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From: Rolf Mantel <news@hartig-mantel.de>
Newsgroups: rec.bicycles.tech
Subject: Re: For those who believe in electricity
Date: Fri, 11 Apr 2025 11:04:00 +0200
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Am 11.04.2025 um 03:56 schrieb Jeff Liebermann:
> On Wed, 9 Apr 2025 12:35:15 +0200, Rolf Mantel <news@hartig-mantel.de>
> wrote:
> 
>> 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.
> 
> This article shows 26 such bicycle USB chargers.  That seems to be a
> popular use for bicycle dynamos.
> <https://www.cyclingabout.com/list-of-hub-dynamo-power-supplies-for-usb-devices/>

Sure, it's common to use a bike dynamo to charge low-power devices. 
Charging mobile phones barely works because many phones stop charging on 
a variable power supply.

I have no direct knowledge of anybody using a dynamo to top up their 
battery lights.