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Discussion board help and admin topics => Half Baked Ideas => Topic started by: broli on October 01, 2013, 02:26:45 PM
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When the rotor is vertical as illustrated most of the flux will prefer to go through the bridging stator piece due to a shorter flux path which has a lower permittivity. When the rotor spins 90° there will be no reason for the flux to still go through the bridging piece, and hence no flux would be going through it. Going from maximum flux to 0 flux will of course cause the coil to generate a voltage.
In the illustration a tiny air gap can be seen as well. I noticed in experiments and femm simulations that having the right permeability is key. Put simply the toroid must have a lower permeability than the bridging piece. If this is not the case the flux will mostly travel through the toroid and not the bridging piece.
The permeability of the toroid can be artificially lowered by introducing an air gap. The air gap need not to go all the way through, a small cut will do however it needs to be symmetrical on both sides or you'll create an asymmetric setup which is not advantageous.
The back torque associated with most electrical generators can hardly be seen in this setup even the cogging due to the air gap is minimal. This has to do with the fact that the field interactions happen mostly transverse to the motion of direction.
Sadly I destroyed my silicon steel toroidal core which I was experimenting with when trying to saw a small airgap through it however the second one is on its way and thought to share the concept in the meantime.
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Hi broli,
Thanks for showing this setup drawing, seems good to me too. :) I mean I tend to agree with your reasoning on the back torque.
Greetings, Gyula
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I wonder if rotor has more then one pair of permanent magnets around the circle
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As you rotate the rotor you will be generating eddy currents in the ring stator... this will cause a drag on the rotor, heating of the stator, and is of course a consequence of the changing flux in the stator as the magnets sweep past. Isn't this also a consequence of Lenz's Law?
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Hi TinselKoala,
Yes but either using laminations or ferrite ring the eddy current issue could be minimized. Of course machining either the air gap in the ferrite or forming the stator from laminations surely makes tinkerer's life harder... 8)
Gyula
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Hi TinselKoala,
Yes but either using laminations or ferrite ring the eddy current issue could be minimized. Of course machining either the air gap in the ferrite or forming the stator from laminations surely makes tinkerer's life harder... 8)
Gyula
The laminations would have to be parallel to the slots, through the thickness of the material, not the flat way parallel to the ring itself, to reduce eddys much, I think. A nonconductive ferrite might work, I don't know if they heat up when subjected to a changing field or not. The ferrite core pieces from a CRT flyback transformer, which is split, with tiny thin spacers in the split, might work for a trial even though it isn't exactly a "ring" shape.
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Indeed it makes it very hard :) .
In the first picture you can see how I ignorantly started cutting the laminated toroid from the outside to the inside. This caused the toroid to open up with great force as it had nothing to hold it in.
In the second attempt I started cutting the toroid radially, the material is holding its own now, that is until you cut all the way through. The hot glue trick in the second one was also a lesson learned quickly. Since the core is not glued together, as you cut radially you start loosening the inner/outer windings of the toroid. This starts out very Innocently but becomes a royal pain in the ass as you go. So either use epoxy or hot glue to hold the laminates, near the cut, together is a smart move.
Ideally I would hit alibaba.com and ask some Chinese manufacturer to send me a perfectly cut toroid :) .
I also have some ferrite toroids, this seem to show the effect of low vs high permeability quite well. They don't need an air gap as the bridging piece is attracted quite well to the toroid. However I have no clue about the properties of these specific toroids, but I would guess that the permeability is too low and they also seem to have an awfully bad retentivity, they are permanently magnetized in some parts just by having had neo mags close to them at some point in time.
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I would also like to add that there are many different takes on this concept I just picked the one that I thought was most practical to build.
Below are some variants. The first uses motor laminates the kind made for slotted motors. Here the rotors is on the inside to prevent eddy currents.
The second is a bit more special in the sense it has one air gap and uses the toroid itself as the generator. So the coil is wound around said toroid. Again since there's a higher permittivityon one side the flux will predominantly flow to one side untill the rotor hits the 90° mark and again you'd have a max to 0 flux scenario which would generate a voltage. However as far as I know the generated toroidal current should have no effect on the spinning rotor.
Lots of food for thought ;)
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Hi Folks,
For those wishing to attempt a build these ideas, I list some toroidal core offers. Unfortunately the cores with reasonable OD for such setups are not really cheap. Most of the cores below have a know permeability.
