A vehicle-mounted electrical generating system has a first voltage system
which operates from a high supply voltage and a second voltage system
which operates from a low supply voltage that is substantially constant,
and an electrical generator for supplying power to operate the first
voltage system at a voltage determined by the level of field current of
the generator, with the field current being derived from the low supply
voltage of the second voltage system. The specifications of the field
winding of the electrical generator can thereby be optimally established
irrespective of the value of the high supply voltage.