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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.

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  • 1
    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. Commented Nov 5, 2023 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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 at 18:07

2 Answers 2

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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.

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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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 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
    Commented Nov 5, 2023 at 19:40
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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

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