At Surplus Sales of Nebraska: http://www.surplussales.com/Inductors/FerToro/FerToro-1.html (http://www.surplussales.com/Inductors/FerToro/FerToro-1.html) these are Amidon cores:
(ICH) MM-T225-6 OD 2.25ˇ h= .55" Mix 6 yellow 6 USD
(ICH) MM-T520-2 OD 5.2" h= .8" Mix 2 red 49 USD
EPCOS manufactures also larger toroids:
OD/ID/h in mm: 87/54.3/13.5 N87 TOROID, Mouser Part No: 871-B64290L0730X087 18.96 Euro
73.6/38.8/12.7 77 TOROID, Mouser Part No: 623-5977011101 16.68 Euro
102/66.0/15.0 N30 TOROID Mouser Part No: 871-B64290A84X830 26.88 Euro
At Farnell (Newark in US and Canada) there are also EPCOS cores like B64290L0084x87, 102/65.8/15 at Newark 30.26 USD
or Ferroxcube cores like TX87/54/14 3C90 21.90 USD at Newark
or TX80/40/15 3C90 19.59 USD at Newark
Of course on ebay you can also find some (OD 2.25" and 2.9") toroids at seller 'alltronics' for instance or others.
I have found an interesting and unusual ferrite cutting "method" albeit it is shown for ferrite rods, it is rather a 'braking' method because it actually brakes the material. But I think the full air gap instead of the partial airgap may not make much difference in the operation of such setup. Nevertheless, it is a risky method for sure because of the cost of the larger OD toroids.
This is the link to Clanzer's video on ferrite rod "cutting": http://www.youtube.com/watch?v=cUWn5m8ASC0 (http://www.youtube.com/watch?v=cUWn5m8ASC0)
But in fact as broli wrote above, ferrite toroids may not need cutting at all in these setups.
Gyula
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Since I'm located in Europe I ordered mine from Magnetec.de:
1 x M-028 = 100,00 EUR
1 x M-071 = 70,00 EUR
1 x M-454 = 70,00 EUR
Hopefully cutting them won't be as painful as the sillicon steel, mentally and physically :p. A good saw blade would be handy.
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Hi Broli,
Perhaps you could ask the Magnetec people what or how they suggest the cutting should be done? Diamond or maybe laser cutters are preferred?? be very careful and maybe look for a good machine shop once you know the how to.
Gyula
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It has been a while since the birth of this concept, sadly nothing much has happened since.
However I'm trying to get the ball rolling again, or better yet, the generator spinning. I got rid of the idea that using a toroidal core might do the trick. The Achilles heel of this concept is unwanted airgaps, and when you coalesce multiple materials together you are playing with so many variables. Hence the new idea to stamp a custom stator core to reduce bridging materials. It makes the generator even more simple I believe as you only need one airgap to worry about and it's on the outside too.
I sort of reached the limitations of what simulation software has to offer. The results don't like to converge and become almost meaningless when reaching small airgap sizes. That and the simulation time increases exponentially with element size.
However in general the torque does decrease the smaller the airgap gets. Femm being the most stable simulation software confirms this fact.
Currently I sent a few quote requests to some Chinese suppliers on alibaba for custom rotor laminates as attached per pdf, to ease the study of the above.
Any other suggestions are welcome as it seems like Europe no longer does anything in regards to stamping motor cores.
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While waiting on responses from the couple core stamping companies, one would like to charge a wopping 3500$ to create the mold alone, in china I was thinking of cheaper ways on building a generator out of the same principle. One way that came up is using cheap EI audio transformers that can be bought everywhere. These can then be arranged in such a way to form a circle. Certainly it has its own engineering challegens but this is a much cheaper alternative than stamping custom laminates.
Here's a video showing the concept: https://www.youtube.com/watch?v=K_NRIuTrjrQ&feature=youtu.be (https://www.youtube.com/watch?v=K_NRIuTrjrQ&feature=youtu.be)
I also added a 2D simulation result to show that indeed most of the flux going through the transformer is going through the leg that the magnet is covering.
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Hi.
I've been thinking about that type of a generator as well. :D
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Hi Broli,
You mentioned audio transformers as off the shelf components and this remembered me to common mode line filters or chokes used at the mains input of many switch mode power supplies. There are such chokes with two ferrite C cores back to back or two ferrite E cores also back to back, usually with a little air gap between the facing surfaces. See some here and these are available in most component shops, I chose Digikey, they have several mechanical sizes with several coil inductance values.
