Generator with ferrite magnets

[scoraigwind]

Thanks for the photos, Max

It could be interesting to try changing some other things in the magnetic circuit while you have this flux meter and it is easy to do tests.  For example I wonder how much the thickness of the steel matters?  And another factor that will make a difference is that you do not seem to have an even number of magnets.    An odd number of magnets will unbalance the distribution of flux somewhat.  All of the flux from the two outer magnet pairs has to try to return through the one inner magnet pair.

have fun

[Flux]

I have always used 3 magnets and measured the flux on the centre one, assuming that the 2 outer readings would be wrong but the centre one would be ok, I suspect the error in this assumption is Small.

It would be a good idea to repeat with 5 magnets and see if there is any difference in the centre reading. I think you need 5 to be absolutely sure.

This will only affect absolute flux and for leakage comparisons the 3 magnets will be ok. I think you will find that with ferrite magnets the steel plates will have to be quite thin to affect the gap flux much. I know people start to worry when washers and paper clips stick to the back of the steel, but I haven't noticed any measurable difference in the gap until quite big things stick to the back. While Max has thing set up this would be an interesting check

Flux

[Menelaos]

I can repeat the readings with 5 pairs of magnets and also with thicker metal but I do not think that either setup will change the readings. The flux of those ferrits is too low to saturate the metal plates as those 3mm are quite a lot...but i will try :-)

But first maybe I make a small simulation on Femm to see what the differences should be in theory :-)

Max

[artv]

Hi Max,..I don't have one of those meters'....Was wondering what the reading would be if you removed the three bottom magnets..
Just have the blank steel plate ,.....would it be half ....Also if you had the mag rotors mounted so the magnetic circut is complete, would you get the same reading or would it be a little higher since the circut is complete??.....I guess I'll have to get one of those meters.....too many things to try.......artv

[Menelaos]

Ok, I did make 2 magnetic simulations on a FEM-Tool to see what the differences of flux and flux loss would be on the modell.

First, I did the simulation with my magnets of 34mm width and 15mm hight with airgap of 16 mm, just like the practical one I made yesterday:






I then medelled the version of magnets attaching each other:





So what do we see?

The theoretical results are quite identical with the practical ones with the flux beeing about 0,2 Tesla in the middle of the airgap and in the center of the magnets.
The distance on the graph is cm, not inch...please mind that.

Towards the edges of the magnets, the flux gets smaller anyways, although it seems to be a bit more on the version with attaching magnets. The difference is what comes from the loss of flux. I do not feel this is too dramatic.

On the 2. graphs, you can see the flux lines spreading. They are still quite well passing towards the opposite magnets although the magnets are attaching each other. I guess some of you might have expectet different results here. What you can also see is, that the 3mm iron bar that the magnets are placed on is by far not saturated. It can take up to 0.6 Tesla before it gets saturated- we are far away from that, so taking thicker peaces of metal bars would not give any benefit concerning the flux...

OK, have a look and tell me what you think about that...
 

What seems to be important to us is not the hight of flux at the peakt level but the average flux between each pair of magnet meassured over the whole surface area...

For the spaced magnets in this example it would be 0,20 Tesla
For the magnets attaching it is 0,175 Tesla

So by leaving no space between the magnets compared to  a space between them that is equal to magnet width we loose about 0,025 Tesla. This difference is what the flux loss takes away. If we use higher magnets like Chris does and maybe reduce the airgap by 2 or 3 mm, this effect will be even smaller!

anyway, for this example we loose about 13 percent of flux density...but by using wedged magnets, I can something like 50 % more magnet area.
I definitively do make the whole alternator more powerful by using using this free space between the "normal" magnet setup which is why this is the way i will go for :-)

[electrondady1]

for me , this thread has been the " hot" topic for some time now .
the renewed interest in using  ceramic/ferrite  magnets is exciting.
 
