Well, not so long ago I wrote an article about, actually this happens for two reasons: when the battery is already dying and needs to be checked, and when the battery is new it also needs to be tested before purchasing. But is it always the battery? Why might it suddenly fail? It’s one thing if it’s winter and it’s really difficult for him to work, but another thing if it’s summer and he’s not “purr-murr” at all. AND even on the instrument panel, the battery sensor begins to blink occasionally, or is constantly on! In such situations, you should not run headlong for a new battery; first you need to establish the reason why it failed, because in 50% of cases it can be the generator. Moreover, the check is quite easy to do without removing it from the car, let’s read more...
Indeed, guys, I have a lot of friends who first ran for a new battery, but later it was discharged to zero. The point is that before purchasing, you MUST check the generator! After all, think for yourself, if it does not recharge the battery (or there is no charge at all), then it will be discharged to zero after a day or two of use, I’ll say more, it’s easy to bring it to the point that even for a new battery, it’s very bad, you’ll immediately lose about 10% of the capacity , DO YOU NEED IT? Therefore, I repeat once again - CHECKING THE GENERATOR IS MANDATORY
Why does the generator fail?
The generator itself has a simple structure; if you want, it’s a regular electric motor (only made to allow for large current generation), try to spin a regular electric motor and attach a light bulb or LED to it, it will start to light up - and there you have it, an elementary current generator.
Someday I will have an article in which I will tell you what the generator consists of. BUT today it is simple and exaggerated - this is the rotor (moving part), stator (fixed part), brush assembly, and of course the housing in which the whole thing is located.
And now the actual breakdowns.
- The bearings are jammed. This is a fairly common problem with already worn-out generators, the rotor in the housing spins on bearings, from time and moisture (dirt), they wear out and simply jam or wedge. If there is a wedge, then this is one thing - the rod stops rotating. But if wedging occurs, it is difficult to notice; the rod may or may not rotate. In any case, with such symptoms, the belt that turns the generator from the engine is more likely to break. THIS IS THE FIRST CALL.
- The winding on the stator or rotor has burned out. It is there in any case and most likely will be on the stator, so - also from moisture (salt on the roads), it can be corroded and it will simply short out or simply burn out, since copper wires are used there. Accordingly, current generation will stop.
- Failure of the brush assembly. This is also very common, brushes are graphite (often square) rods that run along the stator tracks. So, from time to time they simply wear out and need to be replaced.
- Failure of the regulator relay. This relay prevents the generator from recharging the battery, bringing the voltage and current within the desired range. Often it also fails and the battery does not charge at all! Need to watch.
In general, for these 4 main reasons, the generator may not work, so it must be checked before purchasing a new battery. It's likely that this is what you're dealing with.
Car tips
Actually, I already told you about them from above; if the generator refuses to work, then it is easy to notice even inside the cabin.
- All modern cars will be signaled by a warning lamp - “red battery” on the instrument panel. If it lights up or even blinks, then there is nothing good about it, you need to react immediately, otherwise a discharge is just around the corner.
- Weak glow from all instruments. The “warning lamp” may burn out, but if you notice that the instruments begin to glow dimly, this means that the car is running on the battery, and not on the generator. Again you need to check.
- Belt break. If you crawl under the hood and there you see a break in the belt that spins the generator, then you MUST CHECK THE OPERATION! Otherwise, again, you can kill your battery.
These are all obvious malfunctions, but it happens that the battery is dead and everything seems to be fine, but something inside is “gnawing” - maybe it’s the generator? How to check easily and quickly on a car without removing it? Question? And everything is quite easy here
Check without removing from the car
There are two 100% ways that I personally recommend to you.
1) Checking with a multimeter. Of course, not everyone has it, but in fairness it’s worth noting that this is a fairly common device and let’s say your father, neighbor, friend will have it “anyway.” To begin with, we measure with the engine not running, at the battery terminals, there should be about 12.5 - 12.7 V, ideally.
