How to check a car generator with a light bulb

The car's generator serves to power the on-board network, electrical equipment and charge the battery during operation of the power unit. This is a mechanism that produces alternating current by converting the mechanical energy of rotation of the rotor (the “plus” winding) in the stator (the stationary part of the “minus” winding) into electrical energy. Torque is supplied from the crankshaft to the drive pulley.

All generator malfunctions are of two types: mechanical failure of components or electrical failures. In any case, the cause of the violation can be determined by checking the voltage in different areas and elements.

Table of typical generator faults

Symptoms of a problem	Diagnostics	Remedy
The battery charge indicator on the dashboard does not light up when the ignition is on	Battery is discharged	Charging the battery
	The fuse in the unit or the indicator light has blown	Replacing fuse, light bulb
	Broken ground contact on the generator housing	Secure the bolted connection of the contact, cleaning it from oxides
	Broken wiring from the generator to the dashboard terminals, or broken contacts	Repair the break, clean the contacts
	Wear of generator commutator brushes	Replacing brushes or generator
	The gap on the brushes and slip rings of the rotor is broken	Adjust the gap
	Failure of rotor rings	Replacing the rotor or generator
	Voltage regulator relay failure	Regulator replacement
The battery charge indicator goes out when the speed increases	Loosening the alternator belt drive	Adjust tension
	Belt drive break	Replace belt
	Failure of the diode bridge	Replacing the diode block
	The power cable between the battery and the generator is broken	Replacing power cables
	The relay regulator has failed	Relay replacement
The indicator is constantly on	Short circuit in the circuit	Eliminate wiring problems
	Short circuit in the diode block	Check the contacts in the block, replace the wiring
	Failure in the ECU system	Check the controller unit, clear the ECU error
	Battery discharged	Charge the battery
The indicator remains on when the ignition is turned off	Short circuit	Eliminate broken wiring
	Short circuit in the diode block	Clean diode contacts or replace
Overheating and boiling of battery electrolyte	Failure of the relay regulator	Relay replacement

How to quickly check if the alternator is charging the battery

If the car is not charging while driving, you can notice it from inside the car. Such circumstances will be indicated by a warning light. In addition, the glow intensity of all devices will noticeably decrease. A clear sign of a problem is the complete discharge of the battery for no apparent reason.

Multimeter

Every motorist should have this device. It can be purchased without any problems in specialized stores.

To do this, you simply need to move the switch to a certain position.

First, check the voltage at the battery terminals with the engine off. For a fully charged battery it should correspond to 12.6-12.9 Volts.

After this, you need to start the engine and let it run at 2000-2500 rpm. The voltage at the terminals should be 13.8-14.6 Volts.

The voltage on the voltmeter with the engine running should be no less than 13.8 and no more than 14.6 Volts.

Under these conditions, the battery is fully recharged. Then you need to connect the load. This could be a stove, heated rear window, headlights, or radio. The charging voltage at the battery terminals should drop slightly to 13.7-14.0 Volts. If the value drops to 13.0 Volts, then this clearly and clearly indicates charging problems. This situation may be caused by a loose belt or failure of generator elements.

Without a voltmeter by removing the terminal

The charging system can be checked without a voltmeter. The main thing here is to take precautions and strictly follow the verification algorithm. This “antediluvian” method has long proven itself one hundred percent.

The check is carried out according to the following scheme:

After this, you need to observe the operation of the power unit. In cases where the car continues to work confidently, the headlights do not dim, we can talk about the complete serviceability of the generator. If the car immediately stalls after removing the terminal, then this directly indicates a malfunction of the generator itself.

Despite the effectiveness of this method, you need to act carefully, with special attention and caution. The main thing is not to short-circuit the battery.

Symptoms of malfunction

may indicate a generator malfunction :

the warning light on the dashboard is constantly on;
The battery began to discharge quickly, and recharging does not save the situation;
there are malfunctions in the functioning of electrical equipment (ventilation and heating, multimedia devices, alarm system and lighting), even if the motor is working properly;
there was a smell of something burnt in the car interior;
the generator began to whistle or rustle.

