Electromagnetic DC motor consists of stator magnetic pole, rotor (armature), commutator (commonly known as commutator), brush, casing, bearing and so on, the stator magnetic pole (main magnetic pole) of electromagnetic DC motor is composed of core and excitation winding. According to the different excitation (old standard called excitation), it can be divided into series excitation DC motor, shunt DC motor, excitation DC motor and complex excitation DC motor. Because of the different excitation mode, the stator magnetic flux (generated by the excitation coil of the stator magnetic pole) is different.
The excitation windings of the series excitation DC motor and the rotor windings are connected by a brush and a commutator the excitation current is proportional to the armature current, the flux of the stator increases with the increase of the excitation current, the torque approximation is proportional to the square of the armature current, and the rotational speed decreases rapidly with the increase of torque or current. Its starting torque can reach the rated torque of more than 5 times times, short time overload torque can reach the rated torque of more than 4 times times, the speed change rate is large, no-load speed is very high (generally not allowed to run under no-load). The speed regulation can be realized by using external resistor and serial excitation windings in series (or in parallel), or by connecting the series excitation windings in parallel.
The excitation windings of the shunt DC motor are in parallel with the rotor winding phase, the excitation current is more constant, the starting torque is proportional to the armature current, and the starting current is about 2.5 times times of the rated current. The rotational speed decreases slightly with the increase of current and torque, and the Short-time overload torque is 1.5 times times of the rated torque. The speed change rate is small, for $number. The speed can be adjusted by weakening the constant power of the weak magnetic field.