"Tom Del Rosso" wrote in message ...

Oh, and I'm curious about this dynamo vs alternator issue. Some people
have said these things generate AC. If none of us have tested one,
maybe we should assume the worst.

Is that the only reason you oppose the use of a transformer? You might
have said so with less fuss.

Assuming the worst, I'd think to use a full wave bridge and no
transformer.

I, too, am unsure whether hub dynamos produce AC or DC. Larkin's design with
the transformer assumes AC, while Thompson's assumes DC. If his "model"
includes diodes, then their specifications become very important to overall
efficiency, since two diode drops may constitute 1/4 of the voltage. If the
hub dynamo is a true alternator, then AFAIK it would contain diodes (as in
an automotive alternator), and would very likely use three (or six) phase.
But according to the following, the output IS AC, and it must be single
phase if there are only two terminals:
http://www.nscl.msu.edu/~daniel/sreg.htm

Perhaps even greater efficiency may be obtained by using a voltage doubler
consisting of two Schottky diodes and two capacitors. If the dynamo outputs
6 VAC then the doubler should produce about 16 VDC. However, the performance
at low speeds would depend on the frequency of the AC and the size of the
capacitors. The autotransformer is also subject to low frequency limitation,
and in fact may present a heavy load when it saturates at low frequency,
although not if the AC output is proportional to speed.

I think it would be advantageous to design a hub with a three-phase
topology, as it may reduce or eliminate the "cogging" effect that was
discussed in one of the articles. Another topology that might be
investigated is a three phase induction motor, which requires no expensive
magnets and is very rugged. But it does require sophisticated electronics
and a pre-existing voltage source to produce the rotating field. Or it might
be possible to use a SEIG, which could be accomplished with a small PM
generator to power the electronics which can then run off of a small
capacitor during times of no movement.

Since we have broached the subject of wheel hub generators, it opens up the
discussion to hub motors, which may provide enough power to assist the
cyclist on uphill climbs and then harvest the energy of downhill coasting,
even providing some braking force.

http://www.gizmag.com/green-wheel-el...bicycle/11076/
http://www.goldenmotor.com/
http://www.bicycle-power.com/diykits.html

Because of my problems with knees hips, and back, I can't really use an
ordinary bicycle, but one of these may fit the bill. But I may also try a
dog-powered cart, or bike-jouring equipment:

http://www.youtube.com/watch?v=1gwsKBcIrtk
http://youtu.be/12ZlXquqU8g

My dog Muttley sure pulls hard enough!
http://www.youtube.com/watch?v=HfQR5hZfrlk
http://youtu.be/MNOLgALlZuY (he helped pull my mower up the hill)

Paul and Muttley
www.muttleydog.com