Current alternatives
That the coil ignition and alternator-powered electrics on old British motorcycles have been objects of derision should come as little, or no, surprise.
Even in the 1960s, riders were sceptical about their reliability, as the six-volt batteries struggled to feed lighting and ignition through loose or corroded connections. No wonder then that Joseph Lucas, who was the founder of one of the biggest electrical equipment manufacturers of the 20th century, was fondly called the ‘Prince of Darkness.’
But that, I think, is unfair: we only had ourselves to blame. Electrics, as the Lucas epithet suggests, were a mystery to most riders despite their relative simplicity, and were neglected until the lights went out or the engine stopped.
Dynamo charging had been the mainstay on motorcycles since electric lights replaced gas in the 1920s; magnetos had been supplying the sparks since before the First World War. But the complexities of dynamos and magnetos, for all their ubiquity, made them costly to produce. No wonder then that the motorcycle manufacturers and their electrical suppliers looked for a less expensive and easier-to-maintain alternative.
Not for the first time it was the urgency of war that provided the impetus. Initially used on military machines, an alternator was developed in a collaboration between Lucas and BSA and in July 1951 the RM12 was revealed for a civilian application. Intriguingly, it was mounted within the timing chest, on the crankshaft of what appeared to be hailed the prototype as “an important milestone in motorcycle design”, bringing the “AC generator era very much closer”.
