# Motor velocity constant

## Description

The constant Kv (motor velocity constant, or the back EMF constant) is a value used to describe characteristics of electrical motors.

The Kv rating of a brushless motor is the ratio of the motor’s unloaded rotational speed (measured in RPM) to the peak (not RMS) voltage on the wires connected to the coils (the back EMF).

Actually, the motor may not reach this theoretical speed because there are non-linear mechanical losses. On the other hand, if the motor is driven as a generator, the no-load voltage between terminals is perfectly proportional to the RPM and true to the Kv of the motor/generator.

This formula calculates the motor velocity constant.

Related formulas## Variables

Kv | motor velocity constant (rpm/V) |

ω_{NoLoad} | motor's unloaded rotational speed (rpm) |

V_{Peak} | peak (not RMS) voltage on the wires connected to the coils (the back EMF) (V) |