One with C core, horizontally mountable: http://www.digikey.com/product-detail/en/B82733F2232B1/495-2787-ND/1243551 (http://www.digikey.com/product-detail/en/B82733F2232B1/495-2787-ND/1243551)
With E cores, horizontally mountable: http://www.digikey.com/product-detail/en/EH20-0.3-02-33M/817-1000-ND/1928579 (http://www.digikey.com/product-detail/en/EH20-0.3-02-33M/817-1000-ND/1928579) and
http://www.digikey.com/product-detail/en/EH24-1.0-02-10M/817-1009-ND/1928588 (http://www.digikey.com/product-detail/en/EH24-1.0-02-10M/817-1009-ND/1928588)
With E cores, vertically mountable: http://www.digikey.com/product-detail/en/EV35-2.0-02-20M/817-1054-ND/1928633 (http://www.digikey.com/product-detail/en/EV35-2.0-02-20M/817-1054-ND/1928633)
These chokes have double windings next to each other so you could connect them in parallel or in series, or use each separately in case of the C cores.
I am a bit surprised that the simulation shows most of the flux going through the leg that the magnet is just covering, I would have expected more flux going via the side legs because those side legs actually shunt the center leg. It is true though that the side legs each has half as much cross section area than the center leg does (but the two side legs alltogether have equal cross section to that of the center leg).
Maybe the C cores (that would have two legs only vs the 3 legs of the E cores) could also give useful induction, as per common sense, because then there would be two shunting flux pathes vs the three.
So I think these common mode ferrite chokes would serve well to build a cheap low power prototype from this setup, it would not need expensive lamination cuttings.
Gyula
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kEhYo77, that's really cool are you planning on building one too?
gyulasun, thanks for the suggestions. Currenlty I have settled with a silicon steel transformer, to be more precise this one:
http://www.conrad.be/ce/nl/product/514276/Universele-nettransformator----15-V----15-A----225-VA----elma-TT/SHOP_AREA_17430?
The holes make it easier to mount and allign in some sort of fixture. When I have the time I'll try to design a stator to hold 8-10 of these transformers and 3d print it :). The real challenge is building the rotor to be sturdy to avoid having the magnets bend the whole rotor and stick to the transformer when the airgap is small. Any collaboration is welcome :).
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I have got enough transformers and a prime mover DC motor with the shaft extending from both ends so maybe I'll build one :)
Two rotors might be made from small weight lifting iron discs, They would serve as a flywheel and as magnetic flux linkage for those not used sides of the magnets.
I don't know when it is going to happen but the urge is there 8)
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Hi Broli,
I had a look at the transformer you linked to at Conrad, it seems also okay to me (like the ferrite current transformers I proposed), the difference being in size and price. Regarding the coils on the trafos, the only requirement may be to have as small copper DC resistance as possible, this calls for having coils of thick wire.
I agree that there is a mechanical challenge in building robust rotor discs which are able to withstand any bending force coming from attraction. What kEhYo77 suggested (weight lifting iron discs) sounds good to me because those types of discs can be rigid enough indeed. When making such discs, radial ribs on their outside could enhance their rigidness. Perhaps making the discs with a bit higher OD than the stator would have with the transformers, you could place a few supports (distance keepers) between the discs at symmetrically opposite places.
First I thought that eddy currents in the iron discs could cause an unwanted loss but then I figured that the actual flux change via the iron discs must be small by default because the transformer cores insure a continuous quasi-closed magnetic circuit between the discs and their magnets all the way within the full circle. So the magnetic properties of iron material for the discs are not demanding, it seems.
Gyula
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The transformers arrived today. They have very flat sides which is a good thing when wanting the airgap to be as small as possible. They are rated at primary:230V, secondary:15V. This has the advantage to quickly swap between winding ratio and study the difference. In the pictures below you can see the orientation variants I'm thinking of.
Now for the more difficult job, designing the bracket to hold these in place. My new DLP 3d printer will arrive soon, so that will also help.
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Thanks for your update broli
I'm very interested in your idea and still trying to understand why Lenz won't come into play in your generator design.
Looking forward to your tests and wishing you success.
Luc
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Thanks for the feedback Luc.
I did a resistance test across the thickness of these transformers and they all seem to be uninsulated across layers?
Resistance values are mostly low 0.6-5.0 ohm and show no indication of lamination coating. I'm kind of starting to get worried about eddy currents when the magnets start moving close to them.
Perhaps I should have went with ferrite cores from the start: http://www.ebay.com/itm/E71-Transformer-Core-Low-Loss-500mT-Power-Ferrite-x4-/181226270348 (http://www.ebay.com/itm/E71-Transformer-Core-Low-Loss-500mT-Power-Ferrite-x4-/181226270348)
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Thanks for the feedback Luc.
I did a resistance test across the thickness of these transformers and they all seem to be uninsulated across layers?
Resistance values are mostly low 0.6-5.0 ohm and show no indication of lamination coating. I'm kind of starting to get worried about eddy currents when the magnets start moving close to them.
