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From: Jeff Liebermann <jeffl@cruzio.com>
Newsgroups: rec.bicycles.tech
Subject: Re: bike light optics
Date: Tue, 09 Apr 2024 10:38:25 -0700
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On Tue, 9 Apr 2024 08:36:46 -0400, Zen Cycle <funkmaster@hotmail.com>
wrote:

>On 4/9/2024 1:57 AM, Jeff Liebermann wrote:
>> On Fri, 5 Apr 2024 09:36:27 -0700, sms <scharf.steven@geemail.com>
>> wrote:
>> 
>>> What would be nice is a higher-end battery powered light that could be
>>> charged with a dynamo, and operate at lower power directly from the
>>> dynamo, but there is no such animal. A dynamo to USB-C PD adapter would
>>> be perfect but all the dynamo USB commercial products are to 5VDC only.
>> 
>> Good idea, but the dynamo might need to be enlarged to handle the
>> combined load of charging the battery and powering the light.  It is
>> possible to do both with the existing 3 watt dynamos using PWM (pulse
>> width modulation), where the waveforms for powering the light and
>> charging the battery are interlaced so that the dynamo sees only one
>> load at a time. 

>I don't think I've ever heard of a PWM multiplexing scheme before. Is 
>there such a thing?

Neither have I.  There might actually be such a thing but I'm not
going to sift through the patent bone yard looking for one right now.
I have the bad habit of contriving solutions that seem likely, but
might not exist (yet).

In this case, let's pretend you have a power source that delivers
something resembling a constant 3 watt power level.  The power source
needs to operate a 3 watt front light and simultaneously charge a
battery that also presents a 3 watt load.  Connecting the light and
the battery in parallel is going to be a 6 watt load, which the
mythical power source (dynamo) can't handle.  

If the load was only a front light, the usual way to reduce the lights
output is with a PWM (pulse width modulation) light dimmer, where the
output power is proportional to the duty cycle of the PWM waveform.
100% duty cycle is full brightness (3 watts), 50% duty cycle is half
brightness (1.5 watts) and 33% duty cycle would be 1/3 brightness (1.0
watts).

The nice part of PWM is that there is no load BETWEEN pulses.  For
example, if the front light was running at 33% (1 watt) duty cycle,
there would be the remaining 67% (2 watts) available to power
something else, without exceeding the 3 watt limit of the power source
(dynamo).  Therefore, the "extra" 67% could be used to charge the
battery.  Just invert the PWM output that powers the front light to
produce the PWM output the powers the battery charger.  I could
probably throw something together using commodity switching power
supply IC's.

If I wanted to be creative, I could adjust the pulse width using a
control knob.  At one end, all the power goes to the front lamp.  At
the other end, all the power goes to charging the battery (as might be
the case during daylight hours).  However, in both cases, the load on
the dynamo doesn't exceed its rated 3 watts, which is the purpose of
this exercise.

Patent pending (maybe).

>Maybe you can build mux a cable tester in there too.

You seem to be hallucinating.  Were you watching the eclipse without
proper eye protection?


-- 
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558