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 rscamp 01-08-14 07:13 PM

What is the efficiency of the system in generating electrical power supplied to the light?

If you find out, tell us.

 rscamp 01-08-14 08:37 PM

:) The 800 pound gorilla...

 zacster 01-08-14 08:39 PM

Quote:
 Originally Posted by Road Fan (Post 16394922) I agree that it is an amazing invention. Spoke current is an interesting thought, that there is an electric circuit that involves the spokes. So a potential is created, current flows through the spokes, fork blade, brake caliper, and the body of the Magnic. In order to close the circuit across the gap between the Magnic and the rim, the current would have to be an AC current, not a DC current. I don't know if I agree, but it's an interesting hypothesis, not implausible. It could easily be tested by making sure the mount of the Magnic is not conductive. If it isn't conductive, current cannot flow and the light won't work. If the mount is already non-conductive and the light does work, then Unter's spoke circuit hypothesis would be disproven. There is a plastic element in the mounting system, the little snap-bracket that looks like the one that holds a Planet Bike taillight to a seat stay bracket. If anyone with a Magnic can measure the resistance (with an ohmmeter or DMM with this function) from the Magnic to the hub, we could test this hypothesis. Another hypothesis is that the passage of the rim through the magnetic field creates a potential along the rim, spanning the width of the assembly of magnets. A current should then be present in the rim, circulating through its circumference and spokes. Impedance of the spokes should be a lot higher than that of the rim, so rim current should be the dominant effect. But unless that current is AC and the magnet and windings serve as a sort of gapped transformer sensing the current in the rim, I don't see how energy represented by rim current is transferred to the Magnic, to power a small dynamo that actually runs the LEDs.
No, you have it completely wrong. The spokes have nothing to do with it, there is no complete circuit through the spokes or frame. The rim does NOT hold a current generated by magnets. It is entirely the other way around. The rim generates eddy currents, all moving conductors do, and the magnets in the light unit spin with the spinning rim because of it. These magnets then drive the dynamo inside the light itself. The entire circuit is inside the light unit. You can hold it in your hand next to a spinning rim and it will work without touching anything else. It is totally self-contained. The beauty of this thing is that he was able to harness the power from something that most people didn't know exists.

Magnic is a play on magnet and magic.

I f I could tell you something concrete, I would be!

 zacster 01-08-14 08:58 PM

So I just put more of my money into this. I signed up for another rear light on Kickstarter. It really was a really cool light. Maybe I'll again be the only BF'er that has one, unless someone else bought into it.

Quote:
 Originally Posted by zacster (Post 16395189) No, you have it completely wrong. The spokes have nothing to do with it, there is no complete circuit through the spokes or frame. The rim does NOT hold a current generated by magnets. It is entirely the other way around. The rim generates eddy currents, all moving conductors do, and the magnets in the light unit spin with the spinning rim because of it. These magnets then drive the dynamo inside the light itself. The entire circuit is inside the light unit. You can hold it in your hand next to a spinning rim and it will work without touching anything else. It is totally self-contained. The beauty of this thing is that he was able to harness the power from something that most people didn't know exists. Magnic is a play on magnet and magic.
Fine, so the first hypothesis is wrong, because your test with the lamp hand-held disproves it. Good, that's progress.

If you know something concrete and detailed about how it works, please share. I think we'd all like to know something concrete about this. It's not enough to say "it's eddy currents." Of course it's eddy currents. The question is, what about the rest of it? And from a product point of view, how good is it really?

I did not state the hypotheses are correct. Hypotheses are expected to be wrong. Only a few will ever be correct. Scientific method is to propose them and test them to weed out explanations that do not describe reality, like Sherlock Holmes. You've helped me do that, thank you.

Please explain in detail how the Magnic works. I'm especially curious about the electromagnetics. How can the energy transfer be efficient compared to a hub dynamo when the primary magnetic system, unlike both hubs and bottles is based on a solenoidal geometry and hence has huge leakage fluxes? Air core magnetics are not used for reliable, efficient power systems for this reason - flux linkage is usually quite poor compared to using cores to direct the flux.

Quote:
 Originally Posted by rscamp (Post 16395182) :) The 800 pound gorilla...
Yes, that question IS the 800 # gorilla!

 JonnyHK 01-09-14 01:07 AM

Quote:
 Originally Posted by Road Fan (Post 16395460) Please explain in detail how the Magnic works.

http://en.wikipedia.org/wiki/Eddy_current

And watch the video on the Magnic website.

