lets talk alternator design

[bob g]

this is going to drive some of you guys crazy, my hope is it
won't set anyone's hair on fire.

let me preface my thinking a bit

1. neo magnets are more costly and in shorter supply

2. there appears to be some interest in gearing up the driven speed
of generators, in order to reduce size/cost and increase output

3. i would appear there is some interest in using mppt controllers to increase the average wind power

4.  #2 and #3 above even though they work there is a penalty in small reduction in efficiency, gearing eats a bit of power just as mppt controller eat a bit of power.  not arguing for or against their use on this point but just recognizing some losses exist.

5. it is widely accepted that the inner 1/3 of the blade rotor set produces virtually no useable power, in a practical sense.

so... here goes

what if one were to start all over again, accept the premise from above
and increase the diameter of the alternator to something perhaps on the order of 24 inches

lets see what this might afford us

our rim speed is twice that of a 12 inch machine, so we might be able to go with ceramic magnets instead of neo's?

we might go with more poles with more phases so that resistance does not become an issue in the stator.

we might also use a combination of ceramic magnets and wound coil field. (ok, everybody stay in your seats here for a moment)

wound field has its issues, generally shunned for its eating power when the wind speeds are low, however with a ceramic/coil combination we can drop the coil excitation and let the magnets provide the excitation in low wind speeds if that is desirable.

as windspeeds increase the amount of power it takes to supply the field coil is but a small percentage of the total, on the order of 2-3% at full power is within reason.

in any case the power it takes to power the field is significantly less than that which is lost in the mppt converstion/control or the gear drive system. however this is not the attractiveness of this direction

what i find interesting is the ease of control of such a system, it is far easier to control a few tens of watts of excitation than it is to control or convert many hundreds or thousands of watts.

lastly there is a concern with increases in machine diameter necessarily increasing weight to an unacceptable level. i am not convinced this need be a linear relationship.

while it might be said such a machine would be more complicated, i would assert the use of gear/chain drives, mppt contollers and such increase complexity as well.  once the design is worked out, proven, it would not necessarily be significantly more complex than what is going on now.

just kicking this out for some discourse.

bob g

[kitestrings]

bob,

I'll offer my admitted biases.  No hair to burn here.

Neo's are more costly (more so than when I bought mine), but I think they buy you something.  Simplicity.  Far and away the appeal for me of the dual-rotor axial is that up on the tower you can have a machine with basically three moving parts.  I suspect the added cost of Neo's is a trade-off vs. gearing, and it's inherent losses, added build complexity and eventual wear/component maintenance.  I know Chris, Fab and others have been successful with geared machines and will have different opinions on this point.  They also probably are better equiped and skilled at building a geared unit than the average home-builder.

I also agree that with either choice (MPP converter or gearing) there are some losses.  I'm biased towards MPPT in conjuntion, and design integration, with the axial-flux.

I'm not fully convinced that the inner 1/3 of blade has no appreciable contribution.  Many folks have allowed the blade stock selection to preface the expected outcome.  Many of the practical limitations of making blades outway the expected gains, but much is based on intuition as apposed to science (IMHO).

The combination PM/field coil sounds very intriguing to me.  We've operated a field-wound, geared turbine for years.  It has it's limitations (and, in this vintage inefficiency), but you can't say it isn't durable - ours is pushing 30 years - and easily controled.  As long as the wizardry is on the ground I think it has (more) promise.

I also think the impact of weight may be, long-term, underestimated.  We're up to over 100# just for the magnets, rotors, hub and neo's on ours.  It is a concern.

You'll no doubt get some strong opinions, but it should be good discussion, and it is always good to see someone trying a new approach.  My $.02; no charge.

regards, ~ks

[Flux]

Interesting thoughts. virtually everything is practical and it has been tried.

Ideas tend to come and go as technology advances

[redtick]

What we need is an induction generator with just enough residual magnetic field to be "self starting."

[Flux]

Don't know what happened there computer reverted back to email and managed to post part of what I was writing.

I was going to say that ideas come and go as technology advances and sometimes price or availability of things makes it better to go back to older ideas.

I agree aboout the inner third of the swept rotor being useless and it doesn't matter if you use that space for an alternator.  It has been done before but a large and heavy alternator is not without its problems.

