Who can tell us why the permanent magnet of automobile generator is seldom excited by coil at present?

Because the speed of automobile engine changes greatly, from hundreds to thousands, the voltage of permanent magnet generator changes with the speed because of the fixed excitation. At the top speed of the car, the voltage is as high as 40 volts. With such a wide range of voltage changes, it is difficult to stabilize the voltage, because it is not easy to adjust the voltage, so it is rarely used.

The advantage of coil excitation is to stabilize the output voltage by controlling the current of the excitation coil. When the car is at a low speed, the excitation current is increased to improve the voltage, and when the car is at a high speed, the excitation current is reduced to reduce the voltage, so that the voltage is easy to stabilize, and the cost is low, the effect is good, and the maintenance is simple. Nowadays, most cars use coil-excited generators.