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Thread: Magnic Light: contactless bicycle dynamo light

  1. #1

    Default Magnic Light: contactless bicycle dynamo light

    Here's an interesting dynamo light looking for backing.
    http://www.kickstarter.com/projects/...get-new-energy

    I found the above reference on gizmag.com and it sounded very interesting as it uses eddy currents generated from any spinning metallic rim to generate power without magnets being attached to the wheel. Very limited resistance is generated compared to hub dynamos.



    It's still in the prototype stage but looks like a great idea! The video available on either of the links above show a great demo of the light working.
    Last edited by filibuster; 02-17-2012 at 07:16 PM.

  2. #2

    Default Re: Magnic Light: contactless bicycle dynamo light

    Fascinating. Built in brake light effect too!

  3. #3
    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    I may be a cranky old fart (in fact, I'm pretty sure I am), but this seems implausible (or impossible).

    Yes, the rim will generate eddy currents when passing by a stationary magnet. This is a standard way to waste power in stationary bike trainers and even on dynamometers used on internal combustion engines. However.... they induce a DC current in the rim/disc, which will produce a DC magnetic field. As we all know, a DC magnetic field doesn't induce current in a coil of wire. It takes a change in magnetic flux to induce current in a coil.

    Besides... the magnetic field induced by the eddy current merely acts to reduce the externally applied field. I'm at a loss to understand how anyone could extract any useful electric power from this arrangement.

    Anyone know of any eyewitness accounts of this device? All I can find on the web is the press release from the inventor/promoter.

    OTOH, if the rim had some steel segments built into the rim sidewall, such that 20mm was steel, the next 20mm was aluminum, the next 20mm was steel, etc, then you could put a magnet next to the rim. As the rim rotated, the field between the magnet and rim would vary as the steel and aluminum moved past. The field would increase when the steel was nearby, and decrease when the aluminum was near. If you put a coil around this field, the change in the field would induce current into the coil. This is a principle used in variable reluctance sensors, as commonly used to sense the cam or crankshaft rotation in an internal combustion engine.

    I'd love to see a real advance in dynamo technology, but I won't be sending these folks my money any time soon.

    regards,
    Steve K.

    edit: okay..... I've got working theory on how it works. It involves a magnetized disc that gets spun by the eddy currents dragging it around. A coil is positioned on the other side of the magnetized disc. As the disc spins, the changing magnetic poles along the perimeter of the disc induce current into the coil. I'm assuming that the two LEDs are simply wired in opposite polarity across the output of the coil.
    In some regards, it's a lot like a bottle dynamo, except that magnetic fields couple the dynamo's axle to the rim instead of a roller.
    The use of eddy currents produces losses in the rim though, so it does give up some efficiency relative to a hub dynamo. It's still probably more efficient than the average bottle dynamo, though.
    Last edited by Steve K; 02-17-2012 at 01:20 PM. Reason: minor brainstorm

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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Steve K View Post
    I may be a cranky old fart (in fact, I'm pretty sure I am), but this seems implausible (or impossible).

    Yes, the rim will generate eddy currents when passing by a stationary magnet. This is a standard way to waste power in stationary bike trainers and even on dynamometers used on internal combustion engines. However.... they induce a DC current in the rim/disc, which will produce a DC magnetic field. As we all know, a DC magnetic field doesn't induce current in a coil of wire. It takes a change in magnetic flux to induce current in a coil.

    Besides... the magnetic field induced by the eddy current merely acts to reduce the externally applied field. I'm at a loss to understand how anyone could extract any useful electric power from this arrangement.

    Anyone know of any eyewitness accounts of this device? All I can find on the web is the press release from the inventor/promoter.

    OTOH, if the rim had some steel segments built into the rim sidewall, such that 20mm was steel, the next 20mm was aluminum, the next 20mm was steel, etc, then you could put a magnet next to the rim. As the rim rotated, the field between the magnet and rim would vary as the steel and aluminum moved past. The field would increase when the steel was nearby, and decrease when the aluminum was near. If you put a coil around this field, the change in the field would induce current into the coil. This is a principle used in variable reluctance sensors, as commonly used to sense the cam or crankshaft rotation in an internal combustion engine.