If you notice these symptoms, you should immediately go to a car service center for a thorough diagnosis. However, you can check the functionality of the generator on your own, especially if you have the skills to use an autotester.

Testing for functionality without a car using a battery and a light bulb

During the operation of a car, there are situations when it is necessary to purchase individual components and assemblies. For example, when purchasing a used generator, sometimes it becomes necessary to check the operating condition of the device without the car.

The functionality of the unit removed from the vehicle can be easily checked. To do this you will need a 12 Volt battery, a 3 Volt light bulb with two wires attached that easily lights up when exposed to voltage, two separate wires.

The check itself is carried out in the following order:

Such a test allows you to determine the functionality of the generator. In addition, it is important to carefully inspect the unit visually. To do this, you need to remove the plastic cover by pressing the latches and prying it off with a screwdriver.

Here attention should be paid to the integrity of the diode bridges, the absence of melted points, the integrity of the armature, and the absence of severe pronounced wear. In addition, you need to check the serviceability of the bearings when the shaft rotates. They shouldn't make noise.

And one more similar method. You will also need a battery for testing. But as an indicator, you can use a regular 12-volt light bulb from a turn signal.

The procedure is carried out in the following order:

If the generator is working properly, the control light should light up.

Every responsible motorist must monitor the operation of his car’s charging system. This should simply be included in the list of useful driver habits. The methods described above demonstrate high efficiency, accuracy and reliability against the backdrop of accessibility and simplicity. Therefore, it is better to take them into service.

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How to check a car alternator

It is recommended to check the car's generator to determine the cause of its failure in most such unpleasant cases.

Of course, if you don’t want to suffer or are not confident in your technical literacy, then you shouldn’t check your car’s generator. In such cases, it is better to contact a specialist.

But if you look and understand, then you need to have a little knowledge and the necessary equipment to check the car generator for malfunction.

When is the inspection carried out?

Typically, this check is carried out before repairing the generator in order to find out what is the cause of the breakdown, and already know in advance how much it will cost.

The advantage here is obvious, since you will not deceive yourself, and after checking the car’s generator, you will receive reliable information.

In order to check the car's generator, get a special ohmmeter that supports diode testing and the ability to measure high resistances.

Checking a car generator can be divided into four main stages.

Checking the generator stator winding, checking the generator diode bridge, checking the voltage regulator, checking the generator capacitors.

Good to know - Replacing the VAZ 2110 generator bearing, do it yourself, video, photo.

Synchronous alternators

Synchronous generators operate in a similar way, but the shaft speed is maintained at a constant speed. Hence the parameters are more stable. Here are a number of differences that need to be taken into account in order to properly test the generator with a multimeter.

AC winding

The stator (called the armature) often has an alternating current winding that synchronizes the rotation. Its role is difficult to overestimate, and the turns are located, for example, between the windings of the main coil. The role of the poles in this case is synchronizing. A voltage of the required frequency is supplied here, which, through interaction with the inductor (rotor), sets the speed of rotation. Typically the winding dimensions are smaller than the main winding and the resistance is higher.

Subexciter

Large synchronous generators contain auxiliary equipment - a subexciter. This is a synchronous machine whose shaft is equipped with permanent magnets. The voltage generated by the generator is rectified and is subsequently used as current for the exciter. This saves energy. Permanent magnets also reduce the number of current collectors, which has a positive effect on the reliability of the entire system. The subexciter becomes, in fact, a simple synchronous motor; the stator winding is tested by the tester in the usual manner.

Diode bridge

In connection with the above, sometimes it is necessary to check the diode bridge of the generator with a multimeter. By the way, this is relevant for car enthusiasts, where a Larionov circuit is often used to rectify the current. The diode bridge is called depending on the design. In everyday life, the ones shown in the figure are the most common. The first is considered a typical solution for single-phase alternating current, and the second is the Larionov circuit.

According to the given figure we show how to ring. A single-phase diode bridge is safely assessed for the integrity of each diode individually. To do this, the appropriate mode is set on the multimeter, then, regardless of the position of the cathode and anode, the probes are presented on one side, then on the other. As a result, direct connection produces a value of 500 - 700 Ohms, and reverse connection produces a break.

