A Cycling & bikes forum. CycleBanter.com

Go Back   Home » CycleBanter.com forum » rec.bicycles » Techniques
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Eyc headlight problem



 
 
Thread Tools Display Modes
  #91  
Old April 3rd 21, 03:34 PM posted to rec.bicycles.tech
Ralph Barone[_4_]
external usenet poster
 
Posts: 853
Default Eyc headlight problem

Mark J. wrote:
On 4/2/2021 4:13 PM, John B. wrote:
On Fri, 2 Apr 2021 12:32:51 -0700, "Mark J."
wrote:

On 4/2/2021 11:59 AM, Ralph Barone wrote:
sms wrote:
On 4/2/2021 9:00 AM, jbeattie wrote:

snip

I don't love it. I would love a dyno light with a solid 800 lumen
output, a little more upward spew and a stand light that was stronger
than the light on my give-away key chain from Wells Fargo -- and one
with a battery so I could use the light off the bike. We
transportational cyclists often need a light for use off the bike. A
flasher would be nice for dusk and dawn, but not required. And while
we're wishing, how about something lighter and more efficient than a
bunch of magnets whirling around. There must be some other way of
harvesting electrons.

Such a light would be wonderful but it would be a stretch with a 6V/3W
dynamo, even at higher speeds where you can get more than 3 watts out of
it. Some LED makers are claiming 300 lumens per watt, at least in the
lab, but 200-250 lumens per watt are what is available commercially at
this time.

A 12V/6W hub dynamo (or even a 9V/4.5W hub dynamo) would make dynamo
lights with sufficient intensity more practical, including a beam
pattern where some upward spew would be possible. DRL flash capability
is trivial to add, as are internal batteries to be able to use it off
the bicycle. But there is just not much of a market for any of this.


You seem to have it stuck in your head that the internal impedance of a hub
generator is some immutable quantity and not a design parameter. Why not a
6V/12W hub dynamo? Hell, if you were willing to do frequency dependent
series capacitor switching, you can get a lot more than 3W out of a 3W
labelled hub.

And yet virtually all the commonly available bike dynamos come out with
a half amp nominal design. (So that wattage is half of voltage). I'm
told their coils "saturate" (or something like that) at a half amp.

I've only been using dynamos over a span of 50 years. I've owned 6V/3W
and 12V/6W generators, and once I saw an 8V/4W claim. If there was a
big improvement to be had with some other amperage design, I would think
someone would have tried to market it by now. Dynamo design might have
some complications, but surely they are well understood at this date.

Mark J.

It is because cyclists are such puny power supplies. It would be no
problem to design a more powerful generator into the hub of a bicycle
wheel if the power supply were great enough to power it.


No doubt this is why the *wattages* of all these generators are pretty
low. We had a 12V6W bottle generator on our tandem for years. It was
not an efficient model, but still. Even with double the cyclist power,
you could really feel the drag with that thing.

That doesn't explain why the *amperage* is consistently 0.5A on
virtually all the bike generators of the last ~30 years. I'm just
saying this consistency probably has a reason behind it.

Mark J.



Because that’s what Sturmey-Archer did?

Ads
  #92  
Old April 3rd 21, 03:39 PM posted to rec.bicycles.tech
SMS
external usenet poster
 
Posts: 9,477
Default Eyc headlight problem

On 4/2/2021 4:47 PM, jbeattie wrote:

snip

Its nice not just seeing people's feet riding up the road on my standard commute: https://tinyurl.com/53z5dcs8 The good thing about the modern era is that dogs wear lighted vests. On that road, you can actually hit your head on a tree if you're not paying attention.


Jay, how is it possible that a panel truck did not drive by and knock
down any low hanging branches? Why would you need your bicycle headlight
to have any upward spill to illuminate low hanging branches that could
not possibly exist? You need to call your city's public works department
and demand that they send out a tall truck to knock down any low-hanging
branches (for those that are new here, one poster claimed that any
upward spill of lights to illuminate low-hanging branches was
unnecessary because trucks driving by, close to the edge of the road,
would knock down and such branches).