    I'd love to see a real advance in dynamo technology, but I won't be sending these folks my money any time soon.

    regards,
    Steve K.

    edit: okay..... I've got working theory on how it works. It involves a magnetized disc that gets spun by the eddy currents dragging it around. A coil is positioned on the other side of the magnetized disc. As the disc spins, the changing magnetic poles along the perimeter of the disc induce current into the coil. I'm assuming that the two LEDs are simply wired in opposite polarity across the output of the coil.
    In some regards, it's a lot like a bottle dynamo, except that magnetic fields couple the dynamo's axle to the rim instead of a roller.
    The use of eddy currents produces losses in the rim though, so it does give up some efficiency relative to a hub dynamo. It's still probably more efficient than the average bottle dynamo, though.
    Hi Steve,
    I saw the Magnic Light two weeks ago. Dirk is my cousin und we celebrate the christening of my son Jakob. I was really fascinated seeing that it works. But Dirk explains it much better on kickstarter.
    Best wishes from Nuremberg, Germany

    Bernd S.

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    Default Re: Magnic Light: contactless bicycle dynamo light

    Hallo Steve,
    I saw one of the prototypes two weeks ago. Dirk is my cousin und we celebrate the christening of my son Jakob. I was really fascinated seeing that it works. But Dirk explains it much better on kickstarter.
    Best wishes from Nuremberg, Germany

    Bernd S.

  6. #6

    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Steve K View Post
    okay..... I've got working theory on how it works. It involves a magnetized disc that gets spun by the eddy currents dragging it around. A coil is positioned on the other side of the magnetized disc. As the disc spins, the changing magnetic poles along the perimeter of the disc induce current into the coil. I'm assuming that the two LEDs are simply wired in opposite polarity across the output of the coil.
    I doubt there is any moving part within the device. I expect a resonance circuit connected to a coil, maybe with double winding, with the rim inducing and sustaining the oscillations.

  7. #7

    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Steve K View Post
    okay..... I've got working theory on how it works. It involves a magnetized disc that gets spun by the eddy currents dragging it around. A coil is positioned on the other side of the magnetized disc. As the disc spins, the changing magnetic poles along the perimeter of the disc induce current into the coil. I'm assuming that the two LEDs are simply wired in opposite polarity across the output of the coil.
    I doubt there is any moving part within the device. I expect a resonance circuit connected to a coil, maybe with double winding, with the rim inducing and sustaining the oscillations.

  8. #8

    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Steve K View Post
    I may be a cranky old fart (in fact, I'm pretty sure I am), but this seems implausible (or impossible).

    Yes, the rim will generate eddy currents when passing by a stationary magnet. This is a standard way to waste power in stationary bike trainers and even on dynamometers used on internal combustion engines. However.... they induce a DC current in the rim/disc, which will produce a DC magnetic field. As we all know, a DC magnetic field doesn't induce current in a coil of wire. It takes a change in magnetic flux to induce current in a coil.

    Besides... the magnetic field induced by the eddy current merely acts to reduce the externally applied field. I'm at a loss to understand how anyone could extract any useful electric power from this arrangement.

    Anyone know of any eyewitness accounts of this device? All I can find on the web is the press release from the inventor/promoter.

    [snip]
    I'd love to see a real advance in dynamo technology, but I won't be sending these folks my money any time soon.
    Very cranky Steve!

    However it works, the kickstarter page clearly shows a working prototype, so I doubt their claims are fraudulent. I'm also skeptical that it would have moving parts, especially considering that the housing looks like most of the space is taken up with LEDs and reflectors.

    A little more transparency from the inventor would certainly satisfy our curiosity, but I imagine that he probably wants to guard his IP at least while the product is in development.

