Bicycle Lighting

Bicycle Lighting - Generators

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NOMENCLATURE
Dynamos, Generators or Alternators?

'Generator' is a generic term which includes Dynamo (DC producing) and Alternator (AC producing) devices. Most cycle generators are the latter, so 'Alternator' is correct, while 'Dynamo' is not. 'Generator' is also correct, and is a term more often used than 'Alternator', and so is used in these pages. Perhaps the German word 'Lichtmaschine' has some appeal ...

GENERATORS vs BATTERIES
The Case for Generators

Many generator users would argue that to use batteries for cycle lighting is to compromise the integrity of the cyclist. In short, batteries are 'cheating'.
Batteries can run flat at inconvenient times, or might simply be left at home, but a generator system is always there and ready to use when it is needed. The cyclist is never 'caught out' after dark with a generator.
A generator costs nothing to run.
A generator can easily drive a good bright 3W halogen bulb giving a very useful front beam.
A generator system is lighter in weight than a battery system capable of similar power output for more than a couple of hours.
Generator lights are intrinsically more reliable than ( integrated ) battery lights, as they are very light in weight and so not prone to vibration problems.

Some Drawbacks

Noticeable drag is the most significant problem. Many generators are also quite noisy in action.
When a cyclist stops, the lights go out. For a commuter, this makes a turn across the traffic ( in the UK, a right turn ), where the cyclist takes up station in the middle of the road and stops to wait for a gap, somewhat hazardous.
Similarly, at very slow speeds, eg, climbing at around 5mph, the lights go dim. This is particularly noticeable with bottom-bracket types.
And at very high speeds too much voltage can be generated causing the bulb to blow. Again bottom-bracket types are more likely to cause problems, but it is simple and cheap to fit a voltage regulator to any generator system to overcome this.
Generators can slip, with partial or complete loss of output - especially on wet roads or with narrow/slick tyres.
It is possible for a 'bottle' type generator to wear right through a tyre sidewall, creating a potentially nasty situation.
The generator is fixed to the bicycle so the weight is carried even on day rides when lighting is not required.

THREE DISTINCT TYPES
Hub, Sidewall or Roller

Generators Compared
Hub generators are enjoying renewed popularity with several good new models appearing on the market in recent years. Some are among the most efficient cycle lighting generators available. The problem with many of them is that they cannot be completely disconnected, so there is a drag during the day as well as during the night. There are some models which can be declutched to overcome this. Hub generators also tend to be the heaviest of the three types.
Sidewall or bottle generators are lightweight and include the cheapest generators at the utility end of the market, as well as more sophisticated models. They usually achieve their rated output at very low speeds, so are a good choice for utility cyclists or in hilly terrain. Often it is possible to fit an enlarged pulley, or a cap over the existing pulley, to gear them down a bit thus reducing drag while still reaching rated output at medium speeds. They are often the noisiest generators, and there is a significant safety problem if they are used for long periods on thin tyres - they could wear right through the sidewall.
Roller or bottom bracket generators were the most popular type in the '80s, but have lost ground recently to the other two types. They are neat and unobtrusive, and often less noisy than sidewall types. The major problem is that in the intended location - just behind the bottom bracket - they are vulnerable to dirt and moisture thrown up by the front wheel. This results in slippage, and, in the longer term, premature failure.

Schmidt review by Myra Van Inwegen
LightSpin sidewall generator information by Chris Wilby
Schmidt
Nick Ray's Schmidt data page
Bicycles AG sell several exotic generators via mail order - also the Lumotec range of lights
Peter White for Schmidt and Lumotec - good pix
A good comparison of Generators in German
Another good comparison of Generators
Servicing a Dynohub
Pawel Danielewicz Lighting links

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