I would like to attempt to assemble an outrunner BLDC motor from scratch. Its working principle seems ridiculously simple and I'm up for the challenge. There is one thing that I would like to clear up for myself as of now, which is not related to BLDC but rather any electric motor.
Might be a stupid question but I really need to clear this up in my mind, because it's quite foggy at this point. If I provide current to any coil as shown in the schematic above, isn't that going to short it since there is no resistance anywhere?
Best Answer
First, there is resistance in the motor coils. But in a high-performance motor it's not enough to prevent things from burning up.
Second, when a motor is spinning it generates voltage. This is called "back EMF" (Google it).
Third, coils have inductance. So when you PWM the motor voltage fast enough, the current on the coils will be a result of the average voltage applied minus the back EMF.
So when you're PWM-ing a motor, you limit the coil current, either directly by sensing it, or indirectly by being careful about applying the correct voltage to it based on speed.