Hi MIKE.

02-Sep-03 21:59:58, MIKE ROSS wrote to Greg Mayman


 MR> "Greg Mayman" bravely wrote to "Roy J.
Tellason" (02 Sep 03
 MR> 08:39:00) --- on the heady topic of "VEHICLE LED'S"

 GM>> Even with a capacitor input filter, the impedance of the usual
 GM>> cycle dynamo is too high to charge the cap to the peak voltage,
 GM>> as you can do with a mains supply to offset the diode drops.

 MR> The impedance is pretty low, in fact I've thought about adding an
 MR> AC capacitor across the lamp to increase the power factor and thus
 MR> extend the power band somewhat. It's kind of like a resonant
 MR> circuit where the capacitor supplies power when the generator goes
 MR> through zero thus keeping the filament more fully lit on average
 MR> by increasing the voltage across the lamp somewhat. Or more simply
 MR> by cancelling the series inductive reactance as seen by the lamp.
 MR> I haven't taken any measurement of the dynamo's windings yet but
 MR> it should be less than about 10 milliHenry. Otherwise there
 MR> wouldn't be enough voltage getting to the lamp. So the capacitor
 MR> would be about 700uF at 60Hz. Ah, I might have one around to try
 MR> it out...

 GM>> The best form of regulation would be a shunt regulator to bleed
 GM>> off some of the current when the voltage got too high for the
 GM>> bulb. Unfortunately this would increase the load on the dynamo.

 MR> Not on the dynamo... ME!!!   Mr. Motive Source!!! Nobody is
 MR> shunting any of *my* energy to ground on my bike!!! 

with a series inductor the faster you crank the higher the frequency and the
less AC it will pass... it'd tend to limit the current output

putting that capacitor in there could make things interesting when you hit
the resonant frequency..


 -=> Bye <=-

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