Seriously though, it’s strange to see complaints about bicycle lights
that do more than simply illuminate the patch of road directly in front
of the bicycle. Yes, that’s what dynamo lights were originally designed
to do, but it was because that with 2.4-3 watts of power from the
dynamo, and an incandescent bulb, they could not do much else. You also
have the StVZO standards which most dynamo lights adhere to, which is
kind of a Catch-22 when it comes to the U.S. since those very standards
make most dynamo lights less than optimal. Reality is that it's a _good_
thing to have some upward spill and side spill.

One exception in dynamo lights is the Supernova E3 Triple 2
https://supernova-lights.com/en/e3-triple-2/, which give sufficient
upward and side illumination, but it Is NOT StVZO approved, the
Supernova web site states "The E3 Triple light is not available in
Germany, for legal reasons. Customers outside Germany can order it via
phone or e-mail." Peter White sells it for $251. Combine a 70% efficient
SP PD-8 dynamo wheel with the Supernova E3 Triple 2 and you’d have a
good dynamo lighting system for less than $600, depending on the quality
of the rim and spokes you choose. Add in a circuit that simulates a DRL
by enabling switching between standlight and full brightness. Get one
light and one wheel for every bicycle in your fleet.

  #93  
Old April 3rd 21, 03:58 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 10,538
Default Eyc headlight problem

On 4/3/2021 1:45 AM, Jeff Liebermann wrote:
On Fri, 2 Apr 2021 20:47:00 -0400, Frank Krygowski
wrote:

The efficiency of bike dynos varies pretty greatly. I could check
numbers, but IIRC top quality hub dynos can hit 65% efficiency. Cheap
bottles can be as low as 40%.


http://www.myra-simon.com/bike/dynotest.html
See "Normal Speed Efficiency" bar graph. Looks like efficiency varies
from 22% to 61%.


OK, my memory was being too optimistic about the low end dynamos.


The first thing to do is throw out the "voltage regulator" that
reduces output (and decreases efficiency) at high RPM (high
frequencies). Replace it with an electronic voltage regulator.


It's not clear to me that the built-in voltage regulation represents a
loss in efficiency. That is, I don't think the power is being taken from
the rider's input by the coils and magnets, then converted to heat by
the inductive reactance. My understanding is that what would be
increased power at higher speed is simply never produced.

I know from private correspondence that David Gordon Wilson (of MIT and
_Bicycling Science_) said he was once working on a scheme to produce a
constant rpm bike dynamo, but once he understood how they worked, he
stopped thinking about his scheme.

If there was some way to get the dynamo RPM up high enough, an
alternator would be a further efficiency improvement. Extra points
for a fixed RPM mechanism, where the efficiency is optimized for a
narrow range of RPM's.


The rotational speed of a bottle dynamo is pretty high! Over 4000 rpm at
12 mph.

The average cyclist has to deliver about 200 watts to sustain 15 mph
on a level roadway. A 3 watt lighting system with 50% dynamo
efficiency will require 6 watts from the cyclist. That's only 3% more
power needed to maintain 15 mph with the lights on.

However, if you want 800 lumens output using 125 lumens/watt LED's
(including optical losses), it will take:
800lum / 125lum/watt = 6.4 watts
to power the light. If someone produced an oversized 50% efficient
bottle dynamo that delivered 6.4 watts, it would require 12.8 watts
from the cyclist or
12.8 / 200 = 6.4%
additional cyclist power to run the lamps. Try that on an exercise
machine or with a cycling computer on a bicycle. It's possible to do
it for short intervals, but not continuously.

What's needed is a dramatic increase in efficiency. If the dynamo
were 100% efficient, then an 800 lumen light would require only a
little more power from the cyclist than the original bottle generator.
100% efficiency is impossible, but there's plenty of room for
improvement between 50% and 100% efficiency.


