A dynamo is a device typically located in the hub of a bike\u2019s wheel that converts the energy generated by the wheel spinning to electrical energy. That power is then used to run front and rear dynamo lights on the bike, providing always-on illumination without the need to charge lights.<\/p>\n In this guide we\u2019ll explain:<\/p>\n <\/p><\/div> <\/section> A dynamo hub produces electricity by passing powerful permanent magnets, usually embedded into the shell of the hub (the rotor), over a coil of wire (the stator).<\/span><\/p>\n This process is called electromagnetic induction and is, in simple terms, the opposite of how an electric motor works.<\/p>\n Most dynamo hubs produce six volts at a typical maximum power of three watts. The power produced by a dynamo will increase as your speed increases.<\/p>\n The electrical connection on the hub that connects to your lights usually takes the form of a two-prong plug on the driveside of the hub, but connectorless systems that are integrated into a bike\u2019s fork do exist.<\/p>\n Most dynamo hubs are located on front hubs, though a handful integrates the dynamo into the rear hub.<\/p>\n Dynamo hubs are available to fit most bikes, including rim and disc brake variants, as well as thru-axle and quick-release options.<\/p>\n In addition, dynamo hubs are also available to suit different wheel sizes<\/a>. This is because smaller wheels spin faster compared to larger wheels at any given speed.<\/p>\n As such, when riding at high speeds, using a dynamo hub designed for 700c wheels on a 20in folding bike could increase the risk of damaging your light from overvoltage.<\/p>\n A number of wheel manufacturers, including Hunt, Halo and Prime, offer complete wheels with dynamo hubs, but many riders choose to build their own wheels around their preferred hub.<\/p>\n Bottle dynamos (also known as sidewall dynamos) work in a similar way to a hub dynamo. However, instead of being embedded into a hub, a bottle-shaped generator that\u2019s bolted onto the seatstays runs a small wheel on the outside edge of a bicycle\u2019s tyre or rim to generate power.<\/p>\n These have the advantage of being easier to retrofit to a bike and are typically cheaper than a hub dynamo. They can also be fully disengaged when not required.<\/p>\n However, they can slip in wet or muddy conditions and are usually noisier when running.<\/p>\n For the pedants out there, most dynamos are technically single-phase alternators (a magneto if you want to be really specific) that produce alternating current (AC).<\/p>\n The key difference is that a dynamo in the strictest sense of the word produces direct current (DC). As such, it\u2019s technically more accurate to refer to a dynamo hub as a generator hub.<\/p>\n So where did the name \u2018dynamo hub\u2019 come from, and why has it stuck?<\/p>\n As with a Xerox, Velcro or an Escalator, Sturmey Archer is the victim of a form of genericization<\/a>.<\/p>\n Sturmey Archer\u2019s widely-sold Dynohub, which was originally released in the 1930s, became synonymous with generator hubs and \u2018dynamo\u2019 has become everyday parlance in the cycling world (even if the name is technically incorrect). While a dynamo typically refers to the component generating power, it\u2019s also often (albeit incorrectly) used to describe a light powered by a dynamo hub.<\/p>\n A dynamo bike light relies on the power produced by a dynamo to work.<\/p>\n Apart from a small battery or capacitor that keeps the light illuminated for a short time after you stop (known as a standlight), a dynamo headlight requires your wheels to be spinning to provide illumination.<\/p>\n To be absolutely clear, almost all dynamo lights cannot be powered by a battery. Some specialist bikepacking lights, such as the Llum Dynamo Light, can be powered by an external battery, but these are in the minority.<\/p>\n Conversely, most battery-powered headlights cannot be run directly from a dynamo (some lights, such as the Light & Motion Rando 500 allow you to slowly charge the internal battery via a dynamo as you ride).<\/p>\n Modern LED-based dynamo headlights are fairly complex.<\/p>\n To start, they have to convert the AC power produced by the dynamo into DC (this circuit is known as a rectifier). They also typically include over-voltage protection and logic circuit that detect whether the standlight needs to be activated.