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Old 01-11-18, 12:13 PM   #1
agmetal
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What happens if you connect front & rear LED lights to a 2.4w hub?

Will both lights work? Most likely I'd be using B&M Cyo Premium T and Toplight Line Brake Plus
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Old 01-11-18, 01:22 PM   #2
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first, let me say that I don't know the answer, but I do find it to be interesting. While I really like LED lights, I'm not sure that their electrical characteristics are standardized in the way that they were in the days of incandescent bulbs.

The most practical advice I can offer is to ask B&M. If you can tell them what dynamo you want to use, they should be able to say whether their lights will work.

Finally, a question: are dynamos being sold as 2.4W output? I haven't bought a new dynamo since 2008, and only recall 3W versions. A quick look at SJS's web page shows a header stating "all with 6V, 3W output". Of course, that suggests that they get asked what the output voltage & power of their dynamos is.

I'm quite curious as to how this turns out!


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Old 01-11-18, 01:25 PM   #3
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They're most commonly 3W (which I have on 3 of my bikes), but I got a generator wheel in trade for a saddle I wasn't using, and it has a 2.4W hub...so basically I'm wondering how well it'll work with the same lights I have on the other bikes.
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Old 01-11-18, 02:49 PM   #4
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The hub is simply an alternator, it will have to turn faster to put out the same power as the 3 watt hub. Since you have a 3 watt wheel on a bike, try swapping out the wheels and going for a quick ride to see how your lights on that bike perform.

At low speeds you would likely notice less light. You might also have to go faster to get to the point where the light starts to work. At higher speed you should not notice any difference.

If you are in Germany, it might not meet their lighting standards but if you are elsewhere that would not matter.

I assume you mean that you would wire the taillight to the headlamp, that is the typical way to do it. But your question implied that you would wire the taillight directly to the hub which might not work. Peter White website has good information on wiring.
Schmidt/Lumotec wiring instructions
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Old 01-11-18, 02:52 PM   #5
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Report back when you have tried it.
I think Shimano had a headlight only dynohub, for 2.4w load. that what you got?



Cannot give you feedback on stuff I dont own..






....

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Old 01-11-18, 02:53 PM   #6
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The hub is simply an alternator, it will have to turn faster to put out the same power as the 3 watt hub. Since you have a 3 watt wheel on a bike, try swapping out the wheels and going for a quick ride to see how your lights on that bike perform.

At low speeds you would likely notice less light. You might also have to go faster to get to the point where the light starts to work. At higher speed you should not notice any difference.

If you are in Germany, it might not meet their lighting standards but if you are elsewhere that would not matter.

I assume you mean that you would wire the taillight to the headlamp, that is the typical way to do it. But your question implied that you would wire the taillight directly to the hub which might not work. Peter White website has good information on wiring.
Schmidt/Lumotec wiring instructions
Your assumption about the wiring is correct - I would go from the hub to the headlight, and from the headlight to the taillight
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Old 01-11-18, 03:23 PM   #7
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Just since it's not clear from the thread, I'll interject that "from the headlight" means that the hot wire to the tail light is connected to the far side of the on/off switch of the headlight, because it may be too much current if the headlight isn't on. They are wired in parallel of course.
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Old 01-11-18, 03:40 PM   #8
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One more quick comment, I have a couple SP hubs and then I got a Shimano hub after that.

I had massive wiring problems until I finally figured out that one of the connectors from the Shimano hub is grounded to the frame. That is not the case with the SP hubs. Thus I learned the hard way that I had to be more careful when wiring a bike for a Shimano hub.
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Old 01-11-18, 05:06 PM   #9
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LED can provide decent illumination on significantly lower power than incandescent, i.e. you don't need full 3W. Toplight Line takes e.g. in my memory just 0.2W of power rather than 0.6W typical for rear incandescents. You will be completely fine and you connect the lights and dynamo all in parallel. In the case of Cyo, though, as already mentioned in other posts, it will have dedicated wires for the taillight so that its switch controls both lights.
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Old 01-11-18, 05:14 PM   #10
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I got the diminutive Eyc, for my Brompton , they have a wire from the hub, and another wire to the tail light,