I strongly, strongly dispute the need for 800 lumens for riding on the
road at night. To me that's very similar to saying bicycles should all
have motorcycle-duty drive chains and spokes.

--
- Frank Krygowski
  #94  
Old April 3rd 21, 04:01 PM posted to rec.bicycles.tech
SMS
external usenet poster
 
Posts: 9,477
Default Eyc headlight problem

On 4/2/2021 10:45 PM, Jeff Liebermann wrote:

snip

If there was some way to get the dynamo RPM up high enough, an
alternator would be a further efficiency improvement. Extra points
for a fixed RPM mechanism, where the efficiency is optimized for a
narrow range of RPM's.


Just add more poles in the dynamo which would have the equivalent effect.

The average cyclist has to deliver about 200 watts to sustain 15 mph
on a level roadway. A 3 watt lighting system with 50% dynamo
efficiency will require 6 watts from the cyclist. That's only 3% more
power needed to maintain 15 mph with the lights on.

However, if you want 800 lumens output using 125 lumens/watt LED's
(including optical losses), it will take:
800lum / 125lum/watt = 6.4 watts
to power the light. If someone produced an oversized 50% efficient
bottle dynamo that delivered 6.4 watts, it would require 12.8 watts
from the cyclist or
12.8 / 200 = 6.4%
additional cyclist power to run the lamps. Try that on an exercise
machine or with a cycling computer on a bicycle. It's possible to do
it for short intervals, but not continuously.


You have to accept that with the dynamo on you'll be sharing your output
power between forward progress and the light. The bicycle's gearing will
solve this issue, and you'll just be going slower, but you can do it
continuously.

What's needed is a dramatic increase in efficiency. If the dynamo
were 100% efficient, then an 800 lumen light would require only a
little more power from the cyclist than the original bottle generator.
100% efficiency is impossible, but there's plenty of room for
improvement between 50% and 100% efficiency.


There are already SP dynamos with 70%+, so the drag is not as big of an
issue as you make it out to be. 3 watts is enough for a 500 lumen light
(real lumens!) and is certainly sufficient for most road riding. Thermal
issues prevent a single LED from reaching the lumens/watt level
necessary for 500 lumens, but lights like the Supernova E3 triple reach
500 lumens with three LEDs, and have a good beam pattern (not StVZO
compliant).

A hybrid system with the ability to provide higher-output for short
periods of time would be nice. The added weight of a hybrid lighting
system would likely be well worth it as well. Charge the battery in the
daytime, at perhaps 250mA while pedaling on level ground, 500mA when
coasting or on long downhill runs, and 0ma when going uphill. Run the
light solely on dynamo power when full brightness isn't required or when
the battery is exhausted.

But no company is going to make much of an investment in developing such
a system and then tooling up and manufacturing it. The market just isn't
there unless they could get such a system installed at the factory, and
no high-volume bicycle manufacturer wants to that kind of expense.
  #95  
Old April 3rd 21, 04:22 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 10,538
Default Eyc headlight problem

On 4/3/2021 10:39 AM, sms wrote:
On 4/2/2021 4:47 PM, jbeattie wrote:

snip

Its nice not just seeing people's feet riding up the road on my
standard commute: https://tinyurl.com/53z5dcs8* The good thing about
the modern era is that dogs wear lighted vests.* On that road, you can
actually hit your head on a tree if you're not paying attention.


Jay, how is it possible that a panel truck did not drive by and knock
down any low hanging branches? Why would you need your bicycle headlight
to have any upward spill to illuminate low hanging branches that could
not possibly exist? You need to call your city's public works department
and demand that they send out a tall truck to knock down any low-hanging
branches (for those that are new here, one poster claimed that any
upward spill of lights to illuminate low-hanging branches was
unnecessary because trucks driving by, close to the edge of the road,
would knock down and such branches).

