Brushless DC Motors Interview Questions

1. What is the voltage constant?

• RPM
• Volts

2. What is the torque constant?

• Torque
• Current

3. What is the stator?

The Stator contains all the coils of wire which will have voltage induced in them as the magnets pass over them.

4. What is the difference between Wye and Delta windings?

Wye windings give high torque at low rpm, and Delta windings give low torque at low rpm.

5. How do you find the voltage constant?

Take the No load speed and divide by the input voltage applied.

6. What happens when voltage is increased?

The speed of the motor increases as well.

7. What happens when the voltage is decreased?

The speed of the Brushless DC Motor decreases also.

8. If you have two different input voltages and the same torque, what happens to the current and why?

The current will stay the same because of the torque constant. Torque is only relative to Current not voltage.

9. How many phases are in a Brushless DC Motor?

3

10. What is the difference between a Brush DC motor and Brushless DC Motor?

A DC Brushed Motor needs physical contact to pass current through its motor windings to allow commutations. A DC Brushless Motor needs a controller to commutate.

11. How many pulses per revolution in a 4 pole and 8 pole motor for one hall sensor?

4 Pole Motor has 2 pulses per revolution: 4/2 = 2 Pulses
8 Pole Motor has 4 pulses per revolution: 8/2 = 4 Pulses

12. How do you change the direction of the motor by wire swapping?

Switch around the Phases along with the Hall Sensors.