Magnic Light: contactless bicycle dynamo light

filibuster

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Here's an interesting dynamo light looking for backing.
http://www.kickstarter.com/projects/dynamodirk/magnic-light-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.

FrontLight.jpg


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.
 
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Steve K

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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.
 
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berndS

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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.
 

berndS

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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.
 

2_i

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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.
 

2_i

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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.
 

minisystem

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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! :p

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.
 

Steve K

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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.
 

Steve K

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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.
 

Steve K

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Very cranky Steve! :p

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/Howard_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. :)

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.



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/Catalogs/cyclo-pedia-74/p54 accessories 3.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.
 

2_i

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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.
 

Steve K

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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.
 

2_i

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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...
 

fyrstormer

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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.
 
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Steve K

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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.

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.
 

CKOD

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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 ;)
 

dougmc

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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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