Light curtain ensure the safety during testing of rotor spining for
magnetic testing
(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
