How to check the removed generator?

The generator is one of the most important elements of the car, it is responsible for the correct operation of all components that need electricity. Of course, if the car has problems with the power supply, the first "culprit" is the generator. That is why it is important to be able to check it yourself. Let's figure out how to check the operation of the generator using a tester (multimeter).

Checking generator elements

The generator has 4 main components, the performance of which gives a complete picture of the functioning of the generator. If one of the elements is faulty, then the generator will not be able to work correctly. Thus, to check the generator, you need to check each of the elements.

Relay

1. We turn on the multimeter in the DC voltage measurement mode.
2. We start the car.
3. We measure the voltage at the battery terminals - the value should fluctuate in the range of 14 - 14.2 V (otherwise, the relay is faulty).
4. We press the accelerator, monitor the voltage - it should increase by 0.5 V (otherwise, the relay is faulty).

Diode bridge

1. Turn on the sound mode on the multimeter.
2. We "call" each diode (there are 6 of them in the bridge) in both directions.
3. If all the diodes "ring" in only one direction, they are working, otherwise they are not.

generator stator

1. Disconnect the diode bridge from the stator.
2. We inspect the winding - there should be no soot and damage.
3. Switch the multimeter to resistance measurement mode.
4. We measure the resistance value between the stator housing and the winding.
5. If the value is much more than 50 kOhm, the stator is healthy, if the value is close to 50 kOhm, it will soon fail, less than 50 kOhm, it is faulty.

generator rotor

1. We take out the rotor and inspect for visible damage.
2. We check the integrity of the winding.
3. We measure the resistance between the contact rings.
4. If the resistance value is equal to several ohms, the rotor is corrected, if the device shows zero or infinity, no.

That's all the checks that need to be done with the generator. If all checks showed that the generator is working, then you need to look for the problem further.

There are hardware and visual ways to check the machine's generator. However, the owner must know the device and purpose of this electrical appliance in order to diagnose correctly. This guide will help you avoid a trip to the service station and save your operating budget.

The design and purpose of the generator

Before you check the generator with a multimeter on your own, you need at least minimal knowledge about the design of the electrical appliance:

• the belt transmits rotation from the engine crankshaft to the alternator pulley
• mechanical energy is converted into electrical energy
• diode bridge changes alternating current to direct current
• the regulator relay is responsible for recharging the battery when it is discharged during the start of the internal combustion engine
• the rest of the voltage is spent on electrical appliances of the machine

For the battery, both undercharging and overcharging are harmful, so the voltage at the terminals must have stable characteristics at any speed. At the same time, the connecting unit, dimensions, scheme and quality of manufacture of generators can differ significantly from different manufacturers and for specific modifications of the car.

Diagrams and terminals

Before you check the generator on the machine on your own, you need to know wiring diagram this node and the purpose of the terminals on its body. 6 schemes are most in demand, for example, one of them is shown in the lower photo.

For ease of reference, the digital designations on all diagrams are the same:

• generator block
• exciting winding
• stator winding
• rectifier
• switch
• pilot lamp relay
• voltage regulator
• control lamp
• interference suppression capacitor
• block transformer/rectifier
• zener diode
• resistor

The conclusions on the case are not designated the same, which can interfere with the correct diagnosis with a multimeter (tester):

• positive terminal of the power rectifier - BAT; B+; thirty; B or "+"
• exciting winding - FLD; E; EXC; F; D.F.; 67 or W
• output for a control lamp from a backup rectifier - IND; WL; L; 61; D+ or D
• phase - STA; R; ͠ or W
• zero - MP or "0"
• output for "+" battery - B; 15 or S
• terminal for connection with on-board computer– F or FR
• output to the ignition switch - IG

In the Russian Federation, generators are most often operated, the exciting winding of the voltage regulator of which is connected to the on-board network with a "minus". Although there are options attached to it "+".

In cars with diesel internal combustion engines, two-level power plants 14/28 V. Checking these generators is more difficult, it is better to carry it out in a service station.

Self test generator

The simplest option, how to check the generator at home without a trip to the service, is a visual inspection and search for extraneous sounds. However, not all existing defects can be detected by these methods. For example, the glow of a lamp on dashboard Indicates that the battery is not being charged. In this case, the battery itself may be faulty or the generator supplies insufficient voltage to its terminals.

