The vehicle power supply system consists of two sources: batteries and an alternating current generator set. In addition, the system includes a number of intermediate relays, a battery mass switch and a key switch for instruments and a starter

Scheme of switching on the products of the power supply system is shown in fig. 1.

Generator set (GU) G273A is an alternator with a built-in rectifier unit and an integrated voltage regulator (IRN).

Generator set specifications

  • Rated power, W - 800
  • Rated voltage, V - 28
  • Rectified current, not less than, A - 28

Rated rotor speed at ambient temperature and GU 25 ± 10˚С and voltage 27----- 28 V, min-1:

  • - at a load current of 10 A, not more than - 1550
  • - at a load current of 20 A, not more than - 2100

Maximum rotor speed, min-1 - 8000

Excitation current, A - 3.3

IRN setting voltage at a load current of 20 A, a GU rotor speed of 3500 ± 200 min-1, an ambient temperature of 25 ± 5 °С and a switched on battery, V:

  • - in the position of the seasonal adjustment regulator "winter" - 28, - 30.2
  • - in the position of the regulator "Summer" - 27.0 —- 28.0

the pressure of the brush springs on the brushes when the springs are compressed up to 17.5 mm, kgf - 0.3

Mass of GU without pulley, no more than, kg - 5.4

The generator (Fig. 2) is a three-phase synchronous electric machine with electromagnetic excitation and is one of the power sources for electrical equipment.

Equipped with a rectifier unit and an integrated voltage regulator.

Brush holder with IRN for MAZ

The Ya120M small-sized integrated voltage regulator serves to maintain the voltage generated by the generator within the specified limits.

The regulator is an electronic device, closed with a lid and filled with a special sealant. There are 4 outputs on the regulator.

With these terminals, the regulator is installed in the brush holder so that the terminals marked with the letters "Sh", "D", "B", and "P" lie on the current-carrying tires of the brush holder (Fig. 3).

The brush holder also has a 75 ohm make-up resistor 3 to ensure reliable excitation of the generator set at low engine speeds.

The electrical circuit for connecting the generator to the voltage regulator is shown in fig. 4.

Generator Maintenance

After 50,000 km of the car run and in the future with each TO-2, it is necessary to remove the GU from the engine, disassemble it, check the condition of the ball bearings and electric brushes. Damaged bearings and brushes worn down to 8 mm should be replaced.

During the operation of vehicles, the following rules must also be observed:

  • - prevent incorrect connection of wires to batteries or installation of batteries with reverse polarity. This will lead to immediate failure of the rectifier diodes GU and IRN;
  • - do not disconnect the wires from the positive output of the GU and from the batteries when the engine is running. This will drastically reduce the load on the generator, which can lead to failure of the IRN;
  • - do not check the health of the GU by closing the terminals "+", "B", "O" to ground or to each other. This can lead to failure of the IRN or the rectifier unit of the GU;
  • - do not connect the "Ш" terminal of the brush holder. access to which is open through a window in its casing, with terminals "+" of the generator and "B" of the brush holder. This will cause the IRN to fail;
  • - do not check the health of the electrical circuit with a megohmmeter or a lamp with a voltage higher than 26 V when the GU is on. This can lead to failure of the IRN and the rectifier unit;
  • - when carrying out welding work on a car, first disconnect the batteries with a mass switch, remove the wires from the terminals "+" GU and "B" of the brush holder, and when carrying out welding work on a road train - additionally remove Remove the plugs from the brushes of the semi-trailer to avoid burning the connecting electric cable.

At the end of welding, make sure that the wire end on the “+” terminal of the GU is securely clamped with a nut. Loosening the nut in this contact (sparking) will lead to failure of the IRN;

  • - when washing the engine, avoid direct water ingress into the GU.

Possible malfunctions of the generator set and how to eliminate them

- cause of failure


No charging current: the voltage pointer is in the red zone of the scale

- No power to the "+" or "B" terminals of the generator set

Check the power circuit and excitation circuit according to the diagram and troubleshoot

No charging current: the voltage pointer is in the red zone of the scale

There is voltage at the “+” and “B” terminals when the engine is not running

Faulty IRN

Replace IRN

- Contact rings of the generator rotor are dirty or oily

Wipe the slip rings with a cloth soaked in gasoline

- Hanging brushes

Remove brush holder, remove brushes, remove dust

There is charging current: the voltage indicator needle is in the green zone of the scale

When a large load is turned on (headlights or floodlights), as well as when the engine speed increases, the charging current decreases.

The arrow enters the red zone.

- The tension of the belts has loosened

Tighten the straps

- Faulty rectifier unit

Replace rectifier

- Faulty IRN

Replace IRN

- Break in the stator windings of the generator

Replace IRN or stator

Generator repair

For repair, the generator set is removed from the engine, for which it is necessary (Fig. 5):

  • - disable the battery mass switch;
  • - disconnect the wires from the <+" and "B" terminals of the GU (see Fig. 2);

Generator mounted on engine

  • - loosen the bolt 1 (see Fig. 5) of the belt tension bars;
  • - loosen the nut 11 fastening the GU;
  • - loosen bolt 15 of fastening the pin;
  • - unscrew bolt 1;
  • - while holding the GU, so as not to break the mounting brackets, unscrew the bolt 17;
  • - remove finger 14; remove the belts from the pulley; remove the GU from the engine.

