Re: Rechargeable v. throwaway batteries

On Oct 23, 12:00 pm, SMS <scharf.ste...@xxxxxxxxxxx> wrote:
A dynamo powered headlamp
has a number of compromises by definition. It has to be designed to
provide adequate illumination even at lower speeds, so at higher speeds,
where the voltage is too high, it bleeds off the excess energy as heat.

Mr. Scharf remains so totally ignorant of generator physics!

It's a fallacy that generators just waste energy to avoid
overvoltage. It's much more accurate to say that when well designed
(as most modern ones are), they never produce significant excess
energy.

If, as some imagine, voltage would rise without limit and therefore
excess energy (or voltage?) must be converting to heat, then
efficiency curves for generators would nosedive at higher speeds, and
generators run at speed would get hot. They might even come with
cooling fins.

None of that is true. There are minor resistive losses in the
internal coils, but almost all the voltage regulation happens because
inductive reactance increases with frequency, thus with road speed.
That, not resistive losses, fight directly against the increased
voltage otherwise predicted by Faraday's Law. It's not that energy is
produced then wasted as heat; it's more accurate to say it's just not
produced.

Since the available generated power is limited, the beam is a compromise
based on the minimally acceptable illumination.

Well, if you call shining light mostly where it's needed to be
"compromise"! Most people tend to call things like that "good
design."

In any case, LEDs are rapidly becoming far more powerful and far less
expensive. LEDs are an inherently good match to the characteristics
of a bike generator. What I expect to see is the optical and
packaging work quickly following these trends, and LED generator
headlights soon satisfying even those cyclists who think they need
lights as bright as a car's.

Don't get me wrong, dynamo lights have their place, but if you're
commuting, and want a safer system, you need to have a light that's
consuming more power than a dynamo can generate.

:-) Yes, yes, yes, we know you believe that. Many of us have
chuckled about your beliefs for years, while we've safely ridden our
dynamo-equipped bikes at night. "Scharf doesn't believe I can do what
I, and millions of others, are doing right now."

I don't know why the
12V/6W bottle dynamo concept was not copied by some hub dynamo designer.
  I suppose it's because the weight and drag would be too high for many
riders.

Again, you have no idea about the physics of these things.

12 Volts, 6 Watts can be gotten out of many generators with no
changes. See http://www.m-gineering.nl/son12vg.htm

Most people don't do this because they don't need to, despite your
fear mongering. But if you want to, the components are out there for
sale.



I guess people have different ideas of what constitutes simplicity. For
me, a self-contained light is simpler than running thin wires all over
the bike and dealing with flaky connections is not as simple as a
flashlight type light...

Hmm. Perhaps you need more skill at making connections!

plus the typical night rider will be carrying a
flashlight anyway.

I admit, when they first came out I carried a 1/2 ounce coin-sized LED
flashlight for a while. After a while I just forgot about it, except
when touring. For riding around town, was too little need for it.

Simplicity, for me, is a light that works any time I need it, with no
thought about "did I bring it?" or "did it get stolen?" or "did I
remember to charge the batteries?" or "are my batteries too old to
take a good charge?" or "what if I have to ride longer than normal?"
Simplicity is a light system permanently attached to the bike, ready
to work forever whenever I flip it on. Just like my car, just like my
motorcycle.

- Frank Krygowski
.

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