Popular designs of diode bridges

The result is different if the bridge is shorted by resistors somewhere in the circuit, but this rarely happens, and their value is large enough to have no effect. The Larionov automobile bridge is called similarly. If possible, remove it from under the hood. The input of each phase is connected to the positive and negative output. Resistance value – up to 1 kOhm. The reverse connection is easy to check. It is necessary to put the red probe on the plus side and, in turn, make sure that all phases give an infinitely large resistance to the black probe. The mass is checked in the same way. Here the black probe goes along the negative output, and the red one goes through the phases.

First stage

To check the generator stator winding, use the ohmmeter indicated above. Measure the resistance of the generator field winding. Measurement results should be between 5 and 10 ohms. If the results are different, then there may be a break in the winding.

Now you need to check the insulation resistance of the generator. To do this, connect one of the ohmmeter probes to one of the stator contact rings, and touch the stator housing with the other probe.

The measurement result should be infinite resistance. If not, then the winding is “broken” and shorts to the housing (ground).

After the stator, it is necessary to check the generator rotor using the same method.

Testing a dismantled generator

If the result of the first test is negative, that is, it is definitely established that the autogenerator is inoperative, it is removed from the car and tested in disassembled form. Before checking the generator voltage regulator with a multimeter in disassembled form, you will need to check all components separately for functionality.

To do this, the removed generator is disassembled.

Let's move on to the second stage

Checking the diode bridge.

We switch the ohmmeter to the mode in which diodes are checked. We connect the positive contact of the ohmmeter to the central (common) diode bus. We connect the negative terminal to the terminal of the diode that you are testing. If the resistance is infinite or tends to infinity, then the diode is working; if the device shows other parameters, then the diode is faulty.

The next step is to reverse the positions of the ohmmeter terminals. Resistance readings should be close to zero, but not zero.

So it is necessary to check each diode in order to get an accurate result of checking the diode bridge.

Now you need to check whether the diode is breaking through to the ground of the car. To do this, we connect the positive terminal of the ohmmeter to the plate in which the diodes are located, and the negative terminal, as in the previous case, to the terminal of the diode.

If the resistance tends to zero, then the diode is faulty, and if it approaches infinity, then it is faulty.

I would like to add that if you have identified at least one faulty diode, then replace the entire diode bridge, it will be more reliable.

The next step is checking the car generator.

Checking the voltage regulator

This is a little difficult for a non-technically unprepared driver, but still many people use this method and, at the same time, successfully.

The first thing to do is inspect the brushes. They should protrude from the holder no more than 5 millimeters. The brushes must move freely in the holder, they must be intact and not worn out.

Now comes the fun part. Here you will need a current source with which you can change the output voltage using a regulator and a control light.

We connect the positive terminal to the terminal of the device, and the negative terminal to the ground of the voltage regulator. We connect the control to the brushes.

We supply 13V to the voltage regulator, and the control should light up. After you increase the voltage to 14.5-15 Volts, the control lamp should go out because the regulator has stopped supplying voltage to the brushes. This is fine. By reducing the voltage to 13 volts, the lamp should light up again.

It is important to read: Why the battery does not charge, the reasons you need to know about.

Checking the generator capacitor

We connect an ohmmeter to the capacitor. If the capacitor is in good condition, then, regardless of the polarity of the connection, the initial small resistance will gradually increase and soon stop changing. This is normal and is an indicator of the performance of the capacitor.

As you probably realized, checking a car's alternator is not that difficult. You need to have some skill, preparation, and appropriate equipment that can be bought at any car market.

But here we have considered only the electrical component of generator malfunctions, and there are also mechanical problems.

I wouldn’t like to drag out the article, but it’s about the most common problem, which is the failure of the generator bearings.

