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  1. #26
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    Just to be picky, the test would be with the dynamo completely removed from the bike, not just the light turned off. But I think you'd really want to be comparing it to a regular standard hub and wheel.

    J.

  2. #27
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    Quote Originally Posted by Cat-man-do View Post
    Yeah, Li-ion batteries don't like the cold, no question about it. If you are truly into night riding during the winter then a dynamo makes a lot of sense, at least for a bar light.

    Over the years I tried a lot of things to isolate the battery from the cold and nothing really worked. Finally I just gave up on the idea. Likely the only thing that would work would be to mount the battery on an elastic belt and then wear it around your abdomen with the battery wire coming out of your jacket. More than likely this would not be comfortable and also dangerous as the wire could interfere with any effort to bail during a crash.

    I rarely ride in the winter anymore but only because I really do hate riding in the cold. Anything under 45°F and I'm done. Gone are the good old days when I used to brave the winter cold and have a good time while doing so.
    45 isn't cold. I'd have to quit in October if that was the case (Minnesota). But I'm with you, once it gets down near freezing, I like to hang it up. It's fun, but I have a harder time regulating my temperature with clothing and getting dressed up that much is just a hassle.

    Li-ions are fine in the cold as long as you don't freeze them solid (same as any battery). They are not likely to freeze when in use. Shut off and then frozen doesn't do them any good.

    My off season activity is that I'm a ski patroller. We use both NiMH and Li-ion batteries for our radios out in the cold sometimes down near -20F and they last all day all season long (13 hour days). They are typically in radio holsters or holders that are totally exposed, that is not inside a jacket where it's warm.

    J.

  3. #28
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    Quote Originally Posted by JohnJ80 View Post
    Just to be picky, the test would be with the dynamo completely removed from the bike, not just the light turned off. But I think you'd really want to be comparing it to a regular standard hub and wheel.

    J.
    It wouldn't matter. The drag of the dynamo + headlight is already low enough it doesn't show up in real-life testing, and the drag of the dynamo with no electrical load (lights off) is far lower yet, as I can demonstrate by spinning one of my dynamo wheels with the lights off. What's 1% of zero? Yeah

    I think the difference between my DiNotte problem and your portable radios, is that the radios aren't pulling tons of amperage to feed eight Cree XP-Gs all the juice they can handle. My hypothesis is that DiNotte lights detect a low-battery condition based on input voltage, and at low temps combined with high amperage load, their battery pack's output sags enough to fake out the headlight. It probably doesn't help that LED drivers have thermal throttling, and will be able to drive the LEDs harder in cold conditions.

    Anyway, I've corresponded with DiNotte and tried all their suggestions, including a new battery AND charger, but the problem persists, so that may be the last (battery-powered) DiNotte I buy.

  4. #29
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    Quote Originally Posted by JohnJ80 View Post
    Li-ions are fine in the cold as long as you don't freeze them solid (same as any battery). They are not likely to freeze when in use. Shut off and then frozen doesn't do them any good.
    Welcome back John.

    Yeah, Li-ions do work in the cold however the cold alters the internal resistance of the battery. Most electrical devices will continue to work fine but many bike lights contain circuits that monitor the voltage level of the battery. As the resistance within the battery changes it will alter the measurable voltage drops through out the entire electrical loop ( including the battery ). The voltage levels detected by these circuits in the lamp then falsely mistake the change to indicate a drop in battery voltage. That's why lamps that have the colored led indicators tend to go haywire when it gets cold. In and of itself that's not a problem unless there is an automated power-down or cut-off circuit involved as well. That's why I've often mentioned that it would be nice if those features could be temporarily disabled when the weather gets cold.

  5. #30
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    Quote Originally Posted by mechBgon View Post
    Pretty sure there's no production dynamo lights that could or would pull 9 watts, let alone 18. The Cyo pulls maybe 1.5-2 watts in real life. It wouldn't pass StVZO certification if it pulled more than 3 watts, that would be an arbitrary FAIL.
    Someone must have a dyno that goes that high as ktronic claims to have hit 1000 lumen. That requires ~10W. Maybe he's only hitting that in a "burst" mode by pulling power from the caps. If your dyno only outputs 1.5-2W then I can see it feeling neglible. If that is all it can do then you are at about 200 lumens which is pretty marginal for MTB IMO.

