How to Check a Bosch Alternator Relay

How to disassemble the alternator

After the alternator is removed. It must be inspected externally. Check for cracks. The rotor should rotate freely. There should not be any creaking or rattling sounds when it rotates. If the bearings are seized. This also leads to the loss of charge of the generator. The rotor is then sluggish. The force of magnetic flux fluctuates. As a result, it does not create the required voltage.

There must be no radial or axial misalignment of the rotor. This also results in a braking effect on the rotation.

Disassembly of the alternator begins with the removal of the brush assembly. On modern alternators, it is made in conjunction with a relay.

Removing the brush head

You have to unscrew the two mounting screws with a screwdriver. Remove the relay together with the brushes.

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If this is not done first. The slip-rings will be damaged. Because the carbon contacts are pressed against them by springs. And when you further remove the back cover. The contacts will catch on the rings. And pull it out. This can break the wiring.

Unscrew and remove the drive sheave.

the pulley is screwed on with the nut with a lot of force through the graver. So make sure you fasten the pulley firmly in place. To do this you have to put the old drive belt on the pulley. and squeeze it tightly in a vise. Unscrew the nut. Pull the pulley off the shaft with a pulley puller. It may not be possible to remove the pulley without a pulley puller. Because, in addition to being tightened by the nut. The shaft on which the pulley sits. It has a conical shape. That’s why the pulley sits tightly on the pulley

Dismounting the diode bridge

The block with diodes is fastened with screws. The contacts from the stator windings are bolted to it. After all nuts are unscrewed The diode block should be removed.

After the diode bridge is removed, the stator is removed

Remove Alternator Back Cover

Loosen the mounting bolts and remove the rear cover of the alternator. There is a bearing built into the cover. It will hold the cover in place. To remove the cover you need to apply an even force on opposite sides. And try to rock it. To allow the bearing to slide out of its seat.

Remove the front cover from the rotor

The more difficult part is removing the front cover. Because the bearing is pressed on the shaft. And it is fastened to the case from the back side with a special plate. When reassembling, first install the bearing. Then, together with the cover, it is pressed onto the shaft.

Therefore, when removing the front cover. It’s very important not to damage it with the puller. The cover is brittle and easily broken. The bearing seat should be lubricated with a penetrating fluid. For example WD-40.

The most effective way to press the bearing is as follows.

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A block of wood must be placed on a hard surface. Turn the rotor shaft upside down. Holding the cover, hit the end of the shaft against a block of wood. The method is 100% effective. But it doesn’t require any fanaticism. It is desirable not to damage the threads on the end of the shaft. So that there are no problems later on with tightening the nut. Do not hit hard. It may damage the cover.

Light, sharp impacts will gradually press the bearing from the shaft. Do not hit the shaft from above, not even through a block of wood. Because the impact is not exactly on the axis of the shaft. A non-axial shock will not work, and will make removal of the bearing more difficult. In addition, there is a high probability of destroying the front cover.

Replacement of automatic voltage regulator

Replacement of AVR with AVR in good order is not very difficult. It is enough to use a socket wrench to loosen a few screws that fix a protective cover of alternator to get free access to the AVR unit.

The block of automatic voltage regulator itself is an arc-shaped box with wires with sockets for 4 and 2 sockets (or two terminals). To replace AVR of three-phase alternator, it is enough to disconnect wiring harnesses and unscrew two bolts fixing body of the unit. It is necessary to observe polarity of wires instead of removed AVR block and usually terminals are marked with “” and “-“.

How to check the voltage regulator yourself

To check the working condition of the voltage regulator relay can be removed from the car. The second way is to diagnose directly on the machine. To perform the work you will need a control lamp and a tester, a multimeter.

It is also necessary to prepare in advance a special power supply or charger, wires, and make sure that the battery is in working condition.

  • In order to check the relay regulator you need to set the multimeter in voltmeter mode to be able to measure the DC current within the range from 0 to 19 volts.
  • Then connect the poles of the multimeter to the battery when the engine is switched off. Record the data, which shows the voltmeter. The voltage should be 12 to 12.5 volts. After that, the engine is started, and the voltmeter readings are recorded again. In the norm, after the start of the internal combustion engine, there should be an increase in values to an average of 13-13.5 volts.
  • Additionally note that the voltage should also increase with the growth of the engine speed. In the middle range, this figure is about 14 volts, at high speeds it goes up to 14.5.

The main sign, which indicates a malfunction of the regulator relay, is the same voltage both before and after starting the engine. For example, the battery was giving out 12 volt when the engine was stopped and this indicator didn’t change when the engine was started. Add that it is necessary to exclude other possible causes of the lack of charging the battery, after which the regulator relay is removed from the car for further testing.

Removing the Relay for Testing

To begin with, in modern cars, the alternator brushes are often structurally combined with the relay itself. It turns out, the relay regulator acts as a part of the brush unit and is mounted in the rear part of the car alternator (in the area of the armature contact rings). To remove relay unscrew fixing bolts and remove terminals, then relay is removed.