Seriously though, it’s strange to see complaints about bicycle lights
that do more than simply illuminate the patch of road directly in front
of the bicycle. Yes, that’s what dynamo lights were originally designed
to do, but it was because that with 2.4-3 watts of power from the
dynamo, and an incandescent bulb, they could not do much else. You also
have the StVZO standards which most dynamo lights adhere to, which is
kind of a Catch-22 when it comes to the U.S. since those very standards
make most dynamo lights less than optimal. Reality is that it's a _good_
thing to have some upward spill and side spill.


I'm sure the pickup drivers I encounter using their high beams on my
also praise their upward spill and side spill. There are a few of them
that also run LED light bars, or turn them on if someone flashes to
complain about their high beams. It's a MFFY attitude.

But the bit about modern lights "simply illuminate the patch of road
directly in front of the bicycle" is simply false. I've checked several
times and measured nearly a quarter mile to a stop sign illuminated by
my Cyo headlight. The visible beam on the roadway stretches at least 30
feet, and objects on the road are visible farther than that.

As to the panel trucks and overhead branches, I don't know what sort of
bike you ride on what sort of streets if you're got a real danger of
whacking your head on a branch. A bicyclist's head is normally about six
feet off the ground, maximum. That's less than the height of the very
common Ford F-150 pickup. AASHTO's bike facility design manual calls for
a minimum of 8 feet of overhead clearance on a bike path, with 10 feet
desirable.

So somehow motor vehicles are not being damaged by branches six feet
above the road, yet you're at risk of hitting your head? You must be on
an antique high wheeler or some other very unusual bike.
https://en.wikipedia.org/wiki/Tall_bike

Or more likely, are being your usual obtuse self.

--
- Frank Krygowski
  #96  
Old April 3rd 21, 04:29 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 10,538
Default Eyc headlight problem

On 4/3/2021 3:13 AM, wrote:
On Friday, April 2, 2021 at 11:40:08 AM UTC-5, Mark J. wrote:
On 4/2/2021 3:09 AM, wrote:
As for dynamo lights. For randonneuring, they are almost required because you are riding so long in darkness at night. Batteries would not work. But for riding around town, I have been more of a battery person than dynamo person. I have both types of lights. Battery lights are much more powerful and provide a couple hours of light. More than enough for evening recreational rides or commuting. One two hour evening rides a couple times a week or commuting morning or evening are the predominant uses of lights. Batteries work very well for these kinds of rides. Its very uncommon for someone to ride all night long and require a dynamo.

While I like my dyno hub and Luxos headlamp for randonneuring, I did two
of my super randonneur series with batteries, and liked 'em just fine.
And the first one was with lead-acid (heavy!) batteries. It was the
superior beam pattern on the Luxos (bought for my commuter) that
persuaded me to convert the rando bike to dyno.

Frankly, prior to well-engineered LED headlights, dynos just didn't
provide enough light for my tastes. Riding all night is much more
stressful when you have to struggle to see road hazards.

Mark J.


Yes I can see that. Depending on how you ride randonneur rides. 200k, no light needed, 13.5 hour time limit. 300k, 20 hour limit, only need light 1/2 hour in the morning and 2-3 hours maybe in the evening. 400k, 27 hour limit, 1 hour morning, 2 hours evening, stop for sleep, 2 hours next morning. On low power batteries can give 4-5 hours of light. 600k, 40 hour limit, 1 hour morning, 2 hours evening, stop for sleep, 1 hour morning, ride all day and get in before need lights in evening. You may be cutting it a bit close if you do not finish quick enough on the second day of riding. No margin for error. But doable. And for the 1000k at 75 hours and the 1200k at 90 hours, they will also work with batteries but will require a new battery/recharge for the second half of the rides. Again doable with the correct planning and no unexpected emergencies arise.

But dynamo on brevets eliminate most of the worry from the unexpected emergencies and you don't have to do any planning at all for night riding. I'd definitely recommend a dynamo for randonneur brevet riding. On my PBP I had a support car so I could have maybe planned to meet my support at approved stops at the right times before dark and gotten fresh batteries. That would have taken a whole lot of planning and luck to work. Not something I want to count on during a timed 1200k. And of course with the much better LED lights for dynamos now, you can get good lighting out of a dynamo. If you are willing to pay the upfront cost and your usage, riding patterns warrant a dynamo.