Perhaps I should have went with ferrite cores from the start: http://www.ebay.com/itm/E71-Transformer-Core-Low-Loss-500mT-Power-Ferrite-x4-/181226270348 (http://www.ebay.com/itm/E71-Transformer-Core-Low-Loss-500mT-Power-Ferrite-x4-/181226270348)
Hi broli,
I think eddy currents will be less with ferrite. However, start with your steel lamination transformers since you have them as it should be good enough for proof of concept. If it works (no Lenz) and losses are mostly eddies, then you know what to do next.
Don't strive for perfection on the first test model as you'll never get it done. Proof of concept is all you need for now and those transformer should be fine.
All the best and looking forward to your results
Luc
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Hi Broli,
I forgot to mention, it's normal to get conductivity between transformer lamination as some edges touch together. Many transformer laminations are even welded on the outside edges and between the I and E core to hold them together but that doesn't cause too much of eddy losses since the greatest area of a transformer surface is between lamination layers which represents probably more than 95% of the steel surface area and where the insulation is and effective.
Hope this makes sense?
Luc
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Good point, Luc, about eddies.
You just want to keep the speed below 400Hz for a single transformer's core, Broli, and it should provide enough data.
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Hi Broli,
A simple test would be to run some of the transformers from the mains for a certain time with unloaded secondary coils and check the core temperature. Also, the idle current of the primary coil from the mains may also be relevant for the eddy loss (besides the DC coil resistance of course, you can measure the latter). I believe that these transformers would operate normally in this respect. Sometimes the through-hole bolts that fix the L brackets to the core can cause electric short between the laminations as they go through the lamination holes, a thin plastic sleeve (a tape layer) to cover the bolts remedies this if needed.
But perhaps swinging strong magnets above and below the cores in the directions as shown in your proposed generator setup may also be justified to check eddy losses, maybe this would cause a bit more eddy because the close and direct flux from the magnets would act stronger on the laminations than that of coming from the normal 230V excitation. I believe that this would still remain reasonable, "bearable". I agree with Luc's reasonings on the eddy issue.
However, I think Luc was curious to know the normal Lenz effect in such generator design : when you load the output coils then how the load current may affect the prime mover of the rotor.
By the way, your arrangement shown in the second picture would be the preferred one I think because it insures a more continuous flux-closing for the rotor magnets (vs the setup with wider air gaps between the neighboring cores as shown in the 1st picture), this would result in a smaller overall flux change occuring in the rotor plates that hold the magnets. Small overall flux change in the rotor plates is desirable I think because it helps minimize eddy loss in the rotor iron material that hold the permanent magnets (especially if it is indeed made of weight-lifting iron discs hence they have a certain thickness).
Gyula
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I think that would be the case that makes most sense, that is to the transformer being conductive around its outside surfaces. However I'm still concerned about eddy currents as even being one laminate deep they can have a significant effect on the rotating magnets. However as Luc said, it's best to move on with these cores before considering another material/design.
Today I finished designing the rim that will hold these cores, I'm not fully sure on the specs of the 3d printer but if I'm lucky I can print it out in one piece.
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Hi Broli,
Seems to me a good design!
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Wow broli!... excellent design
Looking forward to see this one
Luc
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I think Luc was curious to know the normal Lenz effect in such generator design : when you load the output coils then how the load current may affect the prime mover of the rotor.
Gyula
Exactly... looking forward in seeing that result
Luc
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I would like to say that one of the Chinese suppliers gave me a quotation price today of 1318$ for the custom round stator core. This is a bit more reasonable than the 3500$ price from the other supplier. But in both cases the actual core is not that expensive, it's the stamping mold that jacks up the price, for instance the core alone costs 98$ while the mold is 1220$. So it's reasonable if you're looking into mass production but for prototyping it's a bit pricey. For now I'll leave the quote open untill I finish atleast one prototype based on the transformers.
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Hi kEho, instead of building rotating machine, you can replace p magnets with c shaped electromagnet exited with 50/60 Hz supply.
shantaram
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Progress is still being made on this idea, I decided to pick this concept back up and finish what I started. I had ordered a custom cut toroidal core from China a while back and have most components ready for assembly.
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Very cool Broli 8)
Maybe you can use my Bucking Field Reluctance Motor Design to turn your generator: https://www.youtube.com/watch?v=TeO9iM2-29o
It may be a perfect marriage ;)
Thanks for sharing
Luc
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Thanks gotoluc, I'll have to make sure it runs first before I can let it get married :) .