Therefore, it is better to arm yourself with a tester or its more modern version of small dimensions - a multimeter for high-precision diagnostics. Most breakdowns can be identified locally, to search for and repair the rest, you need to check the removed generator by disassembling it partially.

Safety

In order for the diagnostics to be safe for the user and the electrical part of the car, the following conditions must be met:

• using a tester, multimeter or devices to measure current, voltage and resistance separately
• disconnecting the battery from the on-board network and from the generator additionally
• when replacing the wiring, maintain the length and cross section of the cable, as in the original parts
• make sure the belt is properly tensioned

It is forbidden to perform actions:

• use sources with a voltage greater than 12 V
• turn off consumers when the engine is running and the generator is connected by a belt drive
• close with "mass" or terminal D + (67) output B + (aka 30)
• check the spark on the case with a short circuit

visual inspection

First of all, the owner is interested in how to check the generator on the car without removing this electrical appliance. Therefore, faults can be diagnosed in the following ways:

• recharging light - if it lights up on the panel, either the recharging voltage is insufficient, or the battery has exhausted its resource
• third-party sounds - noise, whistling and rustling indicate a weak belt tension, worn bushing or bearing
• the smell of burning - it can penetrate through the stove into the passenger compartment, the reason for the high-temperature heating of the windings is likely
• interruptions in the work of electricians - indicate insufficient current, which produces a running generator

The belt can be tensioned without removing the entire assembly, other faults are eliminated only after the generator is dismantled.

Bearings (bushings)

The generator shaft rotates in two rolling bearings. The first is fixed on the shaft itself, removed along with the anchor. The second one is pressed into the stator in its central part. In this case, the diagnosis is made by ear and visually:

• whistling and hum at normal belt tension are signs of a worn out bearing or its crumbling cage
• when turning the shaft by hand after removing the belt, it should turn freely, white transverse play

Otherwise, distortions, jamming, burnout of the windings, precipitation of the armature magnets are possible. In any case, a low voltage will reach the battery, insufficient for recharging.

windings

This node is the only one in the generator, the diagnostics of which is visually more effective than using the tester for a number of reasons:

• with intense heating, the lacquer coating of the copper conductor darkens
• there is a burning smell
• the resistance of the windings is too small to accurately diagnose them for a short circuit

It should be noted that before checking the generator for operability, in this case it will be necessary to disassemble it by removing it from seat. If the electrical appliance is in good condition, the lacquer coating will be light by default.

Collector group and brushes

Before checking the generator for wear of these friction parts, you need to disassemble it:

• brushes are adjacent to cylindrical brass contacts - collectors
• brushes wear out most often, it is better to change them as a set
• the wear of the collector group is determined visually by the grooves that have appeared
• collectors can be ground 3 - 4 times, then they will have to be replaced entirely

At this stage, the car owner does not have problems.

Attention: The "old-fashioned" method of checking the generator's performance is to remove the "minus" terminal after starting the internal combustion engine and not stalling the engine, for modern cars unacceptable. Moreover, on injector cars it is better not to let them “light up” with wires from a battery connected to onboard system. It is possible that the "check" error will light up.

Hardware diagnostics with a multimeter

The best option is how to check the car's alternator with my own hands, is the use of instruments: ohmmeter + voltmeter + ammeter or tester (multimeter). The last option, how to check the health of the generator, is preferable, since you can also ring the diode bridge with a universal device.

Diode bridge

Structurally, the bridge consists of 6 diodes - 3 of them are considered negative, the remaining positive. In fact, they are deployed in the diagram in opposite sides, passing current in only one direction.

There are two options for checking a car generator for the integrity of a diode rectifier bridge:

• without removing the unit - diagnostics are performed after disconnecting the "mass" of the battery, the wires from the voltage regulator and the diode bridge, the tester is switched to ohmmeter mode, its plus (red wire) is connected to the 30th terminal of the generator, the minus (black wire) is closed to the body of the electrical appliance, all the diodes are intact, if infinity appears on the multimeter scale, punched - if some value in ohms is displayed
• after dismantling and partial disassembly - positive diodes are checked in a similar way, negative - on the contrary, in both cases, a specific resistance value on the tester indicator becomes a sign of breakdown

Attention: If you make a mistake with the polarity when connecting the battery, it is the diode bridge that goes out of standing.

