Re: LED Headlight and generator?

On Mon, 17 Oct 2005 09:37:49 +0200 Andreas Oehler
<andreas.oehler@xxxxxx> wrote:

>Mon, 17 Oct 2005 12:16:26 +0800, Marty:

>>Don't you have four diodes in a bridge rectifier? And doesn't the
>>current go though two diodes? So yo're actually losing 0.6 watts. And
>>when you look at 0.6 watts out about 5 watts it's 12% of your capacity
>>wasted.

The 0.6V was for a Shottky bridge. They only have about 0.3V forward
drop, less than half that of silicon.

>Thats ugly theory. Two anti-parallel LEDs flicker annoyingly and there is
>no possibility to add a standlight capacitor.

Flicker is something else to be considered. I don't know how bad that
would be. It certainly varies with road speed and generator model.

>Use those two LEDs connected in series behind a Shottky bridge: Double
>light output, less flicker. Possibility to smooth out the remaining
>flicker with a fat low-ESR capacitor. Possibility to ad a Standlight
>capacitor in parallel to one of the LEDs.

We have to keep in mind that even when the polarity is in the right
direction, no current flows at all until the voltage exceeds the total
forward voltage drops of the components. If you draw yourself a nice
AC waveform, you will see that the effect is to produce shorter and
shorter light pulses. The integrated effect is less light. The
capacitor really won't smooth this out, unless you also add in a
resistor, which wastes power....

>Just try out both versions and report what you like better.

A very fair point.

-
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Jim Adney jadney@xxxxxxxxxxx
Madison, WI 53711 USA
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.

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