Signs of a “broken” generator diode bridge

Often, car enthusiasts are faced with the problem of a breakdown of the generator rectifier or diode bridge. This device is necessary to provide the car engine with full-wave current. At one time, the diode bridge became a replacement for the collector, which performed the functions of voltage rectification, and also increased the efficiency of the transformer with stabilization of the magnetic flux level.

Let's figure out why the diode bridge in a car generator burns

The main component in the electrical system of any vehicle is the generator. Without this unit, a serviceable car, even with a new, fully charged battery, will not drive for long. Therefore, this unit must be in working order at all times, that is, fully operational.

In this case, initial diagnostics of the car can be carried out without leaving the driver’s seat. However, repairs or detailed inspections require dismantling the DC source and then disassembling it to gain access to the diodes. But before this, the motorist must know the basic ways to check the diode bridge.

If a malfunction is detected

Diodes are attached to the wafers by pressing into a hole of a smaller diameter, so replacing a faulty semiconductor yourself is a troublesome task that does not guarantee 100% success. Diode bridges for domestic cars are inexpensive, so if a fault is detected, it is replaced with a new one.

Rectifier units of modern foreign cars cost a lot of money, so replacing the diode in such a bridge is economically justified. It is better to entrust this procedure to a specialist.

Faulty diodes are replaced with elements with the same power rating. Power reduction is not acceptable.

The quality of operation of the entire electrical system of the car depends on the condition of the diode bridge. If the previously listed signs of malfunction appear, you must immediately diagnose, repair or replace it.

How to determine the health of the generator

Information about the operating status of the main unit responsible for generating electrical energy in the car is displayed on the dashboard for the convenience of motorists. The icon on the instrument panel that resembles a battery should go out after starting the vehicle’s power unit. This means that the power to the main electrical components has been switched from the battery to the generator. If the indicator does not go out, this indicates a breakdown in the electrical circuit. Problems may also be indicated by insufficient battery charge due to the lack of normal current rating.

Is the generator working or not working?

Automakers displayed information about the operating status of the main unit that generates electricity in the car on the driver’s panel. The icon in the form of a battery with terminals should go out after the car is started. This means that the power has switched from the battery to the generator.

When the signal beacon does not fade away, this fact indicates problems in the circuit. Also, a weak battery charge confirms the failure to receive normal current.

Main signs indicating a faulty diode bridge

A normally operating diode conducts current in only one direction. In the event of a breakdown, a current leak appears, which flows from the on-board network to the starter windings. Today, several types of diode bridges are installed on cars:

• diode bridge without additional cooling;
• diode bridge with passive cooling due to special radiators.

In addition, there are different types of connecting windings and connecting bridge platforms: using welding or soldering. The first sign that the generator is operating unstably due to a broken diode bridge is the rapid and frequent discharge of the battery. There are other reasons why you can indirectly determine the combustion of diodes in a rectifier:

• insufficient spark on the spark plugs;
• headlights with dim light during operation of the power unit;
• interruptions in the sound system;
• significant reduction in cooling fan power;
• poor operation of the air conditioning system.

If any of the above-mentioned signs are noticed, there is no need to panic, but it is better to find out why the diodes burned out, for which you should seek help from the service station specialists.

Generator malfunctions - signs, diagnostics, causes, testing

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Malfunctions of vehicle electrical equipment are very common and occupy one of the leading places in the list of breakdowns. They can be roughly divided into faults of power sources (batteries, generators) and faults of consumers (optics, ignition, climate, etc.). The main sources of power for a vehicle are batteries and generators . The malfunction of each of them leads to a general malfunction of the car and its operation in abnormal modes, or even to immobilization of the car.

We prepare the diode bridge for self-diagnosis

You can check the functionality of the generator bridge on your own if you understand how the diodes are connected. But before you start diagnosing, you need to carry out preparatory measures. To do this, you need to the generator to gain access to the diodes:

• The fasteners (bolts) holding the front and back covers are unscrewed.
• The next step is to disconnect the housing from the starter winding.
• If the bridge structure is collapsible, then the assembly is unscrewed.
• The positive terminal is disconnected from the generator.
• The method of attaching the minus is checked. If the terminal is independent, it is disconnected.
• After removing the front wall, the bridge is disconnected from the windings. For this purpose, a soldering iron is used to heat the leads until the solder boils, after which they are carefully moved to the side using a screwdriver.

