Uninterrupted work modern engine internal combustion is impossible without high-quality and stable sources of electricity. In the process of starting the engine, this role is performed by the battery, and after the engine starts, the function is taken over by the generator. Taking some power from power plant, the generator supplies voltage to all electrical consumers in the vehicle. Additionally carried out.
If, for some reason, the generator does not cope with its duties, then the battery remains the main source of current, and does its job until it is completely discharged. It’s unlikely that anyone will like to stay with a dead battery and an idle generator in the middle of the road, so we’ll tell you how to check the generator on a car without removing it from its mount.
Concomitant factors can signal the presence of problems with the generator. Manufacturers install a control red light on the instrument panel that notifies the driver of a weak battery charge or its complete absence.
Weak lighting fixtures both inside the cabin and outside optics indicates an insufficient charge level. Also, an increased load with the simultaneous inclusion of several electrical consumers leads to a rapid discharge of the battery.
Requires constant battery charging
The motor receives a slight vibration and emits a slightly muffled continuous squeak from the side of the alternator mount. Often even visually noticeable slippage of the belt on the pulley.
It is necessary to check the generator for operability then, when the brightness of the optics becomes directly dependent on the speed power plant. This does not apply to a slight change in illumination during gas flow on Idling. However, if you add the number of revolutions while driving and the light becomes more intense, and when you reset the brightness decreases, then this is evidence of problems with the generator.
Rapid fault diagnosis and repair
In order to check the voltage on the generator, it is not necessary to dismantle this electrical part from its seat. The operation can be done with a multimeter.
Replacing the belt on the alternator pulley
Also, most problems can be fixed without significant labor or time costs.
- The main reason for not charging the battery is weak tension on the belt drive. Deflection of more than 10-15 mm when pressing on the middle must be eliminated. A torn belt must be changed, and a stretched one is often enough to tighten through the tensioner. If the effort is not enough and there is not enough thread for tension, then the belt must also be replaced. The cost of the product is low.
- You need to make sure that nothing interferes with the rotation of the rotor. The generator housing must be free of cracks and dents. The rotor must turn without effort or without clamps around the entire circumference.
- The electrical part must also be in good condition. Fuse can be changed as a preventive measure. Charging relay should also be inspected and replaced if necessary.
You need to know that there are problems with electrical system car similar in symptoms, but their causes may be different.
Testing with a multimeter
The test method using an electronic multimeter is the most popular. To do this, you must set the device to the resistance control mode (ohmmeter). First of all, on a dismantled generator, it is customary to check the rotor, and then the stator. The diode bridge is tested last. Additionally, you can control the assembly with a voltage regulator or the quality of the brushes mating with the surface. Before you check the generator with a multimeter, you need to set the correct modes on the measuring device.
Control measurements with a multimeter
If the brush assembly is clogged, the voltage supply may not be, options with its unstable supply to consumers are also possible. A visual health check can begin with the health of the brushes and how they come into contact with the rings.
Voltage control must begin with in the car. It is customary to consider the interval 12.5-12.8 V for a fully charged device to be acceptable. Further Measurements with a multimeter are made with the engine running.
After the start, a few minutes are given to warm up the engine, and then all consumers of electricity are started, including the stove. Measurements at the battery terminals should be within 14-14.2 V. The occurrence of short jumps up to 0.5 V is considered normal. If the difference is more than 1 V for a long time, the problem may turn out to be a breakdown of the generator. In this way, the relay is tested.
Checks of individual generator units
To obtain more accurate results, you can check the nodes separately. This is done with a multimeter set to voltmeter or ammeter mode.
Checking the dismantled generator
When checking a diode bridge, the suitability of each diode is determined. To do this, the multimeter is set to the beep mode and a test is carried out separately for the diodes. The measurement is carried out on each element twice, swapping the probes. The sound should only be in one direction. If the signal is heard during direct and reverse measurements, then the diode is faulty.
Measurements are also taken with the stator. It is necessary to identify breakdowns of wires on the case. One multimeter probe is attached to the end of the winding, and the second to the case, as a result, the screen should have an infinite voltage value. If the readings are less than 50 kOhm, then this is evidence of a breakdown. Visual inspection should show no burnouts or other visible damage.
Disassembled generator
On the rotor, measurements are also made using a multimeter. The indicator is also controlled in the "resistance" (ohmmeter) mode. Measurements must be taken between slip rings. The result should be a few ohms. If the resistance tends to zero, this situation is a sign of damaged wiring.
Changing the winding on the rotor or stator at home is inefficient. The alternator will have to be completely replaced.
The main source of electricity in the car is the generator. It starts simultaneously with the start of the engine, after which it generates energy and charges the battery. If it fails, the battery charge will not be enough for a long operation of the car, so the driver must monitor the condition of the generator.
