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I know there are dynamos with 3 W as the highest output, but are there commercial dynamos available with even better effect? See, I don't mind pedaling with a bit more drag if I can get better lighting on my bike.

Warren Burton
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MiNiMe
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    As indicated in the answer from Juhist (which is a good one) it would be helpful to know whether your goal is to run multiple existing lights you can just buy, or to also have the light be some kind of extra-bright unicorn. The main thing that good available conventional LED generator lights don't do is project light out in all directions as in an MTB light, which given that kind of use case could be a relevant thing to do with all the extra output. Otherwise I really recommend seeing a good modern light in action (IQ-X, Edelux II) before going too far down this rabbit hole. – Nathan Knutson Nov 05 '23 at 17:30
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    Just a thought: the 6V/3W limit comes from the StVZO (German road code), that is a de facto regulatory basis for bicycle lighting, even in countries where it doesn't formally apply. That doesn't exclude of course niche manufacturers (in this niche) to produce a non-StVZO compliant one, but given 3W can already produce up to 1000 lumens (Supernova M99 DY PRO, for example), I guess that StVZO compliance is preferred over higher outputs. – Rеnаud Nov 05 '23 at 17:40
  • I didn't know the Germans had that much authority, but I do recall that StVZO mark, perhaps on a bicycle light. || @NathanKnutson It is indeed a good answer. I'm not riding a MTB, this is for commuting during night hours. – MiNiMe Nov 05 '23 at 17:47
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    On bicycle lights, StVZO is mentioned for beam forming: StVZO-compliant lights have a vertical cut-out (as automotive lights), to avoid blinding other users. – Rеnаud Nov 05 '23 at 17:51
  • Exactly, those 'inscriptions' in the glass. If it's correct or not, but I call it optics. Actually I'm happy for those StVZO approved lights, other cheap LED lights are just horrible for the night vision. – MiNiMe Nov 05 '23 at 18:07
  • It’s optics, yes. StVZO is the road code, that also covers many other items than bike light specifications (driving licenses, traffic rules,…). It just happens to be more perspective on technical criteria that other road codes. – Rеnаud Nov 05 '23 at 21:13
  • @Renaud Goven StVZO forbids any blinling and blink lights are actually very popular elsewhere, aat least in the rear or during the day, StVZO is not really that much adhered to in other countries. I bought inadvertently on set of such light in a ctore chain mainly known for gardening and it is a PITA with the steady light only. Everything else I see offered at least allows blinking. – Vladimir F Героям слава Nov 05 '23 at 21:55
  • It’s not that the Germans have a huge amount of authority, it’s that StVZO requirements are some of the most stringent in the world for bicycle lighting, so meeting compliance with them (which is not hard to do) means you’re compliant with most bicycle lighting regulations worldwide. That, in turn, makes marketing worldwide much easier, so a lot of the more sensible international manufacturers specifically target StVZO compliance, and as a result it’s actually kind of become a keyword for ‘properly designed bicycle lights’ in some countries. – Austin Hemmelgarn Nov 06 '23 at 02:28
  • @VladimirFГероямслава I didn't express myself properly, it's not that they are enforced everywhere, but they are influential well beyond Germany. In the case of blinking lights, there's an explicit demand for that feature, so it's a different case. MTB lights are also often non-StVZO (the cut-out is an issue and trails are not public roads). But otherwise, if a manufacturer decides to sell a "non-dazzling light" (that is how the text is worded in Belgium for example, and I would not be surprised in other countries as well), taking StVZO as reference seems to be the most common approach. – Rеnаud Nov 06 '23 at 05:33

2 Answers2

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Actually a 3 W dynamo is mislabeled. It isn't 3 W. It is 0.5 A.

A hub dynamo is mostly a constant current device. The faster it rotates, the higher is the frequency and voltage of the alternating current it produces. Also because a hub dynamo has coils which supply the electricity, the coils have an inductance. The faster the frequency of the alternating current is, the higher is the reactive impedance of the coil.

So while you pedal faster, you get more voltage, but you also get more reactive impedance. Both of these increase linearly, so if you short circuit it, you get approximately the same current at every speed.