It works. Don't ask us to explain it - because unless anyone here is a high school physics teacher I don't think we could.

 zacster 01-09-14 07:22 AM

http://www.kickstarter.com/projects/...ess-bicycle-dy

Just watch the video. It shows how it is assembled, plus the critical part of how the magnets pick up the eddy current.

 wphamilton 01-09-14 08:56 AM

Quote:
 Originally Posted by Road Fan (Post 16395460) ... Please explain in detail how the Magnic works. I'm especially curious about the electromagnetics. How can the energy transfer be efficient compared to a hub dynamo when the primary magnetic system, unlike both hubs and bottles is based on a solenoidal geometry and hence has huge leakage fluxes? Air core magnetics are not used for reliable, efficient power systems for this reason - flux linkage is usually quite poor compared to using cores to direct the flux.
I don't know the details any more than you do, and this was my first thought also. But then, why really care? The eddy currents will generate heat and we'll ultimately feel that as a drag, as in magnetic brakes - given that the lights have an acceptable brightness, the drag is the only real issue. I could be wrong but I don't see leakage inductance as looming very large in this application.

 zacster 01-09-14 12:02 PM

There is no noticeable drag when using a single rear light. In fact, when I lost the light I didn't notice that it was no longer operating. Before I lost it when I lifted the bike off the ground and gave the wheel a spin it kept going as if nothing were there. Multiply that by three (2 front, one rear) and maybe, just maybe, the cumulative effect will be perceptible. More likely though is you'll feel the effect of your slightly unzipped jacket catching the wind before you'd feel that.

People say the same things about dynamo hubs, and I don't believe them either. I'm going to find out on my own. Lights on vs. off, dynamo wheel vs. no dynamo. The only dynamo hub I've ever used was on a Citibike and they are so loaded down anyway they don't count.

 wphamilton 01-09-14 01:31 PM

Quote:
 Originally Posted by zacster (Post 16396538) There is no noticeable drag when using a single rear light. In fact, when I lost the light I didn't notice that it was no longer operating. Before I lost it when I lifted the bike off the ground and gave the wheel a spin it kept going as if nothing were there. Multiply that by three (2 front, one rear) and maybe, just maybe, the cumulative effect will be perceptible. More likely though is you'll feel the effect of your slightly unzipped jacket catching the wind before you'd feel that. People say the same things about dynamo hubs, and I don't believe them either. I'm going to find out on my own. Lights on vs. off, dynamo wheel vs. no dynamo. The only dynamo hub I've ever used was on a Citibike and they are so loaded down anyway they don't count.
There will always be drag, starting with the power output to the light and increased by the inefficiencies. Dynamo hubs can have 3 to 9 watts worth roughly speaking, which can be noticeable (moreso at lower speeds). I suspect that there is less drag with this technology than for dynamos with equivalent power outputs.

 njkayaker 01-09-14 03:36 PM

Quote:
 Originally Posted by wphamilton (Post 16396787) There will always be drag, starting with the power output to the light and increased by the inefficiencies. Dynamo hubs can have 3 to 9 watts worth roughly speaking, which can be noticeable (moreso at lower speeds). I suspect that there is less drag with this technology than for dynamos with equivalent power outputs.
Yes, there has to be drag. As far as I can tell, the big advantage of this approach is that it's easy to install. I suspect there might be a low limit to how much power is available from the eddy currents (lower than what is possible for a dynamo).

 wphamilton 01-09-14 04:16 PM

Quote:
 Originally Posted by njkayaker (Post 16397147) Yes, there has to be drag. As far as I can tell, the big advantage of this approach is that it's easy to install. I suspect there might be a low limit to how much power is available from the eddy currents (lower than what is possible for a dynamo).
That's my guess. It just stands to reason that the magnetic fields from induced eddy currents cannot be as strong as the fields from the original magnets. And they're also going to be further away from induction coils. So the power generated would be lower. They compensate by using high quality magnets. Whether that can fully compensate for the weaker magnetic fields, I don't know.

Another advantage over bottle generators is no roller surface, and no bearings and seals. That's really what attracts me to it.

 njkayaker 01-09-14 04:32 PM

Quote:
 Originally Posted by wphamilton (Post 16397273) That's my guess. It just stands to reason that the magnetic fields from induced eddy currents cannot be as strong as the fields from the original magnets. And they're also going to be further away from induction coils. So the power generated would be lower. They compensate by using high quality magnets. Whether that can fully compensate for the weaker magnetic fields, I don't know.
One might suspect that they would have made it brighter if it was possible (being bright appears to make things easier to sell). That it isn't brighter suggests that there's limited power available.

Quote:
 Originally Posted by wphamilton (Post 16397273) Another advantage over bottle generators is no roller surface, and no bearings and seals. That's really what attracts me to it.
It's interesting.

 prathmann 01-09-14 04:57 PM

Quote:
 Originally Posted by wphamilton (Post 16396787) There will always be drag, starting with the power output to the light and increased by the inefficiencies. Dynamo hubs can have 3 to 9 watts worth roughly speaking, which can be noticeable (moreso at lower speeds). I suspect that there is less drag with this technology than for dynamos with equivalent power outputs.
I'd be surprised if it's less for the same power output. The best dynamo hubs have been measured to have efficiency of up to 65% and I'd think that would be hard to achieve with this approach. OTOH, the power output from this device is much lower (according to the maker it has an output of under a Watt at 30 km/h) and partially makes up for that with very high efficiency LEDs - so it might still have less drag than the higher power output hubs.

 njkayaker 01-09-14 07:28 PM

How much higher efficiency are the LEDs than what other dynamo lights are using?

 zacster 01-09-14 09:00 PM

I'll say it again, there is no discernable drag from this light. You out it on and you forget that it's there.

