Automotive electrical has two key components, one is the generator, is responsible for vehicle power supply; the other is the starter, responsible for the car started. The two motors have the same magnetic field, armature and rectifier components, but the former is the mechanical energy into electrical energy, which is the electrical energy into mechanical energy, so the structure of the two are very different.

Before the car generator is a DC generator, with commutator rectifier, from the 20th century, has been phased out since the 1970s, and now the car generators are mostly alternators, with semiconductor rectifier. It has a small size, power, long life, less failure and low-speed charging performance advantages.

The alternator is divided into two parts, the stator windings and the rotor windings. The three-phase stator windings are distributed on the shell at an angle of 120 degrees from each other. The rotor windings are composed of two pole claws. When the rotor winding DC is excited when the excitation, two pole claws to form N-pole and S-pole. Magnetic lines of force starting from the N-pole, through the air gap into the stator core and then return to the adjacent S-pole. Once the rotor rotates, the rotor winding will cut the magnetic lines of force in the stator windings produce 120 degrees of mutual difference between the sine electromotive force, the three-phase alternating current, and then through the six silicon diode rectifier components into DC output.

As the generator output voltage will increase with the engine speed increases, so use the voltage regulator to adjust to meet the needs of use. Modern car generators are relatively compact, the integrated circuit regulator into the generator built into one, and the use of multi-tube form. For example, Xiali car generator has eight semiconductor tube, of which six rectifier, the other two for three-phase neutral voltage rectifier output, in order to improve the power generator.

Modern cars have been widely used air-conditioning devices, EFI engine, electric doors and windows, electric adjustable seats and so on. The more advanced the car, the greater the amount of electricity. Now the high-class cars generators power is generally up to 1 kW. With the improvement of automation and comfort, but also increase the power consumption, but the car's installation space is limited, can not increase the volume by increasing power. Therefore, engineers in the cooling and installation position to make a fuss. For example, the generator installed in the top of the engine, as far away from the heat area; generators are installed on the front and rear fan blades to enhance the cooling effect. Recently, BMW is trying to use water cooling to improve the cooling effect of the generator.

Starter from the motor, drive mechanism and operating mechanism and so on. It is designed to start the engine, requires a strong torque, so the amount of current to be large, reaching several hundred amperes, this feature determines the difference between it and the generator. For example, the use of DC series motor, rotor and stator parts are relatively thick rectangular cross-section copper wire wound; drive mechanism with reduction gear structure; manipulator using electromagnetic magnetism.

The motor consists of magnetic field (stator), armature (rotor) and commutator, in order to increase the torque using multi-polar magnetic field, there are four common magnetic field. When the current through the armature coil, in accordance with the "left-hand rule", the coil will be subject to a torque and rotation. As the DC motor power will have a back EMF, and the engine speed is proportional to, and inversely proportional to the torque, so to meet the requirements of the engine starting. The starting current of the starter is large, so the start-up time must be short. The driving gear of the reduction gear mechanism engages with the engine flywheel to start the engine, and adopts the unidirectional driving mode. When the speed of the pinion on the motor is higher than the speed of the engine flywheel, the motor drives the engine. When the speed of the engine is higher than that of the motor, the power transmission relationship between them is canceled automatically. Small gear small force big, a fault car start will be very strenuous.