Eyc headlight problem

On Fri, 2 Apr 2021 16:45:38 -0700, "Mark J."
wrote:

On 4/2/2021 4:13 PM, John B. wrote:
On Fri, 2 Apr 2021 12:32:51 -0700, "Mark J."
wrote:

On 4/2/2021 11:59 AM, Ralph Barone wrote:
sms wrote:
On 4/2/2021 9:00 AM, jbeattie wrote:

snip

I don't love it. I would love a dyno light with a solid 800 lumen
output, a little more upward spew and a stand light that was stronger
than the light on my give-away key chain from Wells Fargo -- and one
with a battery so I could use the light off the bike. We
transportational cyclists often need a light for use off the bike. A
flasher would be nice for dusk and dawn, but not required. And while
we're wishing, how about something lighter and more efficient than a
bunch of magnets whirling around. There must be some other way of harvesting electrons.

Such a light would be wonderful but it would be a stretch with a 6V/3W
dynamo, even at higher speeds where you can get more than 3 watts out of
it. Some LED makers are claiming 300 lumens per watt, at least in the
lab, but 200-250 lumens per watt are what is available commercially at
this time.

A 12V/6W hub dynamo (or even a 9V/4.5W hub dynamo) would make dynamo
lights with sufficient intensity more practical, including a beam
pattern where some upward spew would be possible. DRL flash capability
is trivial to add, as are internal batteries to be able to use it off
the bicycle. But there is just not much of a market for any of this.


You seem to have it stuck in your head that the internal impedance of a hub
generator is some immutable quantity and not a design parameter. Why not a
6V/12W hub dynamo? Hell, if you were willing to do frequency dependent
series capacitor switching, you can get a lot more than 3W out of a 3W
labelled hub.

And yet virtually all the commonly available bike dynamos come out with
a half amp nominal design. (So that wattage is half of voltage). I'm
told their coils "saturate" (or something like that) at a half amp.

I've only been using dynamos over a span of 50 years. I've owned 6V/3W
and 12V/6W generators, and once I saw an 8V/4W claim. If there was a
big improvement to be had with some other amperage design, I would think
someone would have tried to market it by now. Dynamo design might have
some complications, but surely they are well understood at this date.

Mark J.

It is because cyclists are such puny power supplies. It would be no
problem to design a more powerful generator into the hub of a bicycle
wheel if the power supply were great enough to power it.

No doubt this is why the *wattages* of all these generators are pretty
low. We had a 12V6W bottle generator on our tandem for years. It was
not an efficient model, but still. Even with double the cyclist power,
you could really feel the drag with that thing.

That doesn't explain why the *amperage* is consistently 0.5A on
virtually all the bike generators of the last ~30 years. I'm just
saying this consistency probably has a reason behind it.

Mark J.

Well, how much amperage does one need to power a head and tail light?
Or perhaps more accurately how many watts?
--
Cheers,

John B.