Easiest way to determine pole pairs of a BLDC motor

First ensure the all 3 phase wires are disconnected from controller and not touching anything.

1. Rotate motor until you have a distinct reference for when the motor has been rotated 360 degrees (1 complete turn). In this case i use the valve stem on the motor and the rear spring support on the swingarm.

2. Connect any 2 of the 3 phase wires together, making sure the third is not touching anything.

3. Rotate the motor and feel for the resistance points and count them. Might take a few tries because you need to rotate fast enough to generate the pulse but slow enough to count them. Lol

In this case I have 40 pole pairs. This means inside there are 80 little magnets.

Every programable connector will ask you the pole pairs because there is no controller that can detect them. The controller doesn’t need this information to run properly, but in order to determine RPM, it must know how many magnets are passing a specific hall sensor.

This RPM is only for the human, not the controller. The controller only cares about commutations and it can report everything in commutation per minute but then the human’s brain will explode.

In the Fardriver, if you’re run Autolearn with the default 4 pole pairs set, everything still works fine but all rpm shown in the app will be 10x faster than the real RPM in a 40 pole pair motor. Then the human might say “dang, my motor going 6000 rpm, like a boss”, and rhen everyone else will know you are clueless. Lol

If you later change pole pairs from 4 to 40, the fardriver will auto rescale all RPM references in settings for you. This makes it easier to know what speed your display should be showing because if you measure tire O.D., and know the RPM, and learned 5th grade math, you can calculate speed. If the display is off, there are settings to send more or less pulses to make it accurate. Final calibration is done with GPS.

So while the controller doesn’t need the information to run, its still best to set it correctly from the start, and it may prevent issues down the road.

Even if you think its 24 pole pairs because a little birdie told you so, just check it to be sure. Then set it correctly.

If the motor is opened for any reason, you can count the magnets and divide by 2 to get pole pairs. But don’t open the motor unnecessarily.

0:00 align references points to know when its rotated exactly 360 degrees.
0:15 short any two phase wires together, ensuring the 3rd wire is not touching anything.
0:20 briskly but gently rotate the motor, counting each resistance point you feel.
0:30 1, 2, 3, 4, 5, 6, 7, 8, 9, 10….
0:35 11, 12, 13, 14, 15, 16, 17, 18, 19, 20…..
0:39 21, 22, 23, 24, 25, 26, 27, 28, 29, 30….
0:44 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 pole pairs.