Pioneered by Sturmey Archer during the second world war, the
heavy Dynohub dynamos were a common sight on bikes in the UK until the 1970's. Sturmey
Archer are probably better known for their three speed gear hubs (even the
Raleigh Chopper used them), and they even put both the dynamo and gears into some rear hubs - known as the AG - but, due to lack of investment and cheaper overseas alternatives, they stopped making them completely in the 1980's
. Since then a lot of other makers have come to the fore in the UK.
Busch and Muller from Germany
have been making lights since 1925 - Schmidt Original Nabendynamo (SON),
another German manufacturer, puts out enough power to light two 6 volt lamps in
series at speeds above 12 mph. Shimano also offer a number of hub dynamos under
their Nexus brand, as do SRAM who manufacture the i-Light dynamo. Efficiency is
obviously the key to dynamos and whilst a car alternator can achieve 90%
efficiency, most bicycle dynamo hubs can only manage 65-70% -meaning that just
over 5W of the rider's output is diverted to produce 3W of electrical power at
Sturmey Archer have recently re-entered the
market with their new X-FDD model which combines their new dynamo with a 70mm
drum brake in a lightweight aluminium housing.