Neo has several problems, cost being one of them, I never thought it would become commercially viable ( Samarium cobalt hasn't) but we had a nice few years with relatively cheap neo and it opened up a whole world of new ideas. If we have to go away from it then we basically have to do what we did before.

Wound field machines are possible and were all we had before ceramic magnets. The ceramic ( ferrite) magnets were just gaining some useful ground when neo came along and changed all that.

The drop in flux with ferrite magnets is a major problem and you either need a much bigger alternator or you need to raise the speed. Even with wound field machines higher speed is really needed to keep the size and weight down to something sensible.

Combining ferrite magnets and wound fields is again not without difficulty, basically a permanent magnet behaves as saturated air and you can't effectively compound a magnet with a field coil over it. You beascally are forced to use two machines, one for low winds near cut in and a wound field machine to deal with higher winds.

Field control is very easy with a wound field machine and you can easily keep the prop on its power curve but not with good efficiency if you bog the thing down to constant volts. I wouldn't mind betting that mppt as used with a buck converter would transform many of the older wound field ac or dc machines. You can't get away from high I^2R losses and reactance problems with a variable speed machine bogged down to constant volts. At least keeping the prop on the top of the power curve gives you a good start and you can do better in high winds with wound field than with a stalled neo machine, but using a buck converter would transform the losses and reactance current limiting problems and I suspect you would need little in the way of field control although a bit would be helpful to keep the flux in the right region.

The truth you are going to have to accept is that a wound field machine needs a very small air gap to keep field losses within limits and this means going back to slotted iron cores and it ceases to be a build it yourself option without a full set of workshop facilities.

There is a lot you can do without neo, ferrite magnets were never my choice, I could do as well with wound fields but that was before mppt. I tried gears and they were a real pain and had to be grossly oversized to survive and I think I can reasonably say they have been a pain to the larger wind industry but if designed correctly they can work.

I had virtually come to the conclusion that a chain drive was a better proposition for small wind power and Chris has fully confirmed this, I see it as being a more practical option to the very heavy large diameter ferrite machine with direct drive but there may be an intermediate case for a bigger direct drive ferrite machine and a mppt converter.

Those that want simplicity and choose to ignore mppt can keep the simplicity at the expense of a large and heavyy but not too expensive alternator. If you want the performance associated with neo and mppt then, the alternator will be even heavier or you accept a speed increase.

Transmission loss is small and so is the loss in a mppt converter and you will have to do a lot of hard thinking to even approach the same efiiency with any direct battery charging machine.

I will keep an eye on the developments, but I have seen most of this over the last 60 years, apart from neo and ferrite there really is nothing new in the generator world , we do have the benefits of modern electronics.

Flux

[Flux]

Redtick

Most induction alternators are self starting but an induction machine has many problems for wind. Even if you can solve the excitation problem and do away with capacitors and replace with an electronic phase advanceer you are left with an inherently high speed machine. Beyond 6 poles they are very ineffective so you are virtually forced to use a large speed increase in the transmission. Simple and robust but very difficult to do much with if you want variable speed and good performance.

Flux

[CraigM]

Here's something I've pondered.

Increase the size of the magnet rotors on a typical axial flux type machine from 12” diameter to 24” diameter, and fill those rotors with as many 2” x 2” x 1” thick ceramic magnets as would be practical. As Bob stated, the perimeter speed of that 24” rotor will now be much faster than a 12” rotor at any given rpm.

If you build a typical axial flux stator and fill the entire 24” diameter with coils it's going to be one, very  heavy and two, you'll need a large diameter blade set to match the alternator.

So instead of building a 360 degree stator, build lets say a 90 degree stator or whatever size angle may be needed to fit 9 coils spaced close together and match the 24” diameter arc of the rotor. Would this not give an output similar to the typical 12 neo pole / 9 coil axial flux machine?

I see this as a alternate way to still use direct drive but at the same time obtain the faster speed and pole frequency of a geared drive.

It's still going to be heavy beast and you're not using the number of magnets to their best potential but at an average cost of $2-$3 a magnet you can throw a lot of magnets past those 9 coils and at a much greater rate of frequency and do so with no gearing involved.

CM

[Flux]

If you want to use direct drive with ferrite magnets then you will be forced to use a larger diameter just to get in more magnet to make up for the serious loss of flux.. You benefit from larger diameter by having room for lots more magnet, the increased peripheral velocity is a red herring.

