Like Mariss said: the BEMF depends on RPM only. Not whether it is accelerating or not, or the method the motor is driven. The same happens when the motor is driven by some electronics. That's why it has to supply a voltage higher than the BEMF.
I've used Mariss's method many times and have just one thing to add: Make very sure the motor leads do not shortcircuit. Otherwise things can get very violent! You will not believe how hard the motor will brake if you do! Yes, I did try something similar. But with a motor driving a rail model with me riding onboard. Let's just say it stopped promptly, I did not! Somebody laughed, I did not. |