On a ZIL - 5301 (bull) car, in addition to the voltage regulator relay, which is located to the left of the driver's seat below, there is also an excitation winding relay
The field winding relay is located on the relay panel on the right side, near the push-button fuse panel
This relay protects our field winding during startup with the ECU, and when starting is difficult, especially in the cold season. Therefore, it is observed after startup:
- - no charging or weak charging;
- - tachometer readings at “0”.
After some time, the relay turns on and charging appears.
Some comrades complain about the tachometer readings, like “the tachometer needle starts jumping.”
This defect is caused by burning of the contacts of this relay.
Let us consider below the main malfunctions of the alternator:
Break field winding
With this malfunction, an emf of up to 3-4 V is induced in the stator winding, due to the residual magnetism of the rotor steel.
Contact failure in the brush assembly due to oxidation or oiling of the contact rings of the generator, severe wear or hanging of the brushes in the brush holders, decreased elasticity of the brush holder springs, etc.
The malfunction is accompanied by an increase in the resistance of the generator excitation circuit, therefore the excitation current strength decreases, and at the same time the generator power decreases.
The generator voltage reaches its rated value only at an increased rotor speed.
A turn short circuit in the field winding coil is caused by the same reasons and leads to similar consequences.
The turn circuit is determined by measuring the winding resistance with an ohmmeter.
Short circuit of the excitation winding to the housing most often occurs in places where the ends of the coils are brought to the slip rings.
The short-circuited coil is de-energized, the excitation magnetic flux decreases sharply, so the generator voltage will become lower and no current flows from it to the external circuit.
This malfunction is determined using a voltmeter or a test lamp with a voltage of 220-500 V, connecting one conductor to the rotor iron, and the other to the slip ring.
If there is no current in the circuit for 1 minute, then the winding insulation is good.
Open circuit in the stator phase winding
If there is a break in the connecting wire of one phase of the generator to the rectifier terminal, the phase is turned off, and therefore the resistance of the stator winding increases significantly, which reduces the power of the generator.
If two phases are broken, the entire stator winding circuit is interrupted and the generator will not work.
When the generator is disassembled, to determine a break in the stator phase winding, it is necessary to alternately connect two winding phases to the battery through a light bulb or voltmeter.
The presence of an open circuit turns off the circuit, and there will be no current in it.
Short circuit of the stator winding to the housing occurs due to mechanical or thermal damage to the insulation of the winding and output terminals.
The malfunction significantly reduces the useful power of the generator as a result of a short circuit of the faulty phase windings through the rectifier and housing.
These malfunctions are determined by a test lamp with a voltage of 220-500 V, by connecting one conductor to the stator core, and the other to one of the terminals of the stator winding. Defective insulation is replaced with new one.
In addition to the above-mentioned faults, mechanical faults also occur in DC and AC generators, for example, wear and destruction of bearings, wear of the journals of the armature (rotor) shaft, development of the keyway of the shaft and pulley, damage to the threads on the shaft and nuts, etc.
Identifying and eliminating such faults is not very difficult.
Main malfunctions of generator rectifiers
Short circuit to the “+” clamp body
This malfunction causes the rectifier to short-circuit, and in the circuit - the generator stator winding - the rectifier, a high current strength is established, as a result of which they overheat and possible destruction of the winding insulation and breakdown of the blocking layer of the rectifier diodes.
Diode breakdown most often occurs due to an increase in the generator voltage, which can occur when the main winding of the voltage regulator is broken, the wire connecting the relay-regulator to the housing is broken, the voltage regulator is incorrectly adjusted, the wire is disconnected from the terminal “ +" generator.
In addition, breakdown of the diodes occurs when the rectifier is overheated by a high current that passes through them, as well as when the diodes are mechanically damaged, or when the rectifier terminals are incorrectly connected (when the negative terminal with connected not to the body, but to the terminal of the relay regulator).
At the point of breakdown, the covering layer of metal melts, resulting in the formation of a short-circuited section between the electrodes of the diode.
In the event of a breakdown of the diodes, there will be a large discharge current when the generator is not working.
Aging of diodes. Over time, diodes disintegrate and age, which increases the resistance in the rectified current circuit.
This malfunction causes an increase in the voltage drop at the diode terminals when current flows in the forward direction and an increase in the strength of the reverse current.
As a result, the battery will be undercharged.
The generator is installed on the engine and is driven by the engine crankshaft pulley.
The generator is attached to the engine with two legs through a bracket and with a third leg to the tension bar, when moving along which the generator drive belt is tensioned.
The schematic diagram of the generator is shown in the figure.
Attention! 1. Disconnect and connect wires to the generator only with the battery disconnected.
- Proper operation of the generator is ensured only if there is a reliable electrical connection of all contacts, including between the generator housing and the engine. 3. Operating the generator with the battery disconnected can damage the voltage regulator, as well as other consumers of the on-board network.
- Maintenance and repair of the generator should only be carried out in specialized workshops by qualified specialists.
- Check the rectifier unit only on a disassembled generator with the stator winding disconnected.
Check only from a direct current source with a voltage of no more than 24 V, connected in series with the test lamp.
To ensure the operation of the generator, it is recommended to keep the generator clean and follow the following maintenance rules.
Check the functionality of the generator daily using the readings of the warning lamp and voltmeter located in the instrument cluster on the instrument panel.
When the engine starts, the warning lamp should light up, and after the engine starts, it should go out.
During normal operation of the generator, the voltmeter needle is in the green zone of the “G” scale (generator).
The location of the voltmeter needle in any of the red zones of this scale indicates a malfunction of the generator.
The condition and tension of the drive belts should be checked daily.
During TO-1, the check is carried out using measuring instruments.
Particular attention to belt tension should be paid at the beginning of their operation (1-2 days).
The belt tension is adjusted so that when you press the middle of the belt with a force of 4 kgf, the deflection is within 10-15 mm.
When installing new belts, it is allowed to set a lower deflection value - 10 mm.
The belt tension is adjusted using a tension bar. To do this, after loosening the fastening of the generator to the bracket and the bar, move the generator housing to the required position and secure it.
Attention! If the belt tension is weak, the generator will not deliver full power.
If the belt is over-tensioned or misaligned, the generator will fail prematurely.
The criterion for the limiting state of a belt is delamination of more than 1/3 of the length, the presence of rubber cracks up to the depth of the cord and the impossibility of compensating for elongation in the drive.
When checking the tension and installing a new belt, check for damage, oiliness of the surfaces of the pulley grooves and the location of the pulley grooves in the same plane.
At least once a month it is recommended to monitor the degree of contamination of the batteries, which should be at least 75%.
During TO-2 without removing the generator from the engine, you should check the fastening of the generator to the engine and the fastening of the nuts of the coupling bolts of the covers.
Check the tightness and cleanliness of all connections of wires to the generator and batteries.
If necessary, clean the connections, tighten the contact nuts and screws.
At each seasonal maintenance (without removing the generator), you should check the condition of the brush assembly in the following order:
- Disconnect the wire from terminal "Ш" of the generator.
- Operation Unscrew the screws securing the brush holder and carefully remove it.
- Check the free (without jamming or jerking) movement of the brushes in the brush holder guides.
- Check the height of the brushes, which should be at least 8 mm. If necessary, replace the brushes.