Clarification, I think I mean 3 slots per phase?
Thanks, KennyBobby. I'll try energizing one phase and count the number of strong attractions to that position. Should work, right?Another solution is 18 stator slots would produce cogging at 18 cogs per rev. The magnets are attracted to the stator pole teeth and create a detent position.
But i don't think you can determine the number of rotor poles by counting cogs.
If you measured the frequency of the inverter and the RPM of the motor then you could determine the number of poles.
The number of stator slots can vary depending upon the winding pitch and amount of overlap between phase windings.
Yes, I would expect so... that count will be the number of rotor pole pairs (not poles).I'll try energizing one phase and count the number of strong attractions to that position. Should work, right?
Right, kennybobby, I was blinkered and only thinking in delta. I'm not going to open the motor up. I do have an oscilloscope, and so your suggestion is probably the way I will go. Am I correct in thinking this will work whether the motor is wound wye or delta?How do you energize just one phase--is it a wye-winding with the center tap exposed?
If you can access the 3 leads for the motor windings, then you can build a 3 resistor wye circuit and connect it in parallel to the 3 motor leads. use 100k or larger resistors and solder three ends together. This will create a center tap reference point for measuring the back emf as you manually spin the rotor. Put an oscilloscope lead on a phase wire with ground on the center tap. As you spin the rotor thru one revolution, you will see a cosine wave on the scope. Count the number of number of cycles to determine your pole count. e.g. a 6 pole motor will generate 3 sine waves per revolution. N-S-N-S-N-S