There are a lot of problems due to which the generator can fail during operation. It can be both mechanical and electrical problems. A generator malfunction is also manifested by various symptoms, among which the most common are:
- Appearance extraneous sounds coming from the generator;
- Battery problems: discharging, recharging, electrolyte boiling off;
- Decreased brightness of headlights with increasing speed. This situation is considered normal if it occurs briefly when switching to first gear from idling on a "cold" engine;
- Signaling of a control lamp about the discharge of the accumulator during the movement of the car;
- Electronics malfunctions, including dim headlights and a weak horn.
If the symptoms described above occur, the car's alternator should be checked. Diagnostics is most often performed according to four parameters:
- Checking the strength of the recoil current;
- Diagnostics of the diode bridge;
- Checking the generator voltage regulator;
- Checking the excitation windings.
Depending on the identified problem during the diagnosis, the issue of the expediency of repairing the generator is being decided.
Generator Test Safety Rules
Before proceeding with the test car generator, you should familiarize yourself with the basic safety rules that will allow you to maintain the health of the diagnostician and not disable the unit. The basic rules for safely checking and repairing a generator are as follows:
Please note: If not only the generator is checked, but also welding work with the car body, it is necessary to disconnect the generator and battery completely from the vehicle's on-board network before starting them.
Checking the output current of the generator
For this test of the generator, you will need a multimeter equipped with a special probe for measuring the current flowing in the wire. This probe looks like a clip that wraps around a wire, and most often it comes with a diagnostic device. To check the recoil current of the generator, you must:
- Put a clamp on the wire that goes to the “B +” (“30”) terminal of the generator;
- Next, start the engine and set high speed;
- After that, one by one, it is necessary to turn on the electrical consumers on the car - the radio, air conditioning, steering wheel heating and others. When you turn on each consumer, you should record the readings from the multimeter;
- Next, you need to measure the recoil current when all consumers are turned on together (which were included in the previous test).
When all measurements are received, it is necessary to compare the total indicator of the sequential switching on of consumers and the indicator of the instantaneous switching on of all consumers. It is considered unacceptable if the indicator, when all consumers are instantly turned on, is 5 or more Amperes less than the sum when switched on in turn.
Checking the diode bridge of the generator
To check the condition of the diode bridge of the generator, it is necessary to switch the multimeter to the alternating current measurement mode. Connect one test probe of the diagnostic tool to the output "B+" ("30"), and the second to ground. The voltage with this connection of the probes should be no more than 0.5 volts. If the voltage is higher, the diodes are probably short circuited.
You can also check the diodes for breakdown. To do this, the battery is disconnected from the generator and the wire that goes to the “B +” (“30”) terminal is also disconnected. Next, the multimeter is connected between the disconnected generator wire and “B +” (“30”), after which readings are taken. If the discharge current of the multimeter shows more than 0.5 mA, there is a high probability of breakdown of the diodes.
Checking the generator voltage regulator
To diagnose the state of the automotive generator regulator, you must use a voltmeter or multimeter in voltmeter mode. Before starting measurements, you need to start the engine, turn on the headlights and let the engine run for 15-20 minutes. The measurement itself is carried out with probes that are connected between the mass and the output "B +" ("30") of the diagnosed automobile generator. The obtained values are recorded, after which they must be compared with the normal figures for a particular car model. These figures can be found in technical documentation cars. For most machines, normal voltage ranges from 14 to 16 volts. If there are deviations from the standards set by the car manufacturer, there is a high probability of failure of the voltage regulator, in which case it will need to be replaced.
Checking the excitation windings
To check the serviceability of the excitation windings of the automobile generator, it is first necessary to remove the regulator and brush holder in order to gain access to the slip rings. For diagnostics, you will need an ohmmeter, the probes of which should be applied to the slip rings of the generator. As a result of the test, the resistance should be at a level of 5-10 ohms. It is also necessary to visually verify that there are no breaks in the winding.
To diagnose the short circuit of the excitation winding “to ground”, you will need to connect one ohmmeter probe to any slip ring, and attach the second to the generator stator. As a result of the measurement, the screen should display infinite resistance.
When diagnosing the generator, it is also necessary to inspect it for mechanical damage. Based on the results of all checks, the feasibility of repairing the device or replacing it with a new one is determined.
The car's battery supplies it with electricity in splendid isolation only before the engine starts. After starting the engine, a generator helps him. The task of the generator is to ensure continuous recharging of the battery in all operating modes and under any load on it. But breakdowns happen. How to determine that it is the generator that is to blame?
Signs of its malfunction are:
Nature of the fault | Cause of malfunction |
| The battery "boils out" | Large charging current |
| The battery is running low | Charging current is low or absent |
| The "No battery charge" lamp on the instrument panel of the car is on | No charge current |
| The voltage in the on-board network is unstable | There is no stabilization of the charge current or this current does not exist. |
| Extraneous sounds in the generator | Bearings require replacement or the alternator belt is not tensioned. |
But first things first. The generator is not so easy to remove, and to do this, you need a good reason.
