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[LED lights] Are bottle dynamos and hub dynamos compatible?

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[LED lights] Are bottle dynamos and hub dynamos compatible?

Old 09-30-19, 10:02 AM
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Question [LED lights] Are bottle dynamos and hub dynamos compatible?

Hello,

Days getting shorter is the opportunity to move from the hassles of USB lights.

Before spending time building my very first dynamo-hub wheel, I'd like to try a bottle dynamo, either AXA or Busch & Müller.

But before I buy lights, I need to know if LED lights are compatible, ie. they work just as well with either type of dynamo.

Thank you.

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Old 09-30-19, 10:21 AM
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Originally Posted by Winfried
Hello,

Days getting shorter is the opportunity to move from the hassles of USB lights.

Before spending time building my very first dynamo-hub wheel, I'd like to try a bottle dynamo, either AXA or Busch & Müller.

But before I buy lights, I need to know if LED lights are compatible, ie. they work just as well with either type of dynamo.

Thank you.
Years ago one of the first LED headlights was the B&M D-Lumotec Oval. They made that in a bottle generator model in addition to dynohub model, the difference was that the bottle version did not have an on/off switch because with a bottle generator you can move the generator off of the tire to turn it off. I bought a couple of those lights when they were on clearance pricing. Used them for the first couple years on my dynohub while I was trying to decide what to buy for permanent lights.

Based on that experience, I suspect that the answer is yes. The bottle type generators probably have a much faster frequency of alternating current, but unless you were doing something complicated, I can't see that as being a problem.

OR, if you really wanted to make sure, e-mail or call Peter White and ask him if there would be any problem. If you know which light you want, you could specifically name that light.

I still use one of those bottle type generator LED lights that lacks a switch with my errand bike, photo attached.



I do not suggest you mount a light that low, even something small like fallen tree leaves cause big shadows. But I only use my errand bike on well lit streets, so I mostly use it as a to-be-seen light and the low mount works fine for that.
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Old 09-30-19, 02:56 PM
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as long as it's 6v, it will work
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Old 09-30-19, 05:16 PM
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Yes, I put some modern lights on some antique bottle generators. They worked fine.
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Old 10-01-19, 02:34 AM
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Thanks!

I realise I'm totally clueless about electricity, so it's an opportunity to learn a bit.
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Old 10-01-19, 09:47 AM
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I'll ask here instead of opening a new thread:

1. Considering the width of the fork, I assume I'll have to install the sidewall dynamo in the back using either Axa's or B&M's bracket




2. Do you know of a way to install the front light through the side tab on this frame-mounted rack? If no solution seems available, do you know of a way to install it on the fork?



3. Am I correct in understanding that the current must somehow return to the dynamo, either through a two-core cable or the frame? If the latter, does it work with an aluminium frame? And I guess with a plastic fender, a two-core cable is required to connect the rear light to the dynamo since plastic isn't conducive.

Thank you.
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Old 10-01-19, 02:45 PM
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Originally Posted by Winfried
I'll ask here instead of opening a new thread:

1. Considering the width of the fork, I assume I'll have to install the sidewall dynamo in the back using either Axa's or B&M's bracket

2. Do you know of a way to install the front light through the side tab on this frame-mounted rack? If no solution seems available, do you know of a way to install it on the fork?

3. Am I correct in understanding that the current must somehow return to the dynamo, either through a two-core cable or the frame? If the latter, does it work with an aluminium frame? And I guess with a plastic fender, a two-core cable is required to connect the rear light to the dynamo since plastic isn't conducive.

Thank you.
1 - That is a maybe, depends on the alternator you look at. The vintage Union brand one that I had on my errand bike would go onto a fairly large diameter fork, but there are limits.

2 - Depends on the light. You likely would need a custom bracket if you want the light below the rack shelf. Being new to dyno lights, you might not yet be aware of this, but DO NOT put a light on the rack upside down. Most lights are designed for the waterproofing to assume that rain is coming from above and mounting a light upside down often means that rain can get into the light. If you get a B&M light, Peter White website has a lot of brackets.
https://www.peterwhitecycles.com/light-mounts.php
And if you are handy, you can make your own bracket.

3 - Aluminum will transmit the electricity through the frame just fine. Current flow through the headset is less reliable, so not sure if that would mean you have to run a wire from the light to the frame or not behind the fork or not. Some lights are grounded to the frame, some are not. If you have a light that is grounded to the fork and if it does not work, the headset might be the problem.

I have only used old Union brand sidewall generators, they were grounded to the frame. But I do not know if all others are or not.
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Old 10-01-19, 04:22 PM
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Considering the width of the fork, I guess I'll just install the generator on the right seat stay, and the rear light on the left.

I'll get the acclaimed "Axa Dynamo HR Traction", which has 2x2 connectors, which I assume means running two two-core wires, one to each light.