    I'm not a scientist or anything, but I know power does not come for free. Whatever light you get out the lens requires an input of something like 120% due to losses in the circuitry and optic or reflector.

  6. #31
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    Quote Originally Posted by Vancbiker View Post
    Someone must have a dyno that goes that high as ktronic claims to have hit 1000 lumen. That requires ~10W. Maybe he's only hitting that in a "burst" mode by pulling power from the caps. If your dyno only outputs 1.5-2W then I can see it feeling neglible. If that is all it can do then you are at about 200 lumens which is pretty marginal for MTB IMO.
    I believe Shimano dynamos can manage loads approaching 10W if you want to hook that much up to them. In my example, the Cyo does put out something like "only" 200-300 lumens, but being a German-spec light, it's directing nearly all of it down at the ground, not spraying 50% of it up over the horizon like, say, a Magicshine. It also directs most of it forward. It's a road light. The beam pattern looks ridiculous when projected at a wall, but slant it out across 100 meters of pavement down a dark highway, and it's totally in its element. You're right, it's not a good light for MTB, where a floody light is best.

    I'm not a scientist or anything, but I know power does not come for free. Whatever light you get out the lens requires an input of something like 120% due to losses in the circuitry and optic or reflector.
    Maybe Mr. Ktronic can weigh in with the actual power draw of his 850-lumen light. For myself, my usual climbing output is in the neighborhood of 300W for 10 minutes, and at MTB climbing speeds a dyno headlight would be sipping a fraction of its full-speed appetite, since dynos ramp their output with wheel speed. It's not as simple as Hub X plus Light Y = __ Wattage consumption.

    Anyway, dynamo lights solve a couple real-world problems for me. I already touched on "endless endurance regardless of temperature." Theft resistance is another (I'm about to cruise off to the grocery store, and I'm not too worried about someone unbolting my Cyo).

    For highway use, the German-spec headlights are also relatively friendly to oncoming traffic... I don't need to be making enemies on dark rural roads with an indiscriminate high-beam type of light. In the city, that's another story. This is why I asked Mr. Ktronic if the light has an ON/OFF switch... it could make a nice "high beam" secondary headlight in conjunction with a Cyo or Luxos as "low beam." As he says, it would be simple to wire one in, like this one: Component - Switch: Water resistant On/Off Switch with 6" Long Prewire

  7. #32
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    To Dyno, Or Not To Dyno, That Is The Question

    In my small stable of bicycles are two very fine pavement machines: first is a custom Steelman Signature Road, equipped with D/A 10-speed group and Serotta f3 carbon fork. It's an eye-watering Lamborghini orange, and is solely a daytime, dry weather rig weighing 17.9 pounds with pedals.

    Second bicycle is new for 2012, a custom Kent Eriksen titanium framed all-weather "nightfighter" with a 10sp D/A-Ultegra mix, Honjo Hammertone aluminum rims, and Schmidt-Supernova dyno lighting system obtained from Peter White Cycles. It's 20.7 pounds with pedals, and has a very slightly more upright riding position.

    Both of these use HED C2 Belgium clincher rims, 32 spoked, and both run Chris King R45 rear hubs; the Steelman gets an R45 front, the Eriksen a Schmidt New Son 28 dyno hub rated for 5.4 watts loaded output. Tires and tubes are identical between them, Conti GP 4 Seasons 700x25.

    So what does my Garmin 800 data say? On a shared 33 mile loop of rolling terrain, the daytime Steelman run is typically 7-8 minutes faster than an Eriksen night ride; headlight switched off, split that time difference in half. Some day rides on the KE are faster than Steelman sorties, so chalk that up to motivation and the prevailing winds!

    Subjectively? I do not return from any rides on the dyno bike feeling more tired or burned out. The additional drag, which is quite small, is offset by a slight drop in speed...my perceived effort doesn't really change. And this makes sense: aerodynamic drag changes as the squared function of a change in speed, a little of that goes a long way as you all know from battling winds!

    I am a semi-geezery 55 years old (still a teen inside, though!), with fighting spirit aplenty, 6'3" and 220 pounds.