With the large drop in flux and hence the need for more turns you will struggle with winding resistance and no way is there any logic in only using a part stator. I can only suspect this belief comes from misunderstanding this speed issue, there is no increase in angular speed at the larger diameter.

You won't need large blades to match this alternator as with only 1/3 the flux of neo at best you will struggle to keep the same blade size.

Faster speed is wrong. You can increase frequency by using more of the small magnets or you can increase flux by using fewer magnets of larger area , both will help compensate for the lower flux density in the gap and that is all you can do without a speed increasing transmission.

[bob g]

ok we are concerned about stator resistance when it comes to a larger diameter machine.

we can go with more poles, so why are we locked in a 3phase design, when more phases could make better use of the increase in pole count and in doing so keep the resistance down to an acceptable level.  what do we need to do this? more diodes?

i understand the desire to limit stator phase resistance to the lowest possible level consistent with the output desired, and i can see how a larger diameter and more pole groups using 3 phase would increase the resistance, but it would appear to me by increasing the phase count we can then keep the resistance much lower.  hugh has built 5 phase machines, i have two 6 phase machines and can see no reason why we can't have 12 phases or more.  we just need to rectify them all separately of course and then group them for combined output.

a dc generator with brushes and commutator actually has effectively far more than 3 phase groups on the armature, even though there may be no more than 2 or 4 field poles.

so we could for the sake of  discussion have 12 phases on a 24inch machine, and have maybe 12 poles on the rotor. we could fit the rotors 12 poles with magnets, and also mount another 12 wire wound field poles between the magnet poles.

in doing so we could have a machine that might make some useful power in low speeds using magnets alone, running at X frequency, and then switch in the wound field poles to effectively go to 2X frequency. this presumably would be in higher winds where there is more power available, which would allow for the power required for the field poles.  we could then have a certain amount of control over the power of the machine, actually we might be able to have full control if we used a buck control of the field wherein the wound fields would counter the magnet poles, and in doing so reduce the machines output when the need for power is lower.

*for the record
this is a theoretical discussion of what is possible, not something that i am claiming as new, better than, worse than, or even desirable or useful.  as Flux has stated there really is nothing new in the generator game other than materials used. every possible configuration has been tried, proven and used by the late 1880's including the air core axial machines.

kicking the ball back to center court
bob g

[David HK]

Bob,

Why does neo cost seem to be a point of concern?  With my wind turbines I build them out of materials so that they will last for a minimum of 50 years.

My neos were specially made in Shanghai and air-freighted to Hong Kong (Yes, it can be done with a clever insulation technique).  They were made to a size specification which included recesses for fixing bolts - I can put up a photo for those interested.

Surely the way to go with wind turbines is long life materials, high quality engineering, attention to detail in every way, good weather proofing of all parts and so on.

David in HK

[bob g]

David

i didn't bring up this topic for any other reason than maybe its time to revisit and consider other designs.

here in the states, quality neo's are quite expensive, relatively speaking.
folks are starting to look back on gear drive step up, beit chain or whatever.
folks are looking to mppt controllers,

i might add it was not that long ago that if one were to bring up the idea of a chain drive transmission he would have been summarily dismissed as "we tried all that before and it was a failure" never mind they used bicycle components and cobbed together a piece of crap to start with.

it wasn't but about 10 years ago,  that the idea of using anything like electronic control of the generator output, let alone mppt was met by strong resistance. "we don't want any complexity" "kiss was all the rage" and folks built machines that were so heavily clamped to what was typically a 12volt battery it is a real wonder more of them didn't go up in flames in higher winds.

i only bring this up for discussion at this time.

i mention these things because i was there asking about the others (load matching via electronics and alternate designs) long ago.  and yes i was met with all sorts of reticence at the time.

so i expect a lot of resistance now too.

folks don't like change, and generally will not change unless they have a very compelling reason to do so.  i figure this holds true with wind generator design in spades!

having said that, we should be able to at least discuss the relative merits, pitfalls and perhaps learn something in the process. otherwise we keep doing the same thing? when it is possible that there might be another way that might be better in some cases?

how do we know if we don't at least think about it, talk about it, and maybe approach the discussion with an open mind?

just a thought

bob g

[ChrisOlson]

we can go with more poles, so why are we locked in a 3phase design, when more phases could make better use of the increase in pole count and in doing so keep the resistance down to an acceptable level.  what do we need to do this? more diodes?

