Re: bike light optics

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>

The efficiencies vary radically.  The closer the dynamo resembles a
brushless motor, the more efficient.  Dynamos also have a peak in the
efficiency curve, where low RPM operation is very inefficient, mid RPM
are the most efficient, and high RPM shows a drop in efficiency (from
core saturation).  The core saturation effect act as a voltage
regulator and is designed into the dynamo so that an additional
voltage regulator is NOT required.  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."

Drivel:  Gone to see if there really is such a thing as a free lunch.



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Jeff Liebermann                 jeffl@cruzio.com
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