Tractor’serator: types and peculiarities of selecting the unit

Alternators for MTZ, connection diagram and repair

The generator on the tractor converts the mechanical rotational energy into electrical energy and powers the electrical equipment of the machine, including charging the starter batteries at 12 or 24 volts. The tractors MTZ 80 (82) of previous modifications had Soviet-made self-contracting three-phase generators G304, G305 and G306 with output voltage of 14 volt and power of 400 watt. Additional letters in the abbreviation of modifications of the above generators mean the difference in stator winding data and have a similar unified design with the same technical properties. As part of the G 304 and G 305 had two fixed exciters to produce power on the left and right stroke, G 306 with exciter winding only for the right stroke. A more modern version of the tractor generators has a similar design and is labeled 46 3701.


Design and principle of operation

The design of tractor generators is characterized by high reliability, simple design and maintenance. The unit has no brushes and grinders. The rotor 1 consists of permanent magnets without windings. The permanent exciter winding 4 is placed in a separate cylindrical case, which is attached to the inner side of the cover of the structural group. The electrostimulation field has a metal sleeve 5 with rotorages. Depending on the design of the unit, the stator winding 2 is three-, four- or five-phase. Alternating current to direct current is converted by means of diode rectifier unit 19, located on the inner side of the node cover. A transistor relay regulator 13 provides voltage regulation within a range of 14 or 28 volts, depending on the properties of the alternator and the corresponding machine mains voltage. The regulator unit is located under the outer rear plastic cover 18. The rotor axle 1 rotates on two ball bearings. The unit is enclosed in a cylindrical metal casing and secured with screws. The generator operation is cooled by the impeller 7, located on the rotor axis.


On MTZ 80 (82) node is located on the right side of the machine. The drive is carried out simultaneously with the engine water pump from the belt of the crankshaft through the V-belt gear. The drive is tensioned by turning the brackets on the generator strengthening axis.

Normal tension is checked with a force of 40 N on the drive mechanism “belt-disc water pump – belt-disc generator”. The bending of the belt should be 6-10 mm. Too little belt tension reduces the performance of the alternator, excessive tension also contains the axle support magazines and leads to premature wear.

Wiring and diagram

The alternator circuit consists of three parts: the stator winding and exciter coil, the rectifier diode bridge and the regulator, which is connected to the alternator by a seasonal voltage switch.

generator scheme

The stator phase ends are connected to the diode pairs of the rectifier. The plus pole of the rectifier is led out through the contact bolt, the minus pole is connected to the housing of the unit. Additional diodes of the rectifier supply the excitation winding of the generator. The plus of the excitation winding rectifier is connected to the exciter coil and the output of node D. The positive output of the rectifier diode bridge B is connected to the same-named terminal of the controller. Output B connects the consumer network of the machine and the plus pole of the battery. The minus poles of the rectifier unit and the controller are connected to the machine ground through the alternator housing. The generator and controller outputs are connected and serve to connect the starter interlock relay. If the tractor is started with a starter without a starter, the lead D is isolated with a cap. Output Ø of the controller is connected to the end of the exciter winding. Output C of the controller is connected to the season counter. For proper connection of the controller to the assemblies, when installed or replaced, it is wired through the case lead.

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Disturbances and repairs

The operation of the generator is checked under load by measuring the mains voltage. When switching on electrical appliances watch the dynamics of voltage change. At maximum load, the value should not fall below 12.5 V.

Wasting charging current in the network at engine speed occurs with slippage of the drive belt, oxidation or destruction of mains contacts. If the rectifier or rotating circuit fails, division current occurs. A high charging current indicates a faulty battery.

Generators of the type described are very reliable and operate in dusty and high vibration environments. The main cause of failure of the electrical part of the unit is the wear of the stock and its seats on the rotor axis. Increasing the distance on the rotor supports leads to short-circuiting of the node. If the running rings are destroyed, metal splinters mechanically damage the exciter or stator winding and render the assembly unusable. It is therefore necessary to pay attention to the condition of the assembly stock during operation. Lack of play in the rotor bearings or noise when rotating signalize the urgent replacement of assemblies. And contamination by petroleum products and dust can also lead to short circuits and failure of the diode rectifier.

Scheduled cleaning of the generator is carried out every 500 hours of operation of the unit during maintenance service2.

To diagnose alternator laps, disassemble the controller and the back cover, separate the winding lines. The presence of a short circuit to the housing is checked with a test lamp. The integrity of the stator and exciter winding circles, as well as the state of the rectifier and the controller are checked with a control lamp or accessed with a device.

MTZ tractor generator models

Development of MTZ tractor models and increasing equipment of machines with electrical equipment has led to the use of alternators of similar design with higher performance and appropriate technical properties. Modern MTZ machines with 12 volt are equipped with the units of the following series: G46.3701 with 700W power, G96.3701 with 1000-1150W and G97.3701 with 1400W. For MTZ machines with 24-volt power are used units of series G99.3701 with power 1000-1150 W and 98.3701 with power of 1500 W. Modifications of the nodes differ in design and dimensions of the drive.

