Ducati Singles by MotoScrubs.com

This 6-volt Ducati has a weak generator. The generator works well enough so long as the headlight in not employed, but in many States daytime use of a headlight is required by law.

With constant daytime riding use of the headlight the battery is continually drained of charge in order to support the headlight power requirements until which time as the battery is left with insufficient charge to allow kick-starting of the motorcycle after the engine has stopped. When the battery is overly drained it is not possible using the kick start to rotate the engine fast enough to produce sufficient power from the generator for the ignition system to get the engine to fire and run on its own.

A run and bump method of starting is possible at this point, but the motorcycle runs rough at low RPMs presumably because the slow-spinning generator's output at low RPMs does not provide a sufficiently healthy system voltage to the ignition components and without the battery to bolster the system's nominal operating voltage the spark is weak. As further evidence of this presumption a re-charge of the battery returns the motorcycle to perfect running order.

The problem is then to implement a day-time running light in the headlamp bucket that will visually appear to other motorists as an oncoming headlight from a significant distance, and in turn use significantly less power than the incandescent headlight such that the motorcycle can be operated without the fear of becoming stranded from a depleted battery.

With the supposition that the motorcycle will not be ridden at night the problem is easier to resolve. The solution is to try using powerful white LEDs in the headlight bucket in place of the incandescent bulb and limit all use of the motorcycle to daylight hours.

The modification is NOT LEGAL. The LED light assembly used has not been certified by DOT or any US agency as meeting the legal requirements for headlight usage in the United States.

The Ducati headlight is specified as 25-watts for low beam and 25-watts for high beam. The generator is specified to have a 40-watt power output (when new.) If the generator puts out only 40 watts of power and the headlight consumes 25 watts of the total power budget, that leaves 15 watts for the remaining electrical loads.

The other electrical loads are the tail light (3 watts), the brake light (15 watts when the brake applied), the horn (unknown power rating - but rarely if ever used) the charge warning lamp (1.5 watts when lit) and the ignition system (unknown power rating.) Beyond these power requirements is the need for some power to be returned to the battery so as to have a full charge for the next time the motorcycle engine is stopped and re-started.

The Ducati electrical system, even when new and at peak output capacity, was just barely sufficient to satisfy the demands of the motorcycle when the headlamp was in use. It may be presumed that the designers assumed that headlight usage would be relegated to infrequent night riding in which case the electrical system could probably have been considered adequate.

If you have been to a Brookstone© or Sharper Image© store you have probably seen the LED flashlights that use an LED to supply an incredible amount of light from a 1.5 volt alkaline battery. From a visual inspection the flashlights appear to use the Luxeon© (http://www.luxeonstar.com) series of LED products with collimator which according to Luxeon produces the highest flux per LED in the world.

An observation is made at this juncture that from examining the beam of light from the flashlight in the store the light of a single Luxeon emitter does not produce sufficient light to appear as bright as an automotive headlight in daytime lighting conditions.

Fortunately Luxeon offers a 6-up LED ring* utilizing six white LED drivers which at 81mm (or 3.19") should physically fit within the space confines of the Ducati's 150mm headlight bucket and may appear bright enough having by design 6 times more lighting power than the flashlight to appear to motorists as an oncoming headlight from a significant distance away.

Several problems however impede the direct application of the Luxeon 6-up ring driver to a 6-volt motorcycle. One problem is that the Luxeon ring requires a nominal supply voltage of 10 volts which is not readily available from a 6-volt motorcycle whose system voltage often varies depending on engine RPM.

Another impediment is that even if 10-volts were available, the Luxeon must also be current limited to 700 milliamps so as to maintain a safe operating temperature and permit sufficient heat transfer to the circuit board in order to prevent premature failure of the LED ring.

What does make the use of the Luxeon Ring enticing is that 10 volts at 700 milliamps is a calculated power consumption of just 7 watts (10 volts x 0.7 amps) which is considerably less than the 25 watts required by either beam (high or low) of the stock incandescent headlight.