Rotor and stator

If the check of the mechanical part did not reveal any problems, the operation of the generator is checked further after its disassembly:

• stator - you need to check the generator winding for each turn, the resistance is about 0.2 Ohm, so you need an accurate device, you can use the non-hardware methods discussed above
• rotor - if a modification is used on permanent magnets, you just need to re-install them inside the cage, conventional rotors have only 2 windings, the resistance of each of which is 2 - 5 ohms, if the tester shows infinity, then there was a breakdown of the insulation or a wire break

For a more detailed diagnosis of whether the generator is working, the starter must be checked additionally, but already in the kit. To do this, the resistance is measured between the output of any winding and their common "zero", it should be 0.3 ohms.

Battery charging voltage regulator relay

In order to avoid errors, before checking the charging of the machine's generator, the following nuances should be taken into account:

• normal for a car battery is a voltage of 12.5 - 12.7 V at its terminals, that is, in the entire on-board network with the engine turned off
• at idle with the internal combustion engine on, it reaches a value of 13.5 - 14.5 V, for some foreign cars normal voltage considered 14.8 V
• on increased speed generator voltage drops to 13.7 V
• if the device shows 13 V at operation of the internal combustion engine under load, the generator clearly needs repair
• recharging 15 V is dangerous because the electrolyte boils, acid battery plates begin to crumble
• undercharging of 13 V will not allow accumulating in the battery the electricity spent when scrolling the flywheel at the time of start-up, the next train will be in doubt

Diagnostic operations must be performed sequentially:

1. the engine is started with the starter key
2. the headlights turn on for 15 minutes, the average speed is set for the whole time
3. the voltage is measured between the terminal B + (30) of the generator and its "ground", it should be in the range of 13.5 - 14.5 V

After installing high-quality car audio, for which voltage drops in the on-board network are critical, many owners solve the problem radically:

If you have any questions - leave them in the comments below the article. We or our visitors will be happy to answer them.

Content:

Generators are used in many areas as autonomous sources of electrical energy. These devices are especially widespread in cars. Without a generator, blocks, devices and components that are completely dependent on the availability of electricity will not be able to work normally. It also charges the battery. Therefore, if any problems arise in the electrical system, one of the main questions becomes how to check the generator with a multimeter.

Most the best option there will be an appeal to the service station, for carrying out complete diagnosis. However, this is not always possible, and the car may not be running. The only way out of this situation would be self check all vehicle systems, including the generator.

How to check the diode bridge of the generator with a multimeter

The diode bridge in the generator is a kind of rectifier, with the help of which the alternating current generated by the generator is converted into direct current. It includes semiconductor diodes in the amount of 6 pieces, 3 of them - with a positive value, and 3 - with a negative value. Each of these groups passes current in only one, strictly defined direction.

Alternating current is used when it needs to be transmitted over a long distance. Electrical appliances installed in the car require direct current, including to charge the battery. Since the generator is capable of producing only alternating current, a diode bridge is needed to convert to direct current.

The design includes two metal plates that conduct electricity. Diodes are installed on their plane in order of priority. The alternating voltage produced by the generator changes the direction in which the electrons move. In order to obtain a constant voltage, it is necessary to redirect their movement in the so-called wrong direction, as a result of the further operation of the phases, a direct current will be created. In this circuit, it serves as a kind of capacitor, which successfully dampens voltage fluctuations. If necessary, check the generator with a multimeter.

Quite often, the diode bridge fails. A similar situation occurs when the polarity of the battery is not observed, or the electrical circuit is closed in the generator itself. Any malfunction of the diode bridge negatively affects the entire on-board network. If one of the diodes breaks or the diode is broken, in this case, dips appear in the stable pulsating voltage at the generator output, since the faulty diode stops the voltage supply to the on-board network.

