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From: Roger Merriman <roger@sarlet.com>
Newsgroups: rec.bicycles.tech
Subject: Re: For those who believe in electricity
Date: 8 Apr 2025 20:41:06 GMT
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sms <scharf.steven@geemail.com> wrote:
> On 4/7/2025 5:15 PM, Jeff Liebermann wrote:
> 
> <snip>
> 
>> 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.
> 

Fairly sure it would be very niche use, as modern bike lights tend to have
fairly substantial batteries and thus on low the run time is many hours,
over a day in some cases.

And considering the relative low output from the dynamo even if the light
was off, light on be even less output, note how slowly and generally need
good conditions (ie constant relatively high speeds) to  charge even a
mobile phone in a timely fashion, which is by some measure has smaller
battery.

The question is why would one do that when as when you stop at home etc,
charging the light is fairly quick and painless job, every few days or so.

Ie I can’t see folks saying yes that’s what I need!

Roger Merriman