Contents: Checking the excitation winding ↓ Stator check ↓ Checking the rectifier block valves ↓ Checking additional diodes ↓ Checking the voltage regulator ↓ Check on the car ↓ Checking the removed regulator ↓ Checking the capacitor ↓
Testing the generator on the bench allows you to determine the generator's serviceability and whether its characteristics correspond to the nominal ones. The brushes of the tested generator must be well ground to the contact rings, and the rings themselves must be clean.
The generator is installed on the stand and connections are made as shown in Figure 141. The electric motor of the stand is switched on, the voltage at the generator output is set to 13 V using rheostat 4 and the rotor speed is increased to 5000 min⁻¹. The generator is allowed to operate in this mode for at least 2 minutes, and then the output current is measured. For a serviceable generator, it should be at least 55 A.
Figure 141. Connection diagram for testing the generator on the bench: 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, this indicates faults in the stator or rotor windings, damage to the valves or wear of the contact rings and brushes. In this case, a thorough check of the windings and valves is necessary to determine the location of the fault.
The generator output voltage is checked at a rotor speed of 5000 min⁻¹. Rheostat 4 is used to set the output current to 15 A and measure the generator output voltage, which should be (14.1±0.5) V at an ambient air and generator temperature of (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 in good working order, and repeat the check. 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 valves of the generator.
Checking the excitation winding
Excitation winding (rotor winding) can be checked without removing the generator from the car, by removing only the voltage regulator together with the brush holder. Having cleaned the contact rings with sandpaper if necessary, use an ohmmeter or test lamp to check whether there is a break in the excitation winding and whether it is shorted to the housing.
Stator check
The stator is checked separately after disassembling the generator. The terminals of its winding must be disconnected from the rectifier valves. First of all, check with an ohmmeter or with a test lamp and a battery to see if there are any breaks in the stator winding and if its turns are shorted to the housing.
The insulation of the winding wires must be free of overheating, which occurs when there is a short circuit in the rectifier valves. The stator with such a damaged winding should be replaced. Then, a special defectoscope is used to check whether there are short-circuited turns in the stator winding.
Checking the rectifier block valves
A working valve allows current to flow in only one direction, while a faulty valve may not allow current to flow at all (chain break) 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 of the valves can be checked without removing the generator from the car, after disconnecting the wires from the battery and the generator. Also disconnect the terminal "B" of the voltage regulator from the terminal "30" of the generator and the wire from the terminal "B" of the voltage regulator. You can check with an ohmmeter or with a lamp (1-5W, 12V) and the battery, as shown in Figure 142.
Figure 142. Circuit for testing rectifier valves: a - testing of positive and negative valves simultaneously; b - checking negative valves; in - checking positive valves; 1 - battery; 2 — control lamp, 3 — generator.
In order to simplify the fastening of the rectifier parts, three valves (with red markings) have a "plus" of rectified current on the body (these are direct polarity valves - positive). They are pressed into one plate of the rectifier block, connected to the "30" terminal of the generator. The other three valves (negative, with black markings) have a "minus" of the rectified current on the body. They are pressed into another plate of the rectifier block, connected to the generator body.
First, check whether there are any short circuits in both the positive and negative valves. To do this, connect the battery's "plus" via a lamp to the generator's "30" terminal, and the "minus" to the generator's body (figure 142, a). If the lamp is on, both the negative and positive valves are shorted.
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You can check for a short circuit of the negative valves by connecting the battery "plus" through a lamp to one of the rectifier unit mounting bolts, and the "minus" to the generator body (figure 142, b). The lamp burning means a short circuit in one or more negative valves. It should be remembered that in this case the lamp burning may be a consequence of the stator winding turns shorting to the generator housing. However, such a malfunction is less common than a short circuit of the valves.
To check for a short circuit in the positive valves, the battery "plus" is connected via a lamp to the generator clamp "30", and the battery "minus" is connected to one of the rectifier unit mounting bolts (figure 142, in). Lighting of the lamp will indicate a short circuit of one or more positive valves.
Without disassembling the generator, a break in the valves can be detected only indirectly when checking the generator on a bench by a significant decrease (by 20-30%) in the strength of the output current compared to the nominal. If the windings, additional diodes and voltage regulator of the generator are in good condition, and there is no short circuit in the valves, then the reason for the decrease in the output current is a break 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 generator and the wire from the "B" terminal of the voltage regulator.
"Plus" batteries 1 (figure 143) through lamps (1-3 W, 12 V) connect to terminal "61" of generator 3, and the "minus" of the battery - to one of the bolts of the rectifier block. If lamp 2 lights up, then there is a short circuit in one of the additional diodes.
The only way to find a damaged diode is to remove the rectifier block and check each diode individually.
A break in the additional diodes can be detected with an oscilloscope by the distortion of the voltage curve on the "61" plug, as well as by the low voltage (below 14 V) on the "61" plug at the average rotation frequency of the generator rotor.
Checking the voltage regulator
The regulator operates by continuously and automatically changing the excitation current of the generator so that the generator voltage is maintained within specified limits when the rotor speed and generator load current change.
Check on the car
To check, you need a DC voltmeter with a scale of up to 15-30 V, accuracy class of at least 1.0.
After 15 minutes of engine operation at medium speed with the headlights on, measure the voltage between terminal "30" and the generator housing. The voltage should be within 13.6-14.6 V.
If there is systematic undercharging or overcharging of the battery and the regulated voltage does not fall within the limits specified above, the voltage regulator must be replaced.
Checking the removed regulator
The voltage regulator, removed from the generator, is checked according to the diagram shown in Figure 144. It is better to check it assembled with the brush holder, since in this case you can immediately detect breaks in the brush terminals and poor contact between the terminals of the voltage regulator and the brush holder.
A lamp with a power of 1-3 W, 12 W is connected between the brushes. A power source with a voltage of 12 V, and then 15-16 V is connected to the terminals "B", "B" and to the regulator body. If the regulator is in good working order, then in the first case the lamp should light, and in the second case it should go out.
If the lamp lights up in both cases, then there is a breakdown in the regulator, and if it does not light up in both cases, then either there is a break in the regulator or there is no contact between the brushes and the terminals of the voltage regulator.
Checking the capacitor
The capacitor serves to protect the electronic equipment of the car from voltage pulses in the ignition system, as well as to reduce interference with radio reception. Damage to the capacitor or weakening of its fastening on the generator (deterioration of contact with the body) is detected by an increase in interference to radio reception when the engine is running.
The capacitor's condition can be approximately checked with a megohmmeter or tester (on a scale of 1-10 MOhm). If there is no break in the capacitor, then when the device probes are connected to the capacitor terminals, the arrow should move toward decreasing resistance, and then gradually return back. The capacitor's capacity is 2.2 μF ±20%.