You will find that with ferrite magnets and increase in the number of phases in a stator with non-overlapped coils means less coils in series and it's harder to get the required voltage with the weak flux in the air gap.  The "rim speed" will not make any difference.  It's rps, rpm, or angular speed that is the deciding factor in speed, and how much voltage you'll get.

In addition, with large diameters, ferrite magnet rotors are very, very heavy, and axial runout becomes critical because wide air gaps are not tolerated by ferrite magnets.  This is a little 11" diameter center rotor for one of my dual stator ferrite generators, and it weighs 22 lbs



I can build the above rotor using .250" steel.  At 16" you'll need .375" thickness.  At 24" you'll need to use 1/2" thick steel.  A single bare generator rotor, without magnets, will weigh 65 lbs.  A 24" rotor will fit 30 poles, meaning each generator rotor will weigh approximately 90 lbs - for a generator suitable for a 12 foot turbine that will barely develop 2 kW.

Weight and size is a very real issue.

Edit:
Providing another photo to put some of this in perspective.  The above pictured rotor is for a dual stator generator that runs at 685 rpm at 1.2 kW continuous power output on a 24 volt system.  It will develop a peak of 1,800 watts at 750 rpm.

This below photo is for a single stator ferrite generator, designed for MPPT, that produces 3.0 kW @ 1,200 rpm and peak 4.2 kW @ 1,500 rpm.  It is right on 90% power efficient at 3.0 kW output.  It is 13.8" in diameter and also weighs 22 lbs.



You can count the number of poles there, calculate your "rim speed", or whatever, and see what you can come up with using those examples as guidelines to build a direct drive design.

And this is the stator for the 3.0 kW MPPT generator:



You can see there's a fair amount of room between coils in the stator.  The limiting factor here in reducing the diameter is the size of the magnets.  The first versions of these that I built were wye configuration and ran at 1,000 rpm.  They were in the low 80's for power efficiency.  I used more turns of smaller wire in them with delta configuration, reducing the stator resistance to less than .3 ohm, and increased the rated speed to 1,200 rpm to get 90% power efficiency.

Hope that helps.
--
Chris

[opo]

I think it will be very difficult to obtain a significant improvement to the current available axial flux design. If magnets are getting expensive, then the only way out I see so far is to use smaller magnets of the same grade and come up with a way of concentrating the flux and get about the same results as the built and tested machines. But I have no idea on how to achieve this.

Octavio

[bob g]

ok guys, it has taken me a bit to see your side of the argument

i am asserting that the rim speed of a 24 inch machine is twice that  of a 12 inch machine, and i think we all agree on that.

i am further asserting that the voltage generated in the 24 inch machines pole coil will be theoretically twice that of the 12 inch machine,  this is where we part company

the opposing sides states there will be no difference in the generated voltage, because diameter has no place in the equation, only rpm.

so it occurred to me that if we assume the use of the same magnet and the same pole/coil to be used in both machines, the dead time between poles of the rotor passing in the 24 inch machine offsets the gains over the 12 inch machine,,,, and i generally accept that. however

just because we don't properly utilize the space between the poles in the larger machine does not negate the assertion that the rim speed is higher.

rim speed or peripheral velocity does have a function in the equation, the voltage will be higher in the pole, but because we do not properly use the spaces between these pulses we see no appreciable gains with each revolution,, both machines will produce about the same mean/average voltage.

where the larger diameter starts to make sense is if we increase the pole count by double, if the 12 inch machine is 6 pole then the 24inch machine can fit the same size stator pole coils to make a 12 pole machine. we can do this without changes to the rotor pole count.
(i use 6 and 12 pole as an example only)

the end result is we utilize the added space afforded by the increase in diameter, with the result being elimination of the dead zone between the 6 pole version of the 24inch machine.  in doing so we double the output of the machine, and the reality then is we also gain the increased voltage generated by virtue of the increase peripheral velocity of the larger rotor.

having fun yet?
bob g

 

[ChrisOlson]

Bob, now you're starting to get the idea.  Notice that I'm running my little generator at 160 Hz and the stator resistance below .3 ohm (actual spec is .28) to get 90% power efficiency at 3.0 kW.

