Eyc headlight problem

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

DonÂ’t 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.


I would have thought that the efficiency advantage of inverter based
generators over the older style “hook it up to the generator� type is that
the inverter produces a constant 60 Hz regardless of the incoming
frequency, which gives you the option of reducing motor speed at low load
to reduce frictional losses in the motor when high output power is not
required. Older generators are stuck always turning at 3600 RPM or 1800 RPM
just to get the frequency right. On a bike, unless you want to build a CVT
between the wheel and the dynamo, the prime mover turning at the wrong
speed is just something you have to live with.

On Sat, 3 Apr 2021 10:58:34 -0400, Frank Krygowski
wrote:

On 4/3/2021 1:45 AM, Jeff Liebermann wrote:
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.

Maybe. I need to dig through the available literature and do some
testing to see what really happens. You might be correct as drag
produced by the dynamo is reduces at high RPM's by the increased
frequency which presents a higher inductive reactance. On an output
power vs RPM graph, that causes the curve to become "flat" at high
RPM's creating an effective output power regulator. In theory,
inductive reactances do NOT dissipate power. Only resistances
dissipate power. Since the inductance doesn't change, there would be
no change in efficiency. However, there are also saturation effects
in the inductor (windings) which do dissipate power once the current
exceeds the core saturation limit. That should produce heat at high
RPM's. If you have time, try spinning the bottle dynamo at a high RPM
driven by an electric drill and see of it gets hot. Also, if you have
a motor that can drive the dynamo (or just a spinning bicycle wheel),
try shorting the load (headlight). My guess(tm) is that the motor or
wheel will spin quite easily.

Notice the drop in output power at various loads and RPM's.
http://pilom.com/BicycleElectronics/Dynamo.htm
My guess(tm) is that's mostly core saturation at the high end.

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.

Cool. Anything you can share? I can think of a variety of CVT
(continuously variable transmission) designs that might be suitable.
I'm not so sure he gave up because he thought it won't work. My
guess(tm) is that it didn't provide a sufficient improvement to
justify the cost and complexity.

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.

4000 RPM is only 66.7 Hz for a single pole and 533 Hz for an 8 pole
bottle dynamo. I want to see something in 50KHz range where I can
start using ferrite materials instead of powdered iron. However, that
will require 31,800 RPM, which is probably not practical. More poles
will do it, but that costs more money. Hmmm...

Please note that a hybrid battery plus dynamo contrivance would be a
far better proposition. At low speeds, the light operates off the
battery. At higher speeds (i.e. downhill), where there is power
available, it switches to dynamo. In it's spare time, it charges the
battery.

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.

I think it was Jay Beattie who suggested the 800 lumen number. I
merely stole it from him. I agree that 800 lumens probably too much.
However, if such a high power dynamo product ever arrives on the
market, there will surely be a lumens war among vendors to see who can
advertise the largest number. At that time, 800 lumens will reserved
for purists and regulatory agencies.


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

On 4/3/2021 8:36 AM, Ralph Barone wrote:
Jeff Liebermann wrote:
On Sat, 3 Apr 2021 02:14:42 +0000 (UTC), Ralph Barone
wrote:

Since light bulbs donÂ’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.

snip

LEDs also have thermal issues. Thermal solutions on higher power
automotive LED headlights have elaborate thermal solutions with heat
sinks, heat pipes, and even fans. With bicycle lights, the higher-end,
higher-power lights use multiple LEDs with a collimated beam to address
the thermal issue and will usually use an aluminum case, with fins, as a
heat sink. They'll also have a thermal sensor that reduces power to
prevent overheating. I once had a cheap high-power LED flashlight where
the LED got so hot that it unsoldered itself from the board.

I recall many years ago on this board that someone insisted that a big
advantage of LEDs was that "...LEDs being solid state electronic
devices, not high-temperature bits of super-thin tungsten wire... that
they last very close to forever" (see
https://groups.google.com/g/rec.bicycles.tech/c/0DBl75y7JFQ/m/7LQK0xc-T8YJ).
Well that's true, when an LED is being used as an indicator lamp,
operating at only a 5-20 milliamps, but it was not true for LEDs being
used for actual lighting. A properly cooled high-power LED is going to
last a lot longer than an incandescent bulb, but with most bike lights
when that LED does burn out the entire light needs to be replaced. A few
early bike lights used replaceable LED lamps, but those added size and
complexity.