Menelaos, thanks for posting your femm results.
i am surprised that here is only a 13% loss in average flux density by eliminating magnet spacing.
 i thought it would be greater.
it would seem that we are further ahead by doubling the number of poles and taking the loss.

so now we come to the heart of the matter.
the coil leg width and the percentage of  cancellation of current incurred when over two poles.

[Flux]

Yes this seems to be the next issue to optimise.

You can increase flux per pole with more magnet, even if you don't increase the magnet rotor diameter the leakage flux is not so bad. The final truth is that the space for winding is reduced by the close spacing.

It seems a trade off between keeping turns short to be low Resistance and having room for wire large enough to keep resistance low.

With conventional iron cored 3 phase machines you continue to gain by squeezing more magnet in even though it is used ineffectively. In that case the coil geometry is set by the winding design so length of turn is fixed. If you stick to conventional windings using overlapped coils for 3 phase axial air gap machines you are stuck with that fixed coil turn length. it now remains to see how the factors play when you abandon the conventional windings and are free to play with coil shape.

I am sure it will again come out for one design that gives best value for magnet and copper cost and a different design that gives maximum output for a given diameter of stator with magnet cost not included. I think it will depend on your views of the effect of resistance, if it is part of the design needed to get the prop loading correct you will get a different answer from a design designed to screw the maximum out of a given machine ( which may be the case if you can alter the gear ratio of the drive to get the prop loading).

I really don't see any difference here from the neo case, it just happened that with neo there is so much more flux available that it was not worth trying to use more than the minimum magnet to do the job. With ferrite magnet cost is not such a big issue but the demands on copper are very severe when you need many more turns in a given space and still need low resistance.

Flux

[Menelaos]

I have my own theory about the coil design. I made a lot of test with different coils on the neos, also considering femm- results that I made up. Providing that I use my setup with the magnets beeing wedge shaped an touching each other to form a closed ring, I will make the coils a lot smaller than the magnets. My coils will have a leg width of about just under 20mm. on the inside, I will make the center whole really narrow- about 0,5 cm so that the whole coil will be about 45mm in width then. on the outside I will make the coil hole width about 2/3 of the magnet width...so about 2 cm. That saves a lot of resistance on the top an bottom side and as the flux quickly decreases towards the edges of he magnet, I do not really loose much. Volate will be about 10% less for each col only, the resistance will go down about 20% which about gives me the same situation than before BUT I now can easily fit 12 coils on the same space that was taen for 9 coils before- so there is my benefit agian. WIth the closed magnetring and my coil shape I can get a lot lower resistance with the same voltage on the same space that was used before. In the end I can cut down the resistance to nearly half. I think thats pritty cool :-)

Max

[scoraigwind]

I love the way you can do the theory as well as the practice, Max.

I have been counting the lines of flux between magnets in these diagrams.  I don't know if they are for real or not but you say the real measurements back them up.  What I notice is that the magnets that are well spaced have 20 -25 lines from one magnet to the other, across the gap.  The ones that are packed in close together only have 11-12 lines crossing that gap through the coil.  I know some of the straggly lines in the widely spaced ones will not pass the centre of the smaller coils, but with larger coils, they do link most of the turns.

My logic is that if magnets are expensive (and I know that is out of date so far as ferrite magnets go lately) then I prefer the 20+ lines of flux to the 12 lines and I also like lots of space to put a nice big coil in there. 

I see what you are saying with the small coils that let you fit more coils in there.  So to make a powerful alternator in a small space you are getting a good strategy.  But if you want something that can handle high power then it's not only resistance that matters, it is also the surface area, so you may find that even with lower resistance you can't get more current out of the stator without burning out.

We all have differing goals in different situations.  And it's great to learn the best ways to reach these goals. 

[Menelaos]

Hi Hugh,

The number of flux lines is just a setting, what counts are the colors that indicate areas of high flux as well as the average flux that i calculated.

