Thinking Outside The Box

On 3/12/2012 12:07 PM, Peter Cole wrote:

Yes, perhaps, but that wasn't my point. I question the certainty that 10
lux is bright enough to see by.

The whole German standard appears to be based solely on conspicuity.
Certainly they were well aware when the established the standards that
10 lux was not going to do much in terms of illumination of the road,
but they felt it sufficient for "being seen."

The idea that anyone would want to carry enough batteries to power a
light that would actually be bright enough to see by used to be unthinkable.

The first lighting system in the U.S. that was bright enough to see by
that I remember was the Ed Kearny system back in the 1980's. I wrote an
article for California Bicyclist back in the 1980's offering detailed
plans for a homebrew lighting system using SLA batteries, automobile
driving lights, and xenon strobes, and sent out several hundred copies
of the plans for "free" (just charging for postage and printing), and
also sold systems for a while.

On 13/03/12 06:43, SMS wrote:
On 3/12/2012 9:01 AM, Jeff Liebermann wrote:

Ok, I'll concede the point. With a generator, which acts as its own
voltage and current regulator, a PWM regulator is not necessary.

Actually the dynamo voltage continues to go up with increased speed.
That's why with the older incandescent bulbs you needed a protection
circuit to prevent burning the bulbs out.

We are not talking about incandescent light bulbs as the load on a
dynamo, we are talking about using an LED (or two or more in series).

The I-V curve of an LED is vastly different from an incandescent bulb,
in fact they are almost a mirror image.

http://eznec.com/images/PR3_and_Cree_IV.gif

See that with 3.5V supplied by a source to this LED, the current drawn
is about 1A, and that any increment in supply voltage causes a huge
increase in current. The dynamo simply cannot supply this much current,
so the voltage is unable to reach this level.

With an incandescent bulb the incremental current is far less, which
does allow the voltage to rise slightly, and may exceed the lamps
capabilities.

You ought to measure and plot the dynamo load line on the LED I-V curve
and find the operating point.

--
JS.

On 13/03/12 08:00, sms88 wrote:

The idea that anyone would want to carry enough batteries to power a
light that would actually be bright enough to see by used to be
unthinkable.

That's why they used dynamos instead.

--
JS

On Mar 12, 9:44 am, Frank Krygowski
wrote:
James wrote:
On Mar 12, 3:57 pm, Jeff wrote:

My fading memory of a dynamo was a bottle generator when I was about
16 years old. It was a major drag and I only used it when absolutely
necessary.

My Sanyo Dynapower is not recognized as an efficient device, yet still
the drag is barely noticeable. Perhaps you should try a more modern
device?

I really wonder about all those reports of super-draggy generators form
long ago. Yes, technology has improved, but the old Union generators
I've tried on bikes have not been very bad.


We know of your tolerance for via ability to ignore things that you
don't want to accept.

I'm wondering if the bad old impressions come from two sources:

First, did the kids using them understand about aligning them properly
to the wheel?

I did, but then, I seemed to readily grasp of such things (99th
percentile on the standardized mechanical aptitude tests).

If the axis of a bottle generator's rotation doesn't
intersect the axis of the wheel's rotation, I can imagine lots of
scrubbing and drag.

Explaining the concept for those of us who *still* don't understand
such things, eh? :-)

And the popularity of "block" generators, with
integral headlight, might have promoted bad alignment by kids who
concentrated on the beam direction.


But they have to ride it to run the light and see where it lands, eh?
Might they notice a change in effect when they made adjustment, hence
learning the significance of alignment?

Second, there's the psychology. It seems obvious to me that chain
squeaks cause far less energy loss than psychological loss. The same
was true of the multiple squeaks in my ancient Dahon folding bike.
Maybe the old generators just _sounded_ draggy.


Psychology matters - especially when it's a continuous reminder of the
*real* drag behind it (and weight, and a bike goiter with a wire
hanging out of it). I don't know about anybody else, but I revel in
relatively effortless speed (always liked to downhill, for instance),
and noticed it in very subtle ways.

I used a Sanyo Dynapower similar (probably not identical) to James's.
I'll confirm that the drag level (with halogen headlight) was just
barely noticeable. That's from accidentally leaving it on for a
daylight ride to work, and noticing that I felt just a tiny bit slower
on the bike. With my similar Soubitez, it (accidentally) measured out
to just a one mph difference at about 19 to 20 mph.


That's pretty significant.

James wrote:
On 13/03/12 06:43, SMS wrote:
On 3/12/2012 9:01 AM, Jeff Liebermann wrote:

Ok, I'll concede the point. With a generator, which acts as its own
voltage and current regulator, a PWM regulator is not necessary.

Actually the dynamo voltage continues to go up with increased speed.
That's why with the older incandescent bulbs you needed a protection
circuit to prevent burning the bulbs out.

We are not talking about incandescent light bulbs as the load on a
dynamo, we are talking about using an LED (or two or more in series).