The Luxeon 6-up Ring is configured as two series strings of 3 LEDs each, and one could envision making a ring of three series stings of 2 LEDs per string so as to reduce the nominal operating voltage below 10-volts and closer to 6-volts. However, Luxeon recommends the use of an aluminum core printed circuit board to safely accept and dispense the heat generated by these powerful LEDs. Finding a circuit board fabricator that can make aluminum core circuit boards inexpensively in small quantities is not possible. It will be better to use Luxeon's pre-engineered circuit board substrate and engineer the lighting solution to interface between the motorcycle's electrical system and the commercially available Luxeon assembly.

* I will note here that a 12-up Luxeon ring is available - but with a diameter of 140mm (5.51"), an operating voltage requirement of 21 volts DC, a significant unit cost increase over the 6-ring unit and an estimated power consumption of almost 15 watts the use of a 12-up Luxeon ring for this application was dismissed.

In order to use a 10-volt Luxeon Ring on a 6-volt motorcycle, the DC voltage must be stepped up from 6 to 10 volts. Unlike AC voltages whose voltage can be inexpensively (but not efficiently) stepped up, DC voltage can only be stepped up through the use of a DC to DC converter.

With any power conversion comes a loss of power in the conversion process, and this is what is referred to as the level or percent of efficiency. If the Ducati had plenty of power in the fist place efficiency of the DC to DC power conversion would not be an issue. Since the Ducati's electrical power is what is ultimately trying to be conserved, for this experiment a DC to DC converter with an advertised 85% efficiency was selected.

The DC-DC converter chosen puts out 12-volts of DC power and can supply 1 amp (1000 milliamps) of power, well above the 700 milliamps needed by the Luxeon Ring. Using load resistors and a zener diode, the current flow out of the DC to DC converter flowing into the Luxeon ring can be fixed at around 700 milliamps.

The DC to DC converter can work to as low as 3.5 volts input volts, a level of which should be sustainable at low engine RPMs if not already overridden by the battery's efforts to maintain a nominal 6-volts should the generator and subsequently the voltage regulator's output drop below that level. The DC to DC converter's maximum input voltage is 16 volts which should be higher than any voltage the Ducati's 6-volt regulated charging system is capable delivering to the motorcycle.

The power consumed then is 6 times 2.06 or 12.36 watts. This is much more than the 7 watts which was calculated for the Luxeon ring itself, however it is still roughly half that of the specified 25 watt incandescent headlamp. The extra 5 watts of power loss is likely due to the inefficiency of the DC to DC converter whose efficiency may vary depending upon input voltage, and the power lost in the current limiting zener/load resistors. The use of a more complex current limiter circuit could recoup some of that power, but at the cost of more expensive active semiconductor circuitry.

The Luxeon ring is too powerful to photograph head-on at close range as it overloads the digital camera's optical sensors (CCDs.) In addition, temporary macular degeneration to a close-up onlooker's eyes also occurs, creating 'spots' in the eyes similar to when a camera strobe flash goes off.

Here is a head-on photo of the headlight from about 10 feet away. The headlight appears sufficiently bright, but brightness alone is not the issue. Significantly reducing power consumption is the subject of this exercise and at present the Luxeon ring is using about half the electrical power of the incandescent bulb.

One might also note from the photos that the incandescent headlight appears less bright than the Luxeon ring. It was noted that while the headlight was bright enough to cause an onlooker to squint, it did not cause macular degeneration. However, the science of light waves is beyond me, and perhaps it is the wavelength and not the quantity of light that causes the more severe effect upon eyes and the digital camera.