Out of curiosity: Some generators, such as the "Union Dynamo UN-4105", only have two connectors. In this case, how is the second light connected? By running another pair of wires from the other light (generator → first light → second light)?
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Old 10-01-19, 06:26 PM
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Originally Posted by Winfried
...
Out of curiosity: Some generators, such as the "Union Dynamo UN-4105", only have two connectors. In this case, how is the second light connected? By running another pair of wires from the other light (generator → first light → second light)?
Not familiar with it. In general terms, bottle dynamos that powered two incandescent lights ran two lights in parallel, a 0.6 watt taillight and a 2.4 watt headlamp. But most LED taillights are wired to the LED headlamps. That way if you turn off the headlamp switch, the taillight also goes out. Some LED taillights can't handle all the power from a dynohub and presumably the same goes for a bottle dynamo. Thus, I would suggest you wire the taillight into the headlight wiring according the the headlight instructions.
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Old 10-02-19, 03:41 AM
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Makes sense. Thank you very much!
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Old 10-03-19, 01:04 PM
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Most LED's operate on 1.5V. Running 6V through them without a current limiting resistor runs the risk of burning out the LED. That being said, many LED systems run on 3 to 6V, so my opinion is, it depends on the power requirements of your light.
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Old 10-03-19, 01:51 PM
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Originally Posted by Milton Keynes
Most LED's operate on 1.5V. Running 6V through them without a current limiting resistor runs the risk of burning out the LED. That being said, many LED systems run on 3 to 6V, so my opinion is, it depends on the power requirements of your light.
Maybe the LED circuitry itself is 1.5v, but dyno powered LED headlights have to be able of taking a wide range of voltages of AC because they are expected to produce reasonably good light at a speed as slow as jogging speed, but they also have to continue to work when you are going down a hill at much higher speeds. Thus, they have internal circuitry to handle that.
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Old 10-03-19, 08:17 PM
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Originally Posted by Milton Keynes
Most LED's operate on 1.5V. Running 6V through them without a current limiting resistor runs the risk of burning out the LED. That being said, many LED systems run on 3 to 6V, so my opinion is, it depends on the power requirements of your light.
The question was something other than the one you appear to be answering. He asked if he can power lights designed for a hub dynamo with a bottle dynamo. And you can. Both kinds of dynamos produce a wide range of voltages, so the lights are designed to expect that. Dynamos don't produce a steady 6v. That's just a nominal rating.
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Old 10-04-19, 05:41 PM
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Originally Posted by Milton Keynes
Most LED's operate on 1.5V. Running 6V through them without a current limiting resistor runs the risk of burning out the LED. That being said, many LED systems run on 3 to 6V, so my opinion is, it depends on the power requirements of your light.
just to clarify...
the forward voltage of LEDs varies with the color, with longer wavelengths having the lower voltages and shorter wavelengths having higher voltages.
White LEDs, which use phosphors to convert blue light to other colors, tend to have a forward voltage of about 3V.

Dynamos are designed to have a limited current when shorted. As such, they produce a maximum of about 0.5A. If the LED(s) in the headlight are rated for 0.5A, then no other current limiting circuitry is required.
The exception to this is the Velogical bottle dynamo.

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Old 10-16-19, 07:57 AM
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The package is expected to arrive today.

What does the following mean?

"While the electricity from the dynamo is AC, it is still important to make sure that you keep the "earth" connection consistent through the wiring of your lights. The reason is that the "earth" is connected to the frame of the bike within both the dynamo and some of the lights. Confusions over "earth" can lead to faults such as the switch on a headlight not actually switching off your lights because electricity is flowing through the frame of your bike, or the lights either being very dim or not lighting at all due to a short circuit through the frame."
https://dutchbikebits.blogspot.com/2...ng-dynamo.html

I read that one wire is the phase (where current flows from the generator to the light), and the other is the neutral (light → back to the generator.) Where does ground/earth go then?

And from the above, it appears than ground/earth is a must when using DC, and still recommended when using AC, like in a generator: Why is that?

Thank you.
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Old 10-16-19, 08:17 AM
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I think I would call it the "return" rather than ground or earth. But people are used to power and ground, so that's easier for companies to call it that. The current has to go somewhere, it goes back via the ground.

What they are saying is that one side of the dyno is connected to the frame, so if you swap power and ground, both sides will probably be connected to the frame. If not right away, then in the future.
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Old 10-16-19, 10:31 AM
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the use of the frame as a conductor is not uncommon, but can be problematic.

I've heard of various cases where the user is using wires to carry the electrical current, with no intent to use the frame as a conductor. Unfortunately, some dynamos and lights have one terminal connected to where it connects to the frame. It's not usually obvious that this connection is being made, though. Depending on how the wires are connected, it is possible to effectively short out the dynamo with the frame.

As such, it can be critical to carefully examine the dynamo or light and determine if one terminal is connected to the frame, or "earth". If so, then the "earth" terminal on the dynamo must be connected to the "earth" terminal on the headlight and tail light.

