This is my slightly edited version of the Schmidt hub brochure text.
The generator is a claw-pole-generator as used in almost all modern bicycle dynamos. However, it is designed in such a way as to deliver sufficient voltage, even for the much smaller rotary frequency of the wheel without gearing. In our construction this is realized with the smallest possible weight. The resulting volume was less important for us. That is why Schmidt's Original Hub Dynamo is comparatively big and empty. At electrical load the claw-pole-generator automatically supplies a voltage which does not exceed a certain limit, e. g. 7 Volt, even in case of high speeds. Therefore no energy-wasting voltage limiter electronics (Z-Diodes) are necessary. While manually turning the axle, distinctive halt positions can be felt. These are caused by the attracting and repulsing forces between the permanent magnets arranged inside the ring-shaped hub body and the pole-pieces of the armature fixed on the axle. Because of high-quality materials and a special laminated design, hardly any additional propulsion power is needed with open load circuit. Only if electrical power is consumed, coil and armature become an electromagnet and mechanical energy has to be supplied. Another striking feature of Schmidt's Original Hub Dynamo is the flickering light at low speed (up to 8km/h). This is caused by the low AC frequency. Since it does not disturb the cyclist, we have done without an efficiency reducing smoothing. On the other hand the flickering light is more conspicuous in the situation where less electrical energy is available.
The high-quality grooved ball-bearings of the hub are arranged in the fix-loose order, like common in mechanical engineering. The double-sealing of the lifetime greased bearings and the extremely stiff design of the axle guarantee a long life of the dynamo. In those rare cases where replacement of the bearings is necessary, the hub should be returned to the manufacturer for service. The threadless hollow axle is made of high tensile stainless steel. Usual quick-release sets fit to the axle. However, 5 mm allen-key skewer included (CroMo- steel) makes it easier to get the electrical contacts into the desired position, when the wheel is being mounted. This setup also provides basic anti-theft protection for the front wheel.
In order to meet the requirements of a modern bicycle electric and to avoid the problems caused by using the frame as the second conductive connection, Schmidt's Original Hub Dynamo has two solid 4,8 mm tab connectors . The electrical switch is integrated in a modern 2,4 Watt halogen headlight (Lumotec by Busch & Müller ), delivered with the dynamo. This placement eliminates unsightly and susceptible to interference wiring at the handle-bars caused by a separate switch and reduces the assembly time to a minimum.
The headlight is connected via a 3mm coaxial cable, which inner conductor is optimally protected by the outer wire mesh (grounded at the headlight mounting) and two isolation layers. The cable lugs for the connection to the generator are usually installed and ready to use when delivered. The rear light cable is connected to the headlight by a 2,8 mm cable lug. An explicit earth wiring to the rear light is possible, but in most cases it is sufficient to do without it.
The electrical power output of Schmidt's Original Hub Dynamo fulfills the requirements of the german law (StVZO). In this respect its characteristics correspond with good bottle-type or bottom-bracket generators. However the required propulsion power is about 50% lower, because no mechanical losses occur in a gearless hub generator. The switch-on during the ride can't be felt while riding. The no-load losses are even less. At 15 km/h the generator consumes less then 1 Watt, which is like an additional ascending gradient of 24cm on a 1 km distance. This minimal losses at no-load allows us to have no mechanical switch-off (de-clutch of the generator unit).This keeps the design simple and the operation comfortable.
In Combination with Accumulator Devices
With its steady ability to provide electrical power, a gearless hub generator fits perfectly in a bicycle power supply system with an accumulator battery as a buffer for low speed or stop situations. Our plans for a device consisting of accumulator and controlling electronics which takes special advantage of the continuous power source are still not realized. The dynamo design with no electric connections to the bicycle frame is open to future developments as well as to home build systems with full-wave rectifier.
Because of the low AC frequency most available bicycle accumulator devices won't work correctly. However Schmidt's Original Hub Dynamo could be ideally combined with a capacitor buffered LED tail light (e.g. DToplight-plus by Busch&Müller or safety light by MARWI). Their simple and maintenance free design provides the especially important safety to the back for little money.
Gearless hub dynamos have existed for a long time. In 1992 Wilfried Schmidt was the first to introduce a construction which supplies the required 3 Watt nominal output and weighs no more than a bottom bracket dynamo plus a high quality front hub. Since 1995 Schmidt's Original Hub Dynamo (SON) has been manufactured in the factory of the inventor - with a lot of hand work and care. In the meantime big companies offer similar but cheaper devices which are less optimized with regard to no-load losses, bearings and weight. Schmidt's Original Hub Dynamo is now as before the favorite choice of ambitious cyclists worldwide.
Smaller wheels which turn faster need a different design of the generator inside. The SON20 for 16 "-20" wheels, which looks the same as the standard model. 12Volt/6.2Watt light systems (a new German standard) are difficult to realize with a dynamo. Usual gear-driven dynamos would cause too much drag to supply 6.2 Watt. A slow turning gearless hub dynamo is the best choice, because of its high efficiency. We took the challenge and developed a 12Volt-SON which fits the new standard and exceeds its 6Volt brother with an efficiency of 70%. A series production will be started not before high quality headlights and rear lights are available.
NOTE: There is still no production date for the 12 volt SON.
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This page updated: Wednesday, September 26, 2007
Peter White Cycles