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From: Rolf Mantel <news@hartig-mantel.de>
Newsgroups: rec.bicycles.tech
Subject: Re: For those who believe in electricity
Date: Wed, 9 Apr 2025 12:35:15 +0200
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Am 08.04.2025 um 22:12 schrieb sms:
> On 4/7/2025 5:15 PM, Jeff Liebermann wrote:

>> Not going below 0V is the most common way PWM is used.  However, it's
>> not mandatory or the only way:
>> <https://en.wikipedia.org/wiki/Pulse-width_modulation>
>> Note that the waveform shown goes below 0V.
> Yeah, that is true, it's possible for PWM to go below zero, but that's 
> not the way it's normally used for LED light dimming or PWM fan speed 
> control.
> 
> With LED bicycle lights, it's surprising that no bicycle light company 
> has a dynamo input into their battery powered lights. Even at only 3W 
> from the dynamo, you could power a high-end bicycle light at lower 
> power, and you could be charging the battery during daytime rides when 
> all you have on is the daytime running light.

"No" is a not quite correct, "extremely rare" would describe the market 
better.
<https://nabendynamo.de/produkte/scheinwerfer/ladelux/>

Slightly more common: a "dynamo driven power supply" produces power to a 
USE output, and theoretially you can route that USB power into your bikt 
light but with no fine-tuned optimization the output is too low to make 
it worthwhile in any sense.