I thought I came across a headlight that is hub gen powered, and had a female plug (or pigtail) into which a usb cable could be plugged. Thus a device or battery pack could be charged during daylight.
This would eliminate the need for another interface gadget - Tout Terrain and the like.
Can someone help my senior memory?

Busch & Muller dynamo bicycle lights Luxos U is one option that I know of, but not cheap.

luxos U is cheap relative to the combination of a good light and a usb voltage converter

Yeah, the Luxos U, though you should realize that it doesn't put out light and charge at the same time. It's one or the other. (I don't recall all the specific of if you could charge something that was very light draw, but I've read that you cannot charge, say, a phone and have the light on at the same time).

There's also independent units that do the same thing, like the Supernova "the plug" that integrates into your stem or something.

Is the Luxos U the only dynamo light that gives USB voltage conversion?

My next project is to build a wheel around an SP PV-8 dynamo hub and get a dynamo headlight that can co-exist with an Ortlieb handlebar bag on a Surly Long Haul Trucker. From what I see at Peter White's website, it looks like all of the German dynamo lights can do so. That and having USB voltage conversion will definitely make this worth spending the extra money over something like the Planet Bike Blaze Dynamo.

I would never consider the PB light, it has a circular reflector that wastes a lot of photons. Most of the B and M lights would have a certain amount of trouble mounting on the handlebars, I would figure out a way to mount it on the front rack

The Luxos U is the only Busch and Mueller light that does usb charging, yes. There's another dynamo light from another company on amazon that does it, but despite similar looking specs the beamshots and people's comments suggest it's a very poor light compared to the Busch and Mueller lights.

For the same cost you can buy a light that doesn't do usb charger, and add on one of the several usb-charger accessories for a dynamo that do the same thing but are not integrated into the light.

Also agree that the Planet Bike dynamo is far worse at throwing out light than Busch and Mueller offerings. It's only advantage is if you only need a "to be seen by" light in the front, as it has a blinking mode.

So, it is the Luxos U, which can't charge when the light is on, but is a one party system, OR
a good headlight and thrid party gizmo and a good headlight. Can the third party gizmo (inverter??) charge while the light is on? Is that a function of the light, hub, or inverter? Do the third party gizmos have a battery cache like the Luxos U? That seems like an awfully nice feature.

No, you can never have the light on and charge off it at the same time, no matter what you do. It's a matter of power - the dynamo hub produces a certain amount of power. The light is designed to consume all (or nearly all) of that power. There's no power left to charge something while the light is still on.

Even with the light off, the hub will power charging a cell phone, but not some tablets because the power draw is more than the hub produces.

I am not sure that you can't charge while the light is on. The Luxos U has a battery which gets charged with the light on. It's there to provide power when you go slow, or you can push the button to go into "high beam" mode. Once the battery is charged, you can get some current out of the usb. Depends on the device you are charging, the intermittent nature of the power drives my garmin 800 crazy. Not really crazy, but the "external power lost" warnings get really old really fast.

I'm just quoting myself from earlier here -

when I tried charging my 800 with my Luxos, both were new to me. I couldn't really get it to work reliably. Probably user error in combination with a lot of climbing

I just happen to have my Luxos U instructions handy. "Permanent USB charging with more than 100ma is only possible when all light functions are off. When the cache battery is charged, simultaneous charging and use of the light function is temporarily possible." note the highlights are in the instructions.

It goes on to say the duration depends on hub dynamo, speed and load demand of the device being charged.

no Axa in NL has a dog in the fight , too .

"the Plug" goes in your fork steerer. it has the USB conversion circuity out side of a Headlight.

that's basically what my previous post said. I was having trouble with charging when the light was off too, probably user error somehow, if going too slowly counts as user error. I know people have reported success with this setup. The reports I've seen advise turning the gps off when stopped. I don't know if other devices really need this or not, as I said, I never really got it to work that well. I have been thinking about using the light to charge an external battery

Supernova makes "The Plug." It's popular, but I've heard it only charges at a very slow trickle.

At 6v_3w the source is a trickle .. want a faster charge ? use the mains powered charger while you eat or drink in a place that will serve you. .

