3
\$\begingroup\$

For example the computer's fan motor.

\$\endgroup\$
2
  • \$\begingroup\$ Yeah, double fun. Anyway, yes it can. It's called "sensorless BLDC control". Or it can work with encoder rather than hall sensor. \$\endgroup\$ – Eugene Sh. Nov 23 '17 at 16:12
  • \$\begingroup\$ Yes. There are some consequences, but for a fan, the consequences are not very important. Most quadcopter (sometimes known as "drone") motors do not have Hall sensors. For a car or other vehicle, it is very helpful to have either Hall sensors or a rotor position sensor (shaft encoder). Otherwise, before sensorless control can begin, the motor may briefly spin backwards, which can cause alarm to the rider. \$\endgroup\$ – mkeith Nov 23 '17 at 18:31
2
\$\begingroup\$

If you think about it a BLDC without sensors is just a "three" phase synchronous motor, or maybe even a low pole count stepper motor, so yes you can drive it without sensors.

With sensors of course you can maximize the torque and control the phase angle to a high degree of precision and reduce the power consumed by the motor. Further, with sensors the motor can also drive much more variable loads without stalling.

As Neil suggests there are also ways to use the back-EMF from the motor to control it without sensors too that give you a less precise compromise.

\$\endgroup\$
5
\$\begingroup\$

Hall sensors are necessary if you want a BLDC to start with high torque, or be controlled down to very low speed.

If you simply want a spinning motor for a propeller, then the ESC can work with the back EMFs from the coils themselves to control current and speed, after a few trial pulses have kicked it into motion. This is the so called sensorless mode of control.

\$\endgroup\$
1
  • 2
    \$\begingroup\$ Without either Hall or shaft position sensors, the motor may sometimes turn backwards slightly before control is established. That is OK for fans and propellers, but not OK for elevators. \$\endgroup\$ – mkeith Nov 23 '17 at 18:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.