The classification of the electric motor of direct current takes place considering the type of connection of its fields and thus we have: permanent magnet motor; Motor field series; Parallel field motor (shunt); Independent excitation motor and compound motor.
In the series electric motor, the coils are constituted by turns that are connected in series with the rotor, also called the armature. These turns cause the conductor to be thicker, since only then will it be able to withstand the circulating current.
Due to the magnetic action in this electric motor, the conjugate occurs in a way directly proportional to the inductor flow and the current that circulates throughout the armature.
Thus, this electric motor counts on a steady start and its start and speed regulation is done in the rheostat or by an electronic source that is intercalated in the circuit.
This electric motor is best suited for cases where it is necessary to leave with full load and therefore, this electric motor is used in cranes, elevators and locomotives and as they can suffer with the increase of rotation, it is not indicated that these motors operate at Empty, that is, without any charge. https://www.mrosupply.com/hydraulics-and-pneumatics/hose-reels/2517020_c-l350l-5012l-x_coxreels/