On 4/5/2021 1:53 AM, Sepp Ruf wrote:

snip

This is how a low and high beams, 400 dynamo, optional 400 extra battery
lumens, conversion looks like:
https://www.velomobilforum.de/forum/index.php?attachments/pxl_20210121_153046943-jpg.231317/

That looks like something someone hand-built, modifying an existing
light. Where is the link to the forum post that has this image?

Hopefully they included thermal sensors to automatically reduce power to
prevent overheating.

It's an interesting concept but IMVAIO it's backward. Instead of adding
an optional battery to a dynamo light, it would be more logical (and
much less expensive) to add optional dynamo operating and charging to a
battery powered light. You can get a much more capable fully-featured
headlight, with internal Li-Ion batteries, for 1/3 to 1/4 the cost, and
a circuit to charge the batteries from the dynamo is trivial.

Most USB-chargeable lights can charge at at least 1A so a 6V/500mA
dynamo could provide about 5VDC@800mA via a rectifier and buck
converter. You just need to ensure that the light can operate while
charging, not all battery powered lights have the capability, but many do.

You can buy a converter with a built in bridge rectifier for only a
couple of bucks
https://drive.google.com/file/d/1SIABsLdDoSZgGsAdasmgHyjRcco55nd9/.

While it would work as is, I'd smallen it up and make it a little more
efficient. I'd change the bridge rectifier to four Schottky diodes and
put in some lower-profile, lower-voltage capacitors since you don't need
to go higher than 12V on the input and 6V on the output (it can go up to
50V input and 24V output), change the potentiometer to a fixed resistor,
remove the screw terminals, and use s smaller heat sink since you only
need to put out about 800mA instead of 2.2A.

What would be really nice if some battery powered light manufacturer put
this stuff inside the light. Can you imagine the market for Barry Beams'
Oculus light if he had a version with an AC input from a dynamo? Well
I'm not sure of the market since it would not be legal in Germany, and
the number of cyclists with dynamos on their bicycles in the U.S. is
vanishingly small.