I used the old filament lights on my dynamo in 2007 and the prior year too when I did an extra 1200k to get ready for PBP. Busch Mueller 6V lights. Two of them for my Shimano dynamo. One each side of the front hub. They provided the minimum amount of light. Minimum. You always wanted more light. I have since upgraded to some B&M LED lights. Two. Much, much better. When I rode brevets, I sometimes rode through the night on 400, 600, 600, 1000, 1200 rides. No sleep stops. So I needed longer run times than batteries could provide.


Long ago, I had three friends who entered a 24 hour event - just "How
far can you ride in 24 hours?" going around and around a few miles of
roadway.

Two of my friends (a fast racer and his sport-tourist father) went out
hot, cranking away at high speed. They burned out in about 8 hours, IIRC
and did not finish.

The third guy who I thought of as very elderly (but not as old as I am
now) just rode and rode at his usual moderate pace. For that particular
event he set a record for his age group, something like 315 miles in 24
hours. They said you always knew it was him approaching in the middle of
the night because you could hear his bottle dyno whirring away.

--
- Frank Krygowski
  #97  
Old April 3rd 21, 04:36 PM posted to rec.bicycles.tech
Ralph Barone[_4_]
external usenet poster
 
Posts: 853
Default Eyc headlight problem

Frank Krygowski wrote:
On 4/2/2021 10:14 PM, Ralph Barone wrote:

Pretty much all dynamo design dates back to a time when electronics didn’t
exist. Since light bulbs don’t put out much light at low voltage and tend
to die at high voltage (I seem to recall bulb life being inversely
proportional to the fourth power of voltage), it was important to try and
find a way to produce a constant voltage from a variable speed generator.
The solution that was found was to build the generator with a large leakage
inductance. This inductance provides more and more resistance to current
flow as the frequency (ie: speed) goes up. Since the voltage also goes up
with speed, the two effects cancel each other and you get a reasonably
constant output into a constant resistance load. This became its own
standard (with a 6V output because that was the voltage of three lead acid
cells or four carbon cells).

It is the adherence to this 6 V 500 mA standard which is inhibiting
progress. With modern electronics, it is possible to produce a regulated
output voltage from a variable input voltage. If you have this, there is no
longer the requirement to have so much leakage inductance to regulate the
voltage. The output of the generator also doesn’t have to be 6 V AC, and
if we look at modern LED lights and lithium ion batteries, 6V doesn’t make
sense anymore. 5V actually makes more sense in terms of LED voltage drop,
lithium ion battery voltage and USB powered accessories.

What would make sense to me would be a generator based on modern brushless
DC e-bike motor design, with a maximum output somewhere in the 25 W range,
but normally limited to around half of that (because how much drag do you
want from your dyno hub?). Generate at a slightly higher voltage (for more
efficient rectification, but not so high that the wire in the rotor is too
fragile), then regulate it down to 5V DC for distribution. Add a
controller that figures out how much to ask the generator to produce and
intelligently divides up that power between the battery and the connected
loads and you have a nifty scheme. Unfortunately, the market is to small to
repay the poor shmuck who ends up re-engineering the entire ecosystem.
Maybe somebody with deep pockets (Shimano?) can lay out the standard, then
others can join in.


As an ME, not an EE, your ideas seem technically possible to me, but are
they really practical? ISTM if you view a dyno light system overall as
something that converts rider wattage to road illumination, there's not
much opportunity for big improvements.

Roughly speaking, dyno efficiencies are high enough that you lose maybe
one or two Watts of rider power there. The other inefficiency is
whatever is wasted as heat instead of light in the LED and its
circuitry. I don't know that efficiency as a percent, but it has to be
minor. I know some LEDs are now pushing 200+ lumens per watt. Properly
focused, that should allow 35 mph descents, and almost nobody wants to
go that fast on a bike at night. Headlights using those LEDs should be
enough to satisfy anyone this side of "more lumens are always necessary"
craziness.