We start the car, do not accelerate, and do not turn on any electrical appliances - with the engine running, we measure the voltage, it should be within 13.8 - 14.5 Volts.
However, on modern cars, where a lot of electronics are crammed, manufacturers assure that 14.8 Volts IS ALSO NORMAL. More on this below. Next, we connect the load - headlights, heater, heated rear window, foglights, radio, after that the voltage should drop a little - but not lower than 13.7 - 14.0V. If it is lower, say 12.8 - 13V, then the generator is not working, you need to check it.
Let's summarize a little:
Normal battery voltage is 12.5 - 12.7V
After starting the car - 13.8 - 14.5V, on some modern cars - 14.8V
After turning on the maximum load, it should be - 13.7 - 13.8 V
If the voltage is below 13V, urgently CHECK THE GENERATOR
2) Old grandfather's method. You can check this on almost all machines, and this method works 100%. But everything needs to be done very carefully. So - we start the engine, turn on a small load (for example, headlights or heated rear window). And on a working engine, we need to remove the negative terminal from the battery, everything is unscrewed with a key to “10”. We remove it and put it to the side, you can simply lift it above the terminal.
If the car continues to work confidently, the headlights have not dimmed, then your generator is 100% working. If the car stalls immediately, it means that the generator is 100% not working and it urgently needs to be looked at. So I tested it on a VAZ 2101 and now it works on my AVEO.
Battery overcharge
However, often it is not “undercharging” and “overcharging”.
There are only two devices that ensure the functionality of the car's ignition system. Battery and generator. They function in pairs, complementing each other.
Any of these devices can operate separately from the second for a short time. It is allowed to drive for some time with a faulty generator until the battery is discharged.
Also, a spark in the ignition can only be maintained by a generator, but the problem arises when starting the engine for the first time - without a battery, the crankshaft cannot be cranked.
Moreover, coordinated work will be disrupted not only if the generator breaks down. If the voltage produced deviates from the norm, the battery will not charge, and the vehicle's electrical systems will either not start or fail.
How to check the functionality of a generator with a multimeter?
To understand the process, consider the generator device:
Failure of any of the components will lead to disruption of the entire unit. First, the mechanical part is checked. There is no need to remove the generator; just remove the drive belt from the pulley.
Rotate the shaft by hand and make sure that the rotor rotates freely in the bearings. When the brushes are worn critically, a characteristic grinding noise will be heard.
Then check the integrity and fastening of the power and control cables. If visual inspection does not help to find the fault, the generator will need to be checked with a multimeter.
This procedure does not require a professional device with many functions. Three modes are sufficient: “continuity test”, “resistance measurement”, “voltage measurement”.
Checking the generator with a multimeter on a car
There is a methodically correct sequence of testing - from simple to complex.
Testing the relay regulator
This module is designed to maintain a constant voltage (as much as possible) at the output of the generator. When the car moves, the rotation speed of the generator shaft constantly changes.
The voltage “jumps” in the range from 12 to 20 volts. The regulator limits the value. Not only battery charging depends on its performance. When there is a surge or lack of voltage, all electronic components of the car are unstable and can simply burn out.
How to check the generator voltage with the engine running? Mode: “DC voltage measurement”, measurement limit: 20-50 volts. Measuring points – output contacts directly on the generator, or battery terminals.
The voltage should be between 14-14.2 V, at any crankshaft speed. Ask your assistant to press the accelerator several times while you watch the readings.
A car generator is the main source of energy in the on-board network, and if it fails or fails, you won’t be able to drive for long on one battery. This is why it is so important to monitor the performance of the generator.
The full range of generator checks includes:
In most cases, checking a car's generator with your own hands is not difficult, since no matter what car you check on, the principle is the same. But still, many car owners often wonder: how to check the generator with a multimeter or with improvised means?
How to check the generator without removing it from the car
There are two ways, using a multimeter and without it at all. The first, relatively new, is to do this, and the second, old and proven, is almost the opposite - the battery terminal must be removed with the engine running.
