Generator (alternator) for your car

Electricity from the generator

The dynamo or generator generates the necessary electric current for the car. Until a few years ago, the number of electric consumers in a car was relatively low: light, ignition, starter, horn and radio were the only applications requiring electric energy. This has changed considerably. The increased demands resulted into changes in the generator's layout.

Construction of a generator

A generator consists of

• rotor
• stator
• housing
• consumer
• bearing
• drive

The rotor is a rotating shaft with three or four coils. It is driven by a belt disc within the stater, also consisting of copper coils. Both components generate magnetic fields. Competing fields generate electricity, developing in the rotor and transmitted to a copper ring. Two carbon pins grind against it, taking up the electrons. The carbon pins, alternatively called carbon brushes transmit the electricity to the diodes, where it is made available for the electricity network of the car. Via two cables the electricity is ultimately transmitted to the car.

Defects of a generator

The carbon brushes are the typical wear parts of a generator. They are fixed with a single screw. The carbon brushes can easily be replaced and cost little money. Worn carbon brushes are noticed through falling performance of the generator. Additionally, the copper ring is worn by the permanent grinding of the carbon brushes. Replacing this is more complicated. The bearings are also generator components susceptible to wear. This can be heard by a characteristic rattle. Bearings can be replaced, although this is very complicated and generally not worthwhile If the coils of the stator or rotor burn through, the generator is beyond repair and must be replaced.

Altered requirements

In the past a generator only had to produce 6 Volt. Afterwards, the 12V generators were standard for family cars. Modern and comfortable cars nowadays have considerably more consumers, such as:

• sensors
• seat heating
• steering wheel heating
• heated side mirror
• navigation devices
• entertainment systems

and many more. The generators are required to produce a higher voltage. Presently, 14.4 V is the new standard. The trend continues.

Constructional changes

The increased demands should not only be attained through larger generators, which would unnecessarily increase the weight and price of a car. Instead, the available generator is made to run faster. This results in higher wear for the bearings. For this reason, generators are no longer driven by a V-belt. Standard drive for generator nowadays consists of

• flat belts
• freewheel
• belt tensioner

The freewheel gear allows the generator shaft to accelerate in one direction only. In case of load change it can continue running. Its deceleration is prevented and the bearings are spared. This makes the modern generators equally durable despite their increased performance.

Life span of a generator

At 100.000 km, the generator gradually starts to wear down. Often, the generators can be repaired at the first signs of fatigue by replacing the carbon brushes. If bearings and consumers fail, repair will generally be more expensive than a new generator.

Costs for a new generator

Prices for a new generator from a branded manufacturer start at ca. 150 EUR (c. £135). As a rule, cheaper generators have a shorter life span. A new generator is supplied with fresh carbon brushes, new diodes as well as a new freewheel gear, enabling you to solve all problems in this area with a few actions. A complicated disassembly and repair of an old generator is therefore not really worthwhile.