"I see what you are saying with the small coils that let you fit more coils in there.  So to make a powerful alternator in a small space you are getting a good strategy.  But if you want something that can handle high power then it's not only resistance that matters, it is also the surface area, so you may find that even with lower resistance you can't get more current out of the stator without burning out."

I totally agree with that BUT I do not consider that as a problem. Before I used that setup with block shaped neodymium magnets. With all those improvements I stated, I still will not get the same power that I used to have before. The alternator will definitively still be less efficient, just not as much compared to the size. The heat loss will not be more than before as the blades still provide the same amount of power and overspeed protection still is an issue...even more that before as with those ferrits shorting the alternator to stop the machine will not work anymore, so a good working furling or any other device to protect the machine in high winds is essential.

I do not see any problems here. Dealing with the heat issue, it does not make a huge difference which way to go for the coil geometry on those small machines. It becomes more of an issue with the larger alternators when the stators are 16, 20 or even 25mm thick. My stator will be only something like 10mm high...
The wire I use does take 220 Degrees before it gets funny, the resin is a special venylester mix and I temper those small stators in the oven for some hours. The resin can then take 160 degrees continiously- I have never seen it climbing up to that temperature. I had one of those neodymium alternatrs tested for more than an hour running on more than 800 Watts heat loss in the coils and with peaks of more that 1,5 KW and it kept working. We will never see that much power from such a small sized 2m Machine in the real world and particulary not for such a long time so I am not worried about burnout at all. For lager machines on the other hand I definitely do see a problem with heat dissipation...

Anyway, everybody has his own theory about what works best. For the moment I am struggeling with influenza so I do not feel like going to my workshop but after recovery I will make some more tests on coil dimensions and then prepare the CAD drawings for the laserparts and order some personal magnets from poland.

The best way to find out is to build this genni and see how it behaves and how things turn out :-)

Max

[ChrisOlson]

...even more that before as with those ferrits shorting the alternator to stop the machine will not work anymore, so a good working furling or any other device to protect the machine in high winds is essential.

Max,

I have to disagree somewhat.  I have not had any problems stopping my 3.8 and 4.0 meter machines with the ferrite magnets, even in 20 m/s wind.  I have a bit different situation with the geared generator having a huge mechanical advantage over the rotor shaft when shorted, because of the gearing.  And I would have to work out the braking torque available on a direct drive to see if it could stop it.  But I think, without doing all the math, that it should have no problem.  It's sure to be a more gentle stop, though, than with neos.

When you short a ferrite generator you don't get the big 300-400 amp surge like you do with a neo unit.  But the "drag" is enough to slow the blades to stall speed on my geared machines pretty quickly - less than about 5 seconds in very high winds.
--
Chris

[keithturtle]

I'm new to the ferrite thing.  Is the difference between C5 and C8 pull strength significant?

The sizes they post on that source site don't offer the 2" x 3" x 1" thick that I need, in C8

Turtle

[ChrisOlson]

I'm new to the ferrite thing.  Is the difference between C5 and C8 pull strength significant?

There is so little difference that spending the extra money on C8's is not worth it.
--
Chris

[scoraigwind]

HI Max sorry about your flu.

The number of flux lines is just a setting, what counts are the colors that indicate areas of high flux as well as the average flux that i calculated......

I wonder why you would use a different setting?  I suppose that your meter is directional?  In the case of those magnets that touch each other a fair amount of the flux is going in the wrong direction.

I definitely agree that you need a furling system that works reliably to protect your turbine.  Braking is a very nice option, especially when experimenting, but it won't work if you are not there, so it puts a big burden of responsibility on the user that you do not need in the long term.  I am impressed with the work you are doing on high temperature resins.  In the rare cases where I have seen failures due to high temperature my reaction has been to adjust the furling or build a larger alternator, because heating goes with the square of the current, and I am not good chemist.   Maybe one day you will also share with everyone the secrets of your resin process but I won't presume this.

