Against the background of numerous and varied problems with the battery charging unit, characteristic generator malfunctions are more common than others. If you know about them, as well as about the primary signs of their manifestation, the problem can be found and eliminated in 95% of cases. Moreover, of the ten breakdowns described, about half can be safely discarded, since ordinary users encounter them very rarely. Thanks to this, even novice motorists have good chances to "diagnose" themselves and, possibly, fix the generator malfunction with their own hands.
If self-repair is not expected, the knowledge gained from this article will help to identify the breakdown in a timely manner. And these are already good chances to seek help from a specialist early, and get by with a simple and relatively inexpensive repair, avoiding buying a new generator. In the end, no one has yet canceled the dishonesty of car services. In practice, it has been proven that if you go to the master with at least an approximate understanding of the problem, the chances of cheating you by imposing non-existent problems tend to zero.
A short list of typical generator faults
To begin with, we briefly list the characteristic malfunctions of a car generator without any explanation. This will allow in general terms to assess, so to speak, the scale of the disaster. It is possible that some of the failures listed in the list are already familiar to you. As a rule, these include those that are very common, and almost every first motorist with little experience has come across them at least once.
So, here are 10 characteristic faults of a car generator:
- Poor contact or damage in the battery charging circuit.
- Slip or broken drive belt.
- Worn or damaged rotor bearings.
- Worn or stuck brushes.
- Wear of slip rings.
- Incorrect operation or failure of the voltage regulator relay.
- Interturn short circuit or open circuit in the generator windings.
- Breakdown of rectifier bridge diodes.
- Broken rectifier bridge diodes.
- Insufficient generator power.
We will return to a detailed examination of each of these failures. As well as to the symptoms by which these malfunctions can be identified.
The device and principle of operation of the car generator
First, it would not be superfluous to at least in general terms get acquainted with the device of the generator, as well as with the principle of operation of this vehicle assembly. Many motorists, unfortunately, always skip this stage, immediately proceeding to the diagnosis and repair. As a result, due to a misunderstanding (or misunderstanding) of the principle of operation, things often come to a standstill, serious mistakes are made, short circuits are provoked and more serious breakdowns than they were before. This implies the conclusion that the search for and elimination of any malfunctions of a particular vehicle unit must begin with the study of its structure and principle of operation.
The car generator is designed and works as follows. Actually, the electricity used to power the on-board network and charge the battery is generated by electromagnetic induction. It is removed from the terminals of the stator windings, inside which the rotor rotates on two bearings. The rotor is driven by the crankshaft of the engine, to which it is connected by a belt.
The first feature that you need to know about is the uneven speed of rotation of the generator rotor. It depends entirely on what RPM the engine is running at. Accordingly, if the rotor were fed (for excitation) with the same voltage, then at the output of the generator we would get a jumping voltage, which is unacceptable for the car's on-board network.
This problem is solved quite simply. The rotor is not supplied with a stable voltage, but an adjustable one. The relay-regulator is responsible for this, which “monitors” the voltage at the battery terminals, and, depending on the current indicators, corrects the power supply to the rotor. Roughly speaking, when the generator output voltage reaches the upper allowable mark (for example, 14.4 volts), the relay-regulator circuit stops powering the rotor. The output voltage drops, PPH resumes excitation of the rotor, and so on in a cycle with a very high frequency. Due to this, the voltage of the on-board network is constantly maintained at the same level, and does not depend on the speed at which the car's engine is running.
The second feature of the car generator is that it generates an alternating three-phase voltage. And to power the on-board network and charge the battery, it must be constant. To solve this problem, the generator is equipped with a rectifier bridge consisting of diodes. As a rule, the rectifier has six main diodes (two for each phase), as well as three additional ones.
In principle, this knowledge will already be enough to understand the typical generator malfunctions described below. Although for a successful self-repair it does not hurt to delve into the topic using additional sources of information.
Poor contact or damage in the battery charging circuit
In order for the generator node to work, it must be securely connected to:
- Positive battery terminal.
- Ignition lock.
- "Mass".
Let's start with the last one. The generator is in contact with the "mass" due to its metal case, with which it is fixed to the car engine. As a rule, in this place the contact is always good, and almost never causes a node malfunction. However, it should be remembered that the engine itself is connected to the negative terminal of the battery using a wire. And this is where problems often arise.
The most common of these is poor contact. In most cars, ground is connected to the engine somewhere at the bottom. Dirt, moisture, temperature differences, leaking oil and other factors lead to oxidation and corrosion of the joint. It manifests itself in the form of several symptoms.
Firstly, due to a bad “mass”, there may be voltage drops on the vehicle’s on-board network. As a result - a systematic undercharging of the battery. Secondly, there are significant voltage drops when a serious load is turned on - a stove, an air conditioner, a subwoofer, headlights, and so on.