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The generator is an electrical machine that converts the mechanical energy of the driving machine into electrical energy. The generator serves to supply consumers with electrical energy at a certain speed of the engine crankshaft and to charge the battery.

The alternator is driven by the crankshaft via a V-belt transmission with constant translation, so the speed of rotation of the alternator is directly dependent on the speed of the engine. And since the crankshaft speed in tractor engines from minimum to maximum in the ratio of 1: 3.5 and even more (without a regulator up to 1: 8) can vary, in the case of auto-engines, regulators are installed on the connections of the generator, which keep the voltage within the specified limits.

Since tractor generators work in more difficult conditions than autogenerators (considerable dustiness of the environment, strong vibrations, etc.), the following are carried out: their insides are protected by blind covers; Heat is removed mainly through the surfaces of the housing and the covers. External fans are used for better cooling.

Autogenerators are produced in a protected version – the air flow created by the fan passes through the internal part of the housing and special windows in the casings and intensively cools the heated parts.

Generators are characterized by electric power, voltage, capacity, initial (without load), at which the rated voltage is achieved, and maximum (under load) speed.

Three-phase synchronous alternators with electromagnetic excitation are installed on tractors and automobiles. The magnetic field and the rotor rotate at the same frequency – synchronously. The main magnetic flux is created by the exciter winding connected to the battery or the stator winding (fed through a rectifier). Alternator operation is also possible with a pre-magnetized magnetic system. The stator coils form a three-phase winding, which is less often in star, less often in delta.

A distinction is made between contact and contactless alternators.

In a contact alternator, the excitation current flows through the ground rings and brushes of the rotor winding. Unlike DC generators, there is no sparking here, since the rings and brushes do not take over the function of turning on the electricity. Non-contact generators have no sharpening rings, brushes or rotating windings, they are very reliable and can withstand harsh operating conditions, but are somewhat larger in size and weight than contact generators.

Some consumers need direct current to charge the battery and for power; Some consumers can operate with both direct and alternating current. In the case of automotive electrical equipment, the alternator current is equally equal, which is what the rectifiers, which are usually installed in the alternator, are for.

Alternators are distinguished by their ability to charge the battery at low engine speeds. The relatively high speed of the alternator in this mode allows it to develop sufficient current, freeing up the battery to work. In DC alternators, the nominal speed of rotation of the armature is limited by sparking under the brushes. When the engine is running at low speed, the alternator voltage is lower than the battery voltage and current is generated only in the excitation and regulator coil circuits.

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Installed power of the generator is determined depending on the traction class of the tractor or carrying capacity of the vehicle and is 200-1000 W.

Alternator G272

Alternators with electromagnetic excitation and contactor. On cars (GAZ-53A, ZIL-130, Kamaz, Maz, Kraz, etc.) and some tractors (e.g. with electromagnetic excitation and contactor. Generators are made according to a single scheme and differ mainly in design features and electrical characteristics. Fig. 1. Generator G272: 1, 12 – cover; 2 – contact rings; 3 – brush-holder; 4 – spring; 5 – brushes; 6 – pole tips; 7 – impeller; 8 – pulley; 9 – shaft; 10, 19 – ball-bearings; 11 – bushing; 13 – stator; 14 – excitation; 15 – stator coil; 16 – clamp; 17 – excitation ends; 18 – rectifier unit.

Generator G272 Kama z-Auto consists of a stator 13 (Fig. 1), rotor, 1 and 12, contactor, rectifier unit 18, drive pulley 8 and other elements.

The stator core is made of sheets of electrical steel in a package with evenly spaced around the circumference 18 teeth and is fixed with screws between the aluminum alloy covers 1 and 12. On the teeth are eighteen winding coils 15, which are fixed in the slots of the stator with textolite threads. The coils are wound with 1.16 mm wire (eighteen turns), forming three phases on the star. Each phase consists of six coils connected in series, the ends of which are connected to the three terminals 16 of the rectifier units 18.

The rotor consists of a shaft 9, contact rings 2, two pole tips 6 sleeves 11 and an exciter 14. The pole tips are steel, hexagonal, north (N) polarity. Their arrangement is such that the peaks of one polarity move between the peaks of the opposite polarity. Between the pole tips is a sleeve 11 of wick 14 with 1490 coils of 0.51 mm diameter wire. The rotor rotates in ball bearings 19 and 10 (closed type, requiring no lubrication), which are mounted in the ceiling of the generator through external clamps. Ventilation of the flow is created by the impeller 7 on the pulley 8 and slots in the covers for cooling the generator.

The contact device is formed by two copper contact rings 2, brush holder 3, two graphite brushes 5. The exciters isolated from the shank 14 are soldered to the rings. One (insulated from the ground) brush is connected to the generator clamp, and the second through the generator housings to the ground.

The cover 1 contains a semiconductor rectifier unit of 18 six silicon diodes connected in a bridge circuit. Positive terminals are connected to the cover on the rectifier side of the rectifier. The positive direct polarity terminals are connected to the positive terminal insulated on the panel, insulated to ground. The negative terminal closes the reverse polarity contrast plate to ground.