A certain compensation for failures is taken over by the battery at the expense of its own resources, however, the value of the total mains voltage is still reduced. In addition to instability, dips lead to electromagnetic interference that adversely affects audio equipment. With a large number of such violations, a mandatory check of the diode bridge is most likely required. To this end, you will have to check the generator for operability with a multimeter, after removing it from the engine. The diode bridge is disconnected and called by the tester.

During disassembly, it is advisable to use the instruction manual, because on different machines this operation may vary. On some models, the bridge is fastened with bolts, while on others it is simply soldered. Labels are applied to the diode bridge and generator to avoid confusion during subsequent assembly.

• The multimeter must be switched to the resistance measurement mode and set the sound indication.
• Next, the probes of the measuring device are connected to each output of the diode. The negative terminal - “minus” is connected to a central steel or aluminum plate, and the positive terminal is connected to a metal core made in the form of a tinned bare wire, the diameter of which must be at least 1 mm.
• To check each diode, you must first touch the core or central plate with one probe, and the opposite terminal of the diode with the other probe. After that, the probes must be swapped.
• If the diode is good, the multimeter will only beep when the probes are in a certain position. If the tester beeps with all connection options, this indicates that the diode is broken. If there are no sound signals at all, then the diode is open. Sound signals should be emitted by the device when only one side of the bridge is checked.

There is another method for checking the generator with a multimeter. In this case, resistance is used - the main physical quantity. To carry out measurements in this way, the switch must be set to 1 kOhm. Touching the probes is carried out as in the previous version. When checking one direction, the device should give a result of 500-800 ohms, and when checking the other - infinity. In this case, all bridge diodes are in working order.

How to test the generator voltage regulator with a multimeter

In order to ensure the normal operation of light bulbs, power windows, windshield wipers and other electrical equipment, as well as battery charging, you need to maintain a value direct current at the level of 13.5-14.5 volts. If this indicator is less, then the battery will not charge, and if it exceeds this level, the on-board electrical appliances will fail. High voltage also causes some damage to the battery, shortening its life due to overcharging.

Therefore, to convert the current generated by the generator, there is a special device -. With its help, the on-board network is provided with a current that maintains the required parameters, regardless of the crankshaft speed. Often there are situations when it becomes necessary to check the voltage of the generator with a multimeter.

Modern relays are electronic, and their design is non-separable. In the event of their failure, they are not subject to adjustment or repair, but require complete replacement. This is considered the only drawback of these devices, since otherwise the relays have a lot of advantages: compactness, durability, high accuracy of current parameters.

1. Headlights change the brightness of the glow, depending on the engine speed.
2. There is an insufficient charge of the battery or, conversely, its overcharging, accompanied by the boiling of the electrolyte.
3. There may be a burning smell in the vehicle interior. Damage to the regulator can occur due to moisture ingress, various mechanical damage, short circuits and other non-standard short-term electrical influences.
4. Sometimes the regulator is initially of poor quality if it is a dubious product from unknown manufacturers.

There are different methods on how to check the generator relay-regulator with a multimeter and establish its performance. The easiest is to check with a multimeter, without dismantling the device. For this purpose, the voltage supplied to the battery to charge it is measured. For such a check, an assistant will be required to regulate the engine speed with the accelerator pedal.

The verification procedure takes place in several stages:

• The car engine starts and warms up within 5 minutes.
• Open the hood while the engine is running and connect the multimeter leads to the battery terminals. The connection must be made in accordance with the polarity, and the switch is set to 20 V.
• The evaluation of the charging voltage from the alternator is carried out under certain conditions. You need to check how much the generator produces with a multimeter. The dipped beam must be on, and all other consumers must be off. Crankshaft rotates at a speed of 1.5 to 2.5 thousand rpm. If the voltage is more than 14.8 volts, then the regulator is considered defective and must be replaced. At voltages below 13.5 V, the relay may not be the cause of the malfunction. The fault may lie in the wiring or the generator itself.
• More accurate results are obtained by estimating the intensity of the current flowing at the load. This will require the inclusion high beam, stove fan, windshield wiper and other consumers. In such a situation, the value of the charging current should not be lower than 13.5 volts. If the indicator is still less than this value, then when all electrical equipment is turned on, the battery will not receive a normal charge.

