Magnic Light: contactless bicycle dynamo light

[fyrstormer]

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

 

[Steve K]

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.

 

[fyrstormer]

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.

 

[Steve K]

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.

 

[fyrstormer]

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.

 

[Savvas]

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.

 

[brad72]

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.

 

[2_i]

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.

 

[Steve K]

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/kurtsj00/sets/72157628920533643/

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.

 

[unterhausen]

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

 

[AnAppleSnail]

The trouble here seems to be the assertion of no moving parts. If you have no moving parts and a uniform wheel-magnet separation, then the induced field will not move. With no moving parts to move coils through that stationary (to the device) magnetic field, no power can be produced. It's analogous to a marble on a tabletop - without any tilting, it won't get anywhere...


Edit: Looks like I'm to blame - they don't claim 'no moving parts.'

 

[Steve K]

The trouble here seems to be the assertion of no moving parts. ...

who asserted that there were no moving parts?

I just did a quick re-review of the kickstarter page, and don't see any claim of this type (did I miss it? .. could be..)


Steve K.

 

[Steve K]

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

short answer: Yes

longer answer: yes, but... it seems unnecessary (to me), and it adds cost and complexity. We know that the design uses rare earth magnets, so that pretty much takes care of the method of generating a magnetic field. Maybe it could be used to modulate the magnetic field for some purpose?? Perhaps.. but I'm unable to think of how/why to do this.

Until someone reverse engineers the light, or the designers show us the internal bits, we get to have fun speculating about how it works and no one is right or wrong.

Steve K.

 

[fyrstormer]

Active or passive, the point remains that sufficient energy transfer to light-up a pair of multi-watt LEDs should've stopped the free-spinning wheel in a few seconds. There's something fishy going on here. My guess is the light isn't nearly as bright in real-world use as is implied, or else it's designed to absorb and store power at a very low rate and then burn it off at a much faster rate, i.e. it's not self-sustaining when the light is on.

 

[Steve K]

I tend to agree with the argument that the light isn't as bright as a standard LED dynamo light such as an IQ Cyo. I haven't seen any indication of what the light output is, although I thought I saw someone somewhere say "1.6 watts". I think this would explain why it takes longer for the front wheel to slow to a stop relative to the bike with the hub dynamo.
...edit: the video does say "150 lumens at 16mph", so assuming LEDs that deliver 100 lumens per watt, you could estimate that the power is 1.5 watts.

On the other hand... the Magnic might be at least as effective as the basic incandescent Lumotec that I used for a number of years. The Magnic does cost quite a bit more, though...

Steve K.

 

[dougmc]

longer answer: yes, but... it seems unnecessary (to me), and it adds cost and complexity. We know that the design uses rare earth magnets, so that pretty much takes care of the method of generating a magnetic field. Maybe it could be used to modulate the magnetic field for some purpose?? Perhaps.. but I'm unable to think of how/why to do this.

They've mentioned magnets inside the device. They've also mentioned that it doesn't touch the wheel, and there's no magnets mounted in the wheel -- it's all in that one device that's mounted to the brake.They have not claimed no moving parts, but that device doesn't really have much room for moving parts -- and I don't see how moving parts would help. But certainly, moving parts are not off the table. (Though anything that could be done with moving parts could probably be done without them.)But here's the thing -- generators work by moving a coil and a magnet relative to each other. If both coil and magnet are inside this device (as they must be), they have no relative motion and generate no electricity. You could move the coil and magnet relative to each other in the device, but that would require energy that isn't available unless there's another generator of some sort ...More fundamentally, generators work by putting a coil in a changing magnetic field (and usually the changing magnetic field is generated by moving the magnet and coil relative to each other, but there are other ways). The magnet in the device would create eddy currents in the rim, but with no way to collect them, they'd be wasted to heat.And these eddy currents would also create a magnetic field -- but at the bike light, this field would be static and therefore not useful in generating electricity.As I see it, they've either put magnets in the rim (which they say they have not) ... or it's a complete scam, powered by a battery. (And their video of the wheel being spun by hand suggests the latter, as the wheel didn't slow at all -- and it should have.) Now, perhaps it's not *intended* to be a scam, as they think having the money will allow them to work through the physics have have eluded them so far. Or maybe they know it won't work. Or maybe they really have discovered something fundamentally new that nobody else has discovered in the last two hundred years, something fundamentally new in a field where nothing really "new" has been discovered in quite some time.We shall see.They say it'll be demonstrated at a show this weekend, so maybe somebody not associated with them will get to look carefully at their demonstration models. (Though even if I do see a post from somebody saying it all seems legit, I'm not going to believe it unless it comes with a fairly detailed and plausable explanation of exactly how it works. After all, such a post could come from these people too.)I don't buy their worries about their patents not being issued yet -- what matters is when the request was filed, not when the patent was issued. If they really needed to protect it until then, they need to keep it a secret -- as anbody with some skill this field ought to be able to figure out how it works just seeing the demonstration of it working.