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Maintenance of the alternator G272 (e.g. Kamaz car) consists mainly of cleaning the alternator from dirt, tensioning the drive belt, resulting in the alternator mounting bolts and belt nut (TO-1) should be tightened. During TO-2 check the bolts fastening the alternator banks and the state of contact connections of wires. After run of 50 thousand km (25 thousand km for a new car) remove the brush holder 3. Check the free movement of brushes in the leader holes, inspect and clean the contact rings 2 If necessary, check the elasticity of the feathers 4. The brushes are replaced if their height from the stool level is less than 8 mm.

Contact flow with electromagnetic excitation. A number of tractors are equipped with closed loop-free three-phase alternators of G304, G305, G306 types with built-in rectifiers. Generators G304 and G305 are of the same type in the main parts and differ mainly by winding data. A characteristic feature of these generators is the absence of brush contacts and rotating windings.

Alternator G306

Generator G306, which is one of the improved non-contact alternators with electromagnetic excitation, has 10 ribbon discs 11 pcs. Fig. 2nd alternator G306: A – device: 1 – starter bolt; 2 – insulating block; 3 – back cover; 4 – adapted bolt; 5 – stator; 6 – rotor; 7 – stator winding; 8 – excitation; 9 – cover sheet; 10 Rectifier unit BPV-30; 11 – belt disc with impeller; 12, 15 – ball bearings; 13 – busbar cover; 14 – busbar; 16 – back foot; B – electrical diagram: OV – generator excitation winding; OS – generator winding; GP – rectifier: 1 – direct polarity diodes; 2 – reverse polarity diodes; A – ammeter; VM – mass switch; V, W, M – output terminals; T – transistor; E – emitter; K – collector; B – base; D1 – lock diode; LG – Löschkreis diode; DP – isolation diode; PZ – protective relay; FZ – protective relay holding winding; P3o – protective relay series winding; RZV – counter winding of protective relay; RN – voltage regulator; SBR – seasonal voltage setting switch (screw); Fo – voltage winding; RB – transistor base resistance; RT – temperature compensation resistance; R – acceleration resistance; RD – additional resistances.

Stator 5 is assembled from sheets of electrical steel connected in a package. Nine turns of three-phase winding are evenly distributed along the inner circumference of nine stator teeth. Coils of PEV-2 wire of 1.35 mm diameter with enamel insulation and double coating have twenty-eight turns and are fixed to the teeth with fiberglass wedges. Each phase winding consists of three coils connected in series. The phases are connected in a delta (Fig. 2, b). The phase ends of the OS stator winding are led to the studs 1 (Fig. 2, b) of the AC terminals, which are placed on the insulating block 2 of the rear cover 3 and marked “~”. To the same terminals the outputs of the VP rectifier are connected.

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The rotor shaft is fitted with a six-pointed sprocket consisting of sheets of electric steel connected by rivets. The rotor is supported by closed ball bearings 12 and 15. The front cover 9 is made of steel, on the end of which the excitation coil 8, wound on a steel frame, is screwed on from the inside. The winding consists of 500 turns of PEV-2 wire of 0.74 mm diameter. The beginning of the winding is connected to the generator ground, and the end – to the terminal Ø. placed on the terminal block 2 of the back cover 3. The back cover 3 is cast from aluminum alloy. On the end hole of the cover there are terminals with their designations. To the front cover are welded two feet for mounting the generator and adjusting the drive belt tension.

Rectifier GP (Fig. 2, b) consists of the housing and heat sink, made of aluminum alloy, and six semiconductor diodes with forward 1 and reverse 2 polarity. Diodes 1 are pressed into the heat sink and marked with black paint along the bottom, and diodes 2 are pressed into the housing and marked with red paint. The rectifier body is provided with ribs for better cooling. The rectifier is made by a three-phase bridge circuit. The positive pole of the rectifier is connected with the flexible wire to the terminal B on the terminal block 2 (Fig. 2, a) of the generator. Fixing wires of the rectifier and excitation coil are connected outside the generator and protected by strips 14.

Magnetic circuit of the generator is closed around the field winding 8 by the steel casing 9, the field winding frame, air gap, stator 5 and casing 9. As the rotor rotates, one of the rotor poles is under each tooth of the stator core, causing the magnetic flux through the stator teeth to change in magnitude and direction. When the rotor tooth 6 is in contact with the stator tooth, the magnetic flux in the stator tooth is greatest, and when the stator tooth is in the rotor slot, the magnetic flux in the stator tooth is smallest. The intersection of the stator windings with the pulsating flux induces a variable EMF in them.

In principle, generators G304 and G305 do not differ from the generator G306, but their schemes, construction and materials are not the same. Generator G306 is unilateral, and generators G304 and G305 – bilateral, since they have two excitation coils, each of which is placed in one of the steel housings and connected in parallel to each other. Weight and dimensions of generators G304 and G305 are somewhat larger than the generator G306.

The described generators operate with voltage regulators type РР362, РР362-B.

When maintaining generators G304, G305 and G306 should follow their cleanliness, reliability of fasteners, state of contacts, tension and serviceability of the drive belt [Gurevich A.M., Sorokin E.M. Tractors and cars. 1978].

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