[Menelaos]

Good that you metion that...I forgot to say that on the simulation I used c8 magnets as I did not have my f30 in there. After some research I founf out, that F30 is equal to c5 which again I have in my list. So the calculated flux density will be al little less that what I stated in theory. I already wondered why the maximum of flux was a little higher on the simulation that on my practical measurements....

But thats nothing dramatic...


If shorting the machine will still worl I have to find out...but good to know that it should still be ok :-)

Max

[ChrisOlson]

Max,

The C8's have Brmax of 3850 vs 3800 for the C5's.  The C8's are twice the price (at the place where I get my magnets) so I felt the cost was not justified for a zero air gap difference of only 50 gauss in the magnet.  I don't think that will throw your calculations off too far using C8 values instead of C5 because at the air gaps you're talking about in an axial generator there is no significant difference in the flux density in the air gap between the two grades.
--
Chris

[ChrisOlson]

I totally agree with that BUT I do not consider that as a problem. Before I used that setup with block shaped neodymium magnets. With all those improvements I stated, I still will not get the same power that I used to have before. The alternator will definitively still be less efficient, just not as much compared to the size.

Hi Max,

I haven't followed this as closely the past couple days.  If I understand correctly, you're saying the ferrite generator you are building for your 2 meter machines will not be as powerful as the neo one.  This is probably very true if you don't increase the size of the generator by more than double that of the neo.

When I built my dual stator unit I was not willing to accept less power output.  I wanted the same or more than what the neo unit could make.  When I started looking at designs I came up with the fact that, even with .4375 gearing, in order to fit a single strand of 13 AWG wire in the stator with 50 turns per coil in wye I needed 20 generator poles and 15 coils.  To fit 20 poles on a single stator rotor would have required rotors about 50 cm in diameter and then I would have roughly 12 mm spacing between the inside corners of the magnets.  And further, the maximum amp capacity of the thing would only be about 30 amps, which was half of what I needed.  This was for a three phase.

That's why I gave up on three phase with the ferrites.  There's no way you can put 20 of those heavy magnets on a 50 cm disc and spin it at 900 rpm.  I needed to keep the mass of the rotating assembly in closer to the center of rotation, which meant discs no bigger than 28 cm.  And the most poles I could fit on a disc that size was 10.  That's how the dual stator two-phase configuration was conceived.

It turns out, after I built the second and third ones with 12 AWG (2 mm) wire) and a few less turns, that it is more powerful than the neo three phase of the same diameter.

I have worked out a new design for a 24 volt dual stator, two-phase, direct drive with 14 poles (56 magnets total) and 14 coils per stator for a 3.8 meter turbine.  It should fit under 38 cm (15 inch) generator rotors, and wound with 2 mm wire will have 60 amp continuous output capacity.  It will not match the raw power output of the geared unit because it will require 56 turns instead of 48 per coil, and come in at about .55 ohm internal resistance, as compared to .32 ohm for the geared unit.  But it will keep the stator thickness down to 12 mm and still a reasonable size.

The other direct drive design I looked at was a three phase 28 pole with 21 coils (still 56 magnets total).  The three phase would have to built on 66 cm (26") diameter generator rotors and there is no way it could match the internal resistance or ampacity of the dual stator and still keep the stator at 12 mm thick.  By the time you add all the extra wire length in the winding heads of the coils of the large diameter stator and try to fit two-in-hand 2 mm wire in it, it's not even practical to build such a monstrosity.

So despite all the single stator experts that have never built a machine this size with ferrites, I am strongly considering building the dual stator 14 pole direct drive and hang some 3.8 meter blades on it - just to prove that a high output direct drive ferrite machine can be done, that will match a neo machine in output of the same rotor diameter.