- Checking the battery with a multimeter first it happens at rest - the voltage should be in the range of 12.5-12.8 V. Then you need to measure the readings with the engine running, if 13.5-14.5 V is observed at 2 thousand revolutions, then everything is in order. Moreover, on new cars, even 14.8 V is quite normal, as manufacturers assure - the abundance of electronics affects it. In conclusion it remains check voltage under load, that is, by connecting consumers - stove, headlights, heating, radio. A dip in the range of 13.7–14.0 V is considered acceptable, but 12.8–13 V already indicates a malfunction.
- The second method, like many “old-fashioned” ones, is simple and trouble-free, but at the same time quite dangerous and requires caution. It allegedly works both on VAZs and on relatively new cars, like the Aveo. What is the point - loosen the bolt securing the negative terminal of the battery with a 10mm wrench, start the engine and give a small load, turning on one of the consumers, for example, the headlights. Then remove the terminal while the engine is running - if it does not stall and the headlights do not dim, then everything is absolutely fine with the generator, otherwise you can be sure that it is broken. You should try this method at your own peril and risk.
It is extremely undesirable to allow the generator to operate when consumers, especially the battery, are disconnected. This may cause the relay regulator to malfunction.
Having determined that there is a malfunction, you should dismantle and check the removed generator with a multimeter, a light bulb, and visually. Each of its elements is subject to verification separately.
| List of generator parts and applicable test methods | Visual inspection | Checking with a multimeter | Checking with a light bulb |
|---|---|---|---|
| Brushes | |||
| Slip rings | |||
| Diode bridge | |||
| Voltage regulator | |||
| Stator | |||
| Rotor |
The first step is to make sure that the alternator belt is well tensioned and the bearings are not broken. Extraneous noise and a very hot generator indicate wear of the bearings.
How to check brushes and slip rings
To begin with, the rings and brushes are visually inspected and their condition is assessed. For example, the minimum balance is measured (min. height of current collecting brushes is not less than 4.5 mm, and the min diameter of the rings is 12.8 mm). In addition, they look for the presence of grooves and furrows.
Brushes removed from the regulator brush assembly
Generator rotor slip rings
How to check a diode bridge (rectifier)
Diodes are checked by measuring resistance and detecting conductivity. Since the diode bridge consists of two plates, we check one at once and then the other. The tester should show diode conductivity in only one direction. Now, in a little more detail: we hold one tester probe on the “+” terminal, and with the other we check the diode terminals one by one, and then swap the probes (in one case there should be a high resistance, and in the other there should not be). Then we do the same with the other part of the bridge.
It should be noted that the resistance should not be zero, as this indicates that the diode is broken. Broken bridge diode even when there is no resistance on both sides.
Checking the diode bridge
Checking the slip rings
At least one an unusable diode leads to failure of the entire diode bridge and undercharges the battery.
The generator is the main source of current that powers the vehicle's electrical appliances. A malfunction of a car generator entails insufficient charging of the battery, which leads to a voltage drop, blackout and a complete stop of electrical appliances. For this reason, it is necessary to regularly check the serviceability of the generator and immediately respond to problems in its operation.
The content of the article:
Various signs and symptoms may indicate decreased performance and failure of the generator. The main ones are the appearance of noise of a different nature emanating from the generator, insufficient battery charge or its complete discharge. If the battery is not sufficiently charged, the car either cannot be started, or the engine may stall after some time of operation. This may also indicate that the battery has reached the end of its useful life.
Signs of mechanical damage to the generator
The presence of mechanical damage to the generator can be determined by the nature of the sounds it makes during operation. It can be creaks, whistles, rattling, howling, knocking. More often the problem in this case is wear or insufficient lubrication of the bearings. If the suspicious noises do not disappear after changing the lubricant, the bearings may need to be completely replaced.
The presence of extraneous noise can also be a consequence of an interturn short circuit in the stator winding. In a similar way, a malfunction of connections and contacts, a short circuit of the winding to the housing, manifests itself. All this indicates problems with the interaction of parts during generator operation. They can be identified by visual inspection of the mechanisms. At the same time, it is easy to detect unwanted winding short circuits, bad contacts and connections. Depending on the extent of the detected malfunctions, you can decide whether to fix them yourself or seek help from specialists.
