Re: bike light optics

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.  With such an arrangement, there might be times when
the headlight won't be operating at full brightness, but that's the
price for leaving the stand light running for too long and depleting
the battery.  A 5 position switch will help.
1.  Off
2.  Stand Light
3.  Automagic
4.  Dynamo powers light only (probably night time only).
5.  Dynamo charges battery only (probably day time).

Another problem is charging a single 18650 Li-Ion cell.  These are
typically 3000 ma-hr at 3.7V or 11 watt-hrs.  If all the power from
the dynamo was used to charge this cell, it would take about:
  11 watt-hrs / 3 watts = 3.7 hrs
of pedaling to charge the cell from zero to 100%.  A good BMS (battery
management system) will want to protect the battery by limiting the
SoC (state of charge) from about 20% to 95% and to slow down charging
above 80% SoC.  My guess(tm) is about 3.0 hrs from 20 to 95%.  (Note
that a LiFePO4 cell will tolerated 0 to 100% but costs more).  Anyway,
to deal with the long charge time, an external 115V AC charger or
easily replaceable 18650 cell will be needed.  A smaller cell could be
used, such as a "AA" size 14500 cell (1100 ma-hr at 3.7V or 4.1 watts)
will require 1.4 hrs to charge, which is tolerable.  My guess(tm) is
that the long charge time will make it unpopular with infrequent
bicycle riders who rarely ride long enough to fully charge the cell. 

At these low power levels, I think a LiPo cell might be a better
solution. 

Yes, it can be done, but I think the idea combines the worst
characteristics of dynamo and battery powered lights, instead of the
best.  Also, because it doesn't advertise mega-lumens, it won't sell.

Drivel:  Maybe turning the bicycle suspension shocks into power
generators (electrical dynamic damping) will provide some added power.
I haven't tried this yet, but it looks useful for estimating how much
energy could be recovered.  Only $25.
"Bike Suspension Analysis and Design Software"
<https://www.bikechecker.com>
(Yet another project and diversion).

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