A more complete check is performed on the removed relay-regulator. Usually electronic device stands on top of the generator, closed with a plastic cover. In some cases, the regulator may form a single unit with the brushes. To check, in addition to a multimeter, you need to prepare a 12 V test lamp, with a power of not more than 3 watts, and an adjustable current source. These methods are also suitable for checking the generator integral with a multimeter, that is, an integrated voltage regulator.

The wires from the current source are connected as follows: the "minus" is connected to the regulator's ground, and the "plus" is connected to the terminal marked with the symbol "B". The control lamp is connected through conductors to graphite brushes without observing the polarity. First, a voltage of 13 to 13.5V must be applied to the relay-regulator, at which the light will be on. If this does not happen, then the control device is faulty.

Further, the light bulb remains in a burning state, and the input voltage gradually increases. With a working relay, the light will go out when the voltage reaches 14.2-14.5 V. If, in the event of a further increase in voltage, the control light continues to light, then there is a breakdown in the relay and it is faulty. A malfunction is also indicated by the fact that, at a voltage below 4 V, the light goes out. Such a current will be clearly insufficient to provide power to all electrical appliances and to charge the battery with high quality.

How to check the generator rotor with a multimeter

Faulty rotor car generator First of all, it causes the disappearance of the charging current and the discharge of the battery. This is indicated by the low battery light located on the instrument panel. The position of the voltmeter needle is near the red zone or in the zone itself. In this regard, it becomes necessary to check the generator armature with a multimeter.

When checking the voltage with a multimeter with the engine running, its readings at the battery terminals will be less than the required 13.6 volts. In order to obtain more accurate results, it is recommended to check the battery charging from the generator with a multimeter in advance.

The main malfunctions of the rotor are considered to be a short circuit of the windings and a break in the leads between the excitation winding and slip rings. To check, it is not necessary to remove the generator from the engine and remove the rotor from it. It is enough to remove the voltage regulator relay and perform all the necessary actions through the resulting window.

In order to check for a short to ground in the excitation windings of the rotor, you need to set the multimeter to the mode and press the positive probe one by one against the slip rings. The negative probe is pressed against the mass - the generator housing. If the resistance indicator tends to infinity, then the rotor is working and there is no short to ground. After that, you should check the generator winding with a multimeter for an open circuit. The multimeter is also set to ohmmeter mode, the positive probe is applied to one slip ring, and the negative probe to the other. A resistance value of 5 to 10 ohms indicates the health of the excitation winding. In most cases, a defective rotor must be replaced.

However, not all elements can be verified by testing. For example, it is not possible to check the generator brushes with a multimeter. This procedure involves visual diagnosis after the removal of the brush apparatus. If necessary, the voltage regulator can also be removed. As a rule, the brushes show uniform wear. In normal condition, the length of the brushes is 8-10 mm. If this figure is less than 4.5 mm, then the brushes must be replaced. At the same time, the coal dust formed as a result of the friction of the brushes on the rotor rings is cleaned.

When performing generator diagnostics, rotor failure is the last resort. First of all, other elements that are more likely to cause malfunctions of the device are checked. Low voltage, a burning light on the instrument panel and other symptoms can happen if the diode bridge or relay regulator fails. First they are checked, and only then the rotor itself.

Vehicle battery and alternator check

The malfunction of the car generator belongs to the critical class, in which further operation of vehicles is not allowed. A multimeter can be used to perform a health check on the generator.

Signs of abnormal operation of the car generator may be:

• no "battery" indication on the dashboard when the ignition is turned on;
• the glow of the "battery" light after starting the engine;
• periodic blinking of the signal indicator "battery" in the process of movement;
• the smell of burnt electrical wiring in the generator area;
• failure to start the engine after parking.

The lack of battery charge with a faulty generator leads to problems with starting the engine. More dangerous is a malfunction associated with an excess of current and charge voltage. car battery. Many motorists use to start the engine from a donor battery, after which they disconnect the battery terminals to switch to charging their own battery. At this point, the electrical equipment of the car is powered by a generator.