Alternator Auxiliaries

Alternators, like engines, are often equipped with thermal fuses, tachometers, Hall sensors and other auxiliary equipment. There are also specific stages, for example, a generator protection relay from asynchronous mode (which can lead to equipment failure). In general, keep in mind that ordinary engines are often started in a specific mode. Therefore, you need to be able to check the auxiliary equipment in the simplest possible way:

Thermal fuses are designed for a certain temperature, usually indicated on the housing. When a certain threshold is exceeded, the insulation melts, which can lead to winding failure. If we take generators, they are protected from overload using overcurrent protection relays (overcurrent protection relays), which we consider to be analogous to fuses. The action is based on the power limit requested by the consumer. For example, if one phase short-circuits, it simply breaks off. As for thermal fuses in typical motors, their locations are usually limited to the surface of the magnetic circuit or the insulation of the windings (the bump is clearly visible among the turns). You should find the output terminals and test the circuit from the connector side.
Thermal relays are considered analogues of thermal fuses with reusable operation, protecting the winding from combustion. When the engine has cooled down, current generation can be resumed.
Frequency sensors are usually built on the principle of tachometers. The organization of devices varies, depending on which the check is carried out.

To summarize: each engine can be started in generator mode. This is written directly on Wikipedia. Be that as it may, the design of generators reveals peculiarities. Specific regulation and protection methods differ from those used for motors. The results of the shutdown impose restrictions: if the generator fails, the consequences are much more dire. Already due to the presence of such features, the price is very different.

In conclusion, we will say: according to anecdotal evidence, asynchronous generators have less vulnerability to short circuits on the load side, and the voltage shape is better. In addition, there is no need to maintain the shaft rotation speed, which will be a big plus for practitioners. As for the organization of hydroelectric power plants, they use exclusively synchronous machines due to the obviousness of the requirements of the standards.

Bearing check

It is not difficult to check a car generator for faulty bearings. Usually, with this malfunction, the generator makes unpleasant noises, which are clearly audible when you are near the car. This problem can occur in both old and new generators.

Here, a lot depends on the correct adjustment of the tension of the generator drive belt. If the belt is tightened, then soon get ready for serious repairs to the generator; if it is not tightened, this will usually lead to the battery not being fully charged and causing it to quickly fail, especially in winter.

The first signs of these problems are the blinking of the battery charging indicator light, which is located on the car’s instrument panel.

If you don’t have such a light bulb, which is very rare on modern cars, then purchase a special device with a set of LEDs that is inserted into the cigarette lighter and shows the battery charge level; there are more expensive electronic analogues.

In most cases, to check a car's generator, you need to remove it, so if you don't like holding a wrench in your hands, then just take the car to a car service center.

Good to know - Alternator belt (Main road).

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Recharging the battery

The generator does not always undercharge the battery; it happens quite often when overcharging occurs, that is, the generator unit produces voltage above the prescribed norm. As a rule, the cause of overcharging is a faulty voltage regulator; it does not work as expected, and the generator continues to produce current when the battery is fully charged.

Without removing the generator from the car, the relay-regulator is checked in the same way as with undercharging, only in this case the multimeter shows the voltage of the on-board network when the load is on more than 14.7 V (readings can be even higher, for example, even more than 17 Volts) . Constant overcharging is dangerous because it:

the electrolyte in the battery banks begins to boil;
lead plates of the battery are exposed;
sulfation occurs (destruction of the plates), the battery becomes inoperable;
Due to increased voltage, light bulbs may burn out, electrical equipment may fail, and fuses may burn.

There is still a danger of a battery explosion, which occurs due to clogging of the holes in the plugs of the battery cans when the electrolyte is boiling.

On many VAZ cars of the “Classic” family (in particular, on the VAZ-2106), the voltage relay can be changed quite easily, as it is located separately, located next to the front fender of the car. The relay-regulator of the VAZ-2105 and 2107 type is located in the generator itself, it is a little more difficult to get to, but replacing it is also easy.

There are two power sources in a car - a battery and a generator. The first powers the electrical circuit when the engine is not running. The second is when the engine is already running. In this case, the battery goes into electric current consumer mode and replenishes the energy expended to start the engine.

In practice, malfunctions of one or another power supply are quite common. They often manifest themselves in the same way. The starter refuses to spin the engine, and as a result the engine does not start. When the engine is running, the warning light on the instrument panel with the battery icon lights up. It indicates that a malfunction has occurred and the battery is not charging.