Meanwhile here's an interesting thought experiment. Take a sufficiently long solenoid with a ferromagnetic core inside of it. Get two magnets near it so they attract each other and close their flux path through the core of the solenoid. Now move one of them back and forth as to periodically increase/decrease the total amount of flux the solenoid is seeing in order to induce a voltage. This will give rise to a current if allowed to flow.
Now here's is the interesting bit. How is this induced current of this (arbitrary long) solenoid counteracting the movement of the reciprocating magnet? If you played with long solenoids before you'll know that their effect on anything (even a compass) is negligible near their middle. So where is the back-force, if any, coming from that tries to counteract the movement of the magnet?
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Thanks gotoluc, I'll have to make sure it runs first before I can let it get married :) .
I understand ;) ... maybe later when she's ready.
Meanwhile here's an interesting thought experiment. Take a sufficiently long solenoid with a ferromagnetic core inside of it. Get two magnets near it so they attract each other and close their flux path through the core of the solenoid. Now move one of them back and forth as to periodically increase/decrease the total amount of flux the solenoid is seeing in order to induce a voltage. This will give rise to a current if allowed to flow.
Now here's is the interesting bit. How is this induced current of this (arbitrary long) solenoid counteracting the movement of the reciprocating magnet? If you played with long solenoids before you'll know that their effect on anything (even a compass) is negligible near their middle. So where is the back-force, if any, coming from that tries to counteract the movement of the magnet?
Yes, interesting things when cores get long. To bad eddy currents increase and PM flux spreads all over the core.
If you would be willing to make a video demo of it I would definitely like to see it.
Thanks for sharing
Luc
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The generator has been built for a while but sadly it didn't run very smooth to say the least. One of the lessons learned was that magnets can be too strong and using Neo's can be overkill in a lot of cases. I used waaay to little steel for the flux to be fully captured so the setup was leaking flux all over the place, it looked liked I was using a non ferro metal at times, the magnets were that overpowering, and causing massive eddy current on the bearings. Concerning the bearings I also learned that when the load is mainly axially you are better off using thrust bearings to avoid massive friction. Regular bearings are designed for radial loads not axial loads.
Anyway after this setback I decided to return to the fight. I settled on a relatively "cheaper" design to built. A toroidal core that is only wound for 180°. It's funny how I discovered how similar it looks to this concept:
http://overunity.com/1463/toroid-magnet-generator/#.V2fjRTVBHBw (http://overunity.com/1463/toroid-magnet-generator/#.V2fjRTVBHBw)
Yet noone wondered what would happen if you only used one coil instead of both fighting each other's flux and forcing it out of the core causing it to interact with the rotating magnet. Using a single coil there should be no reason for the generated flux to escape the low reluctance core. But reason is not enough when it comes to violating established laws there we experiment.
I won't go into detail to as to why it is designed that way but it doesn't take a genius to figure it out.
In fact it's currently being built.
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Here's a small update, I haven't made the whole assembly yet but out of curiosity I did a quick and dirty run just spinning it by hand.
https://www.youtube.com/watch?v=vgl0-wF2t8M (https://www.youtube.com/watch?v=vgl0-wF2t8M)
It's surprising to see the signal, it almost looks like a square wave, you don't expect that from an electric generator.
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Hi Broli,
Thanks for the update. Do you have permeability data for the toroidal core used? Just curious, trying to understand the squarewave-like waveform. If you have an L meter, would you check coil inductance without and with the magnet in place at some position?
Does this induced waveform change when you have some kOhm resistive load across the output coil?
Gyula
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The core is standard silicon steel with a strip thickness of 0.23mm. I have an L meter but atm the magnets I used are not the final ones, also the gap distance of the stator core and rotor magnets is too big now as I can't get them too close before they jump to each other. I'll be doing that when I have stator and rotor rigid.
Also I had an assumption and it looks like FEMM confirmed it, the simulation shows almost a triangle like waveform for the flux through the coil over time. This thus should give a square wave like shape for the induced voltage as the below graph shows.
This is quite interesting if you think about it because the interaction between the coil and magnet seems to be only taking place at the edges of the coil, meaning if the magnet is small enough and the disc sufficiently large the coil and magnets interact for only a few degrees and the rest of the way it keeps on changing the flux but the magnets are then so far away from the edges that they no longer interact with it.
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Thanks for the details. Though I thought that saturation could not be a ruling factor in the induced waveform
but I did not think the flux changes like a triangle wave and this results in a square wave-like induced voltage waveform.
I wonder What may cause the coil interact with the magnets only at its edges. Common sense suggests
the coil cannot have definite poles at its two edges when wound onto a closed ring core. Can you explain that?
