12 Volt/6.2 Watt Lighting Systems?

After the planned revised version of the German vehicle standard §67 (lighting systems for bicycles) 12V/6.2W lighting systems will be allowed, in addition to conventional 6V/3W lighting systems. The headlight is to use 5 Watts, the taillight 1.2 watts.

For this strongly increased power output, which in addition can be achieved at a relatively slow cycling speed, only a gearless hub dynamo is a workable solution. With an efficiency of 70% (50% is required, as opposed to 30% with the 6V/3W system) the power production capacity would otherwise be no higher than with a good conventional sidewall dynamo.

The manufacturing expenses would cause problems: Size, weight and price, for many already too large for 3 Watt SON, were expected to increase. Also there would be an inevitable increase of the voltages in no-load (lights off) operation, on whose minimization we attach particular importance.

This problem would end up as a tradeoff between efficiency and increasing voltage as speed increased. It would be more practical to only try to achieve 12V at 15 km/h (10 miles/hr) instead of at 10 km/h (6 miles/hr.) We could probably produce such a hub dynamo with similar size, however the efficiency in the 20 - 30 km/h (12 - 18 miles/hr) speed range would be clearly better.

12V hub dynamos are still a cutting-edge technology, which must move towards a meaningful balance between cost and usability. Since, in addition, 12 V headlights and taillights yet are not easily available, it is uncertain whether and/or when we will offer an approved 12V hub dynamo.
 

12 Volt Usage of the 6 Volt SON

Our current 3W hub dynamo is able to deliver 6W of output, however only at a higher speed. This is achieved by a second lighting system added in series (or, if no second taillight is present, by a second 3W headlight.) The current delivered by the dynamo cannot be increased, however the voltage probably can be, e.g. to 2 x 6V = 12V. However 12 V is only reached at approx. 20 km/h (Figure 1). As well, the efficiency curve is higher towards increasing speed, where at over 15 km/h clearly better values are obtained (Figure 2). In order to supply a single headlight properly at lower speeds, a secondary/auxiliary headlight should be bridged by a bypass switch if one is present (Figure 3).

In principle, supplying power to a 12V/6.2W lighting system is possible, however a voltage regulator would be necessary and switching would not be possible.

The 12 V system is thus only useful for night cyclists traveling at high speeds on unlighted highways who need more light than usual. The series connection of a second headlight is possible, and even should be approved in the new §67 standards. As well, the output can be increased at lower speeds by using the SON28 in a smaller wheel, though this is not approved under the German standards.
 
 

Figure 1:


SON on a 28" wheel: output voltage in no-load operation, on 6V/3W lighting system, and on a 6V/3W lighting system with a 6V/2.4W auxiliary headlight

 

Figure 2:

SON on a 28" wheel compared with a high-quality sidewall dynamo

Efficiency = electrical output / drive power

 
 

Figure 3:

This is a 12V lighting system composed completely of readily available 6V system components

We make the E6-Z headlights with integrated bypass switching based on our E6 headlight, ready to use with properly finished connectors. Detailed info sheet on the E6 in PDF format (German - 1.8 MB!) is here. The E6-Z is added directly at the SON connections in the electric circuit. Detailed information to the E6-Z in PDF format (German - 0.25 MB!) is here.