I'm aware of the reasons for 5V electronics, but given modern electronic
expertise, I'd think it wouldn't be difficult to inexpensively mass
produce an efficient 6VAC to 5VDC transformer.

Disclaimer: Again, I'm a Mechanical Engineer, not an Electrical Engineer.


I know that you’ll probably disagree about the necessity of doing so, but a
lot of the talk recently in this thread has been about the 3W limit and how
to get around it. My opinion is that once you want to get more power, that
throwing out history and redesigning the generator would be a good idea.

Regarding the 6VAC to 5VDC transformer, yes it’s possible, but certain
things get in the way of doing it efficiently, and changing some of the
system parameters would make it easier to get a DC output without throwing
away too much of your precious power.

  #98  
Old April 3rd 21, 04:36 PM posted to rec.bicycles.tech
Ralph Barone[_4_]
external usenet poster
 
Posts: 853
Default Eyc headlight problem

Jeff Liebermann wrote:
On Sat, 3 Apr 2021 02:14:42 +0000 (UTC), Ralph Barone
wrote:

Since light bulbs don’t put out much light at low voltage and tend
to die at high voltage (I seem to recall bulb life being inversely
proportional to the fourth power of voltage), it was important to try and
find a way to produce a constant voltage from a variable speed generator.


I beg to differ. As I understand it, the bulb life is thermal
problem, not a voltage problem. For example, a halogen light needs to
be run a rather high temperature so that the tungsten particles
evaporated off the filament are re-deposited back onto the filament,
thus giving the halogen bulb a longer life. This doesn't work unless
the filament is really hot. Since the temperature of the filament is
mostly determined by the power (watts) dissipated in the filament,
lamps of equal operating wattage will last about the same number of
hours no matter what the voltage. Or more crudely, a 6v 1A lamp
running at rated voltage, will last approximately the same number of
hours as a 12v 0.5A bulb running at rated voltage, because they both
burn the same number of watts and operate at the same temperature.

Notice I wrote "approximately". The difference is the surface area of
the helical filament. A low voltage filament uses heavier wire than a
high voltage filament. Since brightness and tungsten evaporation
amount are partially determined by the surface area (for the same
wattage), things go non-linear in a hurry. We would probably be using
heavy gauge filament wire for maximum surface area if tungsten wasn't
so expensive.

Where the 4th power rule comes in is where the operating voltage is
lowered in order to reduce the current, which reduces the dissipated
wattage, which dramatically increases the bulb life. It's not by the
4th power but rather by the 3.5th power:
https://www.edn.com/incandescent-lamps-and-service-life/
"Candlepower = (Applied voltage / Rated voltage)3.5 × MSCP
or the mean spherical candlepower at the design voltage.
From there, Lumens = Candlepower × 4 pi "

Reality tends to be more complicated. See the section on Pg 7 "Lamp
Life" in:
https://www.alliedelec.com/m/d/04fe4bc2ac7e247d70e8e7d88fe48b19.pdf



Yes, bulb life is a thermal problem, but filament operating temperature
depends on applied voltage. The filament is heated by V^2/R, and cooled by
conduction back to the base (linear thermal model) and radiation into free
space (fourth power thermal model). Light output is optimized as you get
the tungsten closer to the liquid state, which is also, of course when the
bulb fails. Incandescent lights produce a colour temperature in the 3000 K
range, so I assume the filament is also around that temperature. Tungsten
melts at 3687 K, so you can see that the designers of light bulbs don’t
have much room to play before the filament liquifies.

Obviously, my memory was a bit faulty. As per the Wikipedia article quoted
below, bulb lifetime is not proportional to the inverse fourth power, but
closer to the 14th. So the reality is that if you lower the voltage, you
get MUCH longer life, but no light, and if you raise the voltage, you get a
lot more light, but for a vanishingly short time until the bulb burns out.
It is this trade off which drove the design of dynamo hubs to be the way
they currently are.