<\/p>\n Older incandescent dynamo lights could be plugged straight into a dynamo hub because they work with either AC or DC current, so were much simpler. However, these aren\u2019t nearly as bright or reliable as LED lights and are now only seen on the cheapest dynamo headlights.<\/p>\n Another key difference compared to the majority of the best bike lights<\/a> powered by batteries is that most dynamo headlights are StVZO-compliant.<\/p>\n StVZO<\/a> is a German standard that dictates how lights must be designed in order to comply.<\/p>\n The biggest difference compared to a non-compliant light is the use of a specially-shaped cut-off beam. This directs as much light onto the road or trail as possible without dazzling drivers.<\/p>\n Many road riders prefer the shape of an StVZO beam \u2013 those clever optics throw your precious lumens where you want them without dazzling other road users.<\/p>\n However, they don\u2019t provide the type of wide beam shape that\u2019s more useful for riding off-road.<\/p>\n Dynamo lights are most popular in Europe and many key manufacturers (SON, B&M, Supernova and so on) are based in Germany, which is why most comply with this legislation.<\/p>\n Check out our full explainer on StVZO bike lights<\/a> for more info.<\/p>\n Exceptions do, of course, exist. The KLite BikePacker Ultra V2<\/a>, Exposure Revo and Sinewave Beacon<\/a> all use standard round beams, which is typically better for off-road riding. These options are all very popular for bikepacking.<\/p>\n Dynamo rear lights typically attach to cables that run along the length of the bike and plug into the back of a dynamo headlight.<\/p>\n These basic lights are little more than an LED inside a suitable casing with a long cable soldered on. These rely on the standlight circuit within the headlight to remain illuminated when you stop.<\/p>\n\n
What are bottle and hub dynamos, and do they work?<\/h2>\n
![\"SON](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/06\/First-Look-Friday-4th-June-2021-3-334fb32.jpg?quality=90&resize=620%2C413\" "\\"SON")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>![\"Hunt](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/09\/Hunt-MTB-dynamo-wheels-e2d3711-e1631194600170.jpeg?quality=90&resize=620%2C413\" "\\"Hunt")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>What about bottle dynamos?<\/h3>\n
![\"I've](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2019\/03\/img_4656-1519055409439-e05s7q2kl2hr-e6b64da-e1631189454111.jpg?quality=90&resize=620%2C413\" "\\"Bottle")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>Dynamo or alternator?<\/h3>\n
![\"Close](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/09\/GettyImages-157282729-72df74b.jpg?quality=90&resize=620%2C412\" "\\"Close")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>What is a dynamo light?<\/h2>\n
Dynamo headlights<\/h3>\n
![\"SON](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/09\/FAIRLIGHT-2021-LS2-Strael-MK3-Grey-Dynamo-L1260069-66670fd.jpg?quality=90&resize=620%2C413\" "\\"SON")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>![\"The](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2019\/11\/Lauf-14-6c1eca0-scaled-e1631191306970.jpg?quality=90&resize=618%2C413\" "\\"The")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>![\"100](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/09\/100-Lux-IQ-X-cf82e25.jpg?quality=90&resize=619%2C413\" "\\"100")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>![\"The](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2019\/03\/img_4652-1519055409430-1v9zc2bdfbpiv-1e75d89-e1631190795129.jpg?quality=90&resize=620%2C413\" "\\"Everything")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>Dynamo rear lights<\/h3>\n
![\"Rear](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/09\/FAIRLIGHT-2021-LS2-Strael-MK3-Grey-Dynamo-L1260052-f1b964b.jpg?quality=90&resize=620%2C413\" "\\"Rear")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>![\"Rear](\"https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/21\/2021\/09\/FAIRLIGHT-2021-Secan-Orange-L1240500-f23fca1.jpg?quality=90&resize=620%2C413\" "\\"Rear")
\n<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture>\n<\/div>