Checking the "mass" of the engine is very simple. To do this, using a multimeter switched on in ohmmeter mode, the resistance between the negative terminal of the battery and any point on the engine is measured. If the device shows more than 0.05 ohms, the "mass" should be cleaned of dirt and oxides. It may be necessary to replace or even add another wire connected in parallel with the main one. Due to this, the cross section of the “ground” wire increases, and very often problems such as voltage drop or undercharging of the battery are solved.
Absolutely the same with the positive power wire of the generator. It goes directly to the battery, and has a rather serious thickness. If this wire is damaged or has poor contact at the attachment points, the symptoms described above appear. The malfunction is eliminated by simply cleaning the contact pads. If the wire is mechanically damaged (as a result of negligence, corrosion or vibrations), then it must be replaced with a new one, observing the cross section.
Additionally, the condition of the contacts of the control wire coming to the generator from the ignition switch (thin), as well as the signal wire (on the relay-regulator) is checked. Bad contacts at these points also lead to unstable and incorrect operation of the entire battery charging unit.
Slip or broken drive belt
Drive belt slippage can be caused by several reasons. Firstly, its insufficient tension. Secondly, getting water from puddles or engine oil on the generator pulley. Thirdly, the belt stretches over time, sags, and also begins to slip periodically. As a rule, at first, this malfunction appears only when the generator starts to work under serious load. This is because as the load increases, the resistance of the rotor increases.
Very often, belt slippage is determined by the characteristic squeak that is heard when the engine starts, as well as immediately after turning on the load. Quite often, this whistle can be heard in rainy weather, which indicates that water has entered the generator pulley. If this happens, the belt must either be tightened or replaced with a new one.
A broken alternator belt is a more serious malfunction, which is highly desirable to notice immediately after its occurrence. The primary symptom is a warning light on the instrument panel, indicating that the battery is not charging. This lamp should only be on when the ignition is on and the engine is off. In all other modes, it does not glow.
A secondary symptom of a broken alternator belt is a low voltage on-board network. When everything is working normally, the voltmeter should show at least 13.8-14.5 volts. If, while driving, the voltage drops to 12 volts, this means that the on-board network is powered only by the battery. Conclusion - the generator is faulty.
Wear or destruction of rotor bearings
When alternator rotor bearings are worn, several problems can arise. Firstly, due to a violation of the axis of rotation of the armature shaft, it begins to touch the stator with its windings. Secondly, as a result of significant wear, the bearings can generally jam, and the rotor will stop. The first problem will entail, first, a voltage drop in the on-board network, and later - to an interturn circuit in the stator. What will happen when the bearings are jammed - and so it is clear. The rotor will stop.
In most cases, the wear of the generator bearings can be detected in advance by the characteristic hum coming from under the hood. This sound can change volume and tone depending on what load is currently assigned to the car's on-board network. That is, for example, when the headlights are turned on, the hum can increase significantly, which makes it possible to detect a malfunction in advance.
To avoid the problems described, it is highly advisable to periodically check the bearings for play. To do this, just grab the alternator pulley with your hand and shake it from side to side. With good bearings, there should be no play.
Worn or stuck brushes
Brushes are needed in order to supply power to the constantly rotating generator rotor. As a rule, together with the relay-regulator, they are one separate part. The brushes are made of conductive graphite and are spring-loaded to ensure reliable contact with the commutator. If the contact between them and the slip rings is bad (or absent), the generator will not be able to work normally (or will not work at all).
The most common failure associated with brushes is their natural wear. When the graphite wears out, the brushes are simply not long enough to power the rotor. As a rule, at the initial stage, this malfunction manifests itself in the form of abundant sparking inside the generator. Due to wear, the brushes do not always make close contact with the commutator, and sparks form between these parts.
The second characteristic malfunction of the generator is associated with the so-called freezing or sticking of the brushes. This happens due to the ingress of graphite dust or other dirt into the brush guides. The latter become immobile, and therefore can no longer be pressed against the collector by springs. As a result, increased sparking is first observed, and then the generator stops producing electricity altogether.
Along with sparking, critical wear or sticking of brushes can be detected by voltage drops on the on-board network (if there is a voltmeter in the cabin) or by a warning lamp on the instrument panel. It should also be noted that this malfunction can be detected visually without removing the generator from the vehicle. The brush assembly, as a rule, is easily removed together with the relay-regulator, as it is attached with two screws. If the brushes are worn, then this is only a replacement. Sticking can be eliminated by cleaning the guides from graphite and other dirt.
