MODERNISING A CLASSIC DESIGN
A dynamo is essentially just copper wires spinning between two electromagnets. The more current you put into those magnets, the stronger the field becomes and the more electricity the dynamo generates. When the dynamo is not required, turning down the feed to the magnets turns down the output from the dynamo – this is what the regulator does.
The faster you spin a dynamo the more it outputs, so you have to control the output at higher engine revs. Before regulators came into use, they did this in the 1920s by developing the three-brush dynamo – the two main brushes cope with the charging currents, but the third brush picks up current from the commutator and feeds it to the field windings (magnets). Moving the position of this third brush around the commutator changed how much current it picked up and hence the dynamo’s output. Its position would be selected by putting on all the vehicle’s lights, starting