The reality was that managing thermals on an incandescent bulb, where
the heat radiated out the front of the light, was a lot simpler than the
elaborate LED thermal solutions that are necessary on high-power LED lamps.

TDP (thermal design power) used to be something that was of concern
mainly for CPUs and graphics processors, now it's a concern on a lot
more devices.

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.

Uh, have you ever looked at the output of a bicycle dynamo on a scope?
They are alternators. I do recall a couple of DC dynamos in the distant
past.

On Sat, 3 Apr 2021 16:55:07 +0000 (UTC), Ralph Barone
wrote:

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

Don?t 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.

I would have thought that the efficiency advantage of inverter based
generators over the older style “hook it up to the generator” type is that
the inverter produces a constant 60 Hz regardless of the incoming
frequency, which gives you the option of reducing motor speed at low load
to reduce frictional losses in the motor when high output power is not
required. Older generators are stuck always turning at 3600 RPM or 1800 RPM
just to get the frequency right.

Agreed. Notice I said "That's one reason...". Variable engine RPM
provides lower gasoline consumption at low loads and low RPM's. Also,
the noise level is lower at low RPM's. However, the engine efficiency
is optimized for about 1/2 the maximum load, which is where the
generator is expected to spend most of its time. The inverter
efficiency is also load dependent. It's the same problem as solar
inverter systems, where both the source and load powers vary
continuously. The solar inverter efficiency looks something like
this:

where they're reasonably efficient between 10% and 100% load. I
suspect that an inverter-generator has a similar curve. If a
prospective bicycle inverter follows the same curve, then there's
going to be a problem at low speeds, which is easily solved by a
hybrid battery and dynamo combination, where the battery takes over at
low RPM's.

On a bike, unless you want to build a CVT
between the wheel and the dynamo, the prime mover turning at the wrong
speed is just something you have to live with.

A CVT is actually quite easy to build if you have disk wheels. Just
run a rubber roller wheel dynamo along different radius points on the
disk wheel for different RPM. The position of the dynamo will be set
by pulley and cable arrangement where the radius point is determined
by the dynamo RPM. For slow wheel RPM, the dynamo will move near the
tire. For high wheel RPM, the dynamo will be near the hub. Patent
pending.




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

On Sat, 3 Apr 2021 10:22:35 -0700, sms
wrote:

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.

Uh, have you ever looked at the output of a bicycle dynamo on a scope?
They are alternators. I do recall a couple of DC dynamos in the distant
past.

Sorry, I goofed. Others pointed out my screwup. I was thinking of
replacing the magnets with a field winding and was ignoring everything
else. Also, it was late (10:45PM) and I was distracted by several
computah projects, phone calls, and running email exchanges.


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

On Saturday, April 3, 2021 at 12:36:34 PM UTC-5, wrote:

Uh, have you ever looked at the output of a bicycle dynamo on a scope?
They are alternators. I do recall a couple of DC dynamos in the distant
past.
Sorry, I goofed. Others pointed out my screwup. I was thinking of
replacing the magnets with a field winding and was ignoring everything
else. Also, it was late (10:45PM) and I was distracted by several
computah projects, phone calls, and running email exchanges.
You can count the dynohubs I've seen the insides of on one hand, but they all have the windings on the stator with magnets comprising the rotor. This obviates the need for brushes, which would be a wear/service item.

Steve Weeks wrote:
On Saturday, April 3, 2021 at 12:36:34 PM UTC-5, wrote:

Uh, have you ever looked at the output of a bicycle dynamo on a scope?
They are alternators. I do recall a couple of DC dynamos in the distant
past.
Sorry, I goofed. Others pointed out my screwup. I was thinking of
replacing the magnets with a field winding and was ignoring everything
else. Also, it was late (10:45PM) and I was distracted by several
computah projects, phone calls, and running email exchanges.
You can count the dynohubs I've seen the insides of on one hand, but they
all have the windings on the stator with magnets comprising the rotor.
This obviates the need for brushes, which would be a wear/service item.


The terminology here starts to get a bit confusing because of course the
stator is the stationary bit and the rotor rotates, but in 99.9% of
electric motors or generators, the stator is on the outside and the rotor
is on the inside, while in dynamo hubs, it’s the other way around.

