max power indicates theoretical peak wattage at peak torque loading before thermal throttling.
Factors That Affect the Result
- Permanent magnet flux density (NdFeB grade) and stator slot geometry.
- Temperature: Rare-earth magnet remanence drops with heat, reducing Kt and raising effective Kv.
When Should You Use This Calculator?
- Sizing electric actuators, drone multirotor powertrains, and EV traction drivetrains.
- Selecting electronic speed controller (ESC) current ratings.
Assumptions & Limitations
- Assumes sinusoidal or trapezoidal back-EMF with ideal electronic commutation.
- Neglects core iron eddy current and hysteresis losses at high rotational speeds.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Electromechanical conversion Kt = 9.5493 / Kv is exact in SI metric units.