Re: bike light optics

Am 10.04.2024 um 14:36 schrieb Roger Merriman:

Rolf Mantel <news@hartig-mantel.de> wrote:

Am 09.04.2024 um 18:59 schrieb Roger Merriman:

Rolf Mantel <news@hartig-mantel.de> wrote:

Am 09.04.2024 um 07:57 schrieb Jeff Liebermann:

On Fri, 5 Apr 2024 09:36:27 -0700, sms <scharf.steven@geemail.com>
wrote:
>

What would be nice is a higher-end battery powered light that could be
charged with a dynamo, and operate at lower power directly from the
dynamo, but there is no such animal. A dynamo to USB-C PD adapter would
be perfect but all the dynamo USB commercial products are to 5VDC only.

>
Good idea, but the dynamo might need to be enlarged to handle the
combined load of charging the battery and powering the light.  It is
possible to do both with the existing 3 watt dynamos using PWM (pulse
width modulation), where the waveforms for powering the light and
charging the battery are interlaced so that the dynamo sees only one
load at a time.

>
<https://nabendynamo.de/produkte/ladelux/>
will go to market this summer.
>

Seems to be claiming 12 watts from the dynamo somehow? Which unless it’s
using the buffer battery that’s going to increase the rolling resistance
significantly ie 4 fold and at that point likely to be quite noticeable.

>
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.
>

It’s claiming to draw 12 watts from the dynamo which they generally top out
at 3 watts, as most of the hubs on the sites claim as an output.

A normal dynamo is rated "3 watts at 6 Volts sinus AC".  If you run the dynamo at 12 Volts, you'll be able to pull more energy out of the same dynamo at high speed, even with "standard" light bulbs (e.g. a dynamo can run two halogen lamps in series, both emitting as much light as a normal halogen lamp once your speed exceeds 10 mph).
When using LED instead of light bulbs, the situation becomes a lot more complicated.  The exact details of generator electronics are too complicated for me to understand.
Rolf