Maintenance of automobile thyristor voltage regulator

A car's permanent magnet alternator is faulty. The phenomenon is that when the car is driving at night, the brightness of the headlights suddenly increases and then goes out. It is determined that the generator voltage regulator may be damaged, causing the voltage to rise. This generator has no excitation coil and cannot be replaced with a conventional voltage regulator.

This machine is a JFYJ2102 (28V/36A) AC permanent magnet generator with large power and good use effect. The trigger voltage regulating circuit board of this machine has been lost. The actual wiring diagram of the generator is shown in Figure 1. This circuit is a three-phase bridge semi-controlled thyristor voltage regulation and rectification circuit. G is the trigger pole of three unidirectional thyristors, which are triggered at the same time. D7, D8, and D9 are three thyristors KKZ1 and KKZ2 respectively. , The isolation diodes of the trigger pole of KGZ3, C1, C2, and C3, are to prevent the three thyristors from being accidentally triggered by interference pulses, and at the same time protect the trigger poles of the three thyristors from being broken down by excessive triggering high-voltage pulses. , for protection; D4, D5, and D6 are isolation diodes to prevent the cathodes of the three thyristors from being directly connected and causing the three-phase winding of the generator to be short-circuited, so as to apply triggering to the cathodes and trigger electrodes of the three thyristors. pulse.

This circuit consists of a synchronous relaxation oscillator composed of a single-junction transistor BT and a detection control circuit composed of a triode BG. When the B+ terminal is connected to the power supply, the oscillator is powered through the current limiting resistor R6 and the voltage stabilizing tube ZD2. The power supply charges the capacitor C1 through the resistor R2. When the voltage at both ends of G1 rises to the peak voltage of the single-junction transistor BT, BT's The e and b1 poles are turned on, and the capacitor C1 discharges to the primary L1 of the isolation transformer through the e and b1 poles of BT. When the voltage of C1 drops to the valley point of BT, the e and b1 poles of BT resume blocking. Then capacitor C1 starts charging/discharging for the second time, and so on. After the circuit starts to oscillate, the L2 output pulse of the isolation transformer B is added to the trigger electrode of the thyristor through the G and A terminals to turn on the thyristor. Since the power supply is taken from a three-phase rectified pulsating power supply, the output pulses are synchronized with the pulsating power supply, allowing the thyristor to be triggered synchronously. When the voltage at the B+ terminal reaches or exceeds 28V, ZD1 breaks down and conducts, the base potential of BG increases, BG conducts, the collector potential decreases, and diode D2 conducts, short-circuiting both ends of C1, the oscillator stops vibrating, and the thyristor The trigger signal cannot be obtained and is blocked when crossing zero. When the voltage is lower than 28V, ZD1 is not broken down, the BG base is at a low potential, BG is cut off, its collector is at a high potential, D2 is cut off, the oscillator works, the thyristor is triggered to conduct, and the rectifier output current flows outward. powered by. In this way, the rectified output voltage of the generator never exceeds 28V. If the trigger current is too small, the resistance of R in Figure 1 can be appropriately reduced. All resistors in the circuit use 1/2W metal film resistors. B uses a ∮25mm magnetic pot or a radio transformer core with a cross-sectional area of ​​0.5~0.8c㎡, and uses ∮0.23~∮0.25mm enameled wire. L1 is wound around 100T and L2 is wound around 200T.

When the power is turned on, the light bulb LD emits light. As the output voltage of the adjustable regulated power supply increases, when the output is 28V, the light bulb LD suddenly goes out; when the voltage is adjusted below 28V, the light bulb LD lights up again. Otherwise, the values ​​of ZD1 and R4 should be changed. Then connect the trigger voltage regulating circuit board to the corresponding connection of the generator and install it on the car for a trial run. If it works stably, the circuit board can be sealed with silicone rubber to prevent water and dust.

This trigger voltage regulator has good results in actual use, and this method can be used to repair similar types of generators; if it is a 14V generator, the values ​​of R and ZD1 can be changed until ZD1 is exactly 14V and it conducts; at the same time, R6 is changed to 100Ω, ZD2 is changed to a 10V voltage regulator tube.

As shown in the figure, the maintenance circuit diagram of the automobile thyristor voltage regulator

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