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Old February 11th 18, 07:02 PM posted to rec.bicycles.tech
Joerg[_2_]
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Default Battery Replacement on Lights with Internal Li-Ion Batteries

On 2018-02-11 08:25, sms wrote:
On 2/8/2018 4:25 PM, Joerg wrote:
On 2018-02-08 16:01, Frank Krygowski wrote:


[...]


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.


Nice but I am not willing to pay $200 just for a front light when I can
buy a fully adequate one for under $20. Swapping the lens is needed but
done in minutes.


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.



That is how I used dynamos in the past and would like to do that again.
However, in the US it is hard to find a reasonably priced complete front
wheel with a hub dynamo and I don't want to spoke up my own. So it'll
have to be a bottle dynamo (rollers went the way of the dinosuars) and
then I'd like to try Frank's mode with an O-ring and run it on the brake
surface nstead of the tire.

--
Regards, Joerg

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