    I'd like to know what the available power output is. Since virtually all dynamos are rated at 6V3W (0.5A) it would be nice to know how much current he can extract to drive the LEDs.

    Considering the output must vary with distance from the rim as well as rim surface area, its output must vary widely depending on installation and the rim it's used with.

    If it can indeed produce a useful amount of power it would be cool to see just a 'kernel' available to mount next to the rim and act as a power source for third party lights.

  9. #9

    Default Re: Magnic Light: contactless bicycle dynamo light

    glitchy double post
    Last edited by minisystem; 02-21-2012 at 11:30 AM.

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    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by 2_i View Post
    I doubt there is any moving part within the device. I expect a resonance circuit connected to a coil, maybe with double winding, with the rim inducing and sustaining the oscillations.
    Is there a similar sort of design/device used elsewhere in the world? I'm having a hard time thinking of how this would be implemented.

    Steve K.

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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by berndS View Post
    Hallo Steve,
    I saw one of the prototypes two weeks ago. Dirk is my cousin und we celebrate the christening of my son Jakob. I was really fascinated seeing that it works. But Dirk explains it much better on kickstarter.
    Best wishes from Nuremberg, Germany

    Bernd S.
    hi Bernd,

    I'll admit to being skeptical about this light, but the demo looked quite realistic. I was just struggling for a theory of how it worked. I have to give Dirk and the team credit, because it really is a new approach to making a bike light! They must have had a lot of fun developing it, and learned quite a bit in the process. I'd like to hear the story of how the design got started and evolved.

    It will be interesting to see how the project progresses. It's not easy building electronics, and there are a lot of hassles involved with the whole process of selling and supporting a product. I'm assuming that they would like to demonstrate that the light is popular with the cycling public, and then sell the design to B&M or some other bike light manufacturer.

    regards,
    Steve K.

  12. #12
    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by minisystem View Post
    Very cranky Steve!

    However it works, the kickstarter page clearly shows a working prototype, so I doubt their claims are fraudulent. I'm also skeptical that it would have moving parts, especially considering that the housing looks like most of the space is taken up with LEDs and reflectors.
    Well, there are people with videos of perpetual motion machines on the web too, so you can't always believe what you see (especially on the web!)
    http://freeenergynews.com/Directory/...Johnson_Motor/
    This guy even had papers published in journals that dealt with energy conversion and such (back in the days when I was working on satellite power systems). The journals were essentially compelled to publish the papers, but put them in the back with an introduction that said "we realize that these papers are discussing perpetual motion machines that defy known physics, ...." etc.
    However, since no one gets rich by making bike lights, there's very little incentive for a bike light scam.

    Quote Originally Posted by minisystem View Post
    A little more transparency from the inventor would certainly satisfy our curiosity, but I imagine that he probably wants to guard his IP at least while the product is in development.
    Agreed. If it is a great product, the big bike light companies will reverse engineer it soon enough.



    Quote Originally Posted by minisystem View Post
    I'd like to know what the available power output is. Since virtually all dynamos are rated at 6V3W (0.5A) it would be nice to know how much current he can extract to drive the LEDs.

    Considering the output must vary with distance from the rim as well as rim surface area, its output must vary widely depending on installation and the rim it's used with.

    If it can indeed produce a useful amount of power it would be cool to see just a 'kernel' available to mount next to the rim and act as a power source for third party lights.
    I'm also waiting for the technical details! In principle, I think the design could be scaled up to provide any power desired. There are the usual issues of cost, weight, size, etc that go along with increased power. Honestly, I like the arrangement they have now. Very similar to the old "monoblock" dynamos, like the item in the upper left of this catalog page:
    http://bulgier.net/pics/bike/Catalog...sories%203.jpg
    I still have that dynamo! Used it for many years, and was quite handy. Unfortunately, it was also pretty good at slowing my bike!

    Steve K.

