I would like to know if the alternators that carry most cars today auto-excite their rotor internally, or if at all times they need the battery to create the field in the rotor. I know that there are alternators of both types, but I want to know what kind are currently used in cars.
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The output of the alternator of the car, first is ground (through a diode), and the dc voltage obtained by charging the battery, and at the same time provides current to the field inductor through the regulator. Seen so the alternator is self-excited, even though it had not battery However, as in all the alternators are self-excited, the first time it starts up the alternator gives an impossibility: If there is not battery with some load, there is no field, there is no current, and if there is no current, there is not rectified, and not current in the inductor. For this, the first time the system is put into operation, it is necessary to the current provided by a battery with some charge, but in the following, in the iron of the magnetic circuit of the alternator, is the so-called magnetism remnant that provides excitation for the start of the power supply. However, if the alternator, as with magnetism remnant, is actuated without the battery, the regulator does not work well, given that it needs to have a dc voltage which is fixed, such as that provided by the battery, and can produce serious disturbances in the power supply produced for the internal use of the car. For this reason it is recommended, that in no case, will disconnect the battery when the engine is running.