Wear of slip rings
The slip rings are located on the generator rotor shaft. They are designed to transfer power from the brushes to the armature winding. Rings are made of copper, and therefore wear out over time. The symptoms of this malfunction are exactly the same as in the case of brushes - sparking, voltage drops, as well as a complete failure of the generator. To clarify the diagnosis and eliminate the breakdown, dismantling and complete disassembly of the assembly is required. Fortunately, on many common generators, these parts can be changed without problems, and are relatively inexpensive.
Incorrect operation or failure of the RPH
The voltage regulator relay “suffers” from several types of breakdowns, which are quite easy to diagnose even without disassembling the generator. The first sign of its malfunction is the low voltage of the on-board network. Drawdowns can be observed both without load and with it. This happens due to the fact that electronic components burn out in the relay-regulator circuit.
The second known sign of a node malfunction is that the generator does not work at all. This is determined both by the control lamp on the instrument panel, and by the readings of the onboard voltmeter. The latter in such cases begins to show a voltage in the region of 12 volts. As the battery discharges, the performance drops noticeably.
It is worth noting that more than half of the described generator malfunctions manifest themselves in approximately the same way. In particular, low voltage and a lit control lamp may indicate both a failure of the relay-regulator and other breakdowns. To identify the malfunction more accurately, there is a fairly simple method for checking the voltage regulator relay. It is performed using an adjustable power supply and a multimeter according to the following algorithm:
- The relay-regulator is removed from the generator.
- A multimeter is connected to the brushes in the voltage change mode (you can also use a 12-volt control light).
- The minus of the power supply is connected to the "mass" of the relay-regulator.
- Plus is fed to the wire that comes out of the relay-regulator.
- The power supply voltage rises to 14.0-14.5 volts.
- Upon reaching this voltage, a working relay-regulator should work - the control lamp connected to the brushes goes out.
If the control lamp does not light up at all at any voltage, there is an open in the relay-regulator. If the lamp does not turn off when the control voltage is reached (14.0-14.5 volts), but continues to glow further, this is called a relay-regulator breakdown. In practice, the first outcome means undercharging the battery, and with the second, it is overcharged (with boiling, swelling of the case, and even an explosion).
The so-called new-style relay-regulators (with two wires) are a little more difficult to check, but possible. The difference lies in the fact that a simulated alternating voltage must be applied to the second wire during testing. How to do it at home can be found on the Web.
Interturn short circuit or open circuit in the generator windings
The symptoms are the same - first, voltage drops on the on-board network, and then a complete failure of the generator. With an interturn circuit, if you immediately pay attention to this, you can detect a very strong overheating. Unfortunately, it is impossible to more accurately identify these types of generator malfunctions without dismantling and partial disassembly.
Breakdown or breakage of rectifier bridge diodes
Recall that the diode bridge is used to rectify the alternating voltage generated by the generator stator windings. Since there are three phases in a car generator, the bridge also consists of three branches - two diodes each. When a breakdown of one of the diodes occurs, a sharp increase in voltage in the vehicle's on-board network can be observed. A breakdown is when a diode begins to pass current in both directions, but it should only in one.
A break in the rectifier bridge diodes does not threaten anything catastrophic, unlike a breakdown. For example, if one of the diodes goes into a break, then only two of the three phases continue to work. If there is no large load on the on-board network, then this malfunction may not be noticed. However, when the load is turned on, the power of the two phases is no longer enough, and therefore there is a drawdown of the on-board voltage.
It is clear that when all the diodes break, which does not happen so often, the generator stops functioning completely. This can be seen both in the voltage of the onboard voltmeter and in the control lamp on the instrument panel. For a more accurate check of the bridge diodes, it will be necessary to dismantle the generator and partially disassemble it.
Insufficient generator power
A fairly common problem in our time, which, in fact, is not a malfunction. It consists in the fact that after installing any powerful freelance equipment on a car, wild voltage drops are observed. These symptoms may well indicate that the power of the existing generator for the load assigned to it is not enough.
This is most often observed after installing powerful acoustics, xenon headlights, an inverter that allows you to get 220 volt variables on board the car, and so on. This "malfunction" is eliminated very simply - by selecting and installing a more powerful generator. Unfortunately, this decision is often made even when the standard generator cannot withstand the load and burns out.
VIDEO: how to test car generator
Brief summary
Most of the characteristic faults of the car's generator are very easy to identify and eliminate even without the appropriate experience. If the generator is running, but the problem comes down only to voltage drops or sparking in the brush assembly, it is solved by cleaning the contacts or replacing the relay regulator. Extraneous sounds from the generator side - are eliminated by tightening or replacing the belt, as well as installing new bearings. The rest of the faults - short circuits in the turns of the windings, breakdowns and breaks of diodes, etc. - are best left to specialists, since their elimination requires not only bare knowledge, but also experience.
