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From: Roger Merriman <roger@sarlet.com>
Newsgroups: rec.bicycles.tech
Subject: Re: For those who believe in electricity
Date: 11 Apr 2025 09:49:41 GMT
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Rolf Mantel <news@hartig-mantel.de> wrote:
> 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.

Even so it’s quite a power hungry device at least smart phones, so would
need to be cycling at sufficient speed for enough time, and phones
throttling of the charge rate as it probably believes it’s connected to a
faulty power supply, hence folks use of power banks, which also would have
the advantages of not needing to charge and cable up devices on the move.
> 
> I have no direct knowledge of anybody using a dynamo to top up their 
> battery lights.
> 
Considering that the batteries in lights are quite a bit larger capacity
and the device is even more power intensive, and generally can charge back
up relatively quickly, I don’t see much use for it, I get that be a few
folks who’d like the idea of it but can’t see a good use for it.

Even the folks doing a hr or more commute, the lights last multiple days
even in winter and charge it up over night when it’s getting low, or even
at work!

Roger Merriman