    Interesting read, with drag charts: Bicycle Lights and Generators

  8. #33
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    ratings

    Hey, what's this "Rep Power" thing anyway? Is it something people get while I'm out riding?

  9. #34
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    Quote Originally Posted by mechBgon View Post
    As a test, earlier this year I did the same climb with the headlight on versus off, with other factors as comparable as you'll get in a real road test. The difference in time over a 17-minute climb was 1 second, according to my Strava results
    Your test methodology is obviously flawed.

    You should really strap on a battery pack for the light off test
    DIY LED Bike Lights:
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  10. #35
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    Quote Originally Posted by Vancbiker View Post
    Someone must have a dyno that goes that high as ktronic claims to have hit 1000 lumen. That requires ~10W.
    Here... 11W
    Dynamo LED Light Systems for Bicycles (electronic circuits)

    I had a light with 5 XR-E running at 500mA back in the day. Bit overkill for the road and I got highbeamed back a lot from cars and trucks, not nice. This is the only dyno light I've used where the drag was noticeable.
    DIY LED Bike Lights:
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  11. #36
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    I too have been running dynamo lights for many years. Indeed since the SON first appeared in the late '80s. I recall trail riding on a S-A equipped bike before then but my memory is all a bit of a blurred (as were S/A lights!) Anyway, I now use the Philips 60 lux twin-led Saferide dynamo light for 90% of all my riding - just about 100% commuting and utility use - some essentially off-road given the state of bike facilities here! I also have the Schmidt eDelux and the older E6 which are both fine lights too. But I feel for everyday use the Philips is great with its apparently wider beam and better (I think) near-field illumination. Available from several places on-line if you're outside the Eu.

    Like the eDeluxe (and Cyo and other B&M led dyno lights) it has a shaped, 'traffic friendly' and highly focused beam which the regular Supernova and I understand the KTronik and Exposure Revo lack. I find it more than adequate for my style of riding. I have also ridden at night on bush, dirt roads and didn't find it wanting at all. It may well be a bit narrow for true off-road track work but I have plenty of very powerful battery lights in the cupboard which still get used for times when I feel I need floodlights. For well over 90% of the time I find that quite unnecessary (although I must qualify that by saying I nearly always use a battery rear light in addition to my dyno tail light).

    There are lots of choices available in both generators and dynamo lights at several different price points. They are also dead easy to build yourself (as are dyno wheels for that matter). I'd really like a Revo or a KTronik but their somewhat higher cost (over the approx. Au$75 of the Philips) would be difficult to justify unless I was spending lots more time off-road! Naturally it's horses-for-courses and if I was riding in 'adventure-mode' (off-road touring etc) more of the time I'd get a KTronik or Revo in a flash!

    I think the big feature of the KTronik/Revo approach is their use of the low-speed boost circuit. I don't know what the circuit in my Philips light consists of. I stays bright enough at lower speeds for my needs. However I fully concur with Kerry on the value of the boost circuitry he's used. I've built 2, 3 and 4 led lights using Martin's boost configuration and it definitely adds low-speed brightness if you can get it right.

    Someone offered a comment about potential energy lost to the dynamo with lights equivalent to the 9 watt output of his battery light. I don't think it's as simple as this nor do I believe that energy 'lost' is anything like that postulated. Both the CTC and Bicycle Quarterly web sites have delved into this question and found that energy 'losses' associated with dynamo lights currently available are negligible. LED output (or efficiency) is improving all of the time and brightness or light out put or indeed, lighting effectiveness is a more complex outcome than simple 'wattage'. With very powerful battery lights a large amount of energy that goes into the 'wattage' rating is lost as heat. Most also have a very wasteful approach to light management.

    So, in short, I share Kerry's enthusiasm for dynamo lights as the 'future of bike lighting'. I can't comment on the qualities of his light nor that of the the Revo although both look well made. As in all things, you both get what you pay for and should probably only get what you need! As I said, if I needed a really bright dirt road and trail light with a bit of flood it woud be the dynamo and either the KTronik or Revo in a flash!

    Savvas.

  12. #37
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    I'm wondering how you get past the law of the conservation of energy. If the light needs 9W then 9W minimum has to be taken from the legs of the rider.

    J.