Historically hub dynamos were used for halogen lighting by using a 6 volt 0.5 amp 3 watt bulb. However, you could wire up two bulbs in series for a 12 volt 0.5 amp 6 watt system. In this case, the higher output would be obtained at higher speeds -- exactly when you need the higher light output.

So if you want to get lots of light today, you don't need a higher-than-3-watt hub dynamo. You could use a LED light with intelligent switched mode power supply that can take advantage of the higher voltage produced at high speeds.

I'm not sure if anyone makes such a LED light, but it should be doable and it would approximately double the light output at high speeds. With a good enough intelligent switched mode power supply, it doesn't even need to sacrifice light output at low speeds. It could always operate at the maximum power point of the hub dynamo, similar to what MPPT systems do for solar panels.

juhist
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  • I'm working on a MCU based LED-light solution, and prototype works fine with '3 W' itself, more power is for the future plans pipe. – MiNiMe Nov 05 '23 at 17:34
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    @MiNiMe Then all you need is to implement a maximum power point tracker for the solution! You can extract lots of power out of it at high speeds, you don't need to limit yourself to 3 watts. I'm sure the MCU could do the role of the maximum power point tracker if it controls the switched mode power supply. – juhist Nov 05 '23 at 17:35
  • So far the old trusty bridge rectifier with schottky diodes have done a good job, but that MPPT is something I'll remember. Apparently it's tech not only for solar panels. – MiNiMe Nov 05 '23 at 17:39
  • You don't need MPPT. The optimum load is always the same for a given rpm, and you can measure rpm just by looking at frequency. – bobflux Nov 05 '23 at 19:24
  • @bobflux ...assuming you use a certain dynamo model. You don't know what the dynamo is. Maybe it's SON. Maybe it's Shimano. Maybe it's one of the newer Shimano dynamos that produce less than 3 watts, since the Germans realized that 3 watts is no longer necessary for StVZO compliant lights. By simple frequency detection, you need to have all information about the dynamo model, which you don't have. – juhist Nov 05 '23 at 19:40
  • Not a problem if you DIY since you know which one you have ;) my point being you can measure the optimum load according to speed once and then reuse it. Unlike solar where the MPPT has to run constantly. – bobflux Nov 05 '23 at 20:34
  • It's a very detailed and exhaustive answer, but there's one thing it lacks - the answer to my question! If that would be added, and there are no other answers to take into consideration, I'll be happy to mark it as the solution. So no changes to the current text, just add. – MiNiMe Nov 06 '23 at 11:32
  • What you might be able to do is fit one of the better USB-output charging devices, that can give power to a battery and a light if you're going fast enough, then run a second light off that output (probably buffered by a battery). With LED lights it's unlikely that switching in a second light in series at high speed would work, unlike with halogen lamps. – Chris H Nov 06 '23 at 13:09
  • I dimly recall someone installing a hub dynamo in their trailer for a very long bike trip because it had a much smaller wheel diameter and therefore faster rotation (for a given speed). Of course it doesn’t really solve the problem of how to get more electricity out of a normal bike wheel at a certain speed. – Michael Nov 06 '23 at 16:24
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Referring to the answers to an old question of mine one solution would be to run a hub dynamo and the best bottle dynamo you can buy.

Start with a standard hub dynamo setup with a top-of-the range light like the Busch und Müller IQ-X (I've seen a few, and want to upgrade to that from my Axa Luxx 70). That light is really good, with a wider pattern than many dynamo lights, but the top cutoff is too sharp if there's any risk of hazards above the beam, for example on off-road trails.

Personally, my additional lighting is battery powered; it also serves as a work light if I have a mechanical in the dark, can be lent to friends, etc.

But a good bottle dynamo (the Axa HR traction was recommended to me, or the discontinued Nordlicht) could be used to drive a second dynamo light, adjusted to give a higher beam, selected for a wider pattern, or both. The PedalCell rim dynamo/charger combination also looks interesting, combined with lights designed to be run off USB battery packs

Chris H
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