When an electric motor isn't actually moving, the impedance through its coils drops *dramatically*. When the spindle is turning and the coils are actually moving through the static magnetic field, the impedance is much higher. So you end up sucking a *lot* of current through the fan's motor's coils; in some cases more than the wiring in the coils can handle. If you get this much current, it causes the wire to melt. Generally that's bad. ;-P
You get the same effect when you test the resistance of an electromagnet with a multimeter. The multimeter just hooks up a fixed voltage and sees what the current is; it's a pure DC system. The electromagnet is just wire, so its resistance is almost zero.
But if the magnet is moving back and forth through a field, and the voltage on its terminal points is reversing periodically, you get a lot of impedance; the total current is much lower than what a multimeter shows, but the voltage didn't change. Impedance = resistance + reactance; a motor's coils have a high reactance, but very low resistance. DC circuits in a steady state have zero reactance. |
