Re: bike light optics

On Wed, 10 Apr 2024 16:21:04 -0400, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:

On 4/10/2024 2:39 PM, Jeff Liebermann wrote:

On Wed, 10 Apr 2024 12:36:37 -0400, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:
 

On 4/10/2024 7:06 AM, Rolf Mantel wrote:

>
Cheap hub dynamoes have a rolling resistance in the order of 15W to
generate 3W.  A good hub dynamo can probably get those 12W out of a
mechanical resistance in the order of 20W.

>
Wow. I wasn't aware that any hub dynamos were that inefficient. Can you
say which brands those are?

 
Ummm...
<https://www.google.com/search?q=%22cable+test%22+%22PWM%22>

>
Oops. That's related to cable PWM instead of hub dynamos.

Sorry.  I cut and pasted the wrong URL.  I was in a hurry to attend a
free lunch.  This is what I meant to post:
<https://www.google.com/search?q=dynamo+hub+efficiency+graph&udm=2>

More on hub dynamo efficiency:
<https://www.cyclingabout.com/best-dynamo-hub-bicycle-touring-bikepacking/>
Charging Test Averages (Four Different Chargers):
1. SON28 Hub - 57% efficient
2. 3D32 Hub - 44% efficient
3. UR700 Hub - 39% efficient
4. PD-8 Hub - 34% efficient

Lighting Test Averages (Four Different Dynamo Lights):
SON28 Hub - 44% efficient
3D32 Hub - 37% efficient
PD-8 Hub - 31% efficient
UR700 Hub - 30% efficient

 You can see some typical
efficiencies and RPM/efficiency curves at:
<https://pedalcell.com/blogs/blog/maximizing-bicycle-charging-efficiency>
"A rider that tries to charge their phone with a common bicycle dynamo
system can lose over 60% of their power."

>
Which is still better than the "15W to generate 3W." That's why I asked.

Good point.  3w/15w = 20% efficiency.  The numbers I found are bad,
but not as bad as 20%.

BTW, most of the dynamos in that Efficiency bar graph are bottles or
rollers, not hub dynamos. The hubs are at the top, between 45% and 60%
efficient. Again, that's why I asked.

PedalCell looks something like a small bottle dynamo in that it has a
rubber roller that rides on the wheel rim.
<https://pedalcell.com>
<https://pedalcell.com/en-nl/blogs/blog/maximizing-bicycle-charging-efficiency>
The above article claims 70% efficiency.


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Jeff Liebermann                 jeffl@cruzio.com
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