After completing the preparatory work, you need to figure out the question of how to properly check that the diode bridge has burned out ?

Generator repair kits

To eliminate these generator malfunctions, you will need to carry out repairs. When you start searching for a generator repair kit on the Internet, you should prepare for disappointment - the kits offered usually contain washers, bolts and nuts. And sometimes the generator can only be restored to functionality by replacing brushes, a diode bridge, a regulator... Therefore, the brave person who decides to repair it makes an individual repair kit from those parts that fit his generator. It looks something like this, as shown in the table below, using the example of a pair of generators for a VAZ 2110 and a Ford Focus 2.

Signs of diode failure

The main problem in a rectifier bridge is the diodes. You should start checking the unit that generates electricity in the car only after identifying the following indirect problems:

• the voltage at the generator output terminals is below 13.5 Volts;
• the indicator on the instrument panel inside the car continues to light after starting the power unit;
• the arrow on the voltmeter shifts to the red zone when readings are taken;
• The battery indicator does not light up after turning on the ignition.

Similar symptoms are detected when the voltage regulator breaks down; therefore, its serviceability is checked first. There are various reasons why a rectifier bridge fails, which requires its repair or complete replacement.

Types of generator faults

Due to the fact that any generator is an electromechanical device, there will be two types of faults - mechanical and electrical.

The first includes the destruction of fasteners, housing, malfunction of bearings, pressure springs, belt drive and other failures not related to the electrical part.

Electrical faults include winding breaks, diode bridge faults, brush burnout/wear, turn-to-turn short circuits, breakdowns, rotor beating, and relay-regulator faults.

Often, symptoms that indicate characteristics of a faulty generator can also appear as a result of completely different problems. As an example, poor contact in the fuse socket of the generator field winding circuit will indicate a generator malfunction. Suspicion may also arise due to burnt contacts in the ignition switch housing. Also, the constant lighting of the generator malfunction indicator lamp can be caused by a breakdown of the relay; the blinking of this switching lamp may indicate a generator malfunction.

The main signs of a faulty generator:

• When the engine is running, the battery discharge warning lamp flashes (or stays on continuously).
• Rapid discharge or overcharging (boiling) of the battery.
• Dim car headlights, a rattling or quiet beep when the engine is running.
• Significant change in headlight brightness with increasing speed. This may be acceptable when increasing the speed (re-throttle) from idle, but the headlights, having lit up brightly, should not increase their brightness any further, remaining at the same intensity.
• Extraneous sounds (howling, squeaking) coming from the generator.

It is necessary to regularly monitor the tension and general condition of the drive belt. In case of cracks and delaminations, immediate replacement is necessary.

Why does the diode bridge burn out?

There are many situations that can lead to diode failure. However, the most common breakdowns include the following:

• the board was flooded with water;
• dirt, together with engine oil, penetrated inside the bridge and led to a short circuit;
• The polarity of the contacts on the battery has been reversed.

Experts are considering several options for checking the functionality of the generator rectifier. The first method involves using a multimeter. In the second case, a standard car light bulb is sufficient.

Causes of breakdowns

Common causes of generator malfunctions are simple wear and corrosion. Almost all mechanical failures, be it worn brushes or collapsed bearings, are a consequence of long-term use. Modern generators are equipped with sealed (maintenance-free) bearings, which simply must be replaced after a certain period or mileage of the vehicle. The same applies to the electrical part - often the entire components must be replaced.

Also reasons may be:

• low quality components;
• violation of operating rules or operation outside normal operating conditions;
• external factors (salt, liquids, high temperature, road chemicals, dirt).

Diagnostics of a diode bridge using a multimeter

Before you understand why the diode bridge may be burning, you first need to dismantle the broken unit. After which a sound indication is installed on the measuring device. If such a function is not provided in the multimeter, then the test takes place in 1 kOhm mode. Individual measurements are carried out for all diodes. In the process of checking with the working contact, you need to touch the ends of the diode several times, while swapping the probes of the device. In one case, the test shows an infinitely high resistance, and in the second, the parameters should fluctuate in the range from 500 to 700 Ohms. If the measurement results turn out to be the same in different directions, this indicates that the diode under test has failed and needs to be replaced.

