# How is output power of bldc motor calculated?

#### Eartian

Joined Sep 16, 2021
3
How is output power of bldc motor calculated? Can we convert any 3 pase induction motor to bldc motor (diy)?

#### Papabravo

Joined Feb 24, 2006
17,240
The output power of a motor has an upper bound which is the input power. Input power is a function of current and voltage. There will be losses that you can estimate and arrive at an efficiency factor which is then applied to the input power. You can also measure the mechanical power output of a motor by measuring the amount of work done in interval of time.

A key feature of the BLDC motor is the sensing of rotor position to do the communtation at an arbitrary rotational velocity. I don't think that a 3-phase induction motor has this capability, so I would have to answer no without more information.

• Eartian

#### MrSalts

Joined Apr 2, 2020
712
As @Papabravo hinted at, the efficiency (accuracy) of your commutation switching will be key to maximizing output power in a BLDC and, since you don't know how inaccurate you are, there is no reason to calculate the power. Just measure the power by directly connecting a flywheel to the motor and measuring the time to spin the flywheel up to speed. Add some graduation lines to the flywheel with a black market and use a reflection ir sensor to measure the passing of each black line.

Or, if you want to get more complicated, here is a diy dyno project...
https://maker.pro/custom/tutorial/diy-electric-motor-dynamometer-design-principle-and-physics

• Eartian

#### Eartian

Joined Sep 16, 2021
3
The output power of a motor has an upper bound which is the input power. Input power is a function of current and voltage. There will be losses that you can estimate and arrive at an efficiency factor which is then applied to the input power. You can also measure the mechanical power output of a motor by measuring the amount of work done in interval of time.

A key feature of the BLDC motor is the sensing of rotor position to do the communtation at an arbitrary rotational velocity. I don't think that a 3-phase induction motor has this capability, so I would have to answer no without more information.
Thank you

#### Eartian

Joined Sep 16, 2021
3
The output power of a motor has an upper bound which is the input power. Input power is a function of current and voltage. There will be losses that you can estimate and arrive at an efficiency factor which is then applied to the input power. You can also measure the mechanical power output of a motor by measuring the amount of work done in interval of time.

A key feature of the BLDC motor is the sensing of rotor position to do the communtation at an arbitrary rotational velocity. I don't think that a 3-phase induction motor has this capability, so I would have to answer no without more information.
Thank you