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Well here's a video of connecting a dc source to the coil and inspecting the rotor interaction.
https://www.youtube.com/watch?v=nPTEpe6wRNA (https://www.youtube.com/watch?v=nPTEpe6wRNA)
I also did a simulation by applying a DC current and calculating the torque all the way around. Strangely enough it seems the torque is almost constant untill the magnets cross the coil edges and then the torque flips and remains constant again. Again this is not what conventional generator does, usually you see a nice sinusoidal torque graph.
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Thanks for this test. It suggests thinking of some core saturation from the input 6.3 A current
which surely biases the core and probably makes the ring core magnetically asymmetric.
This is the only explanation I can think of why the rotor magnet poles align with the coil ends:
those are the places where the electromagnet poles are created.
It comes from this that at lower input current levels, say under 1 Amper or even less, the interaction
gradually disappears I think because the core cannot become magnetically asymmetric and the
magnetic poles are able to close into each other within the ring core as in any 'normal' closed
magnetic circuits without an air gap.
My observation from the video is that the 'rotor' would always want to align with the coil edges in attraction.
Should you have a ball bearing with even less friction, I think the torque would 'behave' in a more 'sinusoidal' way.
When the rotor is turned to the 12 o'clock and the 6 o'clock direction, it is magnetically the farthest position
from the coil edges and the attraction forces at the coil edges are simply not enough to influence rotation.
Have you thought of replacing the rotor with a compass and see the effect when input current is say 0.1 Amper only?
At such lower level core excitations the saturation should get to a minimum hence the asymmetry
cannot yet develop as much. With the compass 'needle' the sensitivity of your "rotor" may get increased.
Then you could increase input current too and see the behaviour.
Sorry that I dare to assume the bearing is what mainly causes the bitty rotor movement,
especially in the first half of the video, though it works more readily in the second half of the video.
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I wonder how it would respond with the DC current and only a single magnet on the bar.
Suspecting that the magnets could be acting on the field outside the winding and not the field in the core.
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gyulasun, very good point. I haven't considered saturation. I did a quick check in FEMM with sillicon steel and indeed it seems 5A is saturating the core. It's only when I go below 1A the magnetic field strength in the core goes below saturation. Attached graph shows the field strength in the core at different currents in FEMM.
Here's a repeat of the experiment with 0.5A of current instead of 5A:
https://www.youtube.com/watch?v=lnU54W_ikkY (https://www.youtube.com/watch?v=lnU54W_ikkY)
And repeating the experiment at this low currents indeed reduces the torque considerably as you can see, but the question is whether this just a linear relation ie. 10x less current = 10x less torque?
However it might be my imagination but now the torque also seems to be only concentrated near the edges of the coil whereas previously it seemed to be uniformly around the core.
I'm currently doing a torque simulation with much higher elements count to get rid of the jitter I have been getting in the data. The current torque data indicates a non zero AVERAGE torque all the way around... ???
So I upped the accuracy by decreasing the element size in FEMM and I'm collecting data per degree instead of 5 degrees. The initial few data points show a much cleaner data distribution, there's hardly any jitter now, but it will take many hours before the complete run finishes.
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Well the more accurate simulation is complete and as I thought the anomaly all but disappeared, the average is near zero now and the graph is almost jitter free.
However this brings us to the next subject, the torque is almost CONSTANT until it reaches the edges and then it does an instant flip....it's the exact opposite of what I thought would happen. A single pole motor/generator usually has a sinusoidal curve for it's torque vs angle graph. I added the counter torque graph based on the current torque graph and previous induced current graph.
Now let's go a step further and do some power calculation, the average counter torque seems to be 0,00165Nm at 1A output. If we want to keep the rotor spinning at 10000 RPM and extract 1A from the coil it will cost us 1.727W of mechanical power. This seems rather low :).
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.....
And repeating the experiment at this low currents indeed reduces the torque considerably as you can see, but the question is whether this just a linear relation ie. 10x less current = 10x less torque?
I think it is a non-linear relation and the B-H curve is to blame for it. However, the B-H curve has a nearly linear section, in your case it covers input current range from say 20-30 mA to say 1 Amper, this is from your attached graph showing the field strength at different currents, your file 2016-06-22_7-30-16.png
However this brings us to the next subject, the torque is almost CONSTANT until it reaches the edges and then it does an instant flip....it's the exact opposite of what I thought would happen. A single pole motor/generator usually has a sinusoidal curve for it's torque vs angle graph. I added the counter torque graph based on the current torque graph and previous induced current graph.
