On 2/8/2018 4:25 PM, Joerg wrote:
On 2018-02-08 16:01, Frank Krygowski wrote:
On Thursday, February 8, 2018 at 4:14:47 PM UTC-5, Joerg wrote:
On 2018-02-08 12:20, AMuzi wrote:
On 2/8/2018 2:08 PM, Joerg wrote:


Those 2.4W bulbs were a joke. My bikes (after my teenage
years) always had better lighting than that. Now it's all
LED on my bikes but the real stuff with more than 500 lumens.


For years with a Margil cover or, after a Krygowski mod with O ring,
and
without a switch (always on) I have no complaints about function or
longevity. YMMV.


How much does that O-ring reduce the drag? In the old days (with a real
power bus on the bike) I often rode the first miles with the dynamo off
because of the drag. I only put it back to the wheel when the "steam
gauge needle" (remember those?) got too close to the red range.

First, the terrors of dyno drag are mostly a myth. This article deals
with it:
http://www.myra-simon.com/bike/dynotest.html
"the slowing down has more to do with psychology than the actual power
required
to turn it."
and
"All of the generators were easier to turn than riding up a 1 in 300
slope.
Another way of putting that is a rise of 18 feet per mile; and there's
quite a
cluster of sidewall and hub-driven models around the 1/500 line, or 10
ft per
mile."


Well, take another look at your link. I routinely ride at 30km/h at
which bottle dynamos waste 15W or more. That is nothing to sneeze at.


I find it odd that a guy routinely tells us weight doesn't matter to
him, but is
afraid of dyno drag equivalent to riding a 1 in 300 slope.


Hint: In the flatlands and with a nice high tire pressure weight doesn't
make much of a difference. In hilly terrain it's tougher to get uphill
but you win most of that back going back down on the other side. The
only time I feel weight is when I buy something at the brew supply place
or hardware store in the valley and then have to schlepp it up 1300ft.


Regarding the O-ring solution - that is, cutting a groove in the dyno
drive
wheel, snapping in a suitable O-ring and running that on the rim sidewall
instead of the tire - it makes the dyno almost silent. That should
greatly
reduce your psychological stress, Joerg, but it probably reduces the
drag a bit,
too. The deformation and scrubbing of the contact patch between the
tire and
the dyno's roller is responsible for a significant portion of dyno
drag. I think
the O-ring has a lot less scrubbing and a lot less hysteresis loss.


Yeah, I should give that a try. Still got a dynamo on the road bike from
the days when I had NiCd batteries which didn't have the capacity of
Li-Ion. Only issue is, it's a Soubitez dynamo where the wheel is not
removable. I'd have to figure a way to grab it at its outside diameter
with a hose or something and then drive that hose with a power drill at
a speed the dynamo can stomach for a while, then hold the corner of a
file to it.

Also, my last front Gatorskin is still on there and those have
paper-thin sidewalls. I'd have to mount another tire.

The drag on bottle dynamos and roller dynamos is significant, though I
have only owned Sanyo roller and Union bottle, not the high-end German
bottle dynamos. For the hub dynamos it's hard to quantify the
difference. I rode my Dahon yesterday which has an SP hub dynamo
(rebranded as "Joule") but it'd be hard, without special equipment, to
run it with the original wheel, and measure the difference. I have a
high-end LED light on the Dahon, but like most StVZO compliant,
European, LED lights there is no DRL flasher. My back-up dynamo light on
my commute bike has a DRL flasher, but it's too weak to use by itself.
Have to look at this one:
http://www.chainreactioncycles.com/us/en/exposure-revo-dynamo-light-only/rp-prod110884.

You're absolutely right regarding waste of excess power, and there's no
reason for this with a better design. A dynamo charging a 2P Li-Ion
power pack with a buck switcher would solve this problem, at least until
the batteries are fully charged, but then you could choose to disconnect
the dynamo from the load.