1. The Difference Between Sensored and Sensorless Brushless Motors
The key difference between a sensored brushless motor and a sensorless brushless motor lies in whether a Hall sensor is used to detect the rotor position.
A Hall sensor operates based on the Hall effect: when a current-carrying conductor is placed in an external magnetic field perpendicular to the current direction, a potential difference (Hall voltage) is generated across the conductor in the direction perpendicular to both the current and the magnetic field. By using Hall sensors, a sensored brushless motor can directly and accurately detect the rotor position regardless of whether the motor is running at high speed, low speed, or is completely stationary.
A sensorless brushless motor does not use Hall sensors. Instead, it detects the rotor position indirectly by monitoring the back-EMF (voltage) and current changes in the motor windings to determine the commutation timing.
2. Characteristics of Sensored and Sensorless Brushless Motors
| Feature | Sensored Brushless Motor | Sensorless Brushless Motor |
|---|---|---|
| Rotor position detection at standstill | Can detect rotor position at rest | Cannot detect rotor position at rest; the rotor must be rotating to generate detectable back-EMF |
| Starting behavior | Smooth start and stop | May experience shaking or jitter during start and stop |
| Anti-interference | Hall sensors provide accurate position feedback with relatively low susceptibility to electrical noise | More susceptible to interference, especially at low speeds |
| Low-speed performance | Better torque performance at low speeds; can operate accurately even at standstill | Torque performance degrades at low speeds due to weaker back-EMF signals |
| High-speed performance | Good, but Hall sensor signal frequency increases with speed | Well-suited for high-speed operation where back-EMF signals are strong and easy to detect |
3. Application Scenarios for Sensored and Sensorless Brushless Motors
When choosing between a sensored and a sensorless brushless motor, consider the following factors:
- Speed range: For high-speed applications, a sensorless motor is generally recommended. For low-speed applications, a sensored motor is preferred.
- Control accuracy: If high-precision control is required, choose a sensored motor. If the control requirements are relatively relaxed, a sensorless motor is sufficient.
- Cost: Sensorless motors are typically more cost-effective. If budget is a primary concern and high accuracy is not critical, a sensorless motor is a good choice. If high accuracy and stable operation are required, a sensored motor is recommended.
- Cable length: When the cable distance between the motor and the driver is less than 3 meters, a sensored motor can be used. When the distance is 3 meters or more, a sensorless motor is recommended to avoid signal interference on the Hall sensor cables.
Summary: Sensorless brushless motors are well-suited for small- to medium-power, high-speed applications such as fans, drones, and RC models. Sensored brushless motors are better suited for high-precision and high-power applications such as CNC machine tools and industrial automation equipment.