There are two sets of coils in the usual ignition coil, the primary coil and the secondary coil. The primary coil uses thicker enameled wire, usually about 0.5-1 mm enameled wire for about 200-500 turns, and the secondary coil uses thinner enameled wire, usually uses about 0.1 mm enameled wire for about 15000-25000 turns. One end of the primary coil is connected with the low-voltage power supply (+) on the vehicle, and the other end is connected with the switchgear (cut-off). One end of the secondary coil is connected with the primary coil, and the other end is connected with the output end of the high-voltage line to output high-voltage electricity.
The reason why the ignition coil can turn the low-voltage electricity on the car into a high voltage is that it has the same form as the ordinary transformer, and the primary coil has a larger number of turns than the secondary coil. However, the ignition coil works in a different way than the ordinary transformer, the working frequency of the ordinary transformer is fixed 50Hz, also known as the power frequency transformer, and the ignition coil works in the form of pulses, which can be regarded as a pulse transformer, which repeatedly carries out energy storage and discharge at different frequencies according to the different speed of the engine.
When the primary coil is connected to the power supply, a strong magnetic field is generated around the current growth, and the iron core stores the magnetic field energy; when the switching device disconnects the primary coil circuit, the magnetic field of the primary coil decays rapidly, and the secondary coil will induce a very high voltage. The faster the magnetic field of the primary coil disappears, the greater the current at the moment of current disconnection, and the greater the turn ratio of the two coils, the higher the voltage induced by the secondary coil.