View Single Post
  #24  
Old March 6th 17, 10:33 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 6,016
Default More About Lights

On 2017-03-06 10:47, wrote:
On Sunday, March 5, 2017 at 5:26:18 PM UTC-8, Jeff Liebermann wrote:
On Sun, 5 Mar 2017 16:03:30 -0800 (PST),

wrote:

Thanks Jeff. These however all appear to be battery powered
lights. We were sort of looking for lights that operated on the
hub dynamo of 6V 3W or the Globe dynamo of 12V 6W or four times
the power.


Sorry, I thought you were still open to looking at battery powered
lights. Here's what I fished out of my bookmark dumpster. No
reviews and few tests, but some interesting dynamo graphs and
numbers: http://www.myra-simon.com/bike/dynotest.html
http://pilom.com/BicycleElectronics/DynamoCircuits.htm
http://www.eeweb.com/blog/extreme_circuits/power-mosfet-bridge-rectifier



This one is well worth reading (or skimming) and has quite a few test
results:
http://swhs.home.xs4all.nl/fiets/tests/verlichting/index_en.html

This is why the hub generator has so little drag.


Well, let's do some arithmetic. If your dynamo is rated at 3
watts, and your lighting is rated at 70 lumens/watt, then the most
you can perhaps deliver is 210 lumens. 6 watts will get perhaps
420 lumens. Usually, it's less as the losses accumulate.
Rectification losses, optical losses, heat degradation, and
connector losses all conspire to produce lower output.

You might find it useful to know how bright you want your light.
For that, you'll need a Lux meter. I have a Lutron LX-102 which
works nicely, and two junk meters I bought on eBay for sanity
checks: http://www.ebay.com/sch/i.html?_nkw=lux+meter Get one
that has a wide range. Lowest on mine is 1000 lux, and highest
range is 50,000 lux.

Find a dark night and an accomplice to operate the meter and send
them down the road to the farthest distance that you might want to
illuminate with your headlight. Use a headlight or flashlight to
light up that area. Have your accompli's take a reading. It will
probably be zero. Now, cut the distance in half and take a
measurement. It will be 2x as bright (lux) at half the distance or
4x as bright at 1/4th the distance. Adjust the brightness for what
it would have been if the light meter was sufficiently sensitive.

Converting the brightness (lux) to luminous flux (lumens) requires
that you know the distance to the accomplice, and the illumination
angle. (1 lux = 1 lumen/square-meter)

The form below makes a mess of bad assumptions but is good enough
for a rough approximation:
https://www.ledrise.com/shop_content.php?coID=19 Once you know
how many lumens you think you need, and have adjusted for overly
ambitious expectations, you can determine which lighting technology
is suitable.

Lets say you want to see 8 meters ahead and 20 degrees to each
side (or 40 degree conical beamwidth) at 20 lux, which is rather
dim. Plugging into the web page above, I get 485 lumens needed.
You won't be able to do that with a 3w dynamo, but might squeeze by
with a 6w and an oval shaped beam.


-- Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com Santa Cruz CA 95060
http://802.11junk.com Skype: JeffLiebermann AE6KS
831-336-2558


As a very occasional night rider I am interested in battery powered
lights but I think that I was attempting to give a thought to a
commuter that would use his light a great deal.


I use my lights a great deal because they are on during the day as well
except on segregated bike paths.

Recharging is 2nd nature to me. Bike gets parked back in the garage,
li'l round connector gets plugged in, done. Sometimes I deliberately do
not charge past 8V until shortly before a ride. That improves battery
lifetime.

The real McCoy would be a worryfree system like in a car where it
recharges while riding. If I ever switch the road bike front wheel to
one with a hub dynamo I will do that. Right now it only has a bottle
dynamo, too much drag and it eats the left side wall of "modern" tires.
Power output of those is well above 3W at higher speeds if you provide
the proper electronics. I could go into that but it's nerdy tech stuff.
Essentially you need what is called a SEPIC or at least a buck converter
plus some sort of maximum power point tracking (MPPT) control for that
converter. Sounds more complicated than it really is but do not expect
the bicycle industry to deliver anything even remotely close anytime soon.

Realistically you could eke out 4-6W depending on you speed. That's not
enough to feed a MagicShine clone which wants 8W on high plus a watt or
so for the rear lights. And maybe another 1-2W for the MP3 player. Plus
the smart phone. And the electric razor :-)

In my case this would work nicely because I need the full 10W total only
on county roads and in city areas where car drivers tend to misbehave.
Else it drops to a net load of 4-5W or even much lower. So the dynamo
would recharge the watt-hours you used up on the county road. Once the
battery gets full it throttles back. Just like in car.


I notice that a large number of the people in our group have flashing
red rear lights and it isn't long before these batteries run down
enough that the taillight even blinking is almost entirely
unnoticeable. So I don't have much respect for battery power for a
great deal of use.


Yep, that's a major nuisance. However ... one can power these lights off
a regular 8.4V Li-Ion battery or even a dynamo (after rectification) by
providing a 3V regulator. Small enough to fit where the two AAA cells
used to be.

If battery rear lights at least had a low-battery warning. Technically
that would be a piece of cake. But no ... nothing :-(

--
Regards, Joerg

http://www.analogconsultants.com/
Ads
 

Home - Home - Home - Home - Home