Diagnostic of car alternators with oscilloscope

When testing an alternator, it is very useful to use an oscilloscope to visually analyse the amplitude and shape of the voltage it produces. The oscilloscope will show how well the alternator is working and recognise the cause of the fault.

 The most common faults that an oscilloscope test can help to identify are:

• Diode failure or breakage in the diode bridge;
• Short circuit of stator windings (intercurrent, to the stator case or interwinding).

If the fault is present, in these situations, there will be large voltage ripple (large AC component).

Diagnostic Methodology

The use of an oscilloscope when testing an autogenerator, will minimise the list of possible faults. The oscilloscope is used in many areas of electronics. When testing an oscilloscope, an oscilloscope will help you see the waveform and determine if a signal is present at all. But, it is always worth remembering that analysing the operating condition of the generator with an oscilloscope is based on the amplitude of the output voltage fluctuations.

There are some other peculiarities of the procedure that you should be aware of. The difficulty in performing an oscilloscope test lies in the need to obtain a stable oscillogram. Even when the test is successful, you need to be able to interpret the results correctly and intelligently. The results of the test can be understood by someone with the appropriate qualifications and experience in this field.

Professional generator diagnostic equipment

Oscilloscope – is a simple way of checking, which is not suitable for diagnosing all alternators and all cars. That is why services and service stations use professional equipment (benches and tools) to carry out quality diagnostics.

For example, stand MS006 checks 12 and 24-volt auto generators (with a maximum load of 50A and 25A respectively). It helps to determine the cause of the failure and to test the generator after repair. It is already equipped with an oscilloscope, can print out diagnostic results and has many additional features.

The MS002 COM alternator and starter test bench tests 12V generators up to 200A and 24V–100A. It is powered by a 3-phase 380V mains supply.

The MS004 COM is suitable for diagnosing starters and alternators. Maximum load for 12V generators – 100A, for 24V generators – 50A, such load is enough to check the unit for serviceability. The stand is powered from 220V single-phase network. The compact stand is suitable for small workshops, it can be easily placed on the desk of a car service technician.

See more information about MSG Equipment's professional equipment for car workshops and service stations on our website.