A problem-free solution is to use a taillight with an integrated capacitor parking light. While riding, a Goldcap capacitor is charged and when the cyclist stops, the capacitor can supply a bright LED with energy for a few minutes. Manufacturers of such taillights are Busch & Müller (with the DToplightPlus, the 4DlitePlus and the Seculite) as well as JOS/Spanninga.
Likewise, the parking taillight solution is applied forwards in headlights from Busch & Müller. In the Lumotec Oval Plus and Lumotec Oval Plus Senso headlights offered by us are integrated a bright parking LED, which ensures a good visibility when stopped. (However don't expect miracles from an LED with an average power of 0.1W: the light won't be bright enough for reading a book or map or changing a tire by.)
If you need full headlights during very slow travel or when stopped, a parking light system based on rechargable batteries is necessary. The gearless hub dynamo, with its ability to generate a charging current even with the lights off, offers an optimal basis for a battery system independent of outside power sources. The few battery systems for dynamo use available on the market are unfortunately not appropriate for use with hub dynamos. Do-it-yourself construction is an option. In addition, the following contains some ideas:
The SON supplies 550-590mA alternating current at higher speeds, with voltage determined by load resistance. With a Schottky bridge rectifier, a 6V (or also 12V) lead gel rechargable battery (or a set of Hawker/Gates lead cylindrical cells in series), as well as a voltage-regulating shunt connected in parallel (e.g 5W Zenerdiode with 6.9V and/or 13.8V) and a few switches, a reliable, working battery system can be realized. If overcharging is a risk, an overcharging protection device would be useful. When using NiCd or NiMh batteries, determining when to stop charging becomes more difficult. The use of a temperature-sensing safety device, which stops the charging when a certain temperature is exceeded in the battery casing (e.g. 42°C or 108°F) will solve this. Charging could then resume after cycling for a while with the light(s) on. Time or voltage-regulated charging controllers are not appropriate for a dynamo.
We wish you happy tinkering.
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