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.

--
Regards, Joerg

http://www.analogconsultants.com/