Bicycle dynamo

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Hub dynamo
Side runner dynamo

A bicycle dynamo (from ancient Greek δύναμις, dýnamis 'force'; Swiss High German Velodynamo , dynamo for short , also alternator ) is a small electrical generator that ensures the power supply of the bicycle lights by means of a rotary movement while driving .

Construction principle

Disassembled side runner dynamo. Left: Housing with internal permanent magnet rotating by the friction wheel. Right: induction coil

Usually it is a small, single-phase alternator that uses a permanent magnet to drive a wheel. The magnet rotates in a stationary stator winding and induces an alternating voltage there . In modern hub dynamos, the rotor, equipped with permanent magnets, rotates around the inside of the stator.

Bicycle alternators are mostly unregulated, but stabilize the voltage to some extent by the inductance of the generator winding forming an increasing inductive series resistance with increasing speeds (and thus increasing frequency). Since the voltage is heavily load-dependent due to this impedance of the dynamo, a reduced load (e.g. due to a defective headlight) leads to strong overvoltage, which can result in the rear light bulb burning out.

Depending on the model, bicycle alternators have very poor to very high levels of efficiency. Low speeds (large friction wheel, hub dynamo, roller dynamo), as well as ball bearings instead of plain bearings are indications of good efficiency.

Equipment regulations

In Germany, it was mandatory to equip bicycles with a dynamo until July 2013 according to Section 67 StVZO. This had a nominal power of 3  W and a rated voltage of 6  V have. Following a change in the law, it is now possible to use battery or accumulator- operated lighting equipment as an alternative .

Forms of bicycle dynamos

literature

  • Wullkopf, Hellmuth: Small Generators with Permanent Magnetic Runner, ETZ-A, Vol. 80, Issue 4 (February 11, 1959), pp. 117-119
  • Fritz Winkler, Siegfried Rauch: Bicycle technology - repair, construction, production. 10th edition, Bielefelder Verlagsanstalt, Bielefeld 1999, pp. 390–394, ISBN 3-87073-131-1

Individual evidence

  1. ↑ theory of the bicycle dynamo at Enhydralutris
  2. ↑ N-TV.de: Bicycles may also have rechargeable batteries and battery lamps
  3. ↑ ETZ article "Wullkopf, Hellmuth: Small Generators with Permanent Magnetic Runner" at Enhydralutris

Web links

Commons : Bicycle Dynamos  - Collection of Images