To build a direct drive of similar performance you will have to use those numbers and basically match them to get it.  There is no mysterious or "secret" thing you can do.  It's all about frequency and internal stator resistance when dealing with these weak (but cheap) 2 x 2 x 1" thick ferrite magnets.  For a 12 foot turbine that can maybe run up to 350 rpm that means using 54 poles in a direct drive design.  This means your generator rotors are going to be 39" in diameter.

Now, try to get the stator resistance down below .3 ohm with a 54 pole 39" diameter generator.

The virtues of small size and speed should start to become evident.
--
Chris

[bob g]

Chris

just out of idle curiosity

how did you determine the efficiency @90%?

i know how i determine efficiency, but am always up to see how others do it.

thanks
bob g

[ChrisOlson]

By measuring stator resistance with my DLRO and calculating dissipated I²R power using actual measured full rated load output (amps).  Efficiency is actual output divided by the sum of actual plus dissipated power.
--
Chris

[Frank S]

    I know this will not be well received and I will probably be dismissed as  a rambling buffoon but so be-it
With the exception of a few folks on the back-shed almost everyone on most of the forums that I have visited use the homebrew axial design. I tout this as probably being one of the most simplistic ways for someone without certain skills or access to facilities which would allow the radial approach to be looked at. And there is nothing wrong with that. This approach allows many more who want to actually build something with their own hands to get into the game,
 But why not step a little outside of the box and look at radial so far as I know not one of the Power generation generator manufactures build an axial machine for commercial or industrial use
  It also reminds me of 2 science projects done by my youngest daughter when she was in the 5th & 6th grades respectfully, her gr5 project was crude but well made with lots of hand wound coils made out of several different materials for the wire IE iron brass copper aluminum Silver & gold YES I said gold 1/2 oz or 24ct 24AWG to be exact. Any way she did 95% of all of the work to construct her project even made her own multi meter from a radio shack kit. Her project went all the way to the State level and placed 2nd but only placed 10th at the National level.
 For her 6th grade project it was an expansion of the same only by now she had learned how to weld a little and could operate a lathe & a Bridgeport mill so this project was 100 times more refined.
 Near perfect machine wound coils machined acrylic fixtures machined & polished cores weight equalized to the 10th of a gram on a triple beam scale she added a vacuum vessel and used the same multi meter the same steel ball bearings for weights all in all the project did look more like it was done on the High school or fist year college level of expertise BUT that was where the problem started. Her project was too refined even though again she had done virtually everything on her own I only intervened on safety issues  Her documentation fully explained each and every step she went through for construction in her own hand writing not typed and remember this was in the early 80s so no computers or anything like that She did great at her school level but was not allowed to compete any further because of being what they called too advanced for a 6th grader.
 We have here a group of guys who have some skills that would make those at NASA look like idiots.
 Some have explained the functions of generators and electronics to the most detailed limits of imagination way beyond limits of the comprehension of some and yet when someone brings up the topic of alternate possibilities the attack is on
 When Chris O brings up his methods and experimentation's of how he produces his energy he is attacked once in a while.
 When Flux says something even with his knowledge he gets attacked
 Oztules gets attacked, Fabricator gets attacked, Bob G gets attacked, I've even read attacks on Hugh Piggott and Ghurd  Yes I failed to mention many others  my point is we all get attacked for our thoughts .
 I apologize if posting your names offend anyone note I only chose those who have experiences and skills and could not include everyone with experiences who have been one time or another attacked.
 I do a lot of designing that will never be built simply because during a design I may post a few of my thoughts or concepts then during my research I will venture down 100s of avenues using or drawing on the 1000 years of combined experiences on this and many other boards  combining their formulas along with those  formulas from 100s of books & white pages when I hit the proverbial  wall I look to see if someone has found a door, if none has been found can I cut one and pass through or do I need to go around and peruse another venture, and toss what I was attempting before actually wasting the effort to build something that is not going to work according to what others have done 100s of times in the past.
 But most importantly I like to try and find out the why it didn't work before redirecting my approach
 For this reason I am glad this thread was started if for nothing else the amalgamation of different designs or concepts might be looked at
 Now end of Hijack and back to our regularly scheduled programing

[David HK]

Frank,

You're no different from the rest of us and much of your text has a very sound basis.

Without wishing to branch off too much, the following URL leads to a very interesting website that will easily consume an hour or more of any ones time and may trigger some thoughts on water motors, turbines and all sorts of interesting things to read about on a wet cold Saturday evening.

