Typical failures of alternators and starter motors

Some things to consider when looking at a failed alternator or starter motor

Typical failures of alternators and starter motors

AS-PL highlights the most common reasons for failure when dealing with alternators and starter motors.

Why does an alternator fail?

The alternator is an alternating current generator and is used to convert mechanical energy into alternating current. Current is generated in the stationary stator windings by the rotating magnetic field of the rotor.

Stator short circuit

During operation, it is in the stator that the current is converted. One due to short-circuit reasons, the current flowing through the winding may be exceeded. In addition, the battery cell may short-circuit, overload in the vehicle installation or, less frequently, the insulation of the stator winding may become mechanically abraded.

In the stator, the current is produced by the rotor – its work creates a magnetic field, and it is driven by the crankshaft. The defect in this part is related to the wear of the slip rings/carbon brushes that transmit the current from the regulator (the elements responsible for the current flow). The reasons for this defect are most often material wear during operation.

Voltage regulator damaged or burnt

The electronic module is a complex element, a microprocessor controller with the final PWM (Pulse Width Modulation) element, so there are many possible failures. One of the most common reasons is exceeding the current limit of the PWM transistor or mechanical damage to the module (no soldered or welded joints) and worn brushes transmitting current to the rotor.

Defective alternator bearings

A failure can be recognised by loud operation and an increase in noise along with an increase in engine speed. There can be many reasons, from purely operational wear of the parts, to poor quality of the material, to external contamination. Unpleasant noise can also be generated by a worn pulley, which will also damage the V-belt. As a result of prolonged use, the belt may break and expose the car user to high costs.

Why does a starter motor fail?

As long as internal combustion engines do not completely give way to hybrid or electric drives, the starter, i.e. the DC motor, will play an important role in the standard system. It rotates the engine’s crankshaft and gives it the appropriate rotational speed at which the engine can start to work independently.

The starter uses the most electricity from the battery, but only for short periods during engine starting.

No reaction after turning the key

The culprit may be a damaged ignition switch or a discharged battery. However, if the battery is charged, the reason can be found in the starter. It is worth checking if all current and control cables (power supply of the electromagnetic switch/automatic unit) are clean and without any tarnish and that the terminals/ring terminals have been tightened.

Another reason may be damage to the windings of the electromagnetic switch or wear or jamming of the brushes, which results in a lack of connection with the commutator.

Starter turns but is unable to start the engine

The reasons are to be found in the damaged bendix. Its teeth probably do not engage with the flywheel and there is a characteristic noise of the so-called grind. The Bendix is built on the principle of a one-way clutch, which means it passes in one direction, and in the other it should ‘take’/drive the flywheel rim – it happens that the clutch is damaged, i.e. it is passed in both directions.

Breaks can also be a reason for low and irregular rotation in the electrical circuit of the rotor or stator. With such a fault, in an extreme situation, the rotor simply ’will not start’.

The starter is making excessive noise

The symptom may be excessive wear of the coupling sleeve or worn pinion teeth on the flywheel rim. When the starter rotates the flywheel irregularly, the clutch assembly is likely to have failed.

The starter does not finish its work

We can deal with damaged pinions here. Mechanical wedging of the teeth may occur and hence delayed retraction of the Bendix. The longer work of the Bendix with the flywheel rim is manifested by discoloration of this element by friction.

If the starter continues to work after starting the engine and ‘releasing’ the key (the key automatically returns to a lower position), the fault is most often the fault of the ignition switch, and less frequently there is a short circuit in the electrical system or a sticky core of the electromagnetic switch.

In this situation, discolouration will occur as a result of friction and the Bendix will be damaged. It happens that the reason for the further operation of the starter (the bendiks is retracted) are ’welded’ contacts in the electromagnetic switch (‘stuck’ contacts, which remain closed after disconnecting the ignition switch).

This usually takes place when the contacts and the spring in the dome of the electromagnetic switch are already worn – high current flows in a limited place of contact, which causes local melting and ‘welding’ of two planes.

Most often, after a while, the spring in the dome, used to ‘secure’ disconnection of the contacts, causes the splice to break and the circuit to be disconnected. If the spring or vibrations (caused by holes in the pavement) do not release this contact, the rotor and stator will be damaged in a short time, because the electric motor of the starter and its construction are designed for temporary operation. This malfunction is very rare.

Have your say!

0 0

Lost Password

Please enter your username or email address. You will receive a link to create a new password via email.