Car generator voltage diagnostics
The reasons for the malfunction of the generator may lie not only in mechanical damage to its parts. To detect them, you should also check its output voltage. For this purpose, it is necessary to use electrical measuring instruments. Sometimes ohmmeters or multifunctional testers - multimeters - are used for this.
However, most often it is enough to use a voltmeter. It must be connected to the terminals of different poles of the battery and the car engine must be started.
The voltage at the battery terminals when starting the engine should not be less than 8 Volts. At the same time, the accuracy of measurements will be higher if they are carried out in an environment with a temperature of +20 C and a car engine that is already warmed up.
After fixing the indicators when starting the engine, you should gradually increase its speed to 3000 per minute. When such a load is reached, the voltmeter readings must be taken into account again. Recording measurements of less than 12.5 Volts will indicate a malfunction of the generator and the need for its repair.
The faulty generator must be dismantled by first disconnecting it from the battery terminals. Then you should unscrew the voltage regulator fastenings with a screwdriver. After this, carefully inspect and determine the degree of wear of the generator brushes, as well as its slip rings, and clean them if there is carbon deposits. Often the cause of generator failure is a faulty voltage regulator. Therefore, it must be periodically checked and changed if problems are detected.
After troubleshooting, a working generator is mounted in the reverse order of its dismantling. The final step of this process should be to carefully connect the ground.
After installing the generator, you should again check the voltage readings at the battery poles. When the engine is running at 3000 rpm, they should vary from 13.5 to 14.5 volts. These values mean that the generator's functionality has been restored and it is in good working order.
Checking the voltage regulator
The next diagnostic stage will be checking voltage stabilization. To do this, turn on the car's high-beam headlights and use a voltmeter to measure the voltage at the battery poles. A deviation of values not exceeding 0.4 Volts from previous measurements when starting the engine indicates the serviceability of the generator. Deviations towards the larger side indicate unstable operation of the generator; the search for the causes of its malfunction will have to be continued.
Checking the vehicle's power supply circuits
Further search for the reasons for the loss of functionality of the generator consists of diagnosing the vehicle’s power supply circuits. For this purpose you will also need an electrical measuring device. With its help, you first need to check the diode bridge. In this case, the voltmeter is connected to the generator and ground terminals. Device values exceeding 0.5 Volts indicate a malfunction of the diodes. To determine their breakdown, you should connect a measuring device between terminal “30” and the disconnected connecting wire of the generator. An acceptable electric current strength of less than 5 mA is acceptable.
Then the voltage regulator is checked. The engine should be warmed up for about a quarter of an hour at medium speed. In this case, all vehicle lights must be turned on. The field of this is measured at ground and terminal “30”. The optimal performance of the device in this case may differ depending on the type and make of the car, which can be found out from its technical characteristics.
Also, the regulated voltage indicators depend on the modification of the car and its parameters, which can be measured by connecting the tester to the battery. This measurement is carried out at maximum engine speed with all electrical appliances of the car turned on.
The serviceability of the field winding is checked by measuring its resistance. To do this, you can use a multimeter or ohmmeter. At the beginning of this operation, the voltage regulator and brush holder are removed. The winding and its integrity are visually inspected, and if necessary, the slip rings are cleaned. The meter is connected to the rings. The optimal resistance of working parts should be from 5 to 10 ohms.
A multimeter is necessary when diagnosing a short to ground. To do this, put the tester in the “ringing” mode, touch the armature body with one probe, and the contact ring with the second. It's simple: if it doesn't ring, it's working, if it rings, it's faulty.
Conclusion
Guided by these recommendations, you can easily diagnose a car generator yourself. To do this, you will only need certain skills in using the simplest tools for dismantling and assembling, as well as using electrical measuring instruments. However, for a more accurate check and thorough diagnostics, you should contact certified car services, whose qualified specialists, using special equipment, will quickly identify and eliminate all problems with the generator.
