Install the generator on the stand and make connections as shown in fig. 141. Turn on the electric motor of the stand, set the voltage at the output of the generator to 13 V with a rheostat 4 and adjust the rotor speed to 5000 min-1. Let the generator run in this mode for at least 2 minutes, and then measure the recoil current. For a working generator, it should be at least 55 A.
Pic. 141. Wiring diagram for testing the generator on the stand: 1 - control lamp 12 V, 3 W; 2 - generator; 3 - voltmeter; 4 - rheostat; 5 - ammeter; 6 - switch; 7 - battery.
If the measured value of the output current is less, then this indicates a malfunction in the stator or rotor windings, damage to the valves or wear of slip rings and brushes. In this case, a thorough inspection of the windings and valves is necessary to determine the location of the fault.
The voltage at the generator output is checked at a rotor speed of 5000 min-1. Rheostat 4 sets the recoil current of 15 A and measures the voltage at the output of the generator, which should be (14,1±0,5) At ambient temperature and generator (25±10) °C.
If the voltage does not fit within the specified limits, then replace the voltage regulator with a new one, known to be good, and repeat the test. If the voltage is normal, then the old voltage regulator is damaged and must be replaced. And if the voltage still does not fit within the above limits, then it is necessary to check the windings and generator valves.
Checking the field winding
Excitation winding (rotor winding) can be checked without removing the generator from the car, removing only the voltage regulator together with the brush holder. Having cleaned, if necessary, the slip rings with a sandpaper, an ohmmeter or a test lamp, check whether there is an open in the excitation winding and whether it closes to the housing.
Stator check
The stator is checked separately after disassembling the generator. Its winding leads must be disconnected from the rectifier valves. First of all, they check with an ohmmeter or with the help of a test lamp and a battery, whether there are breaks in the stator winding and whether its turns close to the housing.
The insulation of the winding wires must be free from overheating, which occurs during a short circuit in the rectifier valves. A stator with such a damaged winding should be replaced. Then they check with a special flaw detector whether there are short-circuited turns in the stator winding.
Checking the rectifier valves
A good valve only allows current to flow in one direction, a bad valve may not allow current to flow at all (open circuit) or pass current in both directions (short circuit). If one of the rectifier valves is damaged, the entire rectifier unit must be replaced.
A short circuit in the valves can be checked without removing the alternator from the vehicle by first disconnecting the wires from the battery and the alternator. Also disconnect the output «B» voltage regulator from terminal «30» generator and wire from the output «IN» voltage regulator. You can check with an ohmmeter or with a lamp (1-5W, 12V) and battery as shown in Fig. 142.
Pic. 142. Scheme for checking rectifier valves: a - checking both positive and negative valves; b - checking the negative valves; c - checking the positive valves; 1 - battery; 2 - control lamp, 3 - generator.
In order to simplify the fastening of parts of the rectifier, three valves (with red marking) have on the body «plus» rectified current (these are direct polarity valves - positive). They are pressed into one plate of the rectifier block, connected to the output «30» generator. Other three gates (negative, with black marking) have on the body «minus» rectified current. They are pressed into another plate of the rectifier unit, connected to the generator housing.
First, check if there are short circuits at the same time in positive and negative valves. For this «plus» batteries through the lamp are connected to the clamp «30» generator, and «minus» - to the generator housing (pic. 142, a). If the lamp is on, then both the negative and positive valves are shorted.
You can test for a short in the negative valves by connecting «plus» batteries through a lamp with one of the rectifier unit mounting bolts, and «minus» - with generator housing (pic. 142b). A lamp on indicates a short circuit in one or more of the negative valves. It should be remembered that in this case, the burning of the lamp may be due to the short circuit of the turns of the stator winding on the generator housing. However, such a malfunction is less common than a short circuit of the valves.
To check for short circuits in positive valves «plus» batteries through the lamp are connected to the clamp «30» generator, and «minus» batteries - with one of the bolts for fastening the rectifier unit (pic. 142, in). A burning lamp will indicate a short circuit in one or more of the positive valves.
Without disassembling the generator, a break in the valves can only be detected indirectly when checking the generator on the stand for a significant reduction (by 20-30%) the strength of the given current compared to the nominal. If the windings, additional diodes and the generator voltage regulator are in good condition, and there is no short circuit in the valves, then the reason for the decrease in the output current is an open in the valves.
Checking additional diodes
A short circuit of additional diodes can be checked without removing and disassembling the generator by disconnecting the wires from the battery and the generator and the wire from the output «IN» voltage regulator.
«Plus» batteries 1 (pic. 143) through lamps (1-3W, 12V) add to conclusion «61» generator 3, and «minus» batteries - to one of the bolts securing the rectifier unit. If lamp 2 lights up, then there is a short circuit in one of the additional diodes.
You can find a damaged diode only by removing the rectifier unit and checking each diode individually.
An open in additional diodes can be detected with an oscilloscope by distorting the voltage curve on the plug «61». as well as low voltage (below 14 V) on plug «61» at an average frequency of rotation of the generator rotor.
Checking the voltage regulator
The operation of the regulator is to continuously and automatically change the generator excitation current in such a way that the generator voltage is maintained within the specified limits when the rotor speed and generator load current change.
Vehicle check
To check, you must have a DC voltmeter with a scale of up to 15-30 V, an accuracy class of at least 1.0.
After 15 minutes of engine operation at medium speed with the headlights on, measure the voltage between the terminal «30» and generator housing. The voltage should be in the range of 13.6-14.6 V.
In the event that a systematic undercharging or overcharging of the battery is observed and the regulated voltage does not fit within the above limits, the voltage regulator must be replaced.
Checking the removed regulator
The voltage regulator removed from the generator is checked according to the circuit shown in fig. 144. It is better to check it assembled with a brush holder, since in this case you can immediately detect breaks in the brush leads and poor contact between the leads of the voltage regulator and the brush holder.
Between the brushes include a lamp with a power of 1-3 W, 12 W. To conclusions «B», «IN» and a power source is connected to the regulator body, first with a voltage of 12 V, and then 15-16 V. If the regulator is working, then in the first case the lamp should be on, and in the second it should go out.
If the lamp is on in both cases, then there is a breakdown in the regulator, and if it does not light in both cases, then either there is an open in the regulator or there is no contact between the brushes and the outputs of the voltage regulator.
Capacitor check
The capacitor serves to protect the electronic equipment of the car from voltage pulses in the ignition system, as well as to reduce radio interference. Capacitor damaged or loose on alternator (deterioration of contact with the body) detected but an increase in radio interference when the engine is running.
Approximately the health of the capacitor can be checked with a megaohmmeter or tester (on a scale of 1-10 MΩ). If there is no break in the capacitor, then at the moment the probes of the device are connected to the terminals of the capacitor, the arrow should deviate in the direction of decreasing resistance, and then gradually return back. Capacitor capacitance 2.2uF±20%.