  13. #38
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    Hi John,

    I think you've missed the point I was making. I'm certainly not trying to argue that a dyno light does not require a 9 watt draw on the generator to equal the illumination of a 9 watt battery light. What I am suggesting is that brightness, the degree of illumination or if you like the amount of energy available that is converted to light (as opposed to heat), has little to do with the overall 'watts' at which a light is rated. Watts is just a measure of how much energy is drawn from the power source (eg; either generator or battery). If a light expends a large amount of the energy it draws as heat then less will go into illumination.

    Battery lights, with their relatively inefficient chemical power sources, their regulators and (usually) their over driven leds waste (IMHO) too much of the energy they have available, especially if they spread that light indiscriminately in a wide arc vertically as well as horizontally.

    To put it another way, with an led running to spec on a generator, and with proper light management (shaped beam), I suspect that 3-5 watts dyno power may well provide similar illumination levels to that provided by a much more 'powerful' battery light.

    I am not arguing against battery lights. They have their place, particularly in off road situations requiring flood lighting. I guess I am saying that we may have swallowed the manufacturers advertising credo of 'more watts is better' and not understood that more watts may not equate to more illumination.

    Savvas.

  14. #39
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    You are arguing that there are better lights available on a dynamo than on a battery then?

    Battery lights or Dynamo lights are no different - they are the same technology and there would be an analogous light available in the battery world for any light available in the dynamo world (the universe of battery lights is hugely larger than the "universe" of dynamo lights). A light that can be powered by a dynamo, give or take, can be powered by a battery and (almost) vice versa. Volts are volts, amps are amps and watts are watts. The only difference is power sources and ultimately where the power comes from. A light that was better in beam shaping (i.e. Putting light on the targeted area) would be of equal benefit in both cases. So your argument makes no sense.

    What the argument is here is that a dynamo requires power be supplied at the time the light is needed and that power has to come from the rider's legs. The battery is stored energy irrespective of the efficiency with which it was stored there but is capable of suppling the power at the time it is needed. The energy it supplies does not come from the rider's legs.

    Our discussion here presumes that the dynamo is 100% efficient - and it's not. I'd guess (and it's a guess) that the power that goes in from the rider's legs after all the electrical and mechanical losses is probably only about 30% or so efficient by the time it's turned into light. So, that 3-5 watts you hope for is actually probably closer to 9 watts on the input side (i.e. Rider's legs) and that 9 watts is likely higher by a similar proportion. Given that an average power output is probably in the range of 100-150 watts, that represents a significant fraction of the power output of the rider's legs. Personally? Not being either as fit nor as young as I would like to be, I'd rather not give that up. So, it all comes back to the question of conservation of energy again. There is no free lunch on this.

    Dynamos and batteries are not equivalent - a dynamo produces power and doesn't store it. A battery stores power/energy and doesn't produce it. If you need to produce power while riding (as opposed to using stored energy) and never need light when stopped, use a dynamo otherwise a battery is a better choice.

    I do agree that there are likely applications where a dynamo makes sense but I'd be quite surprised to find either an economics case or an efficiency case that makes sense from the perspective of a rider on a bike. I haven't compared the efficiency of the charging of a battery through to the output of the light - and that's a big don't care for me. Charging the battery is pennies to negligible. The only reason to look at it is for the purposes of economic pay back of a dynamo and that's probably so far down in the weeds as to be silly.


    J.
    Last edited by JohnJ80; 01-16-2013 at 09:20 AM.

  15. #40
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    John has it so right here IMO. I'll gladly use the energy stored in batteries rather than the energy in my muscles to power my lights. If I was a commuter or other type of user where charging became a logistic/timing hassle maybe a dyno would make sense.

    I'll not dispute that many of the dyno lights available have highly developed optics (mainly to pass Euro requirements) that put the light in a nice pattern. I would like to see more of that in the battery light world.

  16. #41
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    I have just installed a dynamo hub on my Fargo. I have set it up with a USB port. I find on multiday tours I am more likely to run out of juice on my Garmin or my cell phone at the end of a long day. The other advantage I have found is I can run my commuter light off the USB port even if the battery is completely flat. My commuter light is not powerful enough for night riding on trails. This has started me thinking; why not use a self contained light and run it off the USB port if I need a longer run time? The specific lights I am considering as comparable to the kLite are self contained lights in the 1000 lumen range. The obvious downside I see is the weight penalty of a battery plus a dynamo. What are some other downsides? I am new to this so please help educate me.