  • Check with a tester, a 12 volt bulb with a socket and some wires that have terminals. In addition you will need the above mentioned power supply unit which delivers up to 20 volts. Alternatively you can use a battery charger with current control instead of the charger. Note that the battery charger may not deliver DC current when there is no load. In this case it is necessary to additionally connect the battery to it, i.e. to give the load to the charger.
  • Then the leads and the lamp should be connected to the plus and minus pole respectively through a relay and the charger should be switched on. The control light should illuminate. Then the voltage is increased with the current regulator on the battery charger, with the parallel reading of the tester (or the voltmeter on the battery charger if you have one).
  • The light should continue to burn until the voltmeter reads 14.5 volts or more. After exceeding this level the lamp should go out. Decreasing the voltage will cause the control lamp to light up again.
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Testing a single relay

Similarly you can check the new type of regulator, that is separate, here the checking process is much easier. For example, take the model Ya112B, they were installed on many domestic cars (VAZ) before.

This is a separate element, so just unscrew it from the body (sometimes from the alternator cover) and connect to our stand, once again I want to remind you that it is desirable to have a 12V power supply, then the testing process is much easier. If not, use charger (with regulation modes) and connect according to lower diagram.

Checking is the same: if you increase the voltage up to 14,5V, the lamp should go off, if not, or it goes off at voltage much higher, then the relay is faulty and needs to be replaced.

Recommendations for extending regulator life

In order to increase the life of the voltage regulator, you need to adhere to a few simple rules aimed at implementing preventive measures. Among them:

  • avoid excessive pollution of the alternator, periodically inspect its condition and, if necessary, dismantle and clean the unit;
  • Check the alternator belt tension and retighten it if necessary (by yourself or at a car service center);
  • check the condition of the alternator windings, in particular, do not allow the windings to become dark;
  • check the contact on the control wire of the voltage regulator, both its quality and the presence of oxidation on it;
  • Perform periodic voltage checks on the car battery with the engine running.

Observance of these simple rules will allow you to increase a resource and service life of both an alternator and a voltage regulator of your car.

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Checking voltage regulator is not complicated, and almost any motorist with elementary skills of repair works can cope with it. The main thing is to have the appropriate tools for this. multimeter, power supply with voltage regulator (although you can connect to a battery with a charger), a lamp for 12 V and pieces of wire for mounting the appropriate circuit.

If during checking you found out that the regulator is out of order, it must be replaced (repair work is usually not performed). The main thing is not to make a mistake when choosing it and buy the part that is suitable for your car.

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Possible causes of failure

As the main causes of failure of voltage regulators of alternators are considered:

  • Interturn fault of the field winding. The most dangerous cause of malfunction. After replacement of a voltage regulator the alternator works for a certain period of time without any problems. But the regulator works at higher currents and burns out again after a couple of months. In this case, you must remove the alternator and take it in for testing;
  • Rectifier bridge failure (diode breakdown). Less dangerous, the more this malfunction causes overheating of the alternator, and diodes are replaced in the first place;
  • Re-polarization or reversal of the battery poles. In this case, the rectifier diodes also fail;
  • destruction of brushes;
  • short circuit at the control terminal of a voltage regulator;
  • natural wear and tear.

The consequences of a faulty voltage regulator can be significant:

  • High alternator voltage can cause damage to the vehicle’s electronics, so do not remove the battery terminals when the engine is running;
  • Internal shorting of a voltage regulator relay leads to overheating of the excitation winding and, ultimately, more expensive repairs;
  • Destruction of voltage regulator brushes may cause permanent damage of the alternator, its jamming, belt breakage and more serious consequences.

How to check voltage regulator?

Modern models of relays have a relatively long lifetime. But some factors can lead to premature failure of the element, namely:

Popular brands: Acura ZDX. Audi A7. Citroen C4. Infiniti Q60

Water ingress can also be the cause of malfunction.

On some models of alternators replacement of the electronic regulator relay is also necessary due to wear of brushes. Under normal conditions the service life of the voltage regulator is more than 60 000 km.

Testing of the relay with a dismountable brush unit and as a separate module

Often you can test a voltage regulator as a separate module, which eliminates the effect of possible effects on the results of the other circuits of the electrical equipment of the car. This procedure is possible with the execution of the relay:

  • In the form of a separate integrated module of the brush node;
  • in the form of an independent functional unit, which is mounted in the operating position on the car body using a bracket.

In the first case it is necessary to dismantle the brush unit and additionally remove the relay. In the second case, the relay is disconnected from the wiring and removed from the mounting bracket for convenience. The further procedure is identical to the previous case. The only difference is that the input of the tested object is already direct relay input.

The decision about the necessity of replacement of a relay is made in the same way, i.e. if it does not work or if it works with a voltage over 16 V. The strength of this testing scheme is the unambiguous conclusion about the technical condition of the relay and the precise localization of the failure location.

Checking an alternator with a vehicle oscilloscope

Diagnostics by oscilloscope allows simultaneously determine output voltage of alternator, correctness of voltage regulator and serviceability of diode bridge.

Small voltage fluctuations in the oscillogram are caused by the ignition system, when the power consumers are switched on.

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