  13. #13

    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Steve K View Post
    Is there a similar sort of design/device used elsewhere in the world? I'm having a hard time thinking of how this would be implemented.
    This patent discusses regenerative Eddy braking. I have not had time to analyze it, but on the first glance it seems to replace the idea of a rotating magnet with out-of phase coils.

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    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by 2_i View Post
    This patent discusses regenerative Eddy braking. I have not had time to analyze it, but on the first glance it seems to replace the idea of a rotating magnet with out-of phase coils.
    thanks for the link! It'll take me a bit of time to work out the details, I suppose. The one thing that seems like a problem with this approach is the need to excite the windings that produce the eddy currents in the first place. Or can this be done with a DC field produced by magnets?
    The other part that I'm still struggling with is how to get power from the field produced by the eddy currents. The eddy currents produce a field that is trying to counter the applied field, so it'll never be stronger than the field that you are already generating.

    The patent also mentions that the system needs to know the disc speed so that the 3 phases can be timed correctly. This probably isn't happening in the Magnic light.

    For now, I'm sticking with my theory of operation. Yeah, it has one moving part. That's not unheard of for a bike dynamo.

    regards,
    Steve K.

  15. #15

    Default Re: Magnic Light: contactless bicycle dynamo light

    I think that the design needs to be such that the coils + rim work, from the side of the circuit, act as a negative resistance for finite frequencies. Once that is achieved, the circuit will develop a runaway AC current. An electrostatic runaway example is the Kelvin water dropper. While the moving rim will not change the fundamental frequency of the AC, it can act to change the shape of the pulse, i.e. introduce higher harmonics. Just random thoughts...

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    *Flashaholic* fyrstormer's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    The light itself could use some input current from an internal battery to generate a magnetic field in the vicinity of the rim, and then, because aluminum is paramagnetic, the spinning rim could interact with the field to drain momentum from the wheel and convert it into enough electricity to light the lamp and keep the internal battery topped-off. I don't entirely understand how the aluminum would interact with the magnetic field to produce this effect, but I do know that car alternators work on a similar principle -- there's no magnet inside, just two sets of coils, and one set is energized with power from the battery. Among other things, that way the output power from the alternator can be regulated by lowering the input power to the energized coil when the engine revs up.

    In any event, I doubt this device could generate enough electricity to run a multi-watt emitter without causing a noticeable drain on the momentum of the bike. Even good riders can only output 250-300 watts in a sprint.
    Last edited by fyrstormer; 02-21-2012 at 11:09 PM.

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    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by fyrstormer View Post
    The light itself could use some input current from an internal battery to generate a magnetic field in the vicinity of the rim, and then, because aluminum is paramagnetic, the spinning rim could interact with the field to drain momentum from the wheel and convert it into enough electricity to light the lamp and keep the internal battery topped-off. I don't entirely understand how the aluminum would interact with the magnetic field to produce this effect, but I do know that car alternators work on a similar principle -- there's no magnet inside, just two sets of coils, and one set is energized with power from the battery. Among other things, that way the output power from the alternator can be regulated by lowering the input power to the energized coil when the engine revs up. .

    That's certainly a possibility. From a manufacturing and support perspective, I think this would be disadvantage. After a few years, the battery is likely to lose enough capacity to quit working. Besides, the Kickstarter site said that they used a number of magnets in the dynamo, so that would suggest that they aren't using a battery to generate the magnetic field.

    By chance, I spent some time last week looking at a paper describing ways to improve the regulation in an automobile alternator. It was a good review... they do indeed use battery power to get the field current flowing initially. The field current is adjusted in order to control the output voltage. Problems show up when the load on the battery changes suddenly, and the control circuit takes time to respond. The resulting voltage overshoot can be on the order of 150v for large diesel engines with 24v batteries. It'll be less for 12v autos, but it does show that any LED lights you build for your car need suitable protection circuitry.

