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Old February 9th 18, 01:01 AM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Default Battery Replacement on Lights with Internal Li-Ion Batteries

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."

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.

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.

- Frank Krygowski
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