A bottle dynamo or sidewall dynamo is a small

electrical generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas ...

for

bicycles A bicycle, also called a pedal cycle, bike or cycle, is a human-powered or motor-powered assisted, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A is called a cyclist, or bicyclist. Bic ...

employed to power a bicycle's

lights Light is an electromagnetic radiation, part of which stimulates the sense of vision. Light or Lights may also refer to: Illumination * Light bulb * Traffic light Arts and entertainment Music * Lights (musician) (born 1987), Canadian singer-son ...

. The traditional bottle dynamo (pictured) is not actually a

dynamo file:DynamoElectricMachinesEndViewPartlySection USP284110.png, "Dynamo Electric Machine" (end view, partly section, ) A dynamo is an electrical generator that creates direct current using a commutator (electric), commutator. Dynamos were the f ...

at all (which creates DC power), but a low-power

magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

that generates AC. Newer models can include a

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...

to create DC output to charge batteries for electronic devices including

cellphones A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive telephone call, calls over a radio freq ...

GPS receiver A satellite navigation device (satnav device) is a user equipment that uses one or more of several global navigation satellite systems (GNSS) to calculate the device's geographical position and provide navigational advice. Depending on the s ...

s. 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 A bicycle tire is a tire that fits on the wheel of a bicycle or similar vehicle. These tires may also be used on tricycles, wheelchairs, and handcycles, frequently for racing. Bicycle tires provide an important source of suspension, generate ...

. 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 dynamo A hub dynamo is a small electrical generator built into the hub of a bicycle wheel that is usually used to power lights. Often the hub "dynamo" is not actually a dynamo, which creates DC, but a low-power magneto that creates AC. Most modern h ...

s 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 A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...

. ; Price: A bottle dynamo is generally cheaper than a hub dynamo, but not always.

Disadvantages over hub dynamos

;Slippage: In wet conditions, the roller on a bottle dynamo can slip against the surface of a tire, which interrupts or reduces the amount of electricity generated. This can cause the lights to go out completely or intermittently. Hub dynamos do not need traction and are sealed from the elements. ;Increased resistance: Bottle dynamos typically create more drag than hub dynamos. However, when they are properly adjusted, the drag may be so low as to be trivial, and there is no resistance when the bottle dynamo is disengaged. ;Tire wear: Because bottle dynamos rub against the sidewall of a tire to generate electricity, they cause added wear on the side of tire. Hub dynamos do not. ;Noise: Bottle dynamos make an easily audible mechanical humming or whirring sound when engaged. Hub dynamos are silent. ;Switching: Bottle dynamos must be physically repositioned to engage them, to turn on the lamps. Hub dynamos are switched on electrically. Hub dynamos can be engaged automatically by using electronic ambient light detection, providing zero-effort activation. ;Positioning: Bottle dynamos must be carefully adjusted to touch the sidewall at correct angles, height and pressure. Bottle dynamos can be knocked out of position if the bike falls, or if the mounting screws are too loose. A badly positioned bottle dynamo will make more noise and drag, slip more easily, and can in worst case fall into the spokes. Some dynamo mounts have tabs to try to prevent the latter.

References

{{DEFAULTSORT:Bottle dynamo Bicycle lighting Dynamo, Bottle nl:Fietsdynamo tr:Bisiklet dinamosu

Advantages over hub dynamos

Disadvantages over hub dynamos

See also

References