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Author Topic: Magnic Bike Light  (Read 2354 times)
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wanderingmoose
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« on: May 03, 2012, 05:52:33 05:52 »

Please Read these pages :(magniclight dot com)
Have been looking at this interesting project. They were on kickstarter dot com looking for funds.
They were successful at meeting there funding. Which is a good thing. We need more people looking at bring there ideas to the public.

I have searched the net on how this might work, and all I have found is a lot of "there must be a battery" or "not possible".
I think I know how it was done. But would like a second option on my theory.

My Theory:

Now looking at there design pieces it looks like they have a coil of wire with a magnetic in the middle, hoping with some protection circuit attached to two LED. The LED should be attached in opposing directions to utilize the sign wave style pulse that will come from the coil. (watching the video it does indicate this is how they have done it)

All coil/magnetic induction energy systems require the magnetic field to change to produce a voltage pulse. This is usually done by moving a ferrous metal (gear or propeller) past the coil and getting the desired pulse.

By spinning a bicycle rim past this will not create a changing field, no change in metal mass ....but when you stand back and look at the bicycle wheel....you see the spokes. Now we have a changing metal mass that will then change the magnetic field and thus creating a voltage pulse from the coil of wire. (very much like a gear or propeller)
That is my theory...your thoughts??

Thanks for your time and comments.



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solutions
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« Reply #1 on: May 03, 2012, 09:16:40 09:16 »

The spokes are too far away to generate the 2W needed for the LEDs by variable reluctance.

They claim it's an eddy current generator - maybe one of our friends here can do an IEEE paper search on these, since, if it's not marketing BS, it would be an interesting thing to play with and is something I'm not familiar with.
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Pasca
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« Reply #2 on: May 03, 2012, 12:17:41 12:17 »

I think, but I could be wrong, that inside the body of the lamp there is a magnet that oscillates/rotates due to eddy currents.
A coil will do the rest.
My imagination suggests to me no more.
Bye
Pasca

PS: Very interesting question.
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Terry Dactil
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« Reply #3 on: August 26, 2012, 04:34:34 04:34 »

You are not the only one mystified.

There is an interesting discussion about the Magnic light at http://www.candlepowerforums.com/vb/showthread.php?333266-Magnic-Light-contactless-bicycle-dynamo-light
 
They got a response from the inventor
Quote
I hope you are satisfied with the following answer: We use a technique that provides alternating magnetic fields instead of a static magnetic field. So the same with the eddy currents which are alternating and the same again in our generator.

Also, as the inventors do not claim that "there are no moving parts",  I must agree with you when you say that there must be an oscillating or rotating magnet inside.

I would suggest that this could be a small disk parallel to the wheel with several magnets around its circumference. If its axis of rotation is below the wheel rim, then this disk would spin due to the eddy current braking effect. Each magnet in turn would try to follow the moving rim. Now you can have the alternating magnetic field required.

I suspect that the main advantage of this system is the very low energy extracted to power the LEDs; otherwise it is just a dynamo using eddy current coupling instead of a physical coupling to the wheel. Still, it is rather ingenious.


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solutions
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« Reply #4 on: August 26, 2012, 06:20:46 06:20 »

If your theory is right, it will only work with an aluminum rim.

The advantage is no physical coupling (gimmick...MAYBE a few points increase in drive efficiency...a question of whether friction losses are less than eddy losses).

The generator itself will be similarly efficient to a contact dynamo, so I respectfully disagree with the "very low energy extracted", due to magic, assumption.
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Pasca
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« Reply #5 on: August 26, 2012, 01:11:35 13:11 »

I am fascinated by the fantastic idea of the inventor of Magnic Bike Light.

I agree with Terry for the intuition of the disk with the magnets, but do not understand why, Solutions says that the rim can only be of aluminum. With the rim of iron there would be forces and moments on the axis of the disk with the magnets, but these do not disturb, I think.

I think that the efficiency of Magnic biking light is low, 50% of the energy is lost in coupling magnetic (eddy currents) between the rim and disc, the remaining 50% goes into the generator, and then a portion converted into electrical energy (efficiency <50%).

The strengths of this system are two:
1) the absence of the mechanical coupling between the wheel and the dynamo, which by its nature has a very high losses (probably much higher than 50%).
2) the low power required by high-efficiency LED.

In conclusion Magnic bike light efficiency is <50% and low electric power thanks to super-efficient LED instead of a classical dynamo has an efficiency << 50% and need more power to light the lamps. so Magnic bike light takes less power from the wheel.

Bye
Pasca
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solutions
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« Reply #6 on: August 26, 2012, 11:21:23 23:21 »

The eddy braking effect is very weak in iron due to its poor conductivity. The pickup won't spin with an iron rim, it'll just sit there looking stupid with one pole of the magnet pointed at the minimum reluctance geometry.

Nobody said you can't put a HBLED on a dynamo. You are comparing apples and oranges in reaching your conclusion.

The contact dynamo produces more power because the classical incandescent lamp needs it...as a percentage, the losses will be about the same, more or less. If the dynamo is designed for 1 watt instead of 5 or 6, the bearing loads will be similar and it'll have almost zero friction slip loss. The Magnic will, however, lose power in the eddy brake.
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Pasca
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« Reply #7 on: August 27, 2012, 11:05:57 11:05 »

Hi Solutions,
I am sorry, but with all due respect I do not agree with you on some points.
Iron and its alloys (commonly used) are less conductive than aluminum, but they are always metals and so excellent conductors.
The geometry of disc with magnets  is symmetrical, one magnet want turn disc in one direction and symmetrical magnet do the same in opposte direction, so stupidly one cancels the effect of the other. Thus the disc is free to rotate due to the eddy current braking effect with aluminum or iron rim indifferently. In my opinion.
The dynamo pinion is pulled on side of tire, pinion deforms the tire, so the rotation of the wheel is braking strongly, the side of tire is worn by the contact with the pinion due to friction.
I don't know if you've never noticed that the side of the tire heats up when using the dynamo.
This is a lot of wasted energy, as well as damage the tire. When you said: "it'll have almost zero friction slip loss" doesn't find me agree.
Sorry for divergence.
Bye
Pasca

PS: Apples and oranges are both fruit, belonging to a common category are comparable. The rest I agree with you  Smiley
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solutions
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« Reply #8 on: August 28, 2012, 03:58:28 03:58 »

Out of convenience, you neglect one major point that I had made. An incandescent's (the orange) dynamo is generating 5-10x the power of of a Magnic generator powering HBLEDs (apple). That affects the drive mechanism....severely....5-10x the contact friction, in fact, for the dynamo.

You are also neglecting the reluctance I mentioned, which dominates eddy forces in ferromagnetic materials...by orders of magnitude. Your symmetrical geometry of magnets argument does not work on an off-center rotor because the magnetic attraction varies with 1/d^2 for iron, whereas it's close to zero with aluminum.
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Pasca
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« Reply #9 on: August 28, 2012, 06:44:56 18:44 »

Ok Solutions, you've convinced me, the disc does not rotate with the rim of iron.
I neglected the power of the dynamo because I think it is only 2-3 times greater than magnic light power generated. Tradional dynamo supplies 6V 3W.
Do you think it really works magnic bike light or is it a fake?
Rejected the rotation remains the magnet oscillation hypothesis. The fact that the magnetic force decreases with quadratic factor of the distance could help?
Any idea?
A curiosity, but if the wheel spins in the opposite direction magnic bike light works again?

Bye
Pasca
« Last Edit: August 28, 2012, 06:52:40 18:52 by Pasca » Logged

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