Question

what happens when a motor stalls out, is that the back-emf (ea) being generated by the magnetic field of the rotor winding coupling into the stator winding of the motor disappears, which puts the full power supply voltage (vt) across the coil resistance of the stator winding (ra) (in parallel with the resistance of the rotor winding (rf) through the brushes, but this resistance is large compared to the stator coil, so we can discount it in a rough estimate) you can think of back-emf as a voltage that counteracts the supply voltage of the motor, which gets larger as the motor spins faster, which is why current consumption goes down as the motor spins faster.

Answer 1

When a motor stalls, the back emf, which is proportional to the motor's angular velocity, is disrupted. This phenomenon initially causes a large current draw when the motor is not turning and mitigates the current as the motor speeds up, balancing out when no load is present.

Step-by-step explanation:

When a motor stalls, the phenomenon of back emf (electromotive force) plays a crucial role. Back emf is the generator output of a motor, which is proportional to the motor’s angular velocity (ω). Initially, when the motor is not turning, the back emf is zero, and thus the motor coil receives the full supply voltage, leading to a large current draw. As the motor speeds up, the back emf grows and opposes the driving emf, which causes a reduction in the voltage across the motor coil and lowers the current the motor draws. Conversely, when the motor experiences a mechanical load such as when an electric wheelchair climbs a hill, it may slow down, back emf decreases, and current increases, resulting in more work being performed. However, if the motor runs too slowly, the high current can lead to overheating and potential damage. When there’s no load, the motor speeds up until the back emf nearly equals the driving emf, and at this point, the motor utilizes enough energy solely to overcome frictional losses.