Checking the generator on a car

Table of typical generator faults

Symptoms of a problem	Diagnostics	Remedy
The battery charge indicator on the dashboard does not light up when the ignition is on	Battery is discharged	Charging the battery
	The fuse in the unit or the indicator light has blown	Replacing fuse, light bulb
	Broken ground contact on the generator housing	Secure the bolted connection of the contact, cleaning it from oxides
	Broken wiring from the generator to the dashboard terminals, or broken contacts	Repair the break, clean the contacts
	Wear of generator commutator brushes	Replacing brushes or generator
	The gap on the brushes and slip rings of the rotor is broken	Adjust the gap
	Failure of rotor rings	Replacing the rotor or generator
	Voltage regulator relay failure	Regulator replacement
The battery charge indicator goes out when the speed increases	Loosening the alternator belt drive	Adjust tension
	Belt drive break	Replace belt
	Failure of the diode bridge	Replacing the diode block
	The power cable between the battery and the generator is broken	Replacing power cables
	The relay regulator has failed	Relay replacement
The indicator is constantly on	Short circuit in the circuit	Eliminate wiring problems
	Short circuit in the diode block	Check the contacts in the block, replace the wiring
	Failure in the ECU system	Check the controller unit, clear the ECU error
	Battery discharged	Charge the battery
The indicator remains on when the ignition is turned off	Short circuit	Eliminate broken wiring
	Short circuit in the diode block	Clean diode contacts or replace
Overheating and boiling of battery electrolyte	Failure of the relay regulator	Relay replacement

For what reason can a generator fail?

Since the sign of a generator malfunction is almost always the same, it is impossible to immediately identify the reasons why it failed without special equipment. There are 4 main failures due to which the generator may become inoperable.

Bearing jamming . During operation of the machine, there is a constant movement of elements in the generator, which leads to the disappearance of lubricant and further jamming or complete jamming of spare parts. Since the bearings have a high density, the first thing that breaks is the belt, which is responsible for their rotation. If the belt breaks, then you should think about replacing or rebuilding the generator.
Winding burnout . A burnt winding can occur for various reasons. The most common is the ingress of chemicals and salt that are sprinkled on roads in winter. After the wiring has burned out or simply lost its integrity, the generation of current stops.
Wear or jamming of brushes . Problems in the brush assembly arise because the graphite rods are worn out. This is a fairly common problem, as many car enthusiasts forget to replace brushes in a timely manner.
Regulator relay failure . This part prevents overcharging of the battery and brings the voltage to the specified parameters.

Additionally, we recommend reading our specialist’s article about what a generator overrunning clutch is and where it is located.

Since it is not always convenient to check the generator on a car in the field, it is worth carrying out scheduled maintenance in advance and not neglecting the symptoms of imminent failure.

How to check the serviceability of a car generator without removing it (without dismantling)

A quick on-site check of the generator is carried out using a 12-volt light bulb and a tester. This method provides data on the correctness of the voltage readings in a parallel connection of the circuit with the battery.

Attention! When connecting a circuit, the ground wires are always connected last to avoid a short circuit to the battery.

This testing method gives the general state of the generator’s performance without identifying possible violations in the winding elements, relays, brushes and diodes. For a complete diagnosis, use a multimeter, testing each section separately in various modes.

How to test a car alternator with a multimeter

A complete diagnosis of all nodes in the circuit and internal components makes it possible to identify an incorrectly operating element that malfunctions depending on operating conditions or temperature conditions. Identifying such a weak point in the generator in a timely manner means avoiding more expensive repairs or complete replacement of the entire mechanism. The test is carried out sequentially, measuring each node and circuit for resistance, voltage, current and the presence of breakdowns to ground, short circuits in the stator and rotor windings.

Generator diode bridge

Designed to rectify current and consists of a block that includes six paired diodes (three for minus, three for plus). Before testing the diode bridge, you must disconnect the battery by removing the minus terminal and disconnect all wiring from the unit to the voltage regulator relay. The multimeter is turned on in ohmmeter mode, the red “plus” connector is connected to the positive terminal of the diode block, the black “minus” connector is connected to ground (generator housing). If the diode bridge is working properly, then the value on the multimeter display will show infinity. Otherwise, any resistance means the rectifier is faulty.

