Sorry that my description was not clear enough. I did connect the Simonk 20A ESC to the 12V/150W transformer. Then I used ESC tester to start the propeller and control its speed. Voltmeter did show 12.2V always. What changed was what amperemeter showed for different speeds selected by ESC tester:
Now I did measure again with laser tachometer for 12.2V/2.01A showing of voltmeter+amperemeter. It did show 7635rpm (I must have had more amps in measurement of previous posting).
Then I did place Raspberry v2 NoIR camera (with added M12 mount and M12 lens) above the scene. I tried my 48led IR light and it was good enough to light the scene for capturing with 50µs shutter time (1000lm lamp was not sufficient). https://www.aliexpress.com/item/32856122386.html
This was command used to capture 150fps video with 50µs shutter time after propeller was rotating with 12.2V and 2.01A:
$ raspivid -md 7 -w 640 -h 480 -p 22,50,640,480 -t 0 -fps 150 --shutter 50 -o tst.h264 -pts tst.pts
After aborting the recording I did run ptsanalyze tool on generated tst.pts timestamp file. It reported "535 frames were captured at 150fps" with no frame skips.
Finally I extracted frames from the video and created a 13 frame 2fps animation from the repeating pattern found:
The propeller is rotating clockwise, and it has three blades, with one blade having reflective material. The video is taken at 150fps framerate, and would stand still for exactly 9000rpm speed. But what you can see is that propller reflective blade always does a little less than one full round. If you follow the animation you will see that it looses 2 rounds per 13 frames. Total rpm less than 9000rpm is therefore 150/13*2*60=1385, resulting in 9000-1385=7615rpm.
This is nearly a perfect match for the 7635rpm measured with laser tachometer!
P.S: The video frames show crazy rolling shutter effect of rotating blades. I did take similar video of a mini drone propeller rotation with 26000rpm. I used my technique to make Raspberry v1 camera capture global shutter frames. This video of fast rotating propeller looks much nicer: https://github.com/Hermann-SW/Raspberry_v1_camera_global_external_shutter