BLDC motor, easy simple way to get RPM?

Thread Starter


Joined Nov 23, 2021

I'm trying to work out how to get an RPM signal for an existing BLDC motor, motor is a sensorless type (uses EMF).

Since each winding of a BLDC motor is energized in a positive way for each rotation of the motor, can I just use a current detection circuit on one of the windings to determine an RPM pulse/trigger? May require some circuitry to clean up the signal.

Thank you for any responses.


Joined Jul 18, 2013
A BLDC motor has only two windings energized at any one time, in some cases the BEMF on the unpowered winding is used for detection.


Joined Jan 23, 2018
Rather than hack into the drive circuit to monitor current, it would be much less intrusive to sample the voltage on one of the drive connections. Even simpler will be if the driver module has a speed signal output, which some do. So the very first step will be to read the information that came with the system, and then to examine the driver assembly. Much wiser than hacking in to a system where you have no clues.