SON - Schmidt's Original Hub Dynamo
The SON is a claw pole generator, as are nearly all conventional bicycle dynamos. However, the SON can supply sufficient voltage at lower speed than other generators. The technology developed by Schmidt performs this with minimal weight, trading off weight for size.
Under load, the claw pole generator supplies automatically a current of at most 0.58 amperes, even at high speeds. This will power a 6 volt 2.4 watt headlight & 0.6 watt taillight system, with a standard load resistance of 12 Ohms. The maximum voltage output is 7 volts, so a voltage regulator is only needed in case of a lighting fault.
The generator action of the hub is clearly felt if the axle is rotated by hand; the stops felt are caused by the alternating attractive and repulsive forces between the permanent magnets and the poles. However, due to the high-quality construction and superior materials of the SON, the two forces balance almost exactly and there is negligible net loss of mechanical energy, being almost all turned into current flow if the circuit is closed and the poles acting as electromagnets.
At low speeds (to approx. 8 km/hr or 5 miles/hr) the SON's output will flicker due to the low frequency of the alternating current it produces. This means that it will work at a lower speed than other generators, since as the cyclist is not disturbed by the flicker, it increases the efficiency of the unit to not have an energy-draining smoothing circuit present.
The SON rides on high-quality grooved fixed-floating ball bearings as found in finely engineered machines. The double sealing of the permanently lubricated bearings and its strong construction guarantee a long lifespan. However, if it is a must to remove the bearings, a special tool allows their reattachment. Respoking the hub is no longer necessary.
The threadless hollow axle is made of high-tensile stainless steel. A 5mm skewer of CrMb steel is provided, or a quick-release mechanism can also be used.
The Lighting System
Since the SON is a gearless hub dynamo, it is always running, and the current can be turned on and off comfortably by an electrical switch. This arrangement saves cumbersome and problematic wiring at the steering wheel requiring a separate switch, and minimizes manufacturing costs. The attachment to the headlight is a durable coaxial cable, whose internal conductor is optimally protected by the outside wire mesh. Two solid 4.8mm flat connectors attach the coaxial cable to the SON. For a taillight, a long-life LED model with capacitor parking light (such as the 4D-Lite Plus or DToplight Plus from Busch & Müller) is recommended. The taillight is attached using the 2.8mm lugs at the compatible two-pole headlight. Also newly on the market are headlights with photosensors which switch the lighting system on automatically in darkness.
The power output of the SON resembles, according to the requirements of German vehicle regulations, high-quality side-mounted roller dynamos. However only half as much power is required from the cyclist because the mechanical losses of the SON are so low. Even with the lights on, it is difficult to notice any drag from the SON while riding.
The no-load (lights off) losses of the SON are even smaller. At 15 km/h (10 miles/hr) only 0.5 Watt is lost, hardly more than the internal loss of a high-quality front wheel hub with grooved ball bearings, and is equivalent to an uphill gradient of 12 cm per km (about 1 foot per mile.) Because of these minimal losses, a mechanical off switch would be redundant. The construction is kept simple and the operation comfortable.
Hub dynamos have been around for a long time. But not until 1992 did Wilfried Schmidt introduce this device, which provides the necessary 3 Watts of rated output and weighs only few grams more than a roller dynamo and a good front wheel hub together.
Since 1995, Schmidt's Original Hub Dynamo has been the enterprise of the inventor, with much manual work and care taken in its manufacturing. While other manufacturers offer cheaper but less optimal versions of the SON, Schmidt continues to work on improvement. The new SON with its highly polished housing is smaller than its predecessor and more efficient; the already very small no-load losses have been lowered by nearly half.