Video: how to check the generator
The main source of power in a car is a generator; it is like a “mini-power station”. Incorrect or unstable operation of this unit can result in a bad battery. A failed generator does not provide charging, therefore, the on-board network of the car will work on a battery that will not last long. As a result, the battery is completely discharged, the engine “stalls” somewhere outside the city, and you have a new “headache” and the need to replace the generator.
In order to prevent such a scenario, it is necessary to regularly monitor the condition of this device, as well as the charging it provides. If you notice any interruptions in operation, you need to check the generator, and you will now learn how to do this.
But before that, I think it is necessary to talk about precautions and certain rules that must be followed when checking this electrical appliance in order not to damage it.
!!! It is forbidden:
- Check the functionality of the generator by short circuiting, that is, “to spark.”
- Connect terminal “30” (in some cases “B+”) with “ground” or terminal 67 (in some cases “D+”).
- Allow the generator to operate without consumers turned on; operation with the battery disconnected is especially undesirable.
- Perform welding work on a car body with the generator and battery wires connected.
- !!! Important:
- The test is carried out using a voltmeter or ammeter.
- The valves are checked with a voltage not exceeding 12 V.
- When replacing the wiring of an electric generator, it is necessary to select wires of a similar cross-section and length.
- Before checking the device, make sure that all connections are working and that the drive belt is properly tensioned. A belt is considered to be correctly tensioned if, when pressed in the middle with a force of 10 kg/s, it bends no more than 10-15 mm.
How to test a generator with a multimeter or voltmeter?
Checking the voltage regulator
- In order to check the voltage regulator, you will need a voltmeter with a scale from 0 to 15 V. Before starting the test, you should warm up the engine for 15 minutes at medium speed with the headlights on.
- Measure the voltage between the generator ground terminals and “30” (“B+”). The voltmeter should show normal voltage for a particular vehicle. For example, for a VAZ 2108 it will correspond to 13.5–14.6 V. If the voltage is lower or higher, the regulator most likely requires replacement.
- In addition, you can check the regulated voltage by connecting a voltmeter to the terminals. It should be noted that the result of such a measurement will not be accurate if you are sure that the wiring is 100% intact. In this case, the engine should operate at medium speeds with the headlights and other consumers of electricity turned on. The voltage size must match a certain value for a specific car model.
Checking the generator diode bridge
- Turn the voltmeter into AC measurement mode and connect it to ground and terminal “30” (“B+”). The voltage should be no more than 0.5 V, otherwise there is a possibility of diode failure.
- To check the breakdown for ground, you need to disconnect the battery and also remove the generator wire that goes to terminal “30” (“B+”).
- Then connect the device between terminal “30” (“B+”) and the disconnected generator wire. If the discharge current on the device exceeds -0.5 mA, it can be assumed that there is a breakdown of the diodes or the insulation of the generator diode windings.
- The strength of the recoil current is checked using a special probe, which is an addition to the multimeter. It is something like a clamp or pliers that grips the wires, thus measuring the strength of the current that passes through the wire.
Checking the return current
- To measure the recoil current, you need to cover the wire that goes to terminal “30” (“B+”) with a probe.
- Then, start the engine and take a measurement; during the measurement, the engine should be running at high speeds. Turn on electrical appliances one at a time and take measurements for each consumer separately.
- Then calculate the readings.
- The following test must be carried out with all energy consumers switched on at the same time. The measurement value should not be lower than the sum of the readings of each consumer, when you measured each of them in turn, a discrepancy of 5 A downward is allowed.
Checking the generator excitation current
- To check the generator excitation current, start the engine and give it high speed.
- Place the measuring probe around the wire connected to terminal 67 (“D+”), the readings on the device will correspond to the value of the excitation current; on a working electric generator it will be 3-7 A.
To check the field windings you will need to remove the brush holder and voltage regulator. It may be necessary to clean the slip rings, and also check for breaks in the windings or short circuits to ground.