Doesn't the AXA Luxx70 Plus have USB output?

Also, I was under the impression that of the integrated systems, the Luxos U was the only one that could provide both USB output and light. Am I mistaken?

Some people have rather optimistic ideas about what to expect.

Lights draw a lot of power and reasonable generators don't provide much power (probably, you don't want a generator that adds significant effort to riding).

It's probably a much better idea to charge a "cheap" cache battery than it is to expose your expensive devices to wild swings of power.

None of them can "really" do both lighting and charging at the same time. It's a matter of limited power from the dynamo itself.

The Luxos U can technically charge while the light is running, but the draw is extremely extremely small. Not enough to charge a cell phone if I remember right.

I believe the Luxx70 does also have integrated charging, but it's not a very good light. The Luxos U also has a cache battery to smooth out charging, which I don't think the Luxx70 has.

I think the devices either put out a steady amount of power, or stop putting out power altogether. That's part of the point of the converter.

A cache battery works in some situations but not others. Eventually it needs to be recharged itself, and sometimes that's not possible. Other times it's just a lot easier to run a wire from the front hub up to a phone on the bars, than it is to try to figure out how to mount an extra cache battery there.

You know generators produce more power at higher speeds. It doesn't make sense thowing available power away by capping.

They maintain constant voltage actually. And turning stuff on and off repeatedly tends to increase the rate of failure. Put that risk in something that is cheap and easy to replace (a cache battery).

USB charging has fairly narrow voltage requirements (but looser amperage requirements).

Look at Unterhausen's story about how annoying it was to have his Garmin being directly attached. That would have been completely eliminiated if he was using a cache battery.

??? You charge the cache battery with the generator. You might be able to do away with the generator entirely with a just a much-cheaper cache battery.

You are exaggerating the difficulty here. If you are riding long distances at night, you may need to use a cache battery anyway. During the day, it's possible that you can generate more power than your phone uses (a cache battery lets you capture that power).

I guess I don't really feel like digging into it, but my understanding of converters is that they specifically output a constant amount of power, or not power at all. There's no variation, I believe.

Whether the dynamo produces differing amounts of power at different speeds is a different topic altogether.

I'm not sure that's a problem on all converters, but I know for sure it's not the Luxos U as it has it's own cache battery.

Would you have a link to that story? Curious to see it. (Edit: Never mind, it sounds more and more like you want to get into an endless debate in the topic which I do not have a strong interest in).

You charge the battery with the generator, which you then get rid of the generator. You lost me.

And it seems like you're just trying to be argumentative here about "difficulty". I don't really care to get into a debate on this topic, I'm sure anyone reading can figure out that if the only thing you're charging is a phone how that will work.

Usually the idea is to charge during the day, then you have the dynamo for lighting at night.

They may regulate amperage but they also are required to regulate voltage too (especially for USB charging).

There is some minimum speed at which the generator can't produce enough power to maintain the voltage (so they turn off).


That's one of the reasons the Luxos U has its own cache battery!

If you have a cache battery, you might not need the generator in the first place.

No, it's a good example of where using a cache battery is better than directly charging a device. You just find it convenient to ignore it.

No, you are making up a fake difficulty to make your "argument".

And a using a cache battery can make that be much more effective.

I am confused about what you two guys are debating. The best I can make out is Paul Rivers is pro dynamo hub charging and njkayaker says forget the dynamo and simply use cache batteries which can be charged from some external source.

I have a dynamo hub and usb charger that I use to charge an external battery pack with. I can then use the battery to charge other usb chargeable devices. Yes, I can go to a restaurant and charge the battery and not use the dynamo hub. In my opinion it is nice to make your own power so you don't have to rely on an external source.

There are many USB chargers on the market. A couple (B&M luxos and AXA Luxx 70plus) are integrated with the headlight, a couple utilize the fork steerer cap for the usb outlet, some have integrated batteries and some don't. I have a LightCharge which doesn't have an integrated cache battery but seems to work fine. My hope is that the technology improves and the price comes down because for long distance cyclists providing your own power is really innovative.