The Sturmey Archer GH6 Dynohub
New: see the video -Dynohub powering a cateye LED lamp here (2.5Mb) WMV format
And even a 12 Volt 11w Compact Fluorescent lamp here (665Kb) WMV format
The Sturmey Archer GH6 Dynohub was designed as a means of generating electrical lighting power for bicycles during the second world war. It seemed to me as the perfect 'off the shelf' small scale experimental alternator.
It was in production for almost four decades, first making an appearance in 1943.
It was a 6 volt 3 Watt unit incorporating a 20 pole ring magnet with a stator having a continuous winding.
The GH6 was withdrawn from production in 1984, but can still be found at scrap yards, established bike shops or eBay.
The main feature of the dynohub was that it reached it's rated output at only 12 mph (with a 26" wheel) this equates to a mere 60 rpm, as compared to other alternators requiring 200 + rpm to get any where near there rated output.
This low speed design was ideal for use in small scale wind production, along with it's excellent bearings, it could be mounted easily on one side of the unit.
The name dynohub is a little misleading suggesting that the unit is a dynamo - it is actually a multi pole alternator that would produce alternating current, fine for lighting bulbs, but not so for battery charging. A bridge rectifier would be needed to convert the alternating current (AC) to a more useful Direct current (DC).
Servicing Sturmey Archer Dynohub's here
There is a new Sturmey Archer X-FDD dynohub version available here, it incorporates a 70mm Drum Brake. and rated at 6 volts 3 watts -
Costs approx £60 ($104). You could buy 4 old ones for that price - they usually go for around £15 ($25) on eBay.