  17. #42
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    There is no real economic argument for a dynamo light. That said, I love mine. It does need to be brighter though, significantly. It is, admittedly, several years old. I ride a Supernova E3 Triple which claims about 800 lumens but in reality looks more like about 250. In other words, adequate and no more. I've read that it likely is around 300 lumens.

    While the electrical equations don't change, LEDs have improved over the years, as has efficiency of the lights in general. Hence, bright and long-lasting battery lights.

    The great advantage of the dynamo light is that I never need to worry about the battery depleting, because there is none. Similarly, I just leave the light on the bike and never worry about any other aspect of it. It's a totally seamless experience. And the power loss while riding is minimal. I have no idea how many watts of power I lose but I can barely tell the difference between having the light on or off in terms of perceived drag. I'm not sure I really can, but I have tried to feel a difference. It is tiny, at most.

    I am very curious about the new B&M Luxos, but the reviews I have read seem to indicate the improvement over the IQ CYO is minimal. Still, the B&M my buddy has projects more useable light onto the road in front of us than my Supernova. That is the reflector, which seems to concentrate what light there is.

    We do almost exclusively paved roads, so I can't comment on the MTB possibilities other than to say that I'd think there's not enough light, but again, not worrying about the battery depleting is priceless.

    For a commuter I'd go with the dynamo every day, just for the convenience. The light is perfectly adequate for that application.

  18. #43
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    J said:

    "You are arguing that there are better lights available on a dynamo than on a battery then?"

    Well what I tried to say was: For commuting purposes - Yes! For off-road and other situations where some sort of flood beam may be needed - No.

    "Battery lights or Dynamo lights are no different - they are the same technology and there would be an analogous light available in the battery world for any light available in the dynamo world (the universe of battery lights is hugely larger than the "universe" of dynamo lights)."

    I don't believe this is true. Battery and dynamo lights certainly use different regulators and on the better ones their optics are radically different.


    "A light that can be powered by a dynamo, give or take, can be powered by a battery and (almost) vice versa."

    True for many but not for all. But for the purposes of your argument, I would agree.

    "Volts are volts, amps are amps and watts are watts. The only difference is power sources and ultimately where the power comes from. A light that was better in beam shaping (i.e. Putting light on the targeted area) would be of equal benefit in both cases. So your argument makes no sense."

    My argument such as it is is very simple. I'm just saying that you cannot presume that to get equivalent illumination from a dynamo light you need an equivalent power consumption rating. This is very simply because - for my purposes (commuting etc) - the more sophisticated dynamo lights now available make better use of the watts available. They put the light where it is needed - its not simply sprayed all over the joint. I would never argue that dyno lights defy the laws of physics in some way - just that they are generally better designed. I'm yet to see a battery light that shapes its beam as efficiently as the Philips.

    "What the argument is here is that a dynamo requires power be supplied at the time the light is needed and that power has to come from the rider's legs. The battery is stored energy irrespective of the efficiency with which it was stored there but is capable of suppling the power at the time it is needed. The energy it supplies does not come from the rider's legs."

    True of course.

    "Our discussion here presumes that the dynamo is 100% efficient - and it's not."

    This is not something I would ever presume or say. Good hub dynamos are around 65-70% efficient.

    "I'd guess (and it's a guess) that the power that goes in from the rider's legs after all the electrical and mechanical losses is probably only about 30% or so efficient by the time it's turned into light. So, that 3-5 watts you hope for is actually probably closer to 9 watts on the input side (i.e. Rider's legs) and that 9 watts is likely higher by a similar proportion. Given that an average power output is probably in the range of 100-150 watts, that represents a significant fraction of the power output of the rider's legs."

    This is an area of measurement and contention which I'd not want to stray into too far. I cite some authoritative studies below and there are others available. My contention is simple - dynamo lights can give very useful illumination at very little energetic cost with a very marked 'convenience and reliability' factor. I am not arguing that you or anybody else should use them. I have indicated that there are many circumstances where battery lights (and 'flood' beams) make sense. I would however support what I understood Kerry to be saying, that dynamo lights - whether for on or off-road use have 'come of age' and reached a very competitive stage of development.

