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#91
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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? |
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#92
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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
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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
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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
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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
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Eyc headlight problem
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#97
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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
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Eyc headlight problem
Jeff Liebermann wrote:
On Sat, 3 Apr 2021 02:14:42 +0000 (UTC), Ralph Barone wrote: Since light bulbs dont 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
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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
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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 |
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