If the generator is faulty, the voltage in the on-board network may be more than 17 volts, which leads to a breakdown of the protective zener diodes in the engine control unit. In this case, an expensive repair of the engine control unit is required.

Causes and possible consequences of a malfunction

Generator failure is possible for the following reasons:

• malfunction of the voltage regulator (“pills”, “chocolates” in the slang of motorists);
• wear (destruction) of brushes;
• short circuit of the exciting winding (rotor);
• breakdown of diodes (located in a horseshoe);
• wear of bearings and bushings.

A faulty voltage regulator usually results in no battery charge. In this case, the indicator icon "battery" is lit on the dashboard. The engine continues to run until the battery is discharged to approximately 8 - 9 volts.

During daylight hours, a battery charge can last for 30-50 kilometers, provided that the battery was well charged at the time of the malfunction.

In the event of a breakdown of the output stages of the voltage regulator, a malfunction may occur associated with an increase in the output voltage of the generator to 17 - 20 Volts. This is where recharging takes place. battery. The consequence of overcharging is the process of boiling the electrolyte. If there are signs of corrosion under the hood in the area of ​​​​the battery, it is necessary to check the generator.

Breakdown of the diode bridge can occur when the battery is accidentally reversed (terminals are installed in the wrong polarity). Usually diodes break through in pairs in one shoulder. A faulty diode has a resistance close to zero. The stator winding of the generator in this case operates in short circuit mode, becomes very hot.

After a few minutes of engine operation, the windings overheat, a smell of burnt electrical wiring appears under the hood of the car. To avoid ignition, the engine must be turned off, the generator must be checked.

The wear of the brushes leads to the gradual failure of the generator. First, while driving, the charge indicator light on the dashboard starts blinking, then it starts to glow constantly. In many generator models, the brushes are changed together with the voltage regulator.

Closing the generator windings can lead to a significant change in the output parameters, overheating of the device.

Sequence of initial check

An initial performance check can be made without dismantling the generator. To do this, set the multimeter switch to the "constant voltage 20V" mode. Next, connect the black probe to the negative terminal of the battery, the red one to the positive one. After that, it is necessary to start the engine, let it enter the stable mode. idling. Multimeter readings ranging from 13.5 to 14.5 volts are considered normal.

If the multimeter shows a value less than 12.8 volts, the charge process either does not go at all, or the charge current is extremely small. The generator is operating abnormally. At a voltage of more than 14.8 volts, the battery is being recharged. This can lead to boiling of the electrolyte, an increase in the concentration of acid, and destruction of the battery plates.

To control the voltage at the output of the generator, it is necessary to turn on the car lamp in an open circuit from terminal 30 on the generator (the place of contact with a thick wire leading to the positive terminal of the battery or starter).

Next, connect the multimeter in the "= 20V" mode with a red probe to terminal 30 of the generator, black - to a stripped contact on the engine or body. Start the engine. The readings on the multimeter should not be more than 15.5 volts with any press on the accelerator pedal. Otherwise, further operation of the generator is dangerous for the vehicle's electrical equipment.

When checking, the degree of tension of the alternator belt should be assessed. Using a simplified method, this can be done by pressing on the belt with your finger.

The deflection value should be in the range of 0.5 - 1 centimeter. At the same time, the degree of belt wear should be checked.
To determine the causes of abnormal operation of the generator, perform repair work Generator needs to be removed.

Checking generator nodes

The test begins with monitoring the performance of the voltage regulator. To do this, the regulator is dismantled from the generator and a simple electrical circuit is created.

As an incandescent lamp, any car interior light bulb is used. With a working voltage regulator 3, lamp 6 should not glow on full power. When connected in parallel with the lamp (brushes) of the multimeter, its readings should be from 5.0 to 10.0 Volts. If the multimeter readings go outside these limits, the regulator must be changed. The design of some generator models provides for the possibility of replacing the regulator without dismantling the device.

Further, the exciting winding of the generator is checked for breakdown. To do this, the multimeter is set to the resistance measurement mode to the limit of 200 kilo-ohms. The probes are connected: black - to the collector lamella, red - to the metal part of the armature. The resistance must be more than 100 kilo ohms or higher than the upper limit of measurement, as shown in the photo.

