"Jim Thompson" wrote in message
...

Here you go...

http://analog-innovations.com/SED/Bi...ubSwitcher.pdf

[snip]

I've only followed some of this "discussion" since it's become largely a
****ing match, but I see some questionable aspects of this design. First, I
would want to examine the characteristics of the dynamo, and that may mean
looking at several different models. The following websites list several:

http://sheldonbrown.com/harris/lighting/shimano.html
http://sheldonbrown.com/harris/light...her-x-fdd.html
http://www.sheldonbrown.com/harris/l...g/schmidt.html

http://www.bikequarterly.com/VBQgenerator.pdf (efficiency testing)
http://www.nscl.msu.edu/~daniel/regulator.html (a simple bike generator
charger/regulator)
http://www.peterwhitecycles.com/schmidt.asp (detailed discussion of these
German hubs)

And most modern bicycle lamps are now LED, so the standard 6V 3W hub
generator can now produce a lot more light at the same power, or the same
amount of light with power left over to charge a battery. So the
incandescent lamp model is already obsolete, unless you insist on dealing
with antiques.

Nonetheless, there seem to be flaws in the design. Assume the full 6V at 3W,
for a current of 0.5A. Diode R7 should be a Schottky, which will reduce the
power loss from about 0.5W to 0.2W. The one ohm resistance of the inductor
kills another 0.5W. And the charging current of the battery is not really
controlled in any way, so any excess voltage will just be dumped into the
battery and the power of the lamp will depend on its state of charge, so a
low battery will limit the voltage to the lamp and/or cause possibly
excessive charging current.

Much more efficient, and simpler, would be a center tapped Schottky
rectifier which feeds the lamp from the greater of the generator voltage or
the battery voltage, and then a PIC could be added to charge the battery
using a buck regulator. The lamp should be an LED which entails having its
own buck switching supply which is available for less than a buck to drive a
3V white LED from 6V with at least 90% efficiency. The PIC can monitor the
dynamo voltage and current, and adjust the load for maximum power, while
charging the battery according to optimum current or voltage.

Such a system should give an efficiency of at least 85%, whereas the one
proposed is immediately crippled by losing 1W out of the available 3W, so
the efficiency must be less than 67%.

Anyone care to actually discuss this?

Paul
www.pstech-inc.com