LED lamps have different characteristics (light output is pretty much
proportional to current down to the point where there’s not enough voltage
to overcome the voltage drop of the bulb). Modern electronics changes the
game again. Since nobody currently uses incandescent lamps in any new
lights, the “stuckedness” of the dynamo hub industry on 6 VAC, 0.5 A claw
pole generators is a lost opportunity in my mind.

https://en.m.wikipedia.org/wiki/Lamp_rerating

  #99  
Old April 3rd 21, 04:36 PM posted to rec.bicycles.tech
Ralph Barone[_4_]
external usenet poster
 
Posts: 853
Default Eyc headlight problem

Jeff Liebermann wrote:
On Fri, 2 Apr 2021 20:47:00 -0400, Frank Krygowski
wrote:

The efficiency of bike dynos varies pretty greatly. I could check
numbers, but IIRC top quality hub dynos can hit 65% efficiency. Cheap
bottles can be as low as 40%.


http://www.myra-simon.com/bike/dynotest.html
See "Normal Speed Efficiency" bar graph. Looks like efficiency varies
from 22% to 61%.

The first thing to do is throw out the "voltage regulator" that
reduces output (and decreases efficiency) at high RPM (high
frequencies). Replace it with an electronic voltage regulator.
Actually, that's not quite correct. LED's are current driven devices,
so replace it with a current regulator and take whatever voltage is
available.

If there was some way to get the dynamo RPM up high enough, an
alternator would be a further efficiency improvement. Extra points
for a fixed RPM mechanism, where the efficiency is optimized for a
narrow range of RPM's.


Don’t tell anybody, but dynamos are alternators. They produce alternating
current.

The average cyclist has to deliver about 200 watts to sustain 15 mph
on a level roadway. A 3 watt lighting system with 50% dynamo
efficiency will require 6 watts from the cyclist. That's only 3% more
power needed to maintain 15 mph with the lights on.

However, if you want 800 lumens output using 125 lumens/watt LED's
(including optical losses), it will take:
800lum / 125lum/watt = 6.4 watts
to power the light. If someone produced an oversized 50% efficient
bottle dynamo that delivered 6.4 watts, it would require 12.8 watts
from the cyclist or
12.8 / 200 = 6.4%
additional cyclist power to run the lamps. Try that on an exercise
machine or with a cycling computer on a bicycle. It's possible to do
it for short intervals, but not continuously.

What's needed is a dramatic increase in efficiency. If the dynamo
were 100% efficient, then an 800 lumen light would require only a
little more power from the cyclist than the original bottle generator.
100% efficiency is impossible, but there's plenty of room for
improvement between 50% and 100% efficiency.





  #100  
Old April 3rd 21, 05:12 PM posted to rec.bicycles.tech
Jeff Liebermann
external usenet poster
 
Posts: 4,018
Default Eyc headlight problem

On Sat, 3 Apr 2021 15:36:31 +0000 (UTC), Ralph Barone
wrote:

Dont tell anybody, but dynamos are alternators. They produce alternating
current.


Oops. You're right. I was thinking of getting rid of the magnets and
replacing them with a field winding to provide some better current
regulation. That's one reason why gasoline powered
inverter-generators are more efficient than connecting the load
directly to the generator. I haven't run any numbers, so I'm not sure
if this will work.

Thanks.

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




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
The last headlight you will ever need somebody[_2_] Techniques 115 April 28th 14 02:12 AM
Headlight Tom $herman (-_-) Techniques 16 August 17th 12 03:43 AM
LED Headlight HughMann Australia 12 August 30th 06 11:51 AM
LED headlight problem solved Ron Hardin General 8 April 3rd 06 10:42 AM
Headlight Bruni Techniques 8 August 31st 03 06:27 PM


All times are GMT +1. The time now is 09:55 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Copyright 2004-2022 CycleBanter.com.
The comments are property of their posters.