The resistance between the lamellas (rotor windings) is usually 0.5 - 2 ohms.

The stator check begins with the control of the windings for breakdown. To do this, the red probe of the multimeter is connected to the metal part of the stator, the black one is connected in series to the windings.

The resistance must be above the upper limit of measurement. Then measure the resistance between the contacts of the windings. They should differ by no more than 5%. The measurement limit of the multimeter is set to 200 ohms.

If the winding has an electrical breakdown, a short circuit of the turns or an open circuit, it must be replaced. There are workshops that rewind stators and rotors.

To monitor the health of the diode bridge, the multimeter measurement mode is transferred to the “diode” check. Then the diodes “ring out” in series (their number on the horseshoe is usually 9) in direct and reverse connection. In the forward direction (black probe to the cathode), the resistance is 550 - 700 ohms, with the reverse connection - more than the maximum measurement limit.

When the diodes break down, the resistance in all directions will be almost zero. Such a diode should be changed. The difficulty of replacing the diode lies in the fact that the diodes in the generators are not soldered, but are welded by spot welding to ensure reliable contact at different temperature conditions.

The car's alternator is a significant part of the car's electrical equipment. At the first manifestation of signs of inoperability, it is necessary to check it with a multimeter.

Gone are the days when car dashboards resembled the workplaces of aviation pilots - with a scattering of sensors, instruments and mechanical buttons. Now, among automakers, it is customary not to bother drivers with “unnecessary” information. In particular, you almost never see an ammeter on the dashboard - in modern machines only the warning light remained. If she shows something, then when the trouble has already happened. But if the generator breaks down, the car practically cannot continue to move (maximum, it will drive a couple of kilometers on the battery), there is a chance of “stuck” in the middle of the road. Is it possible to somehow check the generator and insure yourself against unpleasant situation? Can.

In the photo: the generator under the hood of the car

What can go wrong in a generator?

To better understand what can break in the generator, you need to understand its device. It is not as complicated as it might seem. To put it simply, the generator consists of:

Corps,

moving part (rotor),

fixed part (stator),

As well as additional elements, which include a relay-regulator, a diode bridge, and a brush assembly.

The main enemies of the generator are time, water, chemicals and mechanical damage. All problems come from them.

1. The most common cause of generator failure is brush wear. They are graphite and walk along the paths of the rotor, so from time to time and high mileage simply erased. The brushes are usually sold separately, are inexpensive and easy to replace.

2. Much less pleasant malfunction - breakdown of the relay-regulator. If the generator keeps too high or too low voltage, then the problem with a high degree of probability is in it. The relay-regulator is more difficult to diagnose and replace than brushes, but this can also be dealt with at home.

New relay-regulator on the left, on the right - the old one

3. Seized bearings do not bode well. The rotor stops rotating, and without this, the generator will not generate current. The bearings themselves are inexpensive, but their replacement requires experience and special tools, so it is better to carry out such work in a service environment.

Failed alternator bearing

4. When broken diode bridge the generator becomes useless, because the unit itself produces alternating current, and consumers in the car need direct current. This conversion is just what the diode bridge does. This is a very sensitive element that is afraid of water ingress, short circuits and reversed polarity. It can be repaired by changing the diodes, but in modern conditions the diode bridge is usually changed, it's easier.

4. The most unpleasant breakdown option - winding combustion on the stator or rotor. Purely theoretically, it can be restored, but usually in this case it is necessary to consider the feasibility of repair, it will often be cheaper to buy a new winding than to repair it.

How to diagnose a generator without removing

You can understand how well the generator works without dismantling it from the car. The methods are very simple and accessible to any motorist.

1. Need to measure voltage in the on-board network regular tester. Three measurements are required. First, on an unstarted car (the device should show about 12.2-12.7 V, but this is an indicator of battery health).

Then start the engine and turn off all consumers (the normal value in this situation should be in the range from 13.8 to 14.7 V). Finally, you need to turn on several powerful consumers (stove, headlights) and measure again. The voltage will drop, this is normal, as it should be, the main thing is that the drawdown is not lower than 13V. If the numbers turned out to be different, it is dangerous to drive with such a generator.