It is indeed interesting that at 0.5 A current levels there is still some interaction between the coil edges and the rotor magnets. This may mean that at 0.5 Amper the laminated core is still able to develop magnetic poles at the coil edge areas. The reason for this may be in the fully closed ring core shape whenever DC biased even to a small current value. There has to be poles created at the coil ends once your tests show interaction, whatever small it is. But this is now not a drawback.
Now let's go a step further and do some power calculation, the average counter torque seems to be 0,00165Nm at 1A output. If we want to keep the rotor spinning at 10000 RPM and extract 1A from the coil it will cost us 1.727W of mechanical power. This seems rather low. :)
Well, friction and attract forces are the enemies in your setup which may increase the actually needed input power for a certain power output. The attract forces may be balanced by design. Your calculation gives a low input power indeed for a would-be prime mover but it has to have a >90% efficiency figure, the higher the better of course.
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Yes it all depends, this is also why I used the tapered roller bearings from SKF, these are truly amazing even if the attraction forces are large they keep on spinning pretty well (they are rated at 60.5kN),
http://www.skf.com/au/products/bearings-units-housings/roller-bearings/tapered-roller-bearings/single-row-tapered-roller-bearings/single-row/index.html?designation=32305%20J2
They are pricey but standard ball bearings would have locked up long before and the quality is well worth the money.
In the mean time I replaced the magnets with neo disc magnets. The voltage waveform is now much closer to what I see in the simulation as well. And again it's amazing to see it being constant for half a rotation and do a sharp flip as soon as the magnets cross the edges and continue being constant.
https://youtu.be/A9B9HgePgzo
Seeing how the voltage has increased considerably using these new magnets I got excited and just shunted the coil with a low resistance. At first I got disappointing as the current fell to near zero and power output was nowhere to be seen. After playing with a pot meter attached to it I figured what was happening. The inductance was pulling the current down. Even if the coil is loaded it's acting like a full blown inductor, another strange behavior for me. In a transformer for instance the inductance is dropped and the current rises, however this generator does not seem to lose its inductance, which I think might be a very good thing.
So in order to fix this the inductance needs to be balanced by a capacitance. Sadly I don't have an assorted set of capacitors lying around but I'll be ordering these. I'm curious to see what will happen when the LC tank hits its frequency.
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It's possible the current output is low because of the alternate flux path. Once current is generated in the coil, Lenz pushes back and it becomes easier for the flux to take the other path which limits the current output.
Possibly the most efficient configuration would be a coil on four quadrants each with it's own full wave bridge so at the junction of the coils, the flux is forced to take one or both paths and generates full current.
It appears that even better efficiency could be achieved if each quadrants load could be controlled to increase just after passing each quadrant, which could push the flux ahead of the magnet rotor and reduce the forward Lenz pressure in the next quadrant.
You may be on to something here.
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Lumen, what other path? The coil is enclosed around a toroid, when you energize the coil the flux can only follow one path. The flux from the magnet is still splitting evenly across the core as long as you don't reach saturation that is. Femm also shows this.
So I think adding more coils/quadrants will only add more complexity while we lack the basic understanding of the current design.
I said that the circuit behaved like it had a very large inductor in series with it, but even when rotating the rotor by hand at perhaps <1Hz I can still produce an open circuit voltage of around 200mV P2P and STILL the current drops to a marginal low value, I measured 20mA across a 1ohm load, knowing that the resistance of the coil is 1.5ohm this means the voltage dropped from 200mV to 50mV when the inductance of around 80mH should not have act like such a big impedance at this frequency. I'm scratching my head over this. I'm veeeeery eager to see what happens when I attach a capacitor and hit some resonance frequency.
Ironically currently the design seems to be acting more like a back emf free motor, the complete opposite of what I set out to design.
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Broli, The flux should split evenly and it will over time, but with loading on the coil the flux will increase in the side without the winding as it is blocked by Lenz on the coil half.
The effect is that only a small current output can be achieved or the flux will easily increase in the alternate path around the side without the coil.
Flux will still continue to push to get through the coil and balance it's path so it is like a loaded inductor for a short time but never a strong driving push.
I like your idea because it seems to be on the right track by letting the magnet fight Lenz and not the prime mover.
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You reasoning is incorrect though, the coil does not cause a high reluctance path. If you study basic "magnetic equivalent circuits" you will know the coil acts like a voltage source and not a resistance (to the flux):
http://www.tutorialsarea.com/EEE/Electrical%20Machines-I/1/Analysis%20of%20Magnetic%20Circuits.html
This is also shown in FEMM, the total flux is the sum of the flux that the coil would generate as if there was no magnet PLUS the flux due to the magnet as if the coil was not energized. It's simple vector math in this case. So it doesn't matter if current is flowing or not (if stay away from saturation that is).