Until someone reverse engineers the light, or the designers show us the internal bits, we get to have fun speculating about how it works and no one is right or wrong. .

No, somebody is right and somebody is wrong. We just don't know who yet. (This isn't Schroedinger's cat ...)

 

[Steve K]

a short quote from Doug's post above: "They have not claimed no moving parts, but that device doesn't really have much room for moving parts -- and I don't see how moving parts would help."

in the 3rd post in this thread, I offered a theory on how I thought it might work, using a moving part, which is a magnetized disc. I'm copying the relevant part of the post below:

"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. "

Does this seem like a viable theory?

Steve K.

 

[2_i]

Without a changing magnetic field through a coil, you will not get a current out of the coil. With this the Eddy currents need to vary with time. For that you need to initiate them through some primary coil where the current varies with time. But that coil will be inducing Eddy currents not just in the rim but everywhere else. Much of that energy will be just dissipated away. Energy of the magnetic field due to the current in the rim spreads out to all sides. A coil half a centimeter away, on one side, would be collecting just a portion of that energy. No wonder you always try to surround all space, when a field in similar situations is produced, and leave as small gaps as possible.

Putting potential principal working aside, such as at 0.0001% efficiency or 0.0001W power output, the considerations leave the scam as an only option for what is demonstrated in the videos. Incidentally, recent Popular Photography has a discussion of how to initiate a project on Kickstarter. The need to convince the Kickstarter to take you on might be one reason for such desperate measures as making a fake prototype.

 

[Steve K]

Without a changing magnetic field through a coil, you will not get a current out of the coil. With this the Eddy currents need to vary with time. For that you need to initiate them through some primary coil where the current varies with time. But that coil will be inducing Eddy currents not just in the rim but everywhere else. Much of that energy will be just dissipated away. Energy of the magnetic field due to the current in the rim spreads out to all sides. A coil half a centimeter away, on one side, would be collecting just a portion of that energy. No wonder you always try to surround all space, when a field in similar situations is produced, and leave as small gaps as possible.

I'm going to go out on a limb and assume that you are responding to my post....

In my idea, the magnetized disk has multiple poles along its perimeter. The edge of the disk is located near the rim, and the drag of the eddy currents drags it along with the rim, spinning the disk. Once the disk is spinning, it's a minor matter to place a coil and suitable flux path near the disk to make use of the changing magnetic field as the poles on the perimeter of the disk go by. Seems plausible to me. The only part that requires a bit of a leap of faith (for me) is that the eddy currents will cause a drag on the disk's poles. Since eddy current is used to produce drag in dynamometers and bike turbo trainers, it seems reasonable (to me) to think that there must be an equal and opposite drag/force on the magnets that cause the eddy current.

The potential for a scam does exist, as in almost anything where money is involved. I believe the potential for a scam is small. The potential for the business to not make money is quite a bit larger, and many investors may not receive goods that were promised. However, that's not so much a scam as just the usual risks of starting a business.
We'll have to wait and see how it turns out.

Steve K.

 

[dougmc]

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.

That could work -- if there was a strong magnet on the rim. As this magnet spun past your disk, it would cause your disk to move. (You could also skip the middle man and just replace your disk with a coil to pick up energy directly from the changing magnetic field.)

However, they've explicitly said there's no magnets on the wheel. Any magnets are inside the device, right next to your disc.