WHAT IS A DYNAMO SYSTEM?
A dynamo system is a wheel that has a hub that creates an electric current, allowing a rider to power lights, and even charge electronics (with certain caveats). The hub creates a small amount of resistance or drag, usually through magnets inside the hub shell, that it then converts into power. Modern dynamo hubs create relatively low drag, so low that it is hardly noticeable in most applications. The dynamo will only create enough power to reliably run lights over a certain speed, or after a certain amount of time. This will vary depending on the hub size of the wheel.
WHY USE A DYNAMO SYSTEM?
Dynamos are fantastic in applications where lights are often needed or used, such as long distance touring, randonneuring, and commuting. In those applications, the drag from the hub (which is already minimal) is unlikely to be noticeable anyway. There is no need to change or charge batteries, making a dynamo cheaper and more environmentally friendly in the long run, as well as eliminating the risk of being stranded in the dark. Certain lights, such as the Busch & Muller Luxos U have a built in USB charger, which allows riders to power a GPS device or charge a small device while riding, particularly useful in remote areas where power supplies can be limited. For an incredibly in depth look at the beams of various dynamo powered headlights, see this article. The beams for many dynamo lights are very bright, as well as wide, giving the rider increased visibility. Another common feature is a cache battery, which allows the lights to store power in a small battery, meaning the light will continue to run when the rider comes to a stop, in some cases for as long as five minutes.
WHAT ARE THE DOWNSIDES?
There is an increase in drag due to the resistance of the hub, but not much. The big deterrent is weight and cost. The hubs are very heavy due to the internals of the hub, but the weight is not rotational mass so will have less effect on riding. In applications where a dynamo makes sense, weight is generally a secondary concern as well. The other downside is cost, there are not many, if any, machine built dynamo wheels, so you have to either build the wheel yourself, or have the wheel built, which will ultimately result in a stronger, longer lasting wheel. The hubs themselves can be expensive, but there are many newer, cheaper options that claim to have lower drag and higher power output than their more expensive rivals.
WHO MAKES DYNAMO HUBS?
There are a number of hub manufacturers to choose from, ranging drastically in price. The gold standard for longevity, low drag, and power output has been the SON dynamo. These German dynamos have been on the market for quite some time, and have proven themselves in the long run. Shimano has different versions of their Alfine hub, SRAM has an offering themselves, and there are a few smaller, newer entrants into the dynamo hub market. Shutter Precision boasts some incredible numbers, claiming a lower drag coefficient and higher power output than the more expensive SON hub, and, owning one myself, I can say that it works quite nicely.
Come on by to talk more about the advantages of a dynamo system, and discuss options for getting set up with one. Every commuter should be using one!