Steve in Peoria
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Old 10-16-19, 01:58 PM
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I assume it is a Shimano dynohub, they are grounded to the fork. SP hubs are not grounded to the fork. Some lights are grounded to the fork or frame, some are not.

If two or three of your new parts is grounded to the frame or fork, wiring it up wrong can mean it won't work. Otherwise everything should work fine.

Put your system together but do not hook up the taillight wires yet. If the headlight works, great. If the headlight does not work, switch the two wires at the light, that should fix it.

Assuming that the headlight works, hook up the taillight and try it. If both headlight and taillight work, you are done. If something does not work, switch the taillight wires, probably easier to switch them where they are plugged into the headlight. That should fix it.

ADDENDUM: I forgot you were using a bottle type sidewall generator. That likely is grounded to the fork or frame. But otherwise it would function the same as a dynohub.

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Old 10-17-19, 06:30 AM
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Originally Posted by Winfried

I read that one wire is the phase (where current flows from the generator to the light), and the other is the neutral (light → back to the generator.) Where does ground/earth go then?
I re-read your post and see that nobody has addressed this. There is no separate ground and neutral. If there is a neutral connection on the dyno, it is also shorted to the frame.
You can use either the frame or a wire to the neutral connector to complete the circuit. My experience is that using the frame works fine, but sometimes requires a bit of fiddling. And sometimes corrosion causes problems. In any event, you have to keep the fact that the frame is ground in mind when wiring or the system will fail.
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Old 10-17-19, 09:44 AM
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Thanks much for the infos.

To make things easier, the AXA HR Traction has 2x2 plugs (two OUT, two IN), so that using the frame as return/ground/earth is not required. It only takes a screwdriver to remove the black cap and insert the wires.

After swapping the two wires that go to the front light, it worked. And the rear light worked right the first time :


For my — and possibly other newbies' — education:

1. What's the poinf of the two "OUT" plugs in the back of the front light, each with a different symbol attached (thunder and ground)? Can/should I use them?



2. The bracked to hold the dynamo has a sharp screw in the middle to dig into the fork/stay: Do I need this, or can I remove it and avoid damaging the frame?



Thank you.
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Old 10-17-19, 09:57 AM
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The output wire ports might be for the taillight. That way when you turn the light off with the switch, the taillight goes out too. Not sure how you wired the taillight into the system.

Most taillights can't handle the excess power if you try to send all of the generator power to only a taillight, usually only the headlight has the overvoltage protection. By wiring the taillight into the headlight circuitry, that protects the taillight from overvoltage.

But, if you always leave the switch on and only shift the generator off of the wheel to turn it off, overvoltage to the taillight is not a concern because the headlight circuit protects it whenever the generator is in use.

Do the written instructions mirror what i said above?

The generator puts pressure on the tire, without that little pointy screw the bracket might slip on the frame. You could try it first and see if it slips or not.
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Old 10-17-19, 01:14 PM
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Peter White has a list of which B&M taillights can be powered directly from the dyno. Otherwise, they have to go through the headlight. I always go through the headlight, mostly for convenience since none of my dynohubs have double connectors
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Old 10-17-19, 03:17 PM
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Originally Posted by Winfried
.........

For my — and possibly other newbies' — education:

1. What's the poinf of the two "OUT" plugs in the back of the front light, each with a different symbol attached (thunder and ground)? Can/should I use them?
I agree with the earlier comments... I expect that those are where you are supposed to connect the taillight.

Originally Posted by Winfried
2. The bracked to hold the dynamo has a sharp screw in the middle to dig into the fork/stay: Do I need this, or can I remove it and avoid damaging the frame?



Thank you.
The pointy screw is intended to break through the paint and make an electrical connection to the frame. In the modern era where two-conductor wires are standard, I don't see any advantage to using the frame as a conductor.

Steve in Peoria
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Old 10-18-19, 06:26 AM
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there are people that like to use the frame as the return. It allows the use of a high quality wire for the positive side, and requires smaller holes in the frame if you want to hide the wire. Most 2 conductor wiring is somewhat cheap. Even so, my bias is towards using 2 conductor wire.
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Old 10-20-19, 06:31 AM
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Thanks for the infos.

For both lights (Front: Union, Rear: B&M), there were no instructions on the packages, hence my questions about wiring, and the meaning of the two OUT plugs on the front light.

Here's a smartphone audio recording of the Axa HR Traction with the bike on a stand, with the dyno rubbing against the rim of the rear wheel (disk brake, FWIW):
https://vocaroo.com/i/s1KRiFGAerQV

Neither particularly silent nor drag-free, but definitely better than bothering with USB light.

I'll probably build a wheel later with a Shimano or SP hub dyno, and reuse the lights I bought. I learned useful tips in this thread, thank you.

--
Edit: Out of curiosity, I reversed the two wires on the tail light, and it lights up. So, unlike the front light that has an ON/AUTO/OFF switch, it makes no difference how the tail light is wired (OUT thunder and OUT ground).

Last edited by Winfried; 10-20-19 at 06:39 AM.
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