2. Take a closer look at the work of lighting fixtures- if the headlights or interior lighting have become dimmer than before, this is the first sign of low voltage in the network. It is better not to drive such a car on a long journey.

3. A very disturbing symptom is flashing headlights in time with the change in speed. The relay-regulator is responsible for the “evenness” of work in the generator, if it does not stabilize the voltage, regardless of the crankshaft speed, then the car will almost certainly “stand up” soon. We urgently need to deal with this issue.

4. No matter how trite it may sound, it is worth taking a closer look and listening to the generator. Bearings and rollers rarely jam suddenly, almost always a future breakdown is preceded by whistle, howl or extra noise. If you hear from under the hood extraneous noise you need to find its source. The belt can be monitored visually, it also wears out not in one trip, but gradually.

5. If you have an old carbureted car, then another very simple diagnostic method is available to you. Enough disconnect the negative terminal from the battery with the car running, and look at the operation of the machine - if nothing has changed, then the generator is coping with the work, and if the car began to work unevenly, intermittently, you need to find out the reason. Alas, this method is contraindicated for injection cars - it is difficult to predict how fragile will behave the electronic unit control in the event of a sudden voltage drop. In which case, the ECU will have to be changed and the diagnostics will turn out to be very expensive.

What else to pay attention to

Finally, indirect diagnostics of the generator can be carried out on the battery. They work in close conjunction, and the "health" of one can be judged on the performance of the other. If the battery is constantly needed, then the problem may be precisely in the weak charge from the generator (although the problems of the “battery” itself are also not excluded). Sideways will come out for the battery and too high voltage in the on-board network - if the battery suddenly boils away, then you need to diagnose the generator, "just like that" such things do not happen.

It is not superfluous to simply arrange an inspection of the generator. All wires must be securely screwed on - without interruptions and kinks, the body must not be damaged, and the unit itself must not spark during operation.

Diagnostics with disassembly

If preventive measures did not help, and the generator still broke down, then it is necessary to dismantle the unit, disassemble it and diagnose it. If the problem node is not striking, then you need to check all the components of the generator in turn.

1. Rotor. He needs to check the winding for resistance with a multimeter, “connecting” with probes to slip rings. The value of the resistance of a good winding lies in the region of 2.4-5.1 ohms. If there are zeros on the multimeter display, then there is an open in the winding, if there is resistance, but very small, then somewhere in the winding there is an interturn short circuit, if the indicator is higher, you need to look at the contacts and solder the most unreliable of them.

Checking the generator rotor

2. stator. He also needs to “ring out” the winding. The "correct" value of the resistance between the terminals of the windings is 0.2 Ohm, otherwise either an open or a short circuit. It is very convenient to check the stator insulation for breakdown with a regular 220 volt light bulb. If you connect it with one contact to the winding output, and with the second contact to the stator housing, then it should not burn. If it burns, it means a breakdown.

3. Do diode bridge you need to check all diodes for current conductivity. To do this, you need to switch the tester to the ohmmeter mode, bring one probe to the plate, and the second in turn to the diodes that are pressed into this plate. Then the screws need to be swapped. And so check all the diodes in all the plates. The diode bridge is healthy when there is resistance with one of the diode connections, but not with the other. Due to the fact that the diodes have a different charge, it is not worth remembering which connection should give resistance and which should not, the main thing is that in one of the two measurements each diode has resistance. If not, then the diode bridge needs to be changed.

4. Worn to the limit brushes the easiest way to diagnose - here you don’t even need a multimeter. It is enough to measure their length with a ruler, if it is less than 4.5 cm, then the brushes need to be changed. It will not be superfluous to measure the diameter of the slip rings at the same time. It should be at least 13 mm, and even better about 14 mm.

As you can see, checking the generator is not such a difficult task. Simple operations can be carried out directly on the machine, but even if the generator has to be removed and disassembled, there is nothing complicated there. A multimeter, a set of screwdrivers and wrenches will help you make all measurements. Fortunately, spare parts for many generators are freely sold, so you can only replace a worn-out element and independently, without large investments, bring the generator back to life.