Pay attention to Power Generation >>>>   http://www.aqpl43.dsl.pipex.com/MUSEUM/museum.htm

David in Hong Kong

[Flux]

Frank

In the very early days of electrcity radial and axial designs were tried and probably in equal numbers. The first alternators were permanent magnet but magnet technology was virtually non exixtent. Much early work was on alternators for lighthouses and De Meritens, Holms and others used both axial and radial flux machines.

It soon became obvious that with the magnets of that period the way forward was with electro magnets and designs continued in axial and radial form. The major snag with an electromagnet is that a lot of exciting current is needed to produce flux in an air gap, the smaller the gap the better, but the original winding methods needed large gaps to contain the coils.

The thing that changed the design tactics for about 100 years was the introduction of slotted cores and this enabled the air gap to be reduced to a few mm ( or less in small machines).

The problems of a slotted core for an axial machine were severe so the logic was to revert to radial designs which are easier to make and to wind. When things progressed to polyphase machines the radial was very much easier to wind .

Nothing really changed until the introduction of neo magnets. These can produce flux densities equal to or greater than electromagnets in very considerable air gaps. Commercial engineering was slow to change as the slotted core radial machine could do all that was needed cheaply and the design was well established.

It was probably John Fawkes of Marlec and Hugh Piggott who really saw the advantage of air gap alternators for wind power.

Once you get rid of the slotted iron core it makes little difference whether you make it axial or radial except for winding multiphase machines where overlapped coils are tricky with axial. Hugh solved this by leaving out enough coils to fit the remainder in a single layer. For home construction the axial design is easier and it is more forgiving in that if you get the design wrong you can easily change the gap flux by altering the air gap.

Some commercial designs have adopted the axial design ( Marlec being the original pioneer). Commercial small wind turbine manufacturers have ternded to stick to tried and tested designs with slotted iron cores and this provides the cheapest machine and uses less magnet material. There has been some departure from slotted cores with iron loss and cogging, how much this will change will depend largely on the cost of neo.

There is no harm in looking at radial designs, simplicity for the home constructor is not the only consideration.  Personally I prefer a radial design with smooth iron core, magnets on an outer drum and windings stuck to the iron core.  With neo I don't see any advantage for a slotted core with all the problems it causes.

Without neo we can probably find justification to reverting back to slotted cores to make up for the low flux density of ferrite. We then get back to what Hugh was doing in  the AWP days and I think that is the best you can do without adopting a speed increase.

Since the coming of neo it forced me and some others to come up with the electronic converter idea to let the alternator volts  rise with wind speed and now we have this technology it also should help solve some of the problems of the low flux slotted iron cored machine such as reactance limiting and high I^2R loss.

I hope this puts things in perspective. What has changed in the last 150 years is magnets and electronics, nothing new has ever been done in the other patrts of alternator development. ( even the torus goes back over 100 years but only Proven seem to have done anything with it).

Flux

[bob g]

just to make my intentions clear

i am not presenting these idea's as anything that is new, quite the contrary as Flux states there is nothing new that has not been done well over 100 years ago.

all i am presenting here is taking a look at modifying an approach a bit, or at least taking a look at it.

as for attacks, i figure it like this, a certain amount of argument is a good thing, otherwise we get to discuss every crackpot idea that comes down the pike. and do it over and over again.

i don't know about other folks, but i have a pretty thick skin when it comes to arguing a position or discussion of an idea.  i figure it like this, i am not married to an idea or concept, nor should anyone else be. when one becomes married to an idea or concept he effectively has stopped growing or learning and will never know of other ways of accomplishing things, be they better or worse and maybe most important "why".

Chris

have you tested one of your machines to determine efficiency via power in vs power out? and do you account for rectifier losses, or changes in resistance due to heating of the stator, drag, windage or frictional losses?  and shouldn't you include transmission losses in your efficiency number, as you are using a chain drive to get to the output numbers or capability of the machine?

the reason i ask is i have to account for drive losses, windage losses, frictional  losses, copper and iron losses, excitation, rectifier and a plethora of other losses. i do this by measuring the power in vs power output of the machine as measure in btu's to arrive at 80% efficiency.

bob g

[oztules]

Ok Bob,
I will approach this a bit differently.

We can measure the voltage from the power point, and the voltage meter will say 240vac... thats fairly obvious for a 240v system  this country runs. (Aust)
If we look at the oscilloscope, we can see that it is not a 240v pulse at all, but instead rises from zero  up to 320v and back to zero, but the meter said 240vac??

