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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Replacing the voltage regulator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers There was a nuisance - the voltage regulator on your foreign car failed. How to be? The radio amateur will answer this question without hesitation: to assemble a new one. Yes, that it was better than before! How to do this in practice, and the author tells in the article presented here. On a NISSAN-MARCH car, the generator stopped working. The check showed that the cause of the failure was a malfunction of the voltage regulator, as a result of which the generator rotor was left without excitation current. The voltage regulator is structurally made in the form of a hybrid microcircuit installed in the generator brush holder (HITACHI; voltage 12 V, load current 40 A). Since it was not possible to purchase a failed microcircuit, I decided to make an alternative version of the regulator, which would provide high accuracy in maintaining a voltage of 13,8 V at the battery terminals and have dimensions that allow it to be built into the generator brush holder to replace the failed one. The voltage drop at the battery terminals during the operation of the generator with the HITACHI regulator with the majority of consumers turned on (high beam, rear window heater, wiper, heater fan) in the idling mode of the car engine did not exceed 0,5 V. In all other possible engine operating modes and electrical equipment, voltage changes at the battery terminals could not be registered. I carried out the measurements with a PHILIPS universal pointer device PM2502, which has an accuracy class of 1,5 when measuring direct voltage. As the practice of operating a battery in a car has shown, its service life largely depends on the voltage value at its terminals, which should be equal to 13,8 V, and the accuracy of maintaining it [1]. The author of the article [2] notes that the use of a regulator from domestic cars in this case is not advisable, since it does not provide high accuracy in maintaining the voltage at the battery terminals. In addition, domestic relay-regulators require changes to the vehicle's wiring, and it is not possible to install them in place of a damaged device. Meanwhile, as it turned out, the voltage regulator described in [3] completely satisfies the postal requirements. A small number of parts used in it made it possible to place them on a 30x20 mm board and easily integrate it into the brush holder of the HITACHI generator. Similarly, it is possible to restore the performance of generators and other models of foreign cars. The controller circuit is shown in fig. 1. It also shows its inclusion in the vehicle's on-board network. As already mentioned, the regulator from [3] was taken as the basis of the device. Only its output stage has been changed. Transistors VT1 and VT2 are connected according to the circuit of a composite transistor, the collector load of which is the winding of the generator rotor.
When the contacts of the ignition switch SA1 are closed, the voltage from the battery GB1 will be supplied (through pin 2) to the operational amplifier (op-amp) DA1 of the regulator. A stabilized voltage of about 8,2 V will appear at the non-inverting input of the op-amp, taken from the zener diode VD1. A voltage is constantly present at the inverting input of the op-amp, determined by the resistive divider R1R2R3 and equal to approximately 7,3 V. Since the DA1 op-amp operates without feedback, its output will show almost the full voltage of the GB1 battery applied to the pin. 7 OU. This voltage through the diode VD3 and the resistive divider R6R7 will go to the base of the composite transistor VT1VT2. As a result, the transistor VT2 will open and current will flow from the battery through the lamp HL1, the winding of the rotor of the generator G1 and the transistor VT2. The control lamp HL1 will turn on, and a magnetic field will appear in the rotor G1. After starting the engine, the voltage generated by the working windings of the generator is rectified by diodes, applied to the rotor of the generator G1 and through the X1 connector to the battery GB1, providing its recharging. The voltage at both terminals of the HL1 lamp relative to the common wire becomes almost the same, and the HL1 lamp goes out, which indicates that the generator is working properly. As the speed of the engine crankshaft (and the generator shaft associated with it) increases, the voltage at the inverting input of the op-amp DA1 increases. As soon as it becomes equal to the voltage at the non-inverting input, the operational amplifier will switch, its output voltage will decrease to almost zero, which will lead to the closing of the composite transistor VT1VT2 and the termination of the current through the rotor winding of the generator G1. The voltage at connector X1 decreases, the op-amp switches again, and the process repeats. Thus, the average voltage is set at the X1 connector, which is set by the selection of the resistor R2. It is easy to see that the composite transistor operates in a switching mode - either it is securely closed, or it is open and saturated. Resistor R8 ensures that the transistor VT2 is completely closed when the excitation current drops to zero. Resistor R5 has been reduced to 1,5 MΩ, making the op amp's electrical "hysteresis" more pronounced, reducing the likelihood of the output stage going linear. Diode VD2 extinguishes the self-induction EMF of the generator rotor winding, which occurs at the moment of closing the composite transistor. Diode V1 is excluded from the original device, since the connection of the input divider R1R2R3 of the regulator with the output connector X1 is structurally made inside the generator brush holder. The tuning resistor R3 is also excluded, since the device adjusted once at the stand does not require any adjustment during operation. Moreover, the presence of a tuned resistor in conditions of sudden changes in temperature, exposure to dust, moisture (condensation) and vibration would reduce the reliability of the regulator. The device is mounted on a printed circuit board made of one-sided foil fiberglass 1 mm thick. The drawing of the board is shown in fig. 2. Resistors R4, R6, R7 and diode VD3 are soldered on the side of printed conductors. The terminals of the transistor VT1 are bent at an angle of 90 degrees; it is placed end to end of the microcircuit. Place a piece of cardboard about 0,5 mm thick under the transistor.