    Quote Originally Posted by fyrstormer View Post
    In any event, I doubt this device could generate enough electricity to run a multi-watt emitter without causing a noticeable drain on the momentum of the bike. Even good riders can only output 250-300 watts in a sprint.
    With modern hub dynamos, the losses are fairly low. I built a light that drives 4 LEDs at 0.5A, and I really don't notice the drag. In one of the videos on the Kickstarter site, there is a demo of the Magnic and a regular hub dynamo & LED (?) headlight. Two bikes are in workstands, where the one on the left has a regular hub dynamo, and the one on the right has the Magnic. The front wheels are spun by hand, and the Magnic equipped bike takes longer before the wheel stops. I'm assuming that Magnic is generating less power, hence the longer spin time. Or it could be related to the cogging behavior of the two dynamos.... hub dynamos take a noticeable amount of force to move past each magnetic pole in the dynamo. On the other hand, the force from the Magnic light will decrease as the wheel speed decreases.

    Anyway, all I have are guesses about the Magnic's efficiency, operating principles, etc. I'll be interested to learn more about it, and I'm always happy to see people trying new ways to improve familiar devices.

    regards,
    Steve K.

  18. #18

    Default Re: Magnic Light: contactless bicycle dynamo light

    http://en.wikipedia.org/wiki/Squirrel-cage_rotor

    I'd expect its pricipal to be based off of this more than anything else. A car alternator is a poor example as its just an electromagnet spun inside some generator coils.

    If you turn an induction motor by itself, nothing will happen, but if there is any residual magnetism left in the core, and you have a capacitor on the output to provide reactive current, you can run it as a generator. With the right coil geometry to work with the bicycle rim, no reason your rotor couldnt be the aluminum rim. If you can make a rotary induction motor to run as an rotary induction generator, no reason a linear induction motor cant be made into a linear induction generator

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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by CKOD View Post
    [URL] If you can make a rotary induction motor to run as an rotary induction generator, no reason a linear induction motor cant be made into a linear induction generator
    you're correct, and Wiki does have an entry for induction generators.

    The difference in the case of this bike light is that the rotor portion (the rim) doesn't have windings and poles that will rotate. It just has eddy currents that are basically stationary with respect to the stator (the dynamo). The essential element of induction motors (and presumably induction generators) is the rotating fields and the slight difference in angular velocity between the stator and rotor fields. I don't see how you get this with eddy currents in the rim.

    Steve K.
    (now I need to review induction generators....)

  20. #20

    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by minisystem View Post
    However it works, the kickstarter page clearly shows a working prototype, so I doubt their claims are fraudulent. I'm also skeptical that it would have moving parts, especially considering that the housing looks like most of the space is taken up with LEDs and reflectors.
    Their kickstarter page shows a light that goes to full brightness with even a slow spinning of the wheel.

    At 0:31 on their video, they show the light being mounted and the tire being spun -- but if the generator generated one watt, was 100% efficient (ha!) and this road bike tire and rim was a full two pounds (heavy!), and all this weight was at the outside of the tire (a reasonable approximation) and the tire was spun at 8 mph (it didn't look faster than that) -- the tire would be totally stopped after six seconds. (As the wheel would initially have 5.8 joules of energy.) Instead, we get to see the tire spin for five full seconds with no apparent reduction in speed at all. This tells me that this light put a negligible load if any on the tire -- so it must have drawn way less than one watt. Considering that it still seemed fairly bright -- I wonder if their demonstration model was powered by a battery. (And perhaps had a sensor to detect a spinning tire to turn itself on?)

    They claim there's no magnets in the wheel or rim and it doesn't touch the rim. As I see it, they could put coils and magnets in the device, and it wouldn't have any internal moving parts. But any eddy currents would be generated in the rim and therefore unavailable to power the light, and I see no way to make this work.

    The reelight lights work like this -- but they put magnets on the wheel. The physics is sound there. For this, I can't see how it could possibly work -- and yet I have a degree in physics. A homopolar generator comes close, but you'd have to have a bushing on the rim (i.e. touch it) and have good electrical contacts between the rim, spokes, hub, form and light again, and ideally magnets all down the fork -- and even then it would work like crud. Or they could put magnets in the rim, evenly spaced around the rim -- and then it would work just like the reelight. But having those magnets would be totally contrary to their claims.