Diagnostics of the generator on the car with a multimeter / tester
Checked before checks tension and technical condition of the alternator belt. The belt must not be overtightened, but it must not be loosened either. In the first case, the bearings will wear out prematurely, in the second case, the rotor will slip with an increase in electrical load. Slippage, in addition to reducing the voltage in the network, will also lead to premature wear of the belt. The belt itself should not be worn and there should be no cracks on it.
If, when the engine is running, the smell of burnt rubber is felt from under the hood, the "lack of charge" lamp is on - seized alternator bearings. Increased noise, on the contrary, is caused by increasing the gap in them. This is checked by loosening the belt and shaking the rotor shaft in the radial direction. This determines only the play in the front bearing, but it also suffers in the first place.
If the mechanics are in order, they check electrical characteristics . This will require a device that can accurately measure a constant voltage of 12 - 16 V. Moreover, the scale (or digital indicator) at this measurement limit should show values \u200b\u200bin tenths, otherwise the measurements are meaningless. A pointer tester and a multimeter are also suitable.
The device is connected directly to the battery, observing the polarity. Polarity reversal will not harm digital devices, but for analog devices, the arrow will sharply hit the left limiter. You should not be afraid of this, the device will withstand it, but it is not advisable to stay in this position for a long time.
It is better to fix the measuring probes on the terminals. You can use the services of an assistant, but using crocodile clips is more convenient. The main requirement is that when the motor starts (it twitches at the same time), the clamps do not turn off spontaneously.
Before engine start fix the voltage of the battery. It should be within 12.5 - 12.7 V, depending on the degree of its charge, and the entire load is turned off. Do not forget that when you open the doors in the cabin, the light comes on, and this is at least a small, but a load. If the voltage is below 12 V, it is better to charge the battery before the test. A working regulator will greatly increase the voltage, trying to correct the situation and quickly charge the battery. And you will draw the wrong conclusions from this about its malfunction.
Now start the engine, warm it up so that the RPM equals the idle RPM for your model (usually within 800). We control the voltage on the battery, you can start looking at the scale of the device even during the warm-up process. The measured value must lie between 13.5 and 14 V. And so - in all modes of operation.
If at idle the voltage is below 13.0 V, then the problems may be as follows:
Faults related to broken contacts
It is necessary to constantly monitor the cleanliness of the battery terminals, but sandpaper cannot be used to clean oxides. It is better to scrape with a knife, and periodically loosen the contacts and grind the surfaces by turning the clamps on the terminal from side to side. And when checking the oil level, apply a couple of drops of it to the battery contacts.
Contact connections worth checking in case of low charge voltage:
- Positive output: from the battery to the generator;
- Negative output: from the battery to the car body; from the body of the car to the body of the engine.
Contact between the bodies of the car and the engine of VAZ models is provided flexible connection under the bottom in the area of the gearbox. The metal leash rots, additional resistance is added to the electrical circuit. And the minus of the generator is connected with the minus battery through him. Additional resistance is also introduced by rusty elements of the bodies of old cars.
The way out is to install an additional flexible connection from a 25mm2 conductor connected between any of the suitable bolted connections on the engine and the connection point of the battery negative terminal to the body.
Battery malfunctions
When sulfating the battery plates, depleting its resource charge voltage does not increase. The battery itself works as a limiter. To verify this, try to fully charge the battery. If it doesn't work out, replace it with a new one.
If during the operation of the generator the voltage on the battery is more than 14 V, then either it is very discharged, or the voltage regulator is faulty.
Diagnostics of the voltage regulator
The task of the voltage regulator is maintenance of battery voltage in the range from 13.5 to 14 V in all engine operating modes and under any load. Criteria for its performance:
- When you press the gas pedal and increase the engine speed, the voltage rises slightly, without leaving the permissible limits.
- When consumers are turned on: headlights, car radio, heater, air conditioner, the voltage drops below the permissible value only at idle. If at the same time increase the speed (add gas), then it returns to the operating range.
Check the operation of the regulator with the engine running, changing the number of revolutions by pressing the gas pedal. First, the experiment is carried out without load, then the headlights and the heater are turned on, adding a load. The voltage on the battery should not change significantly.
If this is not the case, the regulator is changed. On some models this is possible without removing the alternator, but it is still recommended to remove it. Purpose: to additionally assess the condition of the brushes, remove dirt accumulated during their operation, check the condition of the bearings.
Checking the generator brushes
For a detailed examination of the generator, it is removed from the car. Then it is cleaned of impurities. Remove the brush apparatus, if necessary - the voltage regulator. The brushes must be worn evenly (their length is the same, and the wear from the rotor rings is symmetrical about the longitudinal axis). The remaining length of the brushes should be more than 4.5 mm (8-10 mm is considered the norm). If these parameters are not met, the brushes are changed, even if the fault lies not in them.