The I-V curve of an LED is vastly different from an incandescent bulb,
in fact they are almost a mirror image.

http://eznec.com/images/PR3_and_Cree_IV.gif

See that with 3.5V supplied by a source to this LED, the current drawn
is about 1A, and that any increment in supply voltage causes a huge
increase in current. The dynamo simply cannot supply this much current,
so the voltage is unable to reach this level.

I agree.

In fact, from that curve, a nominal 6V, 3W generator would produce less
than 3.5 Volts when powering that LED, plus whatever the rectification
scheme would eat. Should be definitely less than 6V. As I said
earlier, I'd expect less drag than normal as a result.


--
- Frank Krygowski

On 3/12/2012 3:43 PM, SMS wrote:
On 3/12/2012 9:01 AM, Jeff Liebermann wrote:

Ok, I'll concede the point. With a generator, which acts as its own
voltage and current regulator, a PWM regulator is not necessary.

Actually the dynamo voltage continues to go up with increased speed.
That's why with the older incandescent bulbs you needed a protection
circuit to prevent burning the bulbs out.

Depends on the load. Incandescent filaments increase resistance with
current, so you basically get thermal runaway.


However, the one battery powered bicycle light that I looked at, and
the few that I've read about, all seem to have PWM regulators. The
advantage is longer battery life by not using any dissipative devices.

Yes, for battery powered LED lights with multiple power levels and a
strobe there is a PWM device. Ditto for the better dynamo lights with
strobes like the one from Planet Bike.

Yep. Y'er correct, I'm wrong. No PWM needed or wanted for a
generator powered light.

Alternator or dynamo, not generator.

Alternators and dynamos are types of generator.


The MR16 lamps usually have a
bridge rectifier inside because they need to run off AC or DC. With the
micro-lenses focusing and collimating the beams you get a very good beam
shape for cycling, as long as you choose a good angle (not spot, not
wide flood). The downside of course is that you have to find a way to
mount it to the bicycle, but the upsides over commercially available
dynamo LED lights make it well worthwhile: 1) beam shape, 2) optics, 3)
intensity, 4) cost, 5) mounting security.

The beam shape is conical, the intensity is what it is, but the
efficiency usually isn't state of the art, they're not all that cheap
(compared to other power LED devices), they're much larger than they
need to be, mounting is problematic and they're not weather tight
generally.

On 3/12/2012 8:12 PM, Phil W Lee wrote:
considered Sun, 11 Mar 2012 13:28:47

If the Germans have outlawed the use of a flashing light on a bicycle,
I think they're backward, and I don't care how many ex-spurts I have
just disagreed with.

Accident stats seem to indicate otherwise.
Maybe you are facing the wrong way?

Got those stats?

Peter Cole wrote:
On 3/12/2012 2:59 AM, Sepp Ruf wrote:
Peter Cole wrote:

I think that's what I said. You can can convert lumens to candelas if
you know the beam angle (and it is uniform), from there, you need to
know the target area and distance to compute the illuminance in lux.

Sure. However, at least in the small world beyond toy manufacturing,
passing beams are not at all uniformly angled, and the relation between
source lumens, and a bunch of target illuminances at specified beam
angles is more complicated.

I struggled through what might have been a poor translation. As I recall
10 lux was the minimum for illuminance of the target area. That seems
dim for "seeing", more adequate for "being seen".

The tarmac at 10 meters' distance is sort of immobile, and not
interested in "seeing" you. One needs to consider the differing angular
intra-beam differences between "seeing" and "being seen" parts in a
passing beam.

But here's news, or quite the contrary: The vertical "being seen"
minimum above cut-off is not defined anywhere in the German bicycle
lighting standard. Some disinfo "experts" will never, ever, grasp this,
of course.

From
http://swhs.home.xs4all.nl/fiets/tes.../index_en.html

Well, the guy is really good at boosting Philips LED lamps, recording
his rides, putting up a website, and all that, but he tends to jump to
conclusions rather quickly.

"studying the StVZO requirements for car and motorcycle headlamps, it
all becomes clear.

Bicycle headlamps may only put out a light density of 2.0 lux above 3.4
° above the brightest spot in the beam.

"light density" - not.

With cars and motorcycles, the
measurement is not at 10m, but at 25 m, and their lamps are allowed to
be 1.0 lux maximum above the cutoff. Well, this means cars can blind
oncoming traffic with a light density at 10m of 2.52 x 1.0 lux = 6.25
lux!

Seems like he didn't look up the "car" standards that tend to be a bit
more complicated, even above cutoff. And maybe he missed that cars tend
to employ two of these lamps - which might have helped his argument.

This is more than 3 times what bicycle lamps may put out in that
region! (actually, what they are probably supposed to put out at maximum
there, see the section StVZO's requirement about how bicycle headlamps
should be aimed)

questionable logic, maybe a language problem. As mentioned above, in
German bicyle lamp standards, there is no minimum anything above cutoff.

Also note that bicycle lamps are since several years in
StVZO required to be at least 10 lux.