    If you want to get beyond the guesswork you refer to above, the following links are work a read:
    http://en.wikiphttpedia.org/wiki/Bicycle_lighting
    “Good dynamos can achieve efficiencies of up to 70% (i.e., under 5 W of the rider's output is diverted to produce 3 W of electricity) and provide full output at surprisingly low speeds, often 4 to 6 mph (6 to 10 km/h) is sufficient for full brightness.”
    &
    “To compensate for their limited output, dynamo headlights have good optics which focus the limited amount of light in a narrow beam that lights up the road directly in front of the bicycle; this can be seen in Andreas Oehler's side-by side comparison of beam patterns.”
    &
    “The watt (W) is the unit of power, and is usually quoted for the electrical power input, not the light power output. Electrical power is the product of voltage and current (watts = volts × amperes). Input power is only useful when comparing lights of similar technologies. A 3 W halogen dynamo headlight will light the road up about the same as a rechargeable light of around 7–10 W, but the rechargeable usually outputs much more light to the sides, which is useful on trails (although wide and narrow beam versions are available).”

    http://www.vintagebicyclepress.com/VBQgenerator.pdf
    Testing the Efficiency of Generator Hubs (Jan Heine & Andreas Oehler)

    “Lights powered by generator hubs offer reliable light under most conditions. The added resistance is measurable (Fig. 6), but its importance is easily overstated. It is greatest (in percent of overall power output) at low speed. At high speeds and on uphills, the added resistance becomes negligible compared to the overall power required to propel the bike.”
    &
    “How much harder is it to pedal a bicycle with a hub generator? Compared to a bike without hub generator, the table shows the additional power required to maintain the same speed, as well as speed reduction at the same power output – on level ground. Only the added nighttime resistance (light on) at low and medium speeds will slow the rider noticeably. At high speeds, the added resistance (light on) is less significant. On uphills, hub generator resistance is an even smaller percentage of the overall resistance.”

    On Bike Lights. | Ed Rides Bikes
    “In itself, stating an output in terms of lumens isn’t particularly meaningful – almost as useless as trying to use a light’s power consumption (in Watts) to measure output. Lumens per Watt is a good measure of efficiency. What matters in a light is where those lumens go, and with what uniformity. This is what reflectors are all about.”

    "Personally? Not being either as fit nor as young as I would like to be, I'd rather not give that up. So, it all comes back to the question of conservation of energy again. There is no free lunch on this."

    Yes - I agree wholeheartedly. I guess we may differ as to the degree to whether the costs of the lunch is significant and which we might prefer...

    "Dynamos and batteries are not equivalent - a dynamo produces power and doesn't store it. A battery stores power/energy and doesn't produce it. If you need to produce power while riding (as opposed to using stored energy) and never need light when stopped, use a dynamo otherwise a battery is a better choice."

    Well - yes,,,

    "I do agree that there are likely applications where a dynamo makes sense but I'd be quite surprised to find either an economics case or an efficiency case that makes sense from the perspective of a rider on a bike."

    Well they make sense to me. The 'convenience issue' (in the commuting/everyday context) is the 'biggie' if we are to believe the experiences of millions of users! I suspect that the long-term utility of the dynamo (a projected life of many years compared to the inevitable limited lifespan of even LiPo batteries) may be part of the equation for many.

    "I haven't compared the efficiency of the charging of a battery through to the output of the light - and that's a big don't care for me. Charging the battery is pennies to negligible. The only reason to look at it is for the purposes of economic pay back of a dynamo and that's probably so far down in the weeds as to be silly."

    Well I agree that in simple terms, battery lights can appear to make more economic sense! I guess it depends very much on what you understand the economic argument to include. If you value time not spent charging batteries and dealing with flat batteries then things look different. If you think of economics as a bigger picture than drain on your own wallet (ie; environmental costs etc) then there may well be other arguments to be made. It all depends dunnit!

    Savvas.