LEDs only emit light in a forward direction, therefore a reflector behind the LEDs would seemingly serve little or no purpose. Through the use of optical acrylics above the LED the viewing angle of the LED can be adjusted somewhat, providing a wider viewing angle (the angle at which light is still visible as the eye moves away from the center of the LED) at the expense of less light intensity seen directly at the top of the LED. Of course we would prefer to have both a wide viewing angle and a large quantity of light. The Luxeon ring has been chose for it's brightness and the viewing angle of the Luxeon product is beyond the end-user's control.

In order to better emulate the light output and visible angle of projection of the headlight bulb and reflector system the LED ring might be pointed inward at the basin of the mirrored reflector with the hope that the light would bounce off the reflected surface in a multitude of directions for a wider forward dispersal of the light. However there is an interruption in the reflector basin where the incandescent lamp bayonet base is mounted. Without going to the expense to fashion a parabolic reflector with no voids the existing reflector is probably unusable. In addition, the Luxeon LED ring itself forms a rather significant opaque barrier which will eclipse the light reflected from within a reflector's basin. For this reason the LED ring was pointed forward in the headlight bucket.

The result of this exercise will take time to reveal. It would be hard to imagine that the test would be unsuccessful from an electrical standpoint, having reduced the biggest power load on the system by almost half.

If the charging system was still inadequate to support even the reduced load, the LED ring would at the very least prolong the time between connections to a battery charger.

To perform a reasonable test I should put in a new fully-charged battery and ride the motorcycle daily without any intermediate use of a battery charger. I probably should also carry a voltmeter and chart the voltage after each engine stop to look for signs of quiescent battery output level decay.

The ideal situation would be that the battery would maintain a full charge, having recovered from whatever depletion occurred when starting the motorcycle with excess power from the generator when the engine was running, and having not been further depleted when the motorcycle engine was running; that is to say the generator will have provided all the necessary power to operate the motorcycle.

The other part of the success equation is whether or not the light output in daylight is sufficient to be interpreted by motorists as that of a vehicle headlight, and this too at a reasonable distance. Light from an incandescent lamp and light from an LED are measured in different ways with differing units of measure. This is because incandescent lamps through off light from all directions (hence the need for a reflector) and LEDs are unidirectional in light output. The two units of measurement have no correlation to each other

An Luxeon white LED ring is currently (2006) selling for about $70, but as with all electronics components prices are expected to continually drop.

A high-efficiency DC-DC converter that can take a wide range of lower input voltage and can output a constant yet higher voltage does not come cheap either: about $85.

Add the expense of a circuit board and various discrete components to support the operation and interconnection of the DC to DC converter and this LED headlight cost about $200 in parts alone.

If the Ducati's generator can be removed, re-wound and replaced for around $200 this LED solution probably comes at too high a price, especially given that this LED solution is not street-legal and provides no high-beam/low-beam functionality.

While the future of street legal LED headlamps is certain, they are being developed with the modern and robustly electrical-powered automotive market in mind. I suspect the primary development of LED headlights will not focus on power reduction, but rather they will likely be developed to take advantage of compact sizes and unusual shapes for vehicle styling reasons.

While there may likely be LED headlight retrofits for 12-volt motorcycles based on round LED headlights in the future, the chances that a retrofit for 6-volt motorcycles will come along that will offer equal if not improved lighting while hopefully offering lower power demands than the 25 to 35 watt incandescent headlight bulbs of the 6-volt motorcycle era are probably nonexistent.

The information gained in this experiment is offered to help anyone attempting to develop a street-legal LED headlight suitable for 6-volt vehicle applications. I have no familiarity with the resources and requirements needed to achieve DOT or other required Federal compliance and acceptance for automotive headlights although I presume the path to acceptance would be extremely costly and fraught with bureaucratic pitfalls.

Perhaps the Luxeon ring was not the correct solution and another component is or will become available that can reduce the cost or possibly be DOT legal by inherent certification.

We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.
T. S. Eliot

Disclaimer:

The modification is NOT LEGAL. The LED light assembly used has not been certified by DOT or any other US agency as meeting the legal requirements for headlight usage in the United States.