Transistor VT2 is mounted outside the board, on the inside of the rear cover of the generator in the free space next to the brush holder, through a mica gasket. In the regulator, you can use the capacitor C1-KM-5, KM-6 or K10-17; zener diode VD1 - KS182E, KS191E, KS182Zh or KS191Zh in the KD-2 (KD-3) package. Instead of KD522B (VD3), any of the KD521, KD522 series will do; diode VD2 - any of the KD209 series in a drop-shaped case. The KT817V transistor can be replaced with KT815B-KT815G, KT817B, KT817G. We will replace the KT819V transistor with KT819B, KT819G The fixing screw is isolated from the heat sink flange of the VT2 transistor with an insulating sleeve and washer. The generator cover at the transistor installation site should be cleaned with fine sandpaper. Before the final installation of the transistor, the mica gasket must be lubricated on both sides with KTP heat-conducting paste. In its absence, LITOL-24 grease is used. As practice has shown, the use of LITOL gives even more long-term results than KTP paste. It is not recommended to replace the KR140UD608 microcircuit with others because of their tendency to excite when working in the described regulator. As a last resort, you can try to apply KR140UD708. It is advisable to duplicate those printed tracks of the board through which a significant current flows with a bare copper conductor with a diameter of 0,5 mm. When assembling the generator, make sure that the connecting wires from the VT2 transistor to the regulator board do not touch the generator rotor when it rotates. To do this, after mounting the board, a trial assembly of the brush holder with the board and the back cover is performed and the optimal length of the wires is selected. To establish the device, its outputs 1-3 are connected together and connected to the positive output of an adjustable current source with a voltage of 12 ... 15 V, providing a load current of 3 ... 5 A, and output 5 to the negative output of the source. To terminals 1-3 and 4, a load equivalent (generator rotor) is connected - a wire resistor with a resistance of 4 ohms with a power of 25 ... 50 watts. You can also turn on the generator rotor itself by attaching (without soldering) the wires to the slip rings of the collector. In parallel with the load, a voltmeter with an upper limit of 15 ... 30 V is connected. Instead of resistor R2, a tuning multi-turn resistor SP5-3 with a resistance of 33 kOhm is temporarily soldered, connecting together the middle and one of its extreme conclusions. Turn on the source and set the supply voltage to 13,8 V. If the voltmeter shows a voltage close to the specified one, rotate the trimming resistor screw exactly until the voltage drops on the load. Then the supply voltage is reduced to 12 V, while the voltmeter should again show voltage. Gradually increase the supply voltage until the voltage drops at the load. Switching should occur when the voltmeter reads 13,8 V. If the switching voltage is not equal to the specified one, repeat the previous operation even more precisely. In the case when, when the voltmeter is first turned on, it does not show voltage, by turning the screw of the tuning resistor, the arrow is deflected, and then the described operations are carried out. The adjustment should be carried out quickly, making sure not to overheat both the load and the transistor VT2. After soldering a trimmer resistor from the board, it is possible to more accurately measure its resistance and replace it with a constant of the same resistance. Once again, repeat the indicated operations and make sure that the switching occurs clearly and at the specified voltage. The adjusted board is covered on both sides with two layers of BF-2 glue with intermediate drying. The finished board is glued with VGO-1 sealant into the brush holder, which, in turn, is installed in the rear cover of the generator. Then they mount the transistor VT2, assemble the generator and check its operation on the car. The voltage at the battery terminals is monitored under various operating modes of the engine and electrical equipment. The operation of a car with the described voltage regulator for more than two years has confirmed its reliability and high stability of maintaining voltage in the on-board network. A more powerful (12 V; 60 A) generator of the NISSAN-SUNNY car was repaired in a similar way. Literature
Author: E.Adigamov, Tashkent, Uzbekistan
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