    All together, this makes me think this is an elaborate scam -- either to get the kickstarter money, or just advertising for their "find the oil" game.

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    *Flashaholic* fyrstormer's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Thank you Doug, your application of the Law of Conservation of Energy is what I was trying to explain before.

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    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by dougmc View Post
    They claim there's no magnets in the wheel or rim and it doesn't touch the rim. As I see it, they could put coils and magnets in the device, and it wouldn't have any internal moving parts. But any eddy currents would be generated in the rim and therefore unavailable to power the light, and I see no way to make this work.
    I agree with your train of thought, and ran into the same wall myself. It did occur to me, though, that another method was possible. Eddy currents are still used, but the drag produced by the eddy currents can be used to spin a magnetized wheel inside the dynamo gadget. The magnetized wheel, once spinning, can generate changing magnetic flux which can be directed through a coil to produce AC current. (I really need to do a sketch of this idea...)

    It would be even more fun to just make a quick prototype of the magnetized wheel. and position it next to a wheel while the bike is in a workstand (or the wheel is in a truing stand).

    The whole idea could still be a scam, but it seems like a lot of work just to get the small amount of kickstarter money.

    Steve K.

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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Steve K View Post
    By chance, I spent some time last week looking at a paper describing ways to improve the regulation in an automobile alternator. It was a good review... they do indeed use battery power to get the field current flowing initially. The field current is adjusted in order to control the output voltage. Problems show up when the load on the battery changes suddenly, and the control circuit takes time to respond. The resulting voltage overshoot can be on the order of 150v for large diesel engines with 24v batteries. It'll be less for 12v autos, but it does show that any LED lights you build for your car need suitable protection circuitry.
    At the risk of going off-topic, I don't think this is as much of a problem as the literature you read may have implied. Certainly voltage spikes can happen, but lead-acid batteries can absorb charge about as fast as they can dump it, and they exert considerable "electrical inertia" (my own made-up term) against changes in overall system voltage. With 18-wheeler batteries that can output (or input) >1000amps for a short time, it would take a seriously beastly generator to output enough wattage to keep a voltage spike from drooping back to safe levels. Also, the wiring in the vehicle itself would apply strong resistance to the surge of amperage following a voltage spike, which would be a serious problem if it lasted long enough to generate substantial heat, but for a split-second spike the wires would just act as resistors to keep things under control.

    Obviously a truck alternator would have a stronger effect than the Van de Graaf generators science teachers love to play with, and I wouldn't want to absorb a voltage spike from a truck alternator at all, much less for fun, but the principle would be the same in practice: even an extremely high voltage, when restrained by a strongly resistive medium (whether air or thin strands of heated copper), discharging into an electrical sink with a sufficiently-large storage capacity (whether a human body or an array of large batteries), will have minimal effect.
    Last edited by fyrstormer; 02-23-2012 at 09:48 AM.

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    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by fyrstormer View Post
    At the risk of going off-topic, I don't think this is as much of a problem as the literature you read may have implied.
    check ISO 7637-2, "Electrical transient conduction along supply lines only". This is the EU standard where the alternator load dump pulse is defined for the earthmoving equipment that I work with. This is the standard that earthmoving equipment must meet or it can't be sold in the EU nor other countries that use the EU standard. Here's the introductory text for the load dump pulse:

    "This test is a simulation of load dump transient, occurring in the event of a discharged battery being
    disconnected while the alternator is generating charging current and with other loads remaining on the
    alternator circuit at this moment; the load dump amplitude depends on the alternator speed and on the level of
    the alternator field excitation at the moment the battery is disconnected. The load dump pulse duration
    depends essentially on the time constant of the field excitation circuit and on the pulse amplitude (see
    Annex F). In most new alternators, the load dump amplitude is suppressed (clamped) by the addition of the
    limiting diodes.
    Load dump may occur on account of a battery being disconnected as a result of cable corrosion, poor
    connection or of intentional disconnection with the engine running."

