magnetic flux lines

[artv]

hello ..I was wondering ....if you were to submerge dual rotors in ferrofluid what would be the pattern of flux lines? The diagrams I've seen say that flux travels from north mag on rotor 1 to south mag on rotor 2,at the same time south of #1 travels through steel rotor to neighbouring mag which is opposite polairity, and the same for rotor#2.Wouldn't the lines be drawn to the opposite rotor as well as to its neighbour on both sides. Instead of having straight lines of flux from one rotor to the next (like the diagram shows)...wouldn't they be going in three different directions.........left and right to its nieghbours and straight out to the opposite rotor

[Flux]

Somewhere on the old board there were Femm flux plots that show you where the lines go.

Basically if you ignore leakage you get  flux crossing the air gap from N to S on the other rotor. The return is via the magnets and the steel discs. You have a series of flux bands all round the rotor with flux going straight across from N to S. As magnets are alternate polarity the adjacent bands go alternate ways.

There is also leakage flux from N to S on individual magnet rotors, this is useless as far as the stator is concerned and only becomes a big factor if the magnets are too close or the rotor discs are much too far apart. With the normal layout nearly all the flux crosses between magnet rotors.

Next question?

Flux

[artv]

"in normal layout nearly all the flux crosses between magnet rotors"..Is the rest considered flux leakage? If so where does it leak to?This is why earlier I suggested all north rotor , all south rotor,wouldn't the flux be more concentrated in this design?Just alternate the coil arrangement........thanks          artv

[Flux]

Yes you are right, if you make all N pole on one disc and all S pole on the other the leakage flux is reduced. This arrangement was used by Mordey in about 1860 when they had to use electromagnets that were very long and prone to a lot of leakage flux.

As usual there is a little snag. if you do this with conventional coils each coil cancel the other and you get nothing out. It's probably the dc that you want but it's non existent

You can make it work as Mordey did by leaving out alternate coils, it then comes back to being ac and it works fine but at a price. Instead of linking peak flux in one direction then peak flux in the other you are forced to work between peak flux and zero. You halve the flux linkage and need twice as many turns with thinner wire and increased resistance.

With the electromagnets the gain from reduction of leakage flux outweighed the snags with more turns.The same is hardly going to be true with short fat neo magnets that have very little leakage indeed in the normal layout.

This unipolar idea keeps cropping up, it will work if you understand what you are doing, it won't produce dc and it will be less efficient than the normal arrangement but it is an option for someone to try. We spend our time inventing things that were done 150 years ago. How about square wheels they go up stairs better.

Flux

[ghurd]

See this for Dinges animations,
http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1458&PN=1&TPN=1

G-

[TomW]

This unipolar idea keeps cropping up, it will work if you understand what you are doing, it won't produce dc and it will be less efficient than the normal arrangement but it is an option for someone to try. We spend our time inventing things that were done 150 years ago. How about square wheels they go up stairs better.

Flux

Flux;

Forgive me for a bit of topic drift...

I think we keep coming around to these ideas because folks just read something in one place and do not take the time to look for historical data and research what may have been already documented on these ideas. 

My main philosophy on "Great new Ideas" is similar to yours. It is entirely possible it is an idea that had merit and possibly even worked at some time in the past but with new materials and processing methods the idea was cast aside as a poor option in light of newer materials or processes. Certainly magnetic and electrical physics have not changed just the materials and processes.  There was intense and extremely in depth research done as you say over a hundred years ago into these things. I read a lot of it in my college days which were longer ago than I care to admit.

I also think it is good that folks seek new ideas.

These days energy is like rain in the dustbowl days. Folks desperately need relief and there is a lot of opportunity for snake oil type information.

I appreciate your ability to gently explain for the nth time these things to folks.

Thanks.

Tom

[artv]

Maybe my ideas are arcahic , but I don't understand why we shouldn't look for ways' to improve them,I'm not a snake oil sales man....these ideas have been around for 150 years....... but they didn't have the materials we have today ...and if there are ineffiecienties should be able to improve them. I have basic electronics knolwedge......not a genious by any stretch...You guys are the whizs'.....Flux you said "flux leackage is reduced with all N rotor,S rotor but in the old days they used electromagnets ...which caused alot of flux leackage................well are'nt we beyond this now....ghurd I can't watch animations I 'm on dial up...Tom W ....I'm just trying to get people thinking because if we stop trying we cease to exist........artv

[bob g]

i listed a book either here or on another thread, which goes into vast detail over all the designs that were
either tried or in use from about 1860 to 1900, (depending on which edition you get)

by 1893 they understood silicon steel, and were getting within a percentage point of modern units, (certainly within 2 percent)

yes our materials are a bit better, but mostly from a strength standpoint and what little you will gain from using grain oriented
steels you likely won't improve over what they did back then.

one has to remember those old dudes were educated, lived, ate and breathed alternator/generator/motor design, every waking moment
for 40-50 years of their lives, and in some cases even more.

it is so unlikely that a diy'er today will improve on anything that was done back then, however there is certainly no harm in trying!

having said that, if it were me, (and i have been there, right where you are at) i would avail myself on every book on the subject i could find.
you may as well learn all you can from their successes and their failures, no real sense in reinventing the wheel (even if it is square).

