Bright Lights All Night?
(3 approaches to brighter lighting)
 High-Wattage bulbs and the LVR2
  Twin Headlights with a generator
   Three Micros with Lithium power
With grateful acknowledgement to the denizens of the Bikecurrent mailing list,
whose ideas have contributed so much to these articles. 
Bikecurrent Archive




Twin Headlights with a generator
by Francis Cooke
Schmidt Original Generator plus 2 Lumotec Ovals, mounting and connectors -
total weight 700g, cost £145

Note that the weight quoted above includes the weight of a front hub, which is necessary equipment on any bike and normally weighs around 200g. On the other hand, that total weight is weight you cannot shed during the day.
The cost, unlike the two battery-based systems, has no nightly 'running cost' so can be seen in terms of long-term value.

Note also that the technique described here will work with other 6V headlights, and, perhaps to a lesser extent, with other generators.
However the Lumotec headlights win universal approval from everyone who uses them, and so seem to be a clear first choice among lights optimised for generator use. The new Oval pattern are optically similar to the more familiar circular Lumotec lights.
Similarly, the Schmidt hub generator is recognised as by far the most efficient, in terms of drag, of all cycle generators, both by day and by night. Of course, several other generators including all sidewall and roller types, can be disengaged completely for zero drag during daytime, but none of these come close to the performance of the Schmidt by night.


This is a system that is now in regular use by several riders in the US, the UK and in Europe. Wire the two 6V 3W lights in series to your generator, then bypass one of these two using a single wire between the two contacts on the light, and put a switch in this bypass wire.
Making contact on the switch bypasses the light and gives you normal 6V3W generator running. At higher speeds, downhill or going well on the flat, break the contact on the switch and this puts the second lamp into circuit, giving a 12V6W mode of running.
This works because generators are effectively constant current devices, so as more work goes in, the voltage has to rise. A single bulb might go pop (this is why Lumotec lights have a voltage regulator built in), but two in series simply give more light. Neat.

Of course there's a bit of extra drag, but the Schmidt in particular is so efficient that, at 20kph, this is still less than the drag felt when using other generators running only one lamp.

Lumotec lights are optimised for mounting on the fork crown, and not suited at all to handlebar mounting. So there is a problem of mounting that second light.
Try this - two Lumotec Ovals side-by-side on a fork crown mount.
Use a sturdy pressed-steel mount as designed for a single light - the one provided with the Lumotec is probably not strong enough. Get some 6mm threaded rod from the hardware shop. Cut off a piece about 7cm or 3" long, and mount this centrally on the fork crown mount, then mount one lamp on each end of the rod, using a multiplicity of 6mm nuts and shakeproof washers. The lights will connect to each other electrically through the metal rod - don't rely on this to make the circuit, but be aware of it and design the wiring acordingly.


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