Schmidt E Delux has a similar combination tail light connects to the headlight, headlight connects to the hub.
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Old 01-11-18, 07:05 PM   #11
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It's usually exceeding the maximum rated DC voltage that destroys LEDs. If you buy naked LEDs in white and colors they all have a maximum DC voltage that you can apply to the LED. The little white 3 mm LEDs that are found in toys run on 2.8V and 18 mA. Red will die if you apply more than 1.9V at 18 mA. The only difference between the larger LEDs like the CREE XML-T6 LED found in many flashlights and bike lights is a higher current. The manufacturer builds in a circuit to reduce the 3.7V found in a typical Li-ion battery to an acceptable voltage.

Is the output from your hub DC? Does the voltage vary with speed? I don't think you can just wire up just any random LED bike light to a dynamo and expect it to work or survive.
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Old 01-11-18, 07:13 PM   #12
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It's usually exceeding the maximum rated DC voltage that destroys LEDs. If you buy naked LEDs in white and colors they all have a maximum DC voltage that you can apply to the LED. The little white 3 mm LEDs that are found in toys run on 2.8V and 18 mA. Red will die if you apply more than 1.9V at 18 mA. The only difference between the larger LEDs like the CREE XML-T6 LED found in many flashlights and bike lights is a higher current. The manufacturer builds in a circuit to reduce the 3.7V found in a typical Li-ion battery to an acceptable voltage.

Is the output from your hub DC? Does the voltage vary with speed? I don't think you can just wire up just any random LED bike light to a dynamo and expect it to work or survive.
The commercially available lights from Busch and Mueller or other brands come with voltage protection. They are designed to operate on the hubs discussed. The hubs are usually referred to as 3 watt and 6 volt AC, but going down a hill fast voltage can climb quite high so the lights have to have voltage protection built in. I have measured 33 volts AC with no current flow on a down hill on one of my hubs. But going down such hills do not blow out my LED lights because they have adequate voltage protection.
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Old 01-11-18, 07:41 PM   #13
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Is the output from your hub DC? Does the voltage vary with speed? I don't think you can just wire up just any random LED bike light to a dynamo and expect it to work or survive.
This is like saying that an LED bulb cannot be placed in an AC home socket. The devices are designed by professionals (for a change).
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Old 01-12-18, 09:37 AM   #14
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This is like saying that an LED bulb cannot be placed in an AC home socket. The devices are designed by professionals (for a change).
No it is not. If you pull apart one of those LED bulbs that look like a standard incandescent light bulb you will find a plate in the center of the bulb with the LEDs on it and a DC converter just below it. Just like this case you will have to be careful selecting the bulbs. There are some dimmable LED bulbs on the market but most are not usable with the dimmer switch that works with incandescent bulbs. BTW, the American style bulb which mimics the design of an incandescent bulb is the worst design possible. There are others out there (corn bulbs and COB LED bulbs that look like a CFL) that are way better but they rarely are found for sale in the US.

Tourist in MSN just confirmed what I suspected that the manufacturer builds in a controller to match the voltage and DC current needed to drive LEDs. The question then is where the controller is located. If it is in the lamp, then you should be able to wire these in parallel and not destroy the headlamp and taillamp. I have rewired conventional AAA bike headlights and taillights to work off a 18650 lithium ion battery pack for longer run times. Since the light was designed to operate on three AAA batteries in series (~4.5V) they will work quite well on any number of Li-ion cells (~3.7V) wired in parallel.
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Old 01-12-18, 01:00 PM   #15
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...
The question then is where the controller is located. If it is in the lamp, then you should be able to wire these in parallel and not destroy the headlamp and taillamp. I have rewired conventional AAA bike headlights and taillights to work off a 18650 lithium ion battery pack for longer run times. Since the light was designed to operate on three AAA batteries in series (~4.5V) they will work quite well on any number of Li-ion cells (~3.7V) wired in parallel.
On a bike you do not really run the two lights in a parallel circuit. Typically there are two leads out of the headlamp that then supplies power to the taillight. I have heard that if you wire a taillight into a hub without a headlight that it can blow it out. Thus, I would not be surprised if the voltage protection was all in the headlamp unit only. That is why my comment in a post above about not running the wiring to the hub from the taillight.