What causes the need to replace diodes

Someone will say that it is much easier to take and replace the diode bridge completely. However, the cost of a diode bridge for a foreign car varies from 1000 to 4000 rubles, sometimes the price is even higher. Depends on the brand of the car, the type of generator, whether it is an analogue or an original. New diode bridge or under contract. You ordered a diode bridge online, you thought it was new and original, but an unscrupulous storekeeper put a Chinese equivalent in your package. Go figure it out right away.

Many, having replaced the diode bridge on their generator, prefer not to throw away the old one, but to repair it and leave it in their stash.

The question is that not everyone can independently remove a bad diode and press in a new one. It is best to turn to the services of professional craftsmen at a service station. The diode bridge repair process is streamlined and will not take much time.

Checking the diode bridge using a light bulb

Naturally, not every car owner has a multimeter, and therefore you need to know how to check the vehicle’s generator using improvised means? To do this you need two pieces of electrical wire and a car lamp. The check itself involves the following simple steps:

1. The protective casing of the generator is removed and a diode bridge plate is connected to the negative terminal of the battery.
2. The wire from one end of the light bulb is connected to the positive of the battery, and with the other you need to touch the terminals of the remaining diodes and the connection points of the starter winding in turn.
3. If the lamp lights up at any terminal of the diode, it means that this element is faulty and needs to be replaced.

In some cases, it may be necessary to check the diode bridge for an open circuit, for which you need to carry out the following manipulations:

1. The wire from the negative terminal of the light bulb is connected to the negative terminal of the battery and in the same sequence as checking for breakdown of the diodes, they are tested. The only thing is that in such a situation the light should be constantly on.
2. If, during the test, the light on any of the diode terminals does not light up or its light is very dim, then the part has broken and will have to be replaced.

You can find out why malfunctions occur in the diode bridge of the generator yourself in a garage. In this case, you will need a regular tester, which almost every car enthusiast has, or a car light bulb with two wires.

How to check without dismantling

You can diagnose the device on site without disassembling the generator or desoldering the part. To do this, unscrew all the wires on the generator and voltage regulator, set the tester to ohmmeter mode, and connect the lamp to the battery in the manner described above.

This method allows you to check the serviceability of the entire bridge and individual groups.

Short circuit

For this test, the positive electrode is applied to output 30 of the generator (“plus” of the power rectifier), and the negative electrode is applied to the housing. A resistance value of 1 indicates that the bridge is in good condition.

One end of the lamp is connected to the negative terminal of the generator, the other to the positive terminal. A lit lamp indicates a short circuit.

Negative group

The negative electrode of the tester is connected to the frame of the generator, the positive electrode is connected to one of the diode bridge mounting bolts. The negative group is operational if the resistance is infinity.

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To check with a lamp, connect its minus to the generator casing, and the plus to the axle mounting bolt. The lamp lights up or flashes when there is a malfunction in the negative group of elements.

Positive

The positive probe of the multimeter is connected to the positive terminal, the negative one to the bridge mounting bolt. With a working group, the resistance is infinite.

The negative of the lamp is connected to the bridge mounting bolt, the plus is applied to the positive terminal. A lit lamp indicates a short circuit in the positive semiconductors.

Repair and troubleshooting

All mechanical problems are eliminated by replacing faulty components and parts (brushes, belt, bearings, etc.) with new or serviceable ones. Older generator models often require grinding of slip rings. Drive belts are replaced due to wear, maximum stretching or expiration of service life. Damaged rotor or stator windings are currently being replaced with new assembled ones. Although rewinding is common among auto repair services, it is becoming less and less common - it is expensive and impractical.

But all electrical problems with the generator need to be solved by checking both other elements of the circuit (in particular the battery), and directly its parts and output voltage. One of the common problems that car owners have to deal with is overcharging , or, conversely, low voltage of the generator . Checking and replacing the voltage regulator or diode bridge will help eliminate the first malfunction, but low voltage output will be a little more difficult to deal with. There may be several reasons why the generator produces low voltage:

1. increased load on the on-board network by consumers;
2. breakdown of one of the diodes on the diode bridge;
3. failure of the voltage regulator;
4. slipping of the poly V-belt (due to low tension)
5. poor contact of the ground wire on the generator;
6. short circuit;
7. dead battery.

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