The GU removed from the engine must be cleaned of dust and disassembled in the following order (see Fig. 2):

  • - disconnect screw 20 for fastening wires;
  • - unscrew the two screws securing the brush holder and remove it;
  • - unscrew the two screws securing the IRN and remove the regulator;
  • - unscrew three screws 4 fastening the protective cover of the bearing;
  • - unscrew the four coupling screws 17 and remove the cover 7 of the generator together with the stator;
  • - unscrew the nuts 1 of the phase terminals from the rectifier unit and separate the stator 8 from the cover 7;
  • - unscrew the nuts securing the “+” terminal on the cover 7 and three screws securing the rectifier unit and remove the unit;
  • - unscrew the nut 15 of the pulley and remove the pulley 14;
  • - remove fan 12:
  • - knock out the key 13 and remove the spacer sleeve 11;
  • - using a puller, remove cover 10 from the rotor shaft together with the bearing;
  • - remove bearings from caps 7 and 10.

After disassembling the parts and components of the GU, it is necessary to inspect, make sure that there are no damages, and also check the condition of the windings, the rectifier unit and the voltage regulator.

The height of the brushes must be at least 8 mm. Worn brushes must be replaced.

A chipped pulley must also be replaced. The wear of the pulley grooves is checked with a caliper on two rollers with a diameter of 9 mm, embedded in the grooves.

The dimension across the rollers must be at least 83.5 mm. If the pulley is smaller, it must be replaced. Breakage or cracks in the covers are also unacceptable - such covers must be replaced.

The bearings are carefully examined. If there are no violations in the bearings by external inspection, they can be used for further operation.

When examining cover 7, you should pay attention to the production of a hole for the bearing. The development (ovality) is formed in the upper part of the hole. It is necessary to measure the value of this output.

The size of the bearing hole is Ø 35 mm. It is allowed to increase the size up to 35.40 mm. If the size is larger than allowed, the cover must be replaced.

Bearing holes in drive end cover Ø 47 + 0.02 mm. Wear is allowed up to size Ø 47.04.

The holes in the cover brackets must be within the size of Ø 10.2+0.24. In case of wear, new bushings are pressed in and a hole is drilled to the specified value.

When inspecting the generator rotor, make sure that the bearings are securely fastened to the rotor shaft.

The shaft journals are made Ø 15 mm under the bearing in the cover on the side of the slip rings and Ø 17 ± 0.06 mm under the bearing in the cover on the drive side.

The dimensions of the shaft journals are Ø 14.94 and 16.9 mm, respectively. If the necks are smaller, the rotor must be replaced.

The rotor is checked for a turn short circuit and a short circuit of the excitation winding to the housing.

The resistance of the rotor winding should be 3.7 ± 0.2 Ohm at a temperature of +25 °C. A decrease in resistance indicates the presence of a turn circuit, and the rotor must be replaced.

There may be a tapping of wires from slip rings. In this case, the wires must be soldered to the rings and the soldering area must be painted over.

If the rotor rings have wear, then they must be machined and polished.

The diameter of the rings must be at least 30.0 mm; if the size is less than 30 mm, the rings must be replaced.

The generator stator is checked for a winding short circuit to the housing. The check is carried out similarly to checking the rotor with a test lamp.

The stator winding may have a turn short circuit. This leads to overheating of the stator coils and their failure.

The disadvantage is determined by an external examination by changing the color of the coils and violating their reliable, without backlash, fit into the stator slots. A stator with damaged coils must be replaced.

Rectifier unit test diagram

The correctness of the rectifier unit is checked by a test lamp with a voltage of no higher than 24 V, as shown in fig. 6.

The block is checked forward and backward.

To check in the forward direction, the "+" of the DC voltage source through a test lamp is connected to the "-" of the rectifier unit, and the "-" of the source to the "+" of the unit ("+" of the unit is determined by the shaped hole 6). In this case, the control lamp should be on (see Fig. 6, a).

With a changed polarity (see Fig. 6, b), the lamp should not burn. If these conditions are not met, then the unit is defective and must be replaced.

Voltage Regulator Test Diagram

The integrated voltage regulator is checked using a test lamp connected to a 24 - 26 V DC voltage source (Fig. 7).

To check, the “+” of the power source is connected to the “B” terminal of the regulator, and “-” to the base. The control lamp turns on on the "+" of the power source and the terminal "Ш" of the regulator.

When the regulator is in good condition, the control lamp burns with full voltage evenly. If the lamp does not light or burns incompletely, or flashes, the IRN is defective and must be replaced.

After checking the parts and assemblies of the GU, sorting and replacing the parts, the assembly is carried out in the reverse order.

The assembled GU is checked by turning the pulley by hand. The rotor should rotate easily, without jamming or knocking, which indicates proper assembly.

Next, the generator must be checked for operability, for which the installation is placed on the stand.

The stands of models 532M, KI-968 or any other are used, which allow changing the rotor speed from 0 to 5000 min-1, as well as measuring the operating current up to 30 A with an accuracy of at least 2 A and voltage up to 30 V with an accuracy of 0.1 V.

The procedure for connecting the PG to the stand is determined by the instructions for the stand.

The circuit shown in fig. 4. Switch 2 to connect the GU and begin to rotate the rotor, bringing the frequency of its rotation to 4000 ± 500 min -1.

A working GU should give a working current, which is noted by an ammeter. The amount of current depends on the state of charge of the batteries 1.

The voltage on the voltmeter 11 at the position of the seasonal adjustment regulator "L" (summer) should be 27 - 28 V. It is recommended to maintain the GU at speeds for 3 - 4 minutes in this mode, which is a post-repair break-in.

A genset tested in this way can be installed on the engine. Installation is carried out in the reverse order to dismantling.