I have been trying to decide if my next project is going to be a Jacobs-style variable pitch prop hub or a direct drive ferrite 3.8 meter turbine.  With all this talk of how single stators are so superior to stacked units (which is true with neos, but remains to be seen with ferrites) I've gotten all fired up about building one just to prove the "experts" wrong.
--
Chris

[artv]

Hi Chris,...Why don't you just combine the two?....The direct drive will need blades anyway ,why not the Jacobs style variable pitch??
Maybe the two can't be combined??....
Regardless...I'll be watching for your next project......artv

[Menelaos]

Hi Chris, that sounds very interesting what you write there...
When it comes to variable pitch hubs, I have made my own experiences with that...
I am presently developing a new type of pitch control mechanism for a german small wind turbine manufacturer which I think will outperform the jacobs design.

Except that, I find that the jacobs design is probably one of the most simple and reliable ones.

But lets please talk a litller more abouzt 1-2 and 3 Phase alternators. What would be the advantages of each type? Why do you like the single phase unit that much, which definite advantages do you see over the 3 phase version?

Max

[ChrisOlson]

But lets please talk a litller more abouzt 1-2 and 3 Phase alternators. What would be the advantages of each type? Why do you like the single phase unit that much, which definite advantages do you see over the 3 phase version?

My experience with the two-phase in my geared ferrite generators has shown me that the two-phase works just as good as three-phase.  It just requires four wires to the rectifier instead of three.

With the ferrite magnets it's easier to get the required voltage with more coils in series (single phase windings) without ending up with really fat coils.  I see some practical limitations to the construction of a big three phase with ferrites - the main one being that trying to keep the air gap at 18 mm with a 12mm thick stator at a diameter of 66 cm is not practical.  The runout on the rotors at that diameter require more air gap, which in turn requires more copper.  With neo magnets at that diameter you can run larger air gaps without adding a lot of copper.  With ferrites you can't.

And this is what I mean when I say nobody has ever built one while standing firm by the assumption that a very large single stator is "better".  I know I can build a high output ferrite on 38 cm rotors by stacking two stators, and keep the tolerances where they have to be so it will last.  I have serious doubts about the longevity of a large diameter ferrite three phase unless you make it really inefficient by increasing the stator thickness to make it strong enough, as well as running more air gap to keep the rotors from contacting the stator when in actual operation on the tower.

This is one of those deals where theory meets practical experience and the two clash.  But practical experience is going to win out, despite the fact that theory says one big stator is "better".

The direct drive is going to have slightly over 40% more copper in it than my geared unit.  Therefore it will never perform on the same level as my geared machine.  Lots of people are hung up on direct drives as being the only way to build turbines (they're wrong on that too) so that's why I've become interested in building one.  Nobody else is going to do it until they see one that works.  And when it comes to using ferrites on larger machines than 2 or 3 meters throwing the book out the window is necessary because the neo designs simply do not scale up into something that's practical to build with ferrite magnets.
--
Chris

[Menelaos]

Ok Chris, I get the point but I think stacking rotors or not and chosing between a single, 2-oder 3 phase style is a different storry, isn't it?

Lets assume 2 same alternators, one build as 3 phase, one as single phase. If they both have the same amount of copper, they will both perform the same, right?

Of course with the single one you can get more turns or higher volatge but in the end this will result in different resistance as well which calculates differently again. So neither one should have more heat losses, better efficiency oder highter output capability because that would not be logical and clash with physics :-(

Did I miss something?

Max

[electrondady1]

Did I miss something?

yes max, you missed the fact that Chris forgets he  is a master machinist and millwright.
that while we are envious of his abilities and creations
we admire and encourage his experiments.

[Menelaos]

well that definitively didn't help at all...

I like the way Chris approaches his projects. Some things do not make sense...alt least in theory but sometimes there are other reasons why some things turn out to be more adequate than others. We are trying to find different solutions and discuss about what might work out bestter and why. If now people start fighting wen can also do that via email and none of you will benefit from what we discover and work out. So PLEASE, if you have questions or something you feel that you can contribute than go for it, if not then PLEASE SHUT UP and help us by not spamming with such remarks...!

[ChrisOlson]

Lets assume 2 same alternators, one build as 3 phase, one as single phase. If they both have the same amount of copper, they will both perform the same, right?