  19. #44
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    Quote Originally Posted by Lugano View Post
    I am very curious about the new B&M Luxos, but the reviews I have read seem to indicate the improvement over the IQ CYO is minimal. Still, the B&M my buddy has projects more useable light onto the road in front of us than my Supernova. That is the reflector, which seems to concentrate what light there is.
    I now have a Luxos B and the 60-lux Cyo running in parallel on the same bike. For road use, where you mainly want to see forward straight down the road, the Cyo 60 is the better value. The Luxos B certainly has the broader beam, and some fill light right in front of the bike... a bit too close and too much, IMO. I wish they'd send those lumens down the road to the hotspot.

    With both the Luxos and Cyo running at once, I still don't perceive any drag. Lowering the pressure in my studded tires would make a noticeable difference in drag. Taking off my panniers would make a noticeable difference in drag. Ditto for my pogies, which create significant air drag at higher speeds or into a headwind. Dynamo lights, even two of them at once... not really. I did two time trials recently on the winterbike (purely for the workout), and went about 0.5mph faster with both headlights on, which I put down to the surface being faster that day.

    We do almost exclusively paved roads, so I can't comment on the MTB possibilities other than to say that I'd think there's not enough light, but again, not worrying about the battery depleting is priceless.
    I've gone off-roading with a "glare-free" Supernova E3 Pro (single emitter) and the shaped beam on that variant is a serious problem, even moreso than the output. Diving into a big G-out with absolutely no light reaching the far side is quite a test of faith. For off-road, a floody beam is the way to go for the bike-mounted light.

    For a commuter I'd go with the dynamo every day, just for the convenience. The light is perfectly adequate for that application.
    Great for winter training at low temperatures, too. When I finished my training ride tonight, it was 14F / -10C and my battery-powered light was (predictably) screaming LOW BATTERY! with hardly any use on a full charge, while the dynamo lights were (predictably) working flawlessly and ready to go To Infinity And Beyond if necessary.
    Attached Thumbnails Attached Thumbnails Dynamo lights, the way for the future!?!-dual_dynamo_headlights.png  


  20. #45
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    Savas - just to keep it straightforward, I'm an electrical engineer so I understand power in and power out and how that relates to lighting vs electrical power but you obviously couldn't know that.

    I would bet that by carefully tuning and under optimal circumstances, you might be able to get a good dynamo up to 60-70% efficiency (that would be power from riders legs to power supplied to the terminals of the light) but with most power devices, they have a very narrow range of optimal and efficiencies fall away rapidly when on either side of that narrow range. Dynamos would be worthy of study, but I'd be very surprised if they were much different.

    But optimal is hard, if not impossible, to get in practice. Your chain gets dry, you lose. Your tires get a bit low, you lose. You wear shoes that don't have hard soles - you lose. So, I'd be really willing to put money on the the idea that if you take an average dynamo user and you checked it out, you'd find that in the field and in practice, you'd be running far less than that 70% number and I'd be willing to go with 30-40% as a pretty reliable number.

    Finally, dynamos don't use any different technology in the light itself than do the battery lights and it's a specious argument to say that a dynamo light is better than a battery light. They have to use the same technologies in LEDs, in electronics, optics and interconnect. So they are not and I am absolutely sure that I can find a light in the battery world that has as good as or better optics and brightness as the dynamo light. There are simply so many choices and such diversity in the battery world compared to the dynamo world AND the innovation and excellence of battery based devices is pretty incredible now. The only issue is that would it very likely be brighter. So as far as the light goes, I'd say that they are the same light and concentrating on the delivery of power to the + and - terminal of the light itself is the only difference.

    Dynamos make sense for where you can't charge or where environmental considerations matter. Otherwise, batteries are and will remain the best solution for almost any application except a fringe few.

    As far as power output - pretty impressive power output of 300W continuous. Not many cyclists can do that for sustained periods and the numbers I've seen is that the typical cyclist is averaging pretty close to half that over time. Mass market acceptance requires attention to the average rider not to a well conditioned rider putting out big wattage.

    So, the power drained by inefficiency of the dynamo is still quite significant. I can agree that uphill it's a smaller percentage when power output is higher but seriously, how many of us want to give up ANY power going uphill or upwind? Not me! I want every watt I can get at that point. Given a steep enough hill, that 5% loss will break me.

    J.

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