get charging started, it is required that the field is slightly magnetic (the remanence). the bit of power thus generated, is diverted to the field coil, which
makes it more magnetic, the dynamo then generates more power, the magnetic field
becomes more powerful etc.
resistor is mounted In series with the field
coil. In the start up phase, this is shorted by a relay switch. When the desired
voltage is achieved, the switch opens and less power is sent to the field coil.
This switching goes on several times per second
time, this switch gets dirty ond worn, and the load becomes less effective.
relay switch connects the dynamo to the battery, when the dynamo voltage get
high enough, since otherwise, the battery will be drained.
the electronic control box, this switch is replaced by a large diode
(rectifier), which prevents the current flowing backward, and allows charging to
regulating switch and the resistor is
replaced by a large transistor, no dirty contacts.