On 4/3/2021 10:28 AM, Jeff Liebermann wrote:

snip

prospective bicycle inverter follows the same curve, then there's
going to be a problem at low speeds, which is easily solved by a
hybrid battery and dynamo combination, where the battery takes over at
low RPM's.

Well the growth of the electric bicycle market has created a hybrid
whole machine, not just the light. But even on the more expensive models
with regenerative braking (i.e.
https://www.radpowerbikes.com/products/radcity-electric-commuter-bike)
it's not clear if you can charge the battery by pedaling or coasting, or
if you can operate the lights when the battery is discharged and you're
pedaling. All that the Rad site states is that the regenerative charging
starts when you squeeze the brake levers.

I think that the bottom line is that no company is likely to invest a
lot of money in creating better dynamos to pair with better lamps. We'll
see some marginal improvements if LEDs with efficiency of 300 lumens per
watt become commercially available at not too exorbitant prices. It
would also be nice if some of the higher-end lights had a non-StVZO
model with additional features that are not legal in Germany.

On 4/3/2021 12:57 PM, Jeff Liebermann wrote:
On Sat, 3 Apr 2021 10:58:34 -0400, Frank Krygowski
wrote:

On 4/3/2021 1:45 AM, Jeff Liebermann wrote:
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.

Maybe. I need to dig through the available literature and do some
testing to see what really happens. You might be correct as drag
produced by the dynamo is reduces at high RPM's by the increased
frequency which presents a higher inductive reactance. On an output
power vs RPM graph, that causes the curve to become "flat" at high
RPM's creating an effective output power regulator. In theory,
inductive reactances do NOT dissipate power. Only resistances
dissipate power. Since the inductance doesn't change, there would be
no change in efficiency. However, there are also saturation effects
in the inductor (windings) which do dissipate power once the current
exceeds the core saturation limit. That should produce heat at high
RPM's. If you have time, try spinning the bottle dynamo at a high RPM
driven by an electric drill and see of it gets hot.

Several times I've touched the outside of my Union bottle dyno after a
long ride. It was never more than very slightly warm. Of course, I was
moving so it was losing heat by convection.

Also, if you have
a motor that can drive the dynamo (or just a spinning bicycle wheel),
try shorting the load (headlight). My guess(tm) is that the motor or
wheel will spin quite easily.

I'm sure I did that some time in the past. I may have notes about it...

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.

Cool. Anything you can share?

No, it was just a brief remark - something like "Oh, I thought they just
wasted all the power above 3W. I'll stop thinking about a constant
velocity drive."


I can think of a variety of CVT
(continuously variable transmission) designs that might be suitable.
I'm not so sure he gave up because he thought it won't work. My
guess(tm) is that it didn't provide a sufficient improvement to
justify the cost and complexity.

I think that's what we're up against in this entire discussion. The
relatively simple systems we have now work very well. It's hard to see
how a lot more complexity and expense will pay off.

Please note that a hybrid battery plus dynamo contrivance would be a
far better proposition. At low speeds, the light operates off the
battery. At higher speeds (i.e. downhill), where there is power
available, it switches to dynamo. In it's spare time, it charges the
battery.

From Sheldon Brown's site: https://www.sheldonbrown.com/dynohubs.html

" I used to have a Dynohub on a tandem, and the bulb consumption was
unacceptable. I solved the problem (and some others) by running the
Dyno's output through a full-wave bridge rectifier and then hooking the
DC in parallel with a 6 volt (5 x 1.2v cell) nickel cadmium battery.
This not only provided light when I was stopped, the Dyno would
re-charge the nicads, and, when we went so fast that the voltage rose
above 6 volts, the low internal resistance of the nicads sucked up the
excess, gaining a bit of extra charge and saving the bulb.

"The rectified output of the Dynohub was always connected to the lights.
There was no way to turn the light off while in motion. It would have
been easy enough to rig a switch for that purpose, but I didn't see the
need. The Dynohub has _very_ low drag."

(There are other articles there on generators, lights, etc. )


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.

I think it was Jay Beattie who suggested the 800 lumen number. I
merely stole it from him. I agree that 800 lumens probably too much.
However, if such a high power dynamo product ever arrives on the
market, there will surely be a lumens war among vendors to see who can
advertise the largest number. At that time, 800 lumens will reserved
for purists and regulatory agencies.

Yep, safety inflation is real.

--
- Frank Krygowski