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Generator
A generator (or "dynamo ") is a device for turning mechanical energy into electricity. Generator-powered bicycle lights have been available for many decades. Generators have the advantage of being ready to use at any time and costing nothing to operate.
Unfortunately, the output of a generator depends on the bicycle's speed. Generator lights go dark when the bicycle is stopped, and are dim at low speeds. Fast riding can cause the voltage to rise to the point that bulbs burn out prematurely.
The efficiency of LEDs has made generator lights more practical. Some generator systems now charge a small \battery or capacitor and keep the light shining when the bicycle is stopped.
The widespread availability of rechargeable batteries has considerably reduced the desirability of generator powered systems. The vast majority of bicycle generator systems only put out 3 watts; a very few put out 6 watts (when running at optimal speed.) Since rechargeable systems commonly put out 15 watts or more, at all speeds, they are generally preferable for most applications.
- "Bottle" generators, the most common type, are shaped like a bottle, with a small wheel at the "cap" which rubs against the side-wall of the tire.
- "Bottom-bracket" generators mount below the chainstays, and have a spring-loaded roller which presses against the tread of the tire. Bottom bracket and bottle generators frequently slip and fail when ridden in wet conditions.
- Hub generators are built into one of the wheel hubs. They usually consist of a stationary armature (coil) attached to the axle, with a revolving multi-pole ring-shaped magnet surrounding the armature. The best-known of these is the no longer available Sturmey-Archer Dynohub. Hub generators were unavailable for several years, but they are undergoing something of a renaissance in this century, with models from Busch & Müller, Shimano (Nexus ) and Sturmey-Archer. Hub generators are more expensive than other types, but they are more efficient, more reliable and silent.
