Has anyone heard of Magnic Lights?

[andrew_s]

I note the explanation of these lights says that they won't work on "full carbon" wheels. What do they mean by full carbon?

A lot of carbon wheels have an aluminium braking surface. This will be what they mean.
Trying to get the light close enough to the (steel) spokes to work strikes me as dodgy in the extreme.

[Brucey]

the 'spherical magnet in an aluminium saucepan' experiment is telling too. BTW this kind of response is only possible if the field strength is very high indeed, localised, and changing. The high local field strength required is unlikely to be acheived without use of modern rare earth magnets. A weaker magnet with a large area just won't produce the same effect; the eddy current is at its highest if induced in a small area since it is limited by the ohmic resistance of the current path; thus a small intense area of changing field will induce high currents in a small area and these will cause the most 'drag'.

Note that I said that 'the effect was marked'. To see it you would need to do a timed run-down of a spinning wheel, and/or let a wheel (with good bearings, a welded joint, no eyelets and imperfect balance) 'settle' to its low point. Without the magnet, the wheel goes back and forth a few times before it settles. With the magnet I used there is typically no overshoot at all. The retarding force should be proportional to speed, making it a good damper. I have seen this same principle used elsewhere; I have an OHAUS triple beam balance which is magnetically damped using eddy currents in the same way.

If anyone else wants to 'have a go' with suitably strong magnets, you could do worse than to use the magnets out of an old computer hard drive. These are super-strong. and come with soft iron poles to shape the field. These produce a local field in the pole piece gap of ~2T in air, but a couple of cm away there is hardly any field at all.

cheers

[MikeF]

This device appears to be working as a Faraday Disc. The best household examples of these are old type electricity meters, washing machine controllers and mains powered electric clocks. Here an aluminium disc on a spindle is positioned between the poles of a mains powered alternating current electromagnet, and the interaction of the induced eddy currents in the disc cause it to spin at a speed dependent on the frequency. The difference with this light system is that the the disc ie bicycle rim is turned to generate electricity instead of the reverse.

Regardless of the operation note that this organisation is asking for funding. I think I would need to know a lot more before I supported it!

Also the braking effect of this device is at the rim where the turning moment is large. Would it cause more slowing effect than a hub dynamo generating the same power?

[MikeF]

Just been checking on Faraday Discs as generators. All the examples seem to produce a direct current so need wires, but the examples used magnets. Would coils make a difference? I've used a 3 phase squirrel cage motor as a generator, but his relies on very small residual magnetism to generate AC.

I don't think this device can work with just 1 magnet.

[squeaker]

This video explains eddy currents and magnetic braking well.

Lovely: thanks for the link
As a fit and forget light, I can see the utility for a hack bike, say, but anything else would depend on the beam shape and efficiency of generation. They seem to have raised the money, so watch this space, I guess.

[tripwire]

Regardless of the operation note that this organisation is asking for funding.

They met their funding target way back in March 2012. Since then the estimated delivery date has slipped several times as they kept tweaking the design.

I've been eagerly awaiting the eventual delivery date myself. I'm not a backer, I'm just hoping that someone who is will be curious enough to do a teardown on the light and reveal precisely how it works. I'm sure the comments here regarding eddy currents will prove to be correct, but I'd like to see exactly how the generator is set up to harness them.

[MikeF]

I'm not a backer, I'm just hoping that someone who is will be curious enough to do a teardown on the light and reveal precisely how it works. I'm sure the comments here regarding eddy currents will prove to be correct, but I'd like to see exactly how the generator is set up to harness them.

Me too. And how much power it can produce. I'm very curious.

[jb]

Risky game, electronics. The big boys will simply watch them till they've got it right and established a market, then step in with money and fancy injection moulded shapes producing a product at half the price & a nifty extra resistor to dodge the patent.
Where are Solid Lights now?

[[XAP]Bob]

I think you'd struggle to evade this patent with a resistor, but the money in the lawyers make that moot...

[tripwire]

I got tired of waiting for the lights to ship and dug out the patent details, which are available here: http://patentscope.wipo.int/search/en/WO2013004320. The patent document is at http://patentscope.wipo.int/search/docservicepdf_pct/id00000019762964.pdf?download (in German, but with an Abstract in English and diagrams)

It's much as I expected, the generator contains a rotor which has one or more magnets fitted to it. The rotor spins due to eddy currents in the passing wheel rim, and then the spinning rotor induces current in a surrounding coil. I've seen it described as being similar to a bottle dynamo, but using eddy currents to spin the rotor rather than friction.

[ConRAD]

... the generator contains a rotor which has one or more magnets fitted to it. The rotor spins due to eddy currents in the passing wheel rim, and then the spinning rotor induces current in a surrounding coil...

... indeed ....

here below the "5 LIRE" rotor:

... and here the test:

... and here below the video of the output ...not too much indeed but 3V is better then nothing !!!

[[XAP]Bob]

They might be using better bearings, and stronger magnets, and more coils....

It should be able to match a bottle dynamo, but with lower frictional losses (and properly enclosed). Useful power will still be lost of course, but that's negligible...

[ConRAD]

...they might be using better bearings...

That's the point: the bearing!! ... I really wonder how long bearings will last !!!
On traditional dynamos the rotor is physically maintained into rotation either by tyre dragging or wheel rotation.
In this case there is no direct friction and rotation is exclusively generated by induced eddy currents in the rim ... with no contact at all !!
... so, what will happen as soon as the rotor will tend to stick ??

[Brucey]

if you look inside a (scrap) computer hard drive you can see just how tiny, long-lived and beautifully made small bearings can be.

I think the problem is that such bearings do not tolerate dirt or moisture. Both are drawn into any enclosed housing by temperature changes; hard drives usually have an elaborate series of filters and dryers etc on their vents to prevent damage arising; they accept that the housing cannot be 100% sealed.

Getting a similar level of protection for the bearings at reasonable cost on something that is attached to a bicycle, right where it will see no end of crud, water, extreme temperature changes etc I would regard as 'a very significant engineering challenge' to the point that I don't think this can be a viable and reliable product, not at reasonable cost, anyway.

cheers

[[XAP]Bob]

IIRC schmidt "soloved"t his problem with a balloon valve - simply allow the pressure to equalise and prevent the drawing in of liquids and crud.

However this item requires no bearings or other similar protrusions, so I would not expect sealing it to be an insurmountable challenge.