For example, in the photo there are some loose wires that I have bundled up under the mount. If I was using a wired taillight, those wires are intended to supply the power to the taillight. But I am running a battery taillight so I bundled the wires up so that they would stay out of the way.

In a post above, I cited the website for Peter White, he has a page with good information on wiring these.
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Old 01-12-18, 02:50 PM   #16
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The lights I referred to in my original post are designed to be powered by a generator hub, so all of this talk about "any random LED" is academic at best...
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Old 01-12-18, 06:27 PM   #17
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.....
Tourist in MSN just confirmed what I suspected that the manufacturer builds in a controller to match the voltage and DC current needed to drive LEDs. The question then is where the controller is located. If it is in the lamp, then you should be able to wire these in parallel and not destroy the headlamp and taillamp. .......
on a B&M Eyc, there is a controller in the head light. In fact, it's the little square integrated circuit near the top of the board (in the second photo).





The headlight includes a bidirectional zener that protects the headlight and taillight from excessive dynamo voltage. When I've opened up B&M dynamo taillight in the past, I don't recall seeing any overvoltage protection in it. Of course, that may have changed. Other than that, the tail light controls the current going through it.

Lights such as the Supernova Triple that I've opened up have dedicated a taillight that can't be used with any other manufacturer's headlight. Also, you couldn't use a B&M taillight with the Supernova's taillight output power, IIRC.

When in doubt, it's best to check with the manufacturer.


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Old 01-12-18, 08:33 PM   #18
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this thread got really off track. 2.4 w is enough to drive an led headlight and a taillight. 3W hubs were designed to drive incandescent lights.

Seems like they are all really inefficient, and don't save any effort. So unless it is really cheap, just go with a 3w
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Old 01-13-18, 05:41 AM   #19
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Not sure if it helps but for an extended period I utilised an old vintage Sturmey Archer front dynohub of 1.8 watts to power an Edelux Mk1 which has 2.4w stamped on it.

I bought the Edelux with a Sondelux hub but couldn't initially afford to get a wheel built around it having already broken the bank.

I believe it will work but you mightn't get full brightness from your lights.

People told me my set up wouldn't work but I'm glad I tried (successfully) anyway, as my Edelux was plenty bright enough with what the Sturmey Archer pumped out.

Saying that, my current bike uses a Son28 and I wouldn't look back.
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Old 01-15-18, 02:42 PM   #20
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Will both lights work? Most likely I'd be using B&M Cyo Premium T and Toplight Line Brake Plus

Ill just wait for you to try it and report back , myself..



thanks for opening up the Eyc to see the circuit boards,,, expect they have a robot putting the parts on the circuit board..



..

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Old 01-16-18, 01:02 PM   #21
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I gave it a quick test this morning - unplugged the wheel on one of my generator-equipped bikes, plugged in the 2.4W wheel, and gave it a quick spin with my hands. Both lights came on immediately, so it looks like it shouldn't be a problem!
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Old 01-16-18, 03:15 PM   #22
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I gave it a quick test this morning - unplugged the wheel on one of my generator-equipped bikes, plugged in the 2.4W wheel, and gave it a quick spin with my hands. Both lights came on immediately, so it looks like it shouldn't be a problem!
So did you come upon this wheel cheap?
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Old 01-16-18, 03:16 PM   #23
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So did you come upon this wheel cheap?
Yes. I got it in a straight trade for a saddle I wasn't using, and didn't realize until later that it was a 2.4w hub
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