A spoke dynam o is a bicycle dynamo that is driven by a spoke on the front or rear wheel. For this purpose, a driver of the dynamo is turned over on the wheel, which is placed in the way of the next spoke, so that it is moved by it. If you want to switch off the dynamo, you bring the driver back into the rest position so that the spokes run past it.
Structure and function
The driver can have different shapes. In the photo on the right, it has the shape of a small arrow that can be folded in the direction of the spokes. The electrical connection of the spoke dynamo can be single or double pole, depending on the version. In the single-pole version, the ground connection is made through the frame, while in the version with double-pole connection, the wiring to the lighting is made with double-pole cable and the frame of the bicycle plays no role as a ground connection. The double cable routing is necessary on bicycles with suspension forks (if the spoke dynamo is located on the front wheel), as these often do not allow current to flow through the mechanics of the fork. On new bicycles, double-pole wiring of the lighting system is mandatory for reasons of greater reliability.
Comparison with other types of dynamo
Compared to other bicycle dynamos, the spoke dynamo is more expensive than the classic side-wheel dynamos and rim dynamos. Its advantage lies in its independence from the weather. This is also the case with the hub dynamo, which is maintenance-free and offers a higher degree of efficiency. Compared to the hub dynamo, however, the spoke dynamo has no idling loss (with hub dynamos ~1 W at 20 km/h). The Stiftung Warentest came to the conclusion in the 3/2006 issue of the magazine Test that the “spoke dynamo disappointed. With only 24 percent it had by far the worst efficiency of all tested dynamos”. One reason for the poor efficiency of spoke dynamos is the two-stage toothed belt reduction gear with mostly very simply designed bearings, which have high friction losses. Other tests determined an efficiency similar to that of side-rotor dynamos, but worse than hub dynamos.
Once upon a time, there was a special version of a spoke dynamo that generated 12 V DC. As a rule, spoke dynamos generate AC voltage just like most other bicycle dynamos.
Spoke dynamos have been used to upgrade old bikes inexpensively, as they can be used in conjunction with the existing wheel.
At present, none of the former manufacturers produce spoke dynamos anymore; at best, there are remaining stocks available.
- Michael Gressmann, Franz Beck, Rüdiger Bellersheim: Fachkunde Fahrradtechnik. 1. Edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2006, ISBN 3-8085-2291-7
- Fritz Winkler, Siegfried Rauch: Fahrradtechnik Instandsetzung, Konstruktion, Fertigung. 10. Edition, BVA Bielefelder Verlagsanstalt GmbH & Co. KG, Bielefeld, 1999, ISBN 3-87073-131-1