If we look at a square wave 240vac with an ac meter, it will say 240vac. The oscilloscope will  see that we start at zero, rise instantly to 240v and then drop to zero instantly again at the end of the time span  (note the time for each wave covers 1/100th second for both/all of this discussion.)
The meter is correct in both cases, even though one had a peak voltage of 320v, and the other was 240 peak.

It is the area under the curve that was the same in both instances, even though the peaks were different.

Doubling the diameter and so doubling the speed with the same magnets and coils that the smaller diameter one had, carries the same lesson.
The skinny high peaks of the big diameter and the smaller fatter peaks of the smaller diameter both have the same area under their respective wave form curves..

So we can say there is no difference.
Well no...
In practice there is a difference, and you may recall somewhere recently, Flux said there was a  diameter that  was ideal, and others that weren't.
space is one reason, overlapping flux is another , and both these should be better in the larger diameter... and they are..... but......

Think of the skinny high peak waveform, where the peak was higher the ohms law comes to kick you in the butt.... If your coil R is the same in both instances, but your peak EMF is higher, then Voltage loss in the same coil is higher.... ie I=E/R, so if E is higher, then I is higher for the same rpms with the larger stator.... worse the losses in that coil will be I^2xR...so that  makes it worse still.

So now we can say that the losses in the bigger diameter machine will necessarily be higher than the lower voltage spread over a longer angular interval... because the peak currents are lower through the same resistance.... we lose.... but fun while it lasted.

If we fill in the gaps symmetrically to make twice the size machine, then thats a new machine entirely.

Now:
"*for the record
this is a theoretical discussion of what is possible, not something that i am claiming as new, better than, worse than, or even desirable or useful.  as Flux has stated there really is nothing new in the generator game other than materials used. every possible configuration has been tried, proven and used by the late 1880's including the air core axial machines.

kicking the ball back to center court"

Matching the load is the goal, and we need to match the impedance of the air to the impedance of the battery. This involves a mill with blades, an alternator and a basically fixed impedance battery.

The basic mill tries to match the variable impedance of the air, to the variable impedance of the alternator to the fixed battery.

We can fiddle with blades, blade size, wire, magnets, mill diameter, resistance in the line, black boxes, star delta switching, transformer tapping, high leakage transformer coupling, direct coupling and the list goes on.

The fun thing about mills, is that it HAS to be built with an eye to everything. The moment we try to optomise any part, we alter some other parts.

Folks like Chris optimised the resistance in his alternator. He did this with higher speed, which allowed his resistance to be very very low.... but this makes it virtually unusable for direct coupling, so  black box is needed to match back up all the mismatch imposed by the low resistance.... if he had zero resistance, and no black box, it would never go beyond cut in.

We can use higher resistance stators, and get good low wind performance, but the high winds burn them up... unless we can use a black box, or cool it, or star delta it perhaps... of furl early.

There are other tricks that can be used which you would have seen in your bigger alternators. An automatic star/delta machine can be made with the addition of 2 more diodes, so that when the losses in the star configuration  rise to around 40%, it will use the extra two diodes (from the star point to the + and - outputs, and this will convert the star to delta with no switching..... but then we hit an impedance mismatch because our stator resistance drops to a third of what it was.

You will have seen this when you open a 100A plus alternator... and find 8 diodes in the diode block, not 6.

So next we open the gap to stop stalling, but this degrades the alternator at the same time, or we could add resistance to the line,  we miss out on some power, but take some heat out of the stator, and allow the blades to run better.

We can get out of some of this by upping the voltage and poles,  and using a transformer.... this can be quite cunning, as we can tap change with triacs, and we can wind the transformer to emulate a battery charging transformer by making loose coupling with plenty of leakage, this will help match the prop to the air, and shift the heat out of the stator to some extent, and if the mill has an iron core (motor conversion, radial iron core (AWP, F&P etc)), we can mitigate some of the effects of armature reaction, and match the loads much better.

In fact we could emulate a full blown mppt with a jump table,lower leakage transformer and a bunch of taps and triacs if we were keen, and liked rats nests.

What I'm getting at is we can get hung up on alternator design. If we build an mppt (analogue or digital whatever), we can use virtually any old thing and match the load to the air.... then it's simply a matter of how powerful we want..... