A hub dynamo
is a small electrical generator built into the hub of a bicycle
wheel to power lights
. Modern hub dynamos are regulated to 6V 3W, although the best will drive 0.5A at up to 12V.
The market was largely pioneered by Sturmey-Archer with their Dynohub
product of the 1950s-1970s, which competed effectively with contemporary sidewall (bottle) and (later) bottom-bracket units. The Sturmey product was heavy, having a steel case, and like all bicycle dynamos of the time tended to overdrive the lamps at high speeds. Modern hub dynamos are greatly more sophisticated. Their electircal design is largely self-regulating, and lamp failure due to overvolting is now rare.