Generator Checks (VAZ-2101)

Checking the generator on the car

If the battery charge indicator light is on when the engine is running, then the generator's serviceability is roughly determined as follows:

• by slightly pulling out the carburetor air damper control handle, bring the crankshaft speed at idle to 1000-1500 rpm;
• briefly disconnect the wire from the "-" terminal of the battery. If the engine stops, this indicates that the generator is faulty and all consumers are powered by the battery.

Testing the generator on the bench

Testing the generator on a stand allows you to determine the generator's serviceability and whether its characteristics correspond to the nominal ones. The connection diagram for testing the generator is shown in Fig. 154. The brushes of the tested generator must be well ground to the contact rings of the collector, and the rings themselves must be clean.



The stand's electric motor is switched on, the generator output voltage is set to 14 V using rheostat 4, and the rotor speed is increased to 5000 rpm. 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 44 A.



If the measured value of the output current is less, this indicates faults in the stator and 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.

If there is a suspicion of a rectifier valve malfunction, the output current strength is checked on a warmed-up generator. Such a check allows better detection of a valve malfunction by a sharp decrease in the output current with an increase in the generator temperature. To warm up, it is necessary to let the generator run for at least 15 minutes at a rotor speed of 5000 rpm and a voltage of 14 V at the generator output. Then measure the output current strength, which on a warmed-up generator should be at least 42 A.

Checking the generator with an electronic oscilloscope

The oscilloscope allows you to accurately and quickly check the generator's serviceability and determine the nature of the damage based on the shape of the rectified voltage curve. To check, set the generator rotor speed to 1500-2000 rpm, feeding the generator excitation winding from the battery, but disconnecting the battery from the "30" terminal. With serviceable valves and stator winding, the rectified voltage curve has a sawtooth shape with uniform teeth (fig. 155, a). If there is a connection fault in the stator winding or a break or short circuit in the valves, the shape of the curve changes dramatically: the uniformity of the teeth is disrupted and deep depressions appear.




(The source is on the website: «VazBook»)

Checking the rotor excitation winding. The serviceability of the winding and the reliability of the brushes' contact with the contact rings can be checked on a stand without disassembling the generator by measuring the resistance between the "67" plug and the generator body. If the winding does not have short-circuited turns and the brushes are well ground to the contact rings, then the resistance should be 4.4^+0,3_-0,2 Ohm at 20°C.

After disassembling the generator, check the excitation winding resistance between the two contact rings, which should be (4.3±0.2) Ohm at a temperature of 20°C. In this case, it is necessary to monitor the reliability of the contact between the rotor rings and the conductors connected to them.

Stator check

The stator is checked separately after disassembling the generator. The terminals of its winding must be disconnected from the rectifier valves. First, check with an ohmmeter or 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 traces of overheating, which occurs when there is a short circuit in the rectifier valves. A stator with such a damaged winding must be replaced. Then check with a special defectoscope to see if there are any short-circuited turns in the stator winding.

Checking the rectifier 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).

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. You can check with an ohmmeter or with a lamp (25-40 W) and a battery, as shown in Fig. 156.



First, check whether there is a short circuit in both the positive and negative valves. To do this, connect the "+" of the battery through a lamp to the "30" terminal of the generator, and the "-" of the battery to the generator body (fig. 156, a). If the lamp is on, then both the negative and positive valves are shorted.

You can check for a short circuit of the negative valves by connecting the "+" of the battery through a lamp to the plug of the neutral wire of the stator winding, and the "-" of the battery to the generator body (fig. 156, 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 "+" of the battery is connected through a lamp to the "30" terminal of the generator, and the "-" of the battery is connected to the stator winding zero point terminal plug (fig. 156, 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 testing 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 generator windings 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.