Voltage regulator

Designed to stabilize the voltage from the generator to the on-board network. Depending on the type of power unit and the make of the car, the normal value of the relay may differ, so before the test you need to determine the indicator given in the technical description of the engine. Procedure:

Generator excitation current

Must match the rated current of the circuit. To take measurements, turn on the multimeter in ammeter mode and connect terminal “67” in series to the positive contact, and the negative contact to ground. Start the engine and maintain high speed for 3-5 minutes. The normal value is considered to be from 3 to 8 Amps.

Return current

Allows you to identify short circuits in the circuit in a specific area and the stability of the generator output current. To measure, a multimeter in ammeter mode is connected in series to terminal “30” (B+) and the generator ground. Next, the unit is started at high speeds and all electricity consumers are activated simultaneously. After 2-3 minutes, read the current reading and turn off the electrical equipment. A new measurement is taken for each individual circuit: low beam headlights, air conditioning, audio system, dimensions, high beam, turn signals. When each individual consumer has been measured, all values are added up and compared with the total. The error should not exceed 5 Amps.

Windings

Responsible for the electromagnetic induction of the generator. To diagnose them, you will need to dismantle the mechanism, remove the relay-regulator and brush holders. The multimeter is turned on in ohmmeter mode and the resistance readings are taken at the terminals of the slip rings: one probe of the device on any rotor ring, the second on the stator. The standard winding resistance indicator should be in the range from 2 to 8 ohms.

Asynchronous alternating current generators

These generators are called asynchronous because the frequency of the generated current differs from the speed of rotation of the shaft (even taking into account the number of poles). Structurally, such a machine is considered a typical motor with a wound or magnetized rotor. Shaft winding differs from synchronous winding in the absence of a section between the poles. Due to this, the plus and minus are less pronounced. So, depending on the type of design of an asynchronous motor, the method of starting it in generator mode differs.

For a squirrel-cage rotor, it is necessary to pre-magnetize the shaft. This is done using a short but strong current pulse. The location of the poles depends on the polarity. Please note that the relatively small cross-section of the shaft will not allow creating a strong magnetic field. This means, in accordance with the above, we come to the conclusion that it will not be possible to obtain high voltage using the described generator. It is much more profitable to magnetize a phase rotor from plates by applying voltage to the coils. Voltage will begin to be removed from the stator. The driving force is:

Burning gases or car engine shaft.
Wind wheel.
Bike.

Electricity is generated by changing the field. Magnets can be permanent (squirrel-cage rotor) or electric (wound rotor). The second type of device needs to be powered with current, for example, from a battery through a slip ring (ring on the shaft). In accordance with this design, methods for testing the multimeter generator emerge. In the case of a squirrel-cage rotor, we test exclusively the stator. The number of pins depends on the power phase and other features:

Asynchronous type generator

The stator windings of a three-phase generator are connected in a star circuit. They form a common point, and the three opposite ends are placed on phases A, B and C. In this case, you should check the generator in pairs with a multimeter for the resistance value. The answer is always the same.
Then the insulation on the body is checked. This will require special equipment: a 500 V test voltage driver and a current clamp (one option among others). The insulation resistance according to the standard is not less than 20 MOhm. If there is a short circuit, the motor is built according to a circuit with a solidly grounded neutral, which is typical for voltages up to 1 kV. In this case, the design is specified according to technical characteristics. It’s easier to find data on an asynchronous motor on the Internet.
The stator of a household asynchronous motor is much more complex. Such machines are not used as generators, but... we will show you how to check their functionality. More often there are two windings, one is powered through a capacitor and becomes a starting or auxiliary one. In our case, it is permissible to relieve tension from each. The resistance of the auxiliary (or starting) winding is usually slightly greater than that of the working one. This is easy to check with a tester. Then the insulation resistance on the generator housing is measured.

The rotor is tested together with current collectors. Three-phase circuits are designed to work with an isolated neutral; to check the generator winding with a multimeter, you should measure the resistance between all three rings in pairs. The values must be equal. Sometimes there is a short circuit to the housing (circuit with a solidly grounded neutral). It all depends on the design features of the engines (generators). If there are one or two rings, we conclude that the power supply is single-phase. By calling the coil, we check the insulation on the body.

