BLDC Motor Rotor Armature Testing Equipment BEMF Magnetic Detection Single Station

(2) Testing item and accuracy

1. BEMF Testing, back electromotive force voltage

2. Magnetic Detection

If the rotor magnetic is strong enough

When the BDLC motor rotates, each winding generates a back electromotive force voltage (BEMF),

which, according to Lenz's law, is in the opposite direction to the main voltage supplied to the winding.

The polarity of this back EMF is opposite to the excitation voltage. Therefore, the voltage drop across

the winding can be calculated from the supply voltage minus the back-EMF value.

The back electromotive force constant is designed using the following method: When the motor is

running at rated speed, the potential difference between the back EMF and the supply voltage is

sufficient for the motor to consume the rated current and provide the rated torque. If the motor speed

exceeds the rated speed, the back EMF will increase significantly, reducing the voltage drop across the

winding and reducing the current, resulting in a drop in the torque curve.

Because the motor work is mainly reflected in the RMS voltage, the back EMF test is mainly to test the

effective value of the back EMF. Back-EMF mainly depends on three factors:

(1) Rotor angular speed ... is the servo drag speed for the test equipment

(2) The magnetic field generated by the rotor in this problem,This is a constant when the product is fixed

(3) Number of stator winding turns This is a constant when the product is fixed,

Back-EMF constant: Ke Unit: V/rpm or V/Krpm or V/rad/s,

therefore it is recommended to test the rotation speed at 1000 rpm.

Formula:

BEMF=(E)∝ NLRBω

N: the number of turns per phase winding

L: the length of the rotor (magnet part)

R: the inner diameter of the rotor

B: rotor magnetic field density

ω: the angular speed of the motor