    Steve K.

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    Default Re: Magnic Light: contactless bicycle dynamo light

    Oh, well, if the voltage spike is caused by removing a defective battery from the circuit (whether accidentally or on purpose), then obviously that battery can't act as an electrical sink to absorb the voltage spike. Yeah, I can see how that could cause a bigger problem than if the electrical system isn't being physically altered. That would (almost) never happen in a car, though, because there's no provision to change a car battery while the car is running, and cars generally aren't used heavily enough to cause the battery wires to disconnect accidentally.

  26. #26

    Default Re: Magnic Light: contactless bicycle dynamo light

    Soooo - could someone remind an old bloke again please.... exactly what was it that's wrong with my hub dynamo (sitting down there safe and unbreakable within the wheel, unable to fall off or get bent, connectable to all sorts of home made lighting contraptions and working with negligible 'drag')?

    Savvas.

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    Default Re: Magnic Light: contactless bicycle dynamo light

    I agree with your train of thought, and ran into the same wall myself. It did occur to me, though, that another method was possible. Eddy currents are still used, but the drag produced by the eddy currents can be used to spin a magnetized wheel inside the dynamo gadget. The magnetized wheel, once spinning, can generate changing magnetic flux which can be directed through a coil to produce AC current. (I really need to do a sketch of this idea...)

    This was my thought as well. How are they harnessing the eddy currents? A rim with magnets mounted inside and then balanced on the other hand would produce the desired affect then coils in the light head could possibly harness the energy. There is a downside of coarse and that is the rotating mass would require more energy from the rider to get the bike moving compared to a standard dynamo hub, but once spinning at speed it would not to bad. Also is there enough energy produced to charge caps to stop flicker and give usable light when going slow or stopped.

    They have apparently generated $19,000 so far but is it real, only time will tell. If it is real then good on them for designing something very different and left field.
    Last edited by brad72; 02-23-2012 at 09:32 PM.

  28. #28

    Default Re: Magnic Light: contactless bicycle dynamo light

    As a matter of experimentation, I brought a compass needle next to a spinning alu rim. For the life of me, I cannot get a deflection - at best some hesitation in the needle. From the literature on high-speed trains, Eddy brakes are not usable at low speeds.

  29. #29
    Flashaholic* Steve K's Avatar
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    Default Re: Magnic Light: contactless bicycle dynamo light

    Quote Originally Posted by Savvas View Post
    Soooo - could someone remind an old bloke again please.... exactly what was it that's wrong with my hub dynamo (sitting down there safe and unbreakable within the wheel, unable to fall off or get bent, connectable to all sorts of home made lighting contraptions and working with negligible 'drag')?

    Savvas.
    nothing wrong with a nice hub dynamo, which explains why I have them on two bikes!
    However, both of these bikes are commuter/utility bikes that could be ridden on a moment's notice in all conditions.
    Sometimes I like to ride a fast bike, and might be riding after dark for a short while. For those instances, I bring along a battery powered light (see link below: )
    http://www.flickr.com/photos/kurtsj0...7628920533643/

    It might be nice to have a small dynamo light that could be quickly clipped onto the bike as needed, without the concerns that come with battery powered lights. As I mentioned earlier in this thread, I used to use a little bottle dynamo that had a headlight attached. When I thought I might be out late, it only took one bolt to attach the light to the bracket on the fork. Very handy! The downside was that it produced a significant drag, as does every bottle dynamo.

    I think there is a market for this sort of light, but it's not really for commuter/utility bikes.

    regards,
    Steve K.

  30. #30

    Default Re: Magnic Light: contactless bicycle dynamo light

    is it possible it's partially active, analogous to the field windings in a field controlled dc motor? My physics stinks

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