I don't know that this is the point, Max.

Yes, I have found thru practical application that the two-phase stacked design performs as well as a neo, or a single stator.  Whether or not it makes better use of materials, or the magnets, is not the issue.

I am looking at the mechanical limitations of the axial design using ferrite magnets.  My practical experience has shown me that keeping the air gap as tight as possible, without contacting the stator(s) is more important with ferrites than with neos.  If you increase the air gap too much with ferrites to prevent mechanical contact of the rotating assembly with the stator during real world operation, you have to add  a lot of copper to make up for it.  With neos you don't.

To keep efficiency up and copper use to a minimum, I'm running 18 mm air gap on those big magnets with a 12 mm thick stator in between.  Try that with 66 cm rotors?  It will hit in actual operation.  Bench testing does not simulate the flexing and stresses a wind turbine is put under when it experiences 30 m/s wind.  You try to build a machine with that diameter rotors, with that air gap and stator thickness and it will fail.

Reducing the diameter of the rotating assembly keeps axial runout tolerances in check when things flex under high load conditions.  You can safely run those tight air gaps on smaller rotors without contacting the stator.

This is what I'm talking about when I say I see some practical design considerations here with people claiming without doubt that a very large single stator is "better".  When you use neo magnets I think that's right.  When you use ferrites there are other issues when you try to design efficiency into it, as well as a design that will hold up on the tower in real world conditions.

Blindly applying theory to a design without considering the practical limitations of theory, yields poor designs.
--
Chris

[electrondady1]

"well that definitively didn't help at all..."

sorry, perhaps i was too subtle.
i was trying to point out that with Chris's abilities and areas of expertise he would choose to build with different techniques than yourself.

"So PLEASE, if you have questions or something you feel that you can contribute than go for it, if not then PLEASE SHUT UP and help us by not spamming with such remarks...!"

here are a few questions:
would you post a diagram or photo of your magnet and the coil you propose to use overlaid on it.
you gave dimensions of the coil but not of the magnet.
you simply side stepped my previous question in regards to cancellation and i am curious.
could you post am oscilloscope image of your output or even give an estimate of what percentage of time your coils will actually be producing current?

 
"gut, dass definitiv überhaupt nicht helfen ..."

sorry, vielleicht war ich zu subtil.
Ich habe versucht, darauf hinzuweisen, dass mit Chris Fähigkeiten und Kompetenzen er wählen würde, um mit verschiedenen Techniken als selbst zu bauen.

"Also bitte, wenn Sie Fragen haben oder etwas, was Sie fühlen, dass Sie dazu beitragen können, als für ihn gehen, wenn nicht, dann schalten Sie bitte UP und uns helfen, indem sie nicht Spamming mit solchen Bemerkungen ...!"

hier sind ein paar Fragen:
Möchten Sie nach einem Diagramm oder ein Foto von Ihrem Magneten und der Spule Ihnen vorschlagen zu bedienen überlagert.
Sie gab Abmessungen der Spule, aber nicht von dem Magneten.
Sie einfach Seite trat meine vorherige Frage in Bezug auf die Kündigung und ich bin gespannt.
Sie könnten post am Oszilloskop Bild Ihrer Leistung oder sogar eine Schätzung, wieviel Prozent der Zeit Ihrer Coils tatsächlich produzieren Strom?


 

[ChrisOlson]

you simply side stepped my previous question in regards to cancellation and i am curious.

electrondady1,

I think Max has found out, like I have also, that cancellation is not as big of an issue as most think.  The flux of the magnets is least near the edges and most in the center.  So making coils with a hole smaller than the magnet works fine in most cases.  It is the change in flux in the air gap that causes the current to be generated in the coils and laying out your coils because of the shape or size of the magnet does not follow exactly what that changing flux looks like when the rotor is going around.

So, from my own experience with this; you can use a wedge shaped coil with big square block magnets and it looks like it will "cancel".  But in reality, the reduction in resistance of the coil (less copper used in it) more than makes up for the very slight difference in voltage you get by making the coil hole the size of, or bigger than, the magnet.