How to check the operation of a generator in a car without measuring instruments

The functionality of the generator can be checked without a multimeter or tester by removing the minus terminal while the engine is running. This method is only suitable for older car models where the power circuit is not controlled by the ECM (Electronic Engine Control System). If you use this method on modern internal combustion engines, then as a result of a sharp surge in voltage, part of the electrical equipment may fail, the fuses in the unit may blow, the adjustment of many sensors may be disrupted, and the system will display a “Check Engine” error.

On old-type units, the check is performed as follows:

During the process, pay attention to the drop in speed when the terminal is removed: installing it in place should significantly increase torque without opening the throttle.

Important! Touching the battery power cables with bare hands is strictly prohibited. The terminal must be removed using insulating gloves, carefully moving it to the side.

How to test a 12-volt generator removed from a car at home

At home, a generator removed from the engine can be checked by “ringing” the circuit of elements in series with an ohmmeter. Using this method, you can determine the condition of the windings, diode bridge and relays.

The voltage is measured by securely securing the generator in a vice and connecting the adapter head from the drill to the center nut of the drive. Turn on the drill and use a voltmeter to measure the voltage at the terminals. If the indicators, depending on the speed, are in the range of 12.2 - 14.8 Volts, then the generator is working.

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How to check a car's alternator? 5 Easy Ways to Test with a Multimeter

The generator is the source that is responsible for recharging the battery while driving. If the generator does not work properly or is unstable, the battery discharges too quickly and requires constant recharging from the electrical network. Since you can check the generator at home, if you have a problem with the battery quickly discharging, it is not necessary to go to a service station for diagnostics.

If a generator is suspected of malfunctioning, the car owner first tries to identify the breakdown himself. There are several verification methods that involve measuring both a removed and an undismantled device. The verification in both cases will be reliable. In addition to knowing how to check the generator, you need to find out the reasons why it may fail. Although the generator is a fairly reliable device, incorrect or careless operation of the car can cause it to fail prematurely.

Why do you need a generator?

The generator provides electricity to the receivers. Installed in the car, items such as the battery, lighting, heating, air conditioning, computer and stereo system. The generator produces current only when the car engine is running.

It consists of 2 basic devices: a stator and a rotor, or armature. The first is stationary, and the second is movable. The generator stator housing contains copper coils through which electric current passes. Running the vehicle's engine through the car's alternator belt activates the rotor. When it rotates, a current is created in the stator windings, which is used to operate the internal systems of the car and to charge the battery.

Note! Before checking the generator with a multimeter, the user must know where it is located. It is located at the front of the car, usually on the right, and is connected to the engine by a belt.

Check Features

You need to know how to check the operation of the generator on a car correctly, otherwise you may encounter the fact that a working part will be completely damaged. By following just a few simple rules, you can avoid unexpected breakdowns.

The main condition under which it is possible to check a generator at home is to maintain its working condition. If the device is disassembled or has received damage that prevents it from functioning, then diagnostics will not allow us to determine the suitability of the device for further operation.

We also recommend reading our expert’s article, which talks about how to remove the generator on a Priora.

You may also be interested in our specialist’s article on how to remove a generator on a VAZ-2114.

We recommend that you additionally read our expert’s article, in which he talks about how to repair a VAZ-2106 generator.

There is a list of actions that absolutely cannot be performed during verification:

How to test a generator for performance at home

There are two main verification methods. One of them, although very old, allows us to reliably understand the performance of the device. The second works more subtly and is able to respond to minor system flaws. Using the second method, you can identify the slightest deviations in the operation of each element.

How to check a generator on a car without removing it and without having the necessary tools

There is an ancient way to identify a generator malfunction. It is very simple, but the result can only consist of two points:

Since anyone can check a car generator at home using this method, its popularity is fully justified. You need to start the engine and turn on the low beam. You need to remove the negative terminal from the working engine. If the headlights are on evenly and the engine is not out of sync, then the generator is working properly. If the internal combustion engine operates uncertainly or the brightness of the headlights changes, it is necessary to perform a more in-depth diagnosis, since the device is in a faulty state.