I ordered some capacitors today to start testing out LC tank operation of this motor/generator. However I first need to build a proper frame to achieve high RPM's. Would be glad to see others building this as well as I know there are much more clever people in the community that can do and see things I don't.
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You reasoning is incorrect though, the coil does not cause a high reluctance path. If you study basic "magnetic equivalent circuits" you will know the coil acts like a voltage source and not a resistance (to the flux):
If it were not for the copper ring on a shaded pole motor delaying (resisting the flow of) flux, the motor would not start.
That small single loop of copper will delay the passage of flux because it induces a current in the ring and it generates a flux in the opposing direction. (Lorentz force)
In a static condition the flux will balance, but dynamically the coil with a load will oppose change.
I'm just saying it's my view of where a problem with low current will arise. Low current is not always the enemy, as little for free is better.
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Hi Broli,
Okay on your ball bearing type, it has surely got good quality and I understand that it is the attract force which makes the rotor move bitty. This can be solved by say a double rotor setup where two attract forces act on the toroidal core so they may cancel each other.
I'm curious to see what will happen when the LC tank hits its frequency.
Well, if you tune out the 80mH coil inductance, say you use a series capacitor, then there remains the DC resistance of the coil to set the load current together with the load resistance you would use. To achieve power match (=maximize power transfer), you would need to use an equal value load resistance to the coil's DC resistance. This way half of the induced voltage would appear across the load resistance at the chosen rpm you tuned out the 80mH with a series capacitor.
By the way, you mention 1.5 Ohm for coil DC resistance but in your video tests the voltage and current values shown by your power supply V-I displays give about 1.2 Ohm calculated Dc resistance that includes the connecting wires to the coil too. Of course this is not a big difference vs 1.5 Ohm but may count when the induced voltage in the coil is only 200 - 300 mVpp. And in the some Amper range the crocodyle clips may introduce further losses.
Some numbers to get the series capacitor values for different rpms:
60 rpm= 1Hz at 80mH needs 316665uF tuning capacitor
600 rpm= 10Hz at 80mH needs 3166uF
3600 rpm= 60Hz at 80mH needs 88uF
6000 rpm=100Hz at 80mH needs 31.6uF
You have surely arrived at similar capacitor values and ordered some for some chosen rpm rotor speed.
Thanks,
Gyula
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Broli, Thank you for sharing your experiment. I have been thinking about it for several days because it has this sense of design that seems to skirt the Lenz effect but not totally.
I would like to offer an extension to the same design that appears in concept to totally eliminate Lenz and still output large current.
The thread at this time is mainly composed of you and Gyula so if either object to me posting a modified CAD drawing of your device in your thread I will reserve it until I find some time to construct it.
If nothing else it could be food for thought.
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No problem at all, it's always nice to see ideas sparking off new ideas. That's the power of sharing your work.
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You may have already envisioned this concept as it is based on your design as you can see.
The picture shows the position where the field in the core is almost non-existent, but as rotation occurs, the field becomes very strong and rotor direction is always moving in the same direction as any generated Lenz forces.
See also the animation.
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Hi Lumen,
Interesting setup, did you mean the upper and the lower rotor arms (which the magnets are fixed to) are made of ferromagnetic materials? (except the shafts of course)
I think the setup would also work with non-ferromagnetic rotor arms, right?
Thanks for showing this idea, looks promising. Maybe you have attempted a test setup on it too?
Gyula
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Hi Gyula,
It would help contain some unwanted stray fields if the arms were ferromagnetic.
I'm looking to finish my current project in a week or so and should be able to move onto some fun projects like this device.
Broli may have something operational where he can get some output to input data by then.
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Sorry, I don't get it. Both arms rotate parallel?
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Sorry, I don't get it. Both arms rotate parallel?
No, the arms rotate in opposite directions. View the animation file.
The image seems to indicate they rotate as one, but that would not produce any current in the windings.
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That's what I thought. So, this way it makes sense, thanks.
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Lumen, in that design you will have considerable leakage flu when both coils generate current, because their fields will oppose each other and just like in a standard transformer the field will escape the core.. Yes you will get much higher output currents but this is because the inductance gets destroyed just like in a transformer.The point is keeping the interaction of the core with the magnets at a minimum by maintaining a circular magnetic field inside of the core.
I'll be waiting on the capacitors, since I ordered 1000x 10µF multilayer ceramic capacitors from ebay. This might take a month before they arrive, meanwhile I can work on the frame/bearing holder and other projects.