Generator checks

Checking the generator on the car

If the battery charge control lamp is on when the engine is running, then you can roughly determine the health of the generator as follows:

• slightly pulling out the carburetor choke control knob, bring the idle speed to 1000-1500 min^-1;
• briefly disconnect the wire from the terminal «minus» battery. If the engine stalls, this will indicate that the generator is faulty and all consumers are powered by the battery.

Checking the generator on the stand

Testing on the bench allows you to determine the health of the generator and the compliance of its characteristics with the nominal ones. The generator under test must have its protective cover 6 removed (rice. 7-4), the brushes must be well lapped to the commutator slip rings, and the rings themselves clean.

Install the generator on the stand and make the connections as shown in fig. 7-6. Turn on the electric motor of the stand, set the generator output voltage to 14 V with rheostat 4 and bring 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 must be at least 44 A.




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

If you suspect a malfunction of the generator rectifier unit valves, check the output current on a warm generator. Such a check allows you to better identify the malfunction of the valves by a sharp decrease in the recoil current with an increase in the temperature of the generator. To warm up, let the generator run for at least 15 minutes at a rotor speed of 5000 minutes^-1 and a voltage of 14 V at the output of the generator. Then measure the recoil current. On a warm generator, it should be at least 42 A.

Checking the generator with an electronic oscilloscope

The oscilloscope allows you to accurately and quickly check the health of the generator and determine the nature of the damage by the shape of the rectified voltage curve.

To check, rotate the generator rotor with a frequency of 1500-2000 min^-1, feeding the excitation winding from the battery, but from the clamp «30» disconnect the battery.

With serviceable valves and stator winding, the rectified voltage curve has a sawtooth shape with uniform teeth (pic. 7-7). If you have * an open in the stator winding or an open or short circuit in the rectifier valves - the shape is crooked; changes dramatically: the uniformity of the teeth is disturbed, deep depressions appear (pic. 7-7, II and III).

Checking the excitation winding of the rotor

The health of the winding and the reliability of the fit of the brushes to the slip rings can be checked on the stand without disassembling the generator by measuring the resistance between the plug «67» and «weight» generator.

If the winding does not have short-circuited turns and the brushes are well ground to the slip rings, then the resistance should be 4.4^+0,3_-0,2 Ohm at 20°C. In this case, it is necessary to monitor the reliability of contact between the rotor rings and the conductors attached to them.

Stator check

The stator is checked separately, after disassembling the generator. Its winding leads must be disconnected from the rectifier valves.

First of all, check with an ohmmeter or with the help of a test lamp and a battery, whether there are any breaks in the stator winding and whether its turns are closed on «mass».

The insulation of the winding wires must be free from overheating, which occurs during a short circuit in the rectifier valves. Replace a stator with such a damaged winding.


Finally, it is necessary to 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. Faulty - may not pass current 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 of the rectifier 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 (25-40W) and battery as shown in Fig. 7-8.

Note. In order to simplify the fastening of parts of the rectifier, three valves are on the body «plus» rectified voltage. These are valves «positive» and they are pressed into one plate of the rectifier block. Other three gates «negative» have on the body «minus» rectified voltage and pressed into another plate of the rectifier unit.

First check if there is a short circuit at the same time in «positive» and «negative» valves. For this «plus» connect the batteries through the lamp to the clamp «30» generator, and «minus» - to the generator housing (pic. 7-8, I). If the lamp is on, then «negative» and «positive» valves are short circuited.

Short circuit «negative» valves can be checked by connecting «plus» batteries through a lamp with a plug of the neutral wire of the stator winding, and «minus» - with generator housing (pic. 77-8 II)

Burning lamp means a short circuit in one or more «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 a short circuit in «positive» valves, «plus» connect the batteries through the lamp to the clamp «30» generator, and «minus» — with plug for outputting the zero point of the stator winding (pic. 7-8, III). Burning lamp will indicate a short circuit of one or more «positive» valves.

An open in the valves without disassembling the generator can only be detected indirectly when checking the generator on the stand, by a significant reduction (by 20-30%) the magnitude of the output current compared to the nominal. If the generator windings are in good order, 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.