How to test a generator with a multimeter

Measuring with a special device will reveal even a small failure. There are a number of indicators that are considered optimal for all types of machines. The battery without load has a voltage in the range of 12.5 - 12.7 V. Since a load is placed on the battery when the engine starts, the normal readings are 13.8 - 14.8 V. After receiving the maximum load, the voltage reading should drop to 13 ,8. If this does not happen or the voltage drops even lower, then the generator will need to be checked.

Since not all car enthusiasts can ring the generator correctly, if a malfunction is identified, but if it is not possible to carry out diagnostics yourself, it is better to contact a service center. Experienced technicians will be able to suggest the reasons for the breakdown and explain why it was not possible to carry out the research on their own.

Checking the voltage regulator

The sequence of actions is as follows.

Checking the generator diode bridge

This method is one of the ways to test a generator without a car. For diagnostics, you will need access to the battery and the device itself. The voltmeter is used in measurement mode and is connected to ground and the B+ terminal on the battery. After turning on the special equipment, the indicator in its window should not exceed 0.5 mA. If the indicator is higher, this indicates that the diodes have failed or the integrity of the insulation on the windings has been damaged.

Checking the return current

This check is carried out only with the motor connected. This method is quite problematic and requires a lot of time and scrupulousness. The essence of diagnostics is to measure the current of devices that consume electricity. The engine must be started and the speed reached as high as possible. The probe is installed on the wire that goes to the 30 or V+ terminal.

One by one, you need to turn on all the electrical appliances of the car, and record the readings from the multimeter. After the results have been obtained, the numbers must be added. Next, you should turn on all electrical appliances and compare the readings on the measuring equipment with the sum of past studies. An indicator of 5 A less than the amount received is considered normal, but an increase indicates a malfunction of the spare part.

Checking the generator excitation current

The engine should operate at the highest possible speed. The multimeter is connected to terminal 67. The device will immediately display the result and the magnitude of the excitation current. For a normally operating generator, this indicator is in the range of 3 - 7 A.

Lamp test

A lamp test is testing a generator using a “fog light”. The diagnostic task is to determine whether the generator rotates correctly when exposed to drill speeds. In this case, the light bulb plays the role of an indicator - if the generator rotates normally, then it (the light bulb) should light up.

Alternator test lamp

It is important to know that a working generator should produce a voltage within 14.1-14.5 V. And at the same time, the voltage should not jump or have differences. In other words, the voltage must be stable.

To carry out this type of testing, the autogenerator will have to be removed from the car and the following steps must be taken:

clamp it in a vice so that it is convenient to work;
integrate a battery with the generator.

It is highly recommended to be careful when connecting the battery to the generator and not to mix up the contacts. An incorrect connection will lead to a short circuit, which can easily burn out the dynamo.

We also advise you to find out the type of generator before diagnosing. As you know, they are different in terms of connection. This means that the units may have a different number of contacts. There are 2-pin, 3-pin or 4-pin generators.

4-block generators contain the following contacts:

a plus of a constant type, marked by the Latin S;
plus associated with ZZ - IG;
contact for control unit marked M;
for the warning lamp – L.

We continue with a series of actions:

a positive cable is run from the battery to both “+” dynamos;
a lamp with a value of 50 W is integrated to the desired contact;
voltage is applied to the lamp;
the generator is rotated using a drill;
The indicator light is tested.

So, if the light is bright and the voltage on the dynamo is within normal limits, then the generator is fully operational. In any case, it is capable of recharging the battery.

The connection between the generator and the battery is an important tandem. Under no circumstances should you disconnect the battery while the engine is running! Ask why? This unnecessarily loads the voltage stabilizer and generator, which causes a failure in the overall system. This can even be seen from the indicator: if the lamp under test is disconnected from the battery, then if the dynamo is working, it will continue to glow, but the voltage will no longer be stable.

Is the generator shorting or not?

The battery should also not be disconnected due to a simple short circuit. A short circuit will burn not only the unit itself, but also the electronic units installed in the car.

So, the rule not to remove the terminals from the battery under any circumstances must be included in the list of the main canons of the motorist. Those who like to “light” the battery do the wrong thing, which often happens in the winter season. Keep a charger in your car and don't push your luck. Once or twice you'll be lucky, but on the third you can burn down the entire electrical system.