I realize this sort of goes against what is accepted as "the proper way to do it".  But I have done it the "wrong way", using a coil hole that is "too small" with great success for some time.
--
Chris

[electrondady1]

thanks for your reply Chris.
this is your thread and i will not post on it again .
danb and others have been shrinking the centre hole for some time now and i understand the advantage .
as well, in his use of round magnets, dans magnet spacing has been reduced without penalty
.
in describing his coils,max implied that the outside of his coils were smaller than the magnets.
that is what i wanted to make clear.
as that is quite a departure from convention.
perhaps i have misunderstood.

i have two areas of interest in common with this thread ,
the use of ferrite mags,
 and  the use of two phase stators
both of which i have been experimenting with for some time now.
good luck.

[ChrisOlson]

electrondady1 - it's everybody's thread.  I just happened to build a unit that uses ferrite magnets, is all.  I'd really like to see somebody try to build one of these large three phase ferrite generators for a 3-4 meter machine, though, to see how it works out for efficiency and power compared to what I have come up with.  I think it would a very hard build.

As to the two-phase, I would like to make a distinction between true two-phase and two-phase loading.  What I have is two single phase stators that are individually rectified.  Being they're skewed 90 electrical degrees that gives me two phase loading but it is not true two--phase.

You can get a 1.414x voltage increase with a two-phase winding by connecting the two phases together like the "star" connection in a three phase, and using the other two leads for power.  My design went for maximum amp capacity of the windings using the IRP configuration.  But it would be possible to reduce the number of turns by connecting the windings together and using the 1.414x voltage increase you would get from it too.

You could also build a flat two-phase ( I think I figured out that it takes four poles for every two coils to do that).

Two phase power was used in the past like in the generators at Niagara Falls that were installed in 1895, and were the largest generators on earth at the time.  They had four wire two-phase and three wire where one wire was bigger than the other two (the neutral) because it carries the vector sum of the current in the other two wires.  Three-phase eventually replaced two-phase  because three phase can transmit power with less conductor mass, using three wires instead of four.

On the wind turbine I see no difference between the power efficiency of the two phase setup vs three phase if the stators are the same resistance.  None.  The two phase runs quieter and requires four wires down the tower instead of three.  Otherwise I see no difference between them in performance.
--
Chris

[artv]

Electrondady1.....if you choose not to post on this thread anymore ,....it's our loss....
This is an open forum ,to any and all members..
Max.....I don't think you should be telling anybody to "shut-up" , especially such a respected member ...(maybe me might be acceptable and understandable)....

Chris ...you said building big diameter rotors will fail because of the "flex" under high load conditions in the real world,..I think this only applies to hawts, a vawt , doesn't experience the same conditions??
I'm just a newbie with alot of crazy ideas .....maybe I should shut-up now.........artv 

[fabricator]

Shut up Art.

[niall2]

thats not nice fab....

this isnt a  5 year Thesis Submission from a university....which nobody will ever understand and will be stuck in pdf,s on the net

lets all roll with it for a while ...

[fabricator]

I only did it with his permission.

[Menelaos]

"in describing his coils,max implied that the outside of his coils were smaller than the magnets.
that is what i wanted to make clear.
as that is quite a departure from convention.
perhaps i have misunderstood."

Yes you did get it wrong. What I related to were the coil enter spaces. I do make them smaller than the magnet surace area. The coil itself of course will still be larger than the magnet.

Chris already explained his results with coils that have smaller inside space than magnet width. I did make quite the same observations and have started ro make the coil space more narrow quite a wile ago. It really gives benefits due to the resistance dropping a lot.

so the next step for me is to get the drawings done and my new magnets ordered. In the meantime I have to get my coil geometry set up and done. I will let you know once I have the genni finished and can come up with some results.

In the meantime I will continue on my wood gasifier project :-)

Max