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A bottle dynamo or sidewall dynamo is a small electrical generator for bicycles employed to power a bicycle's lights. The traditional bottle dynamo (pictured) is not actually a dynamo, which creates DC power, but a low-power magneto that generates AC. Newer models can include a rectifier to create DC output to charge batteries for electronic devices including cellphones or GPS receivers.〔(Treehugger.com ) Pedal & Power phone charger〕 Named after their resemblance to bottles, these generators are also called ''sidewall dynamos'' because they operate using a roller placed on the sidewall of a bicycle tire. When the bicycle is in motion and the dynamo roller is engaged, electricity is generated as the tire spins the roller. Two other dynamo systems used on bicycles are hub dynamos and bottom bracket dynamos. == Advantages over hub dynamos == * No extra resistance when disengaged: When engaged, a dynamo requires the bicycle rider to exert more effort to maintain a given speed than would otherwise be necessary when the dynamo is not present or disengaged. Bottle dynamos can be completely disengaged when they are not in use, whereas a hub dynamo will always have added drag (though it may be so low as to be irrelevant or unnoticeable to the rider, and it is reduced significantly when lights are not being powered by the hub). * Easy retrofitting: A bottle dynamo may be more feasible than a hub dynamo to add to an existing bicycle, as it does not require a replacement or rebuilt wheel. * Price: A bottle dynamo is generally cheaper than a hub dynamo, but not always. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bottle dynamo」の詳細全文を読む スポンサード リンク
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