Knowledge of Automotive Alternators

After the engine is started, the engine crankshaft pulley drives the belt to drive the generator to generate power to provide power for the vehicle's electrical system. The power of the Alternator for trucks, the capacity of the battery, and the power demand of the vehicle electrical equipment must match each other, To meet the needs of electrical balance. Next, the current mainstream vehicle generators are introduced from the basic principles of generator power generation, rectifiers, regulators, and overvoltage protection.

1. The working principle of the generator is the principle of electromagnetic induction. The belt drives the rotor to rotate to generate a rotating magnetic field. The stator coil winding is cut. The star-connected stator winding generates a sinusoidal alternating voltage, which is rectified by a full-bridge rectifier. After that, it outputs direct current and supplies it to the whole vehicle. The rotor magnetic field can be generated by permanent magnets, but it is not controllable and the excitation current is small. Therefore, the magnetic field is generated by energizing the excitation coil of the rotor. The number of turns of the coil and the size of the excitation current determines the strength of the magnetic field. Changing the size of the excitation current can be Adjust the magnetic field strength to control the magnitude of the induced voltage.

2. Both the charging of the rectifier battery and the electrical system on the car require direct current. Therefore, the alternating voltage generated by the generator must be rectified into a direct current voltage. In order to allow the positive and negative half-waves of the alternating voltage to be effectively used for power supply, Full bridge rectification can be used. The bridge rectifier circuit is composed of 6 diodes, and each branch is composed of 2 power diodes, one of which is connected to the positive side and the other is connected to the negative side. Diode conduction conditions during rectification: a. For three anode diodes (D1/D3/D5), at a certain instant, the anode tube of the highest voltage phase is turned on. b. For 3 cathode diodes (D2/D4/D6), at a certain instant, the phase with the lowest voltage is turned on, but only two tubes are turned on at the same time, one for each of the positive and negative electrodes. The envelopes of the positive half-wave and negative half-wave voltages are superimposed to produce a rectified voltage with less fluctuation. The batteries connected in parallel at both ends of the generator or the capacitors of the vehicle electrical system can further smooth the DC output of the generator.

In addition, the rectifier diode in the generator can not only rectify the generator voltage and excitation voltage but also prevent the battery from discharging through the three-phase stator winding.

 Alternator For Trucks

3. Under the condition of constant excitation current of the regulator, the output voltage of the generator depends on the speed and load, while the engine speed fluctuates in different working conditions. If there is no regulator, the output voltage of the generator will increase with the speed. Constantly changing, unable to meet the requirements of the working voltage of the whole vehicle electrical appliances, so in order to keep the voltage of the vehicle electrical system constant within the engine speed range, a voltage regulator is required to adjust the size of the excitation current, thereby controlling the magnetic field strength in the rotor, and then controlling The output voltage of the generator. Generally, the electric system of the whole vehicle that uses a 12V battery has a voltage setting value of about 14V. The principle of voltage regulation: When the voltage exceeds the upper limit of the set value, the end drive stage of the voltage regulator is disconnected. Due to the self-inductance of the excitation coil, the excitation current passes through the freewheeling diode, the excitation current is weakened, and the generator voltage decreases. When the voltage is lower than the set value, the voltage regulator switches on the excitation current again to increase the excitation and increase the voltage. When the voltage exceeds the upper limit of the set value again, the control process is the same as above and the cycle continues. Since the control step length is milliseconds, the average value of the generator voltage can be better close to the preset characteristic curve under the action of the voltage regulator.

The current mainstream vehicle regulators are divided into multi-function regulators and smart regulators with LIN communication. The intelligent generator can control the output voltage of the generator according to the vehicle acceleration and deceleration combined with the state parameters of the battery. When the vehicle is accelerating, the output voltage of the generator is reduced, and when the vehicle is decelerating, the output voltage of the generator is increased. When idling and driving at a constant speed, The appropriate generator voltage is determined according to the SOC of the battery, so as to achieve the purpose of partial recovery of vehicle braking energy, fuel-saving, and emission reduction, and the intelligent generator regulator also has a fault diagnosis function.

4. Overvoltage protection The electrical system of the whole vehicle generates overvoltage in the following situations: (1) Regulator failure (2) Battery failure, virtual connection. ③Switch the load with large inductance. Overvoltage is a voltage peak in milliseconds with an amplitude of up to 350V. Usually, when the negative electrode of the battery is not tightened or a large load is disconnected, the load dump will occur, and the generator voltage will have a peak. The method of overvoltage protection: 1. Replace the power diode with a Zener diode to limit the large energy voltage peak that appears within the allowable range.

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