Quote:
 Originally Posted by wphamilton (Post 16396787) There will always be drag, starting with the power output to the light and increased by the inefficiencies. Dynamo hubs can have 3 to 9 watts worth roughly speaking, which can be noticeable (moreso at lower speeds). I suspect that there is less drag with this technology than for dynamos with equivalent power outputs.
There will always be drag, but will it always be perceptible? Hub dynamos and bottles have cogging as the poles interact with the permanent magnets. This causes noticeable vibration that is mistaken for drag but really doesn't add to drag, since it is an energy storage effect. The Magnic (I assume) has no vibration, so the drag should feel smooth, like very gentle braking.

I don't really see why the efficiency in this system will be a lot better, if at all, than that of a recent SON or SP. Slowing down the rider is slowing down the rider, whether or not the rider can perceive it. If into the bargain it puts out half the light or half the illumination (this group still hasn't grasped which of these performance metrics is actually important), then it is not a step forward despite the novel technology. Not even when version 2 brings its functional spec close to the level where Germany could consider certifying it. The performance target is still to match a SON/Edelux 2, SON/Luxos, or a SON with one of the other top-level B&M lights. If we want to argue about price/performance, just substitute the Shutter Precision PV-8 for the SON, at \$130 each versus \$200+ each, with a Lyt or other mid price but high-end B&M. I still think "efficiency" is a case that must be proven: Lumens per mechanical watt or illuminance per mechanical watt.

 zacster 01-10-14 07:01 AM

Quote:
 Originally Posted by Road Fan (Post 16398373) like very gentle braking.
Not even like very gentle braking. Maybe if you are coasting you'll stop about a foot short.

Quote:
 Originally Posted by wphamilton (Post 16397273) Another advantage over bottle generators is no roller surface, and no bearings and seals. That's really what attracts me to it.
How well is the Magnic sealed? It contains an electronic circuit board, so water ingress could damage circuit boards unless they are waterproofed. And in mass production it's difficult to conformal coat all surfaces except the ones that provide electrical contact and maintain optical integrity. Or does it have a good drip control system?

 tcs 01-10-14 07:55 AM

The LED lighting revolution has come upon us pretty quickly, and aplications are still being sorted out. Everybody seems to be all over Magnic's eddy current thing, but IMO the true evolutionary step is a new design paired dynamo and headlamp with power and regulation optimized to work as a single, cohesive unit.

(The Velogical rim dynamo is another, different step in this direction: optimized to work with a short list of modern LED headlamps.)

Most other tire and hub dynamos are legacy designs expected to power anything from modern LED headlamps to old 3W filament bulbs, and modern LED headlamps are designed to be powered by anything from a Shutter Precision PD-7 to a 60 year old Soubietz bottle dynamo.

With a hand-in-glove matched optics, LED, electronics and purpose designed, dedicated dynamo, I think there even might be some life left in the all-in-one headlamp and tire driven dynamo design, well under the price point of Magnic. Or maybe not! :)

One thing Magnic could learn from the past: redesign the heads to place the lamps above or below the dynamo, rather than out to the side. Magnic's current layout with the lamps on the same horizontal plane as the tire/rim maximizes shadowing.

 wphamilton 01-10-14 08:46 AM

Quote:
 Originally Posted by Road Fan (Post 16398373) ... I don't really see why the efficiency in this system will be a lot better, if at all, than that of a recent SON or SP. Slowing down the rider is slowing down the rider, whether or not the rider can perceive it.... I still think "efficiency" is a case that must be proven: Lumens per mechanical watt or illuminance per mechanical watt.
Because a bottle generator will have bearing friction, the magnets or coil spinning on an axis. It will also have some loss in the rolling surface interfacing with the tire. In this kickstarter generator it's the magnetic eddies that are moving, the flux lines cutting across fixed coils, so there is no mechanical friction. When I visualize this, all of the drag is directly related to the power generated, so I expect it to be more efficient in that sense than bottle generators. A hub generator, maybe not much difference but depending on the engineering.

We already know that the drag is greater than the ultimate power consumed by the light and we've got some pretty good data, here and there, on drag from various dynamos so that side doesn't really need any proving. The actual drag from this tech, yes I agree that we need some measurements to put the question to rest. That may be a little tricky for DIY tests though, since a coast-down doesn't get precise enough for that small amount of rolling drag and simply spinning the wheel unloaded doesn't actually translate to the drag on a loaded wheel. So we may have to wait for someone with more sophisticated equipment and a little time on their hands.

 himespau 01-10-14 08:50 AM

I see they have a mount for V-brakes. I wonder if it'd work for cantilevers too.

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