Along the way, it will be necessary to remove the coal dust formed during the friction of the brushes on the rotor rings.
To replace the voltage regulator or brushes, further disassembly is not required, but if the fault has not yet been found, open the back cover of the generator. Before this, you will need to unwind the positive output pin.
Rectifier test
The generator generates a three-phase voltage rectified by six diodes. The positive and negative terminals of the rectifier are made in the form of aluminum plates, which at the same time are radiators for cooling the diodes.
To check their health, you will again need a multimeter or tester. We transfer the device to the resistance measurement mode. Then we alternately measure the resistance of each diode in the forward and reverse directions. To do this, change the polarity of connecting the probes of the device. In the forward direction, the resistance is small (but not zero). In reverse - equal to infinity. If this is not the case, the diode has failed.
If one diode is damaged, at least two more fail. Accidentally leaving a breakdown unattended will not work. They change the diodes in a group, together with the radiator.
Generator stator diagnostics
The stator winding is made with a thick wire, so breaks in it are rare. Unless the contacts are soldered at the points of its attachment to the diodes, which needs to be checked.
Then inspect the winding in search of mechanical damage. They appear if the rotor shaft shifted to the side during operation due to an increase in the output of bearings. At the same time, its impeller touches the turns of the stator winding and damages them. Result: breaks, coil shorts or ground shorts.
The insulation of the stator conductors is restored. To do this, a varnished cloth is laid between the turns. For fixing, the damaged area is coated with bakelite varnish and dried. The use of insulating tape is unacceptable, under the influence of the operating temperature inside the generator, it will melt.
In the absence of visible damage, it is possible that the turns of the winding short circuit between themselves and on the case. A turn short can only be detected by changing the color of a group of winding turns. It will not be possible to detect a defect by measurements, since the cross section of the wire is large, the number of turns, on the contrary, is small. The change in phase resistance is so small that it is comparable to the transition resistance at the point where the probes of the device are connected. But the probability of a turn circuit, fortunately, is small.
But short circuits on the case happen more often. To identify them, measure the resistance between any terminal of the winding and the housing. Use the highest limit of the multimeter to measure resistance. It is better to use a special device - a megohmmeter, but only on condition that the voltage it produces does not exceed 100 V. The operating voltage of the generator is 12-16 V, using megohmmeters to test for a higher voltage will damage the insulation.
For any problems with the stator winding, the best way out is to replace it. The stator is sold with a winding wound inside it. And rewinding it yourself, even with the involvement of wrapping specialists, will not justify itself.
Diagnostics of the generator rotor
When inspecting the rotor, pay attention to:
- development on slip rings: there should be no grooves formed under the brushes;
- winding color: uniform, different from black (black color - the winding burned out).
To smooth the surfaces of the slip rings, they can be ground by holding the rotor in lathe, be sure to center it. For grinding, sandpaper is used, the grain of which is reduced as it approaches the desired shape of the rings.
To diagnose the rotor winding, its resistance is measured with a multimeter or tester. For different models of generators, this value varies 2.3 to 5.1 ohms.
Alternator bearings
Pullers are used to remove bearings. The use of improvised means for this purpose is possible only with appropriate experience.
If during the diagnostics of the generator it turns out that more than two of its parts are to be replaced, it is better to purchase it as a whole. And if you are not confident in your abilities, immediately use the services of the specialists of the nearest service station. This will save you time, nerves, and possibly money.
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 normal work light bulbs, power windows, windshield wipers and other electrical equipment, as well as battery charging, you need to maintain a DC value 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 causes some damage to the battery, reducing the life due to overcharging.
Therefore, to convert the current generated by the generator, there is special device- . With its help, the on-board network is provided with a current that maintains the required parameters, regardless of the speed. crankshaft. 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 the rest of the relays have a lot of advantages: compactness, durability, high accuracy of current parameters.
- Headlights change the brightness of the glow, depending on the engine speed.
- There is an insufficient charge of the battery or, conversely, its overcharging, accompanied by the boiling of the electrolyte.
- There may be a burning smell in the vehicle interior. The failure of the regulator can occur due to moisture ingress, various mechanical damage, short circuits and other non-standard short-term electrical influences.
- 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. The 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 of 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 the electronic device sits on top of the generator, covered 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". Pilot lamp connects through conductors with graphite brushes without observing 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 burn, 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
A faulty car alternator rotor primarily causes the charging current to fail and the battery to drain. 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 alternately 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
A car generator malfunction belongs to the critical class, in which further operation vehicles 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 indication of "battery" on 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 a donor battery to start the engine, 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 will recharge the 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 the 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 spot-welded 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.