The rated voltage of an automotive supply system is only a nominal value, such as 12 V, 24 V or 36 V.In reality this voltage will vary by some volts (to higher or lower values). Occasionally it could also vary by some ten volts or some hundred volts.
There are several reasons for such transient disturbances: Starting of the engine, alternator ripple, contact-braking spikes, alternator load dump or a chattering relay contact.
Now, automotive electronics should be capable to operate under these circumstances - without getting disturbed and, most of all, without getting destroyed.
As proof for this capability there are several standardized test methods, such like DIN 40839 part 1, ISO 7637-1,
In these standards there are EMC phenomenas described, such as switching-off of inductive loads or motor loads, the start of a combustion engine or a broken battery cable (alternator load dump).
But as individual as a particular type of car is, as individual is the supply system. For this reason every car manufacturer has it´s own requirements regarding EMC and supply system characteristics.
Those requirements could comprise special test methods or special wave shapes, which could be different from standardized test methods.
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