i have spent the better part of 40 years collecting, studying and researching alternator/generator design, there really is very little new that
has come on the topic save for modern electronics, grain oriented steel, better insulation, and stronger materials in the last 50-60 years.

after everything i have read the single best resource i have ever come across was the book i referenced, second edition 1893.

you really should go out and find a copy,  everything you are asking can be found and answered in that book quite easily, along
with questions and answers you haven't even dreamed of yet.

i always figured an education is expensive, so a 20 dollar used book is quite a bargain

bob g

[SparWeb]

Bob,
I know exactly what you're talking about, but there are some exceptions:

I have an old book from 1940 called Strength of "ANC-5 Aircraft Elements, Army-Navy-Civil Committee on Aircraft Requirements".  It's based on numerous other publications going back as far as the early 30's.  It contains things like allowable strength values for many grades of aluminum and steel for use in aircraft (obviously).  Back in 1940, aircraft designers allowed a maximum 95,000 psi tensile stress in steel fuselage trusses.  Today's designers would allow a maximum... 95,000 psi tensile stress.  The material hasn't really evolved.  The mill's just moved to China.

But new composite materials have been developed that improve the structural efficiency of many vehicles and machines.  These materials are also very accessible to do-it-yourselfers (fiberglass boats/planes/artwork/you name it).  Every time a new tool or technology falls into the hands of clever people with an inventive nature, new uses of these technologies are bound to arise.

So do not despair!  About 120 years ago most scientists agreed that everything to be invented had been invented.  Then some gawky grad student published a paper supposedly solving the photoelectric effect, and the whole thing had fallen ashambles by the time he published his next paper about "relativity".

[Flux]

Perhaps it may be useful to steer this discussion in another direction.

Generators for wind power are odd things. We don't normally use air gap alternators for other purposes for the simple reason that conventional things are more efficient. Most alternators are designed to run on full load and the efficiency is made as high as possible at this point. Large machines reach over 97% efficiency, these little air gap machines don't even come close for many reasons.

Where they do come out far better is that the part load efficiency is very high compared with conventional machines. It would be inconceivable to run a big turbo alternator at 10% full load but wind machines spend a lot of time there, they virtually never run for a significant period at full load.

Now this is why these axial air gap machines have opened up a new possibility for wind. If you can devise a proper way to load them to match the blades you can make another major improvement. As things are normally done at present you are wasting your time chasing higher efficiency, the better you make the alternator the worse the blade matching and the overall performance becomes worse than ever.

If you want to chase alternator efficiency for the love of it and let others attack the matching problem then fine, someone else will benefit one day. If you have basic electronic knowledge then this is where you could make a really major improvement ,the improvement possible in alternators is quite limited even if you can solve the power match problem.

As I see it, any conventional generator works at fixed speed and fixed voltage and works best near full load, the big ones can still be improved and these improvements are still coming, if you gain 0.5% it doesn't matter to the user of the power but it does mean many kW of heat less to dissipate from the power station operators point of view.

Small alternators are always less efficient, most small devices are bad compared with their big brothers and there reasons that will prevent you reaching over 90% in a small machine. Even so if cost and size is no real object you should be able to get these air gap axial machines up into the 90% region. If you can do something to be able to rectify this to dc at the 90% region then you will have made a big step forward. The conversion process does drop efficiency quite a lot and it's not directly an issue of diode drop, that can be tiny in higher voltage machines.

I suppose this will send you back down the route of generating dc in a machine directly but that is not going to happen unless some totally revolutionary concept is discovered.

The next problem is adapting the machine to produce a roughly fixed output voltage with variable speed, this will be the only real way forward in terms of raising full load efficiency without detracting from the low wind results. if you have enough turns for low wind you have far too many for high wind. If you can halve the turns you reduce the resistance by a factor of 4. If you use a third of the turns the factor becomes 9, you just can't get round this one with a single fixed winding.

Overall with wind at best you can only capture a tiny % of the total energy in the wind, with the present set-ups some may manage 30% at cut in and will probably drop below 10% ay full load. Playing with 5% of alternator efficiency if you can match things is not useless but with the present matching schemes it will actually make it worse.

If you want to look for new materials to get major improvements the only direction I can see any real gain is to explore superconductors, probably not very practical for an amateur but it really is only resistance that is going to get you anywhere, improvements from such issues as flux leakage are minimal, just use 5% more magnet , but if you don't change that winding ratio you will need 900% more copper.

Wind power is one area where far too many factors are inter related, just concentrating on the alternator was worth it when things were really bad, That improvement came more than 10 years ago and we are now struggling with new issues that were not even though about before neo became available. None of us could produce a cost effective alternator light enough for wind use that would get near stalling the blades, now with present set ups this is the limiting factor.

Flux

[artv]

thanks agian to all ..........what is power matching?........artv

[SparWeb]

Hi Art,
Without getting into too much detail, I'll offer the cole's notes version.  The wind drives the prop with a certain amount of power.  If the generator receives that much power but can't handle it, they will run so fast that either the generator burns out or the blades fly off.  If the generator requires more power than the prop can deliver, then they just don't get turning at all.  Somewhere in the middle is the "sweet spot".  It still isn't as simple as this, because there is lots of power in strong wind, very little power in light wind, so making the generator's characteristics MATCH the prop in strong wind or light wind is a choice to be made.  Then you live with the consequences.