20 lux for higher rated source flux levels

This is the intensity of the beam
measured at 10 m, not the intensity of what the cyclist will see from
what's reflected back to him! So it's clear why a halogen lamp that puts
out 10 lux at 10 m on a wall is useless to see the road on parallel
roads, because you're going to get far less than 10 lux back to your
eyes, and yet you're getting up to 6.25 lux into your eyes from car lamps.

overly simmplifying the visual process; not employing real-life glare
illuminances at eye level. Okay, he also rides an incumbent, and thus
is prone to getting hit by much more than 6 lux.

Why are the rules so much less strict for cars? (again, when assuming
the rules for bicycles were meant to allow only 2.0 lux or less above
the horizon, not when taking what they really imply, see the section
StVZO's requirement about how bicycle headlamps should be aimed) And did
the StVZO people really expect cyclists to see anything on parallel
roads?

ranting.

Do the StVZO people actually ride bicycles?

As far as I know, some of them once tried, but somehow, the whole thing
didn't quite work out. Might have been the mandatory helmet law that
backfired:
https://upload.wikimedia.org/wikiped...fahrtruppe.jpg

On 13/03/12 09:43, Dan O wrote:
On Mar 12, 9:44 am, Frank

Second, there's the psychology. It seems obvious to me that chain
squeaks cause far less energy loss than psychological loss. The same
was true of the multiple squeaks in my ancient Dahon folding bike.
Maybe the old generators just _sounded_ draggy.


Psychology matters - especially when it's a continuous reminder of the
*real* drag behind it (and weight, and a bike goiter with a wire
hanging out of it). I don't know about anybody else, but I revel in
relatively effortless speed (always liked to downhill, for instance),
and noticed it in very subtle ways.

Make no mistake, Dan, I like to ride fast and effortlessly too! I still
don't feel impeded by my dynamo in operation, on a recreational ride
that is. I take it off for a race, but then I don't go as far as some,
who spend mega bucks to save a couple of pounds.

I used a Sanyo Dynapower similar (probably not identical) to James's.
I'll confirm that the drag level (with halogen headlight) was just
barely noticeable. That's from accidentally leaving it on for a
daylight ride to work, and noticing that I felt just a tiny bit slower
on the bike. With my similar Soubitez, it (accidentally) measured out
to just a one mph difference at about 19 to 20 mph.


That's pretty significant.

I ride the same route 2-3 times a week. The average speed goes up and
down by more than that depending on the elements and how I feel.

For Frank's experience, he might have repeated the test a few more times
to get a better picture. He might have found the difference to be less
(or more, we'll never know ;-)

--
JS.

On 13/03/12 10:05, Frank Krygowski wrote:
James wrote:
On 13/03/12 06:43, SMS wrote:
On 3/12/2012 9:01 AM, Jeff Liebermann wrote:

Ok, I'll concede the point. With a generator, which acts as its own
voltage and current regulator, a PWM regulator is not necessary.

Actually the dynamo voltage continues to go up with increased speed.
That's why with the older incandescent bulbs you needed a protection
circuit to prevent burning the bulbs out.

We are not talking about incandescent light bulbs as the load on a
dynamo, we are talking about using an LED (or two or more in series).

The I-V curve of an LED is vastly different from an incandescent bulb,
in fact they are almost a mirror image.

http://eznec.com/images/PR3_and_Cree_IV.gif

See that with 3.5V supplied by a source to this LED, the current drawn
is about 1A, and that any increment in supply voltage causes a huge
increase in current. The dynamo simply cannot supply this much current,
so the voltage is unable to reach this level.

I agree.

In fact, from that curve, a nominal 6V, 3W generator would produce less
than 3.5 Volts when powering that LED, plus whatever the rectification
scheme would eat. Should be definitely less than 6V. As I said earlier,
I'd expect less drag than normal as a result.



Most certainly. If you connect a pair of LEDs in parallel so that one
is forward biased while the other is reverse biased, there is no need
for a rectifier. They form their own rectifier. The losses are
minimised. Most certainly in this instance the voltage will be held at
something near 3.5 V, and drag from the dynamo will be less than 3 W /
efficiency.

If you want more light (and subsequently more drag) use 4 LEDs as pairs
in series. One pair conducting while the other pair are reverse biased.
This is what I've done. I barely notice the dynamo is on. I should
do some coast down tests on the back wheel, and after determining the
moment of inertia and air and bearing resistance, I could calculate the
dynamo drag ;-) Maybe one wet winters day...

More light and drag can be achieved by using 6 LEDs, which will cause
the LEDs to start operating at slightly higher speed (until the dynamo
voltage increases to 10.5 V).

It's so simple and reliable. I rode to the race on Saturday and left
the dynamo on the bike, 'cause I had to marshal on a corner. Several
vets saw the lights on the bike and noticed the dynamo. A few said "Oh,
I remember using one of those. I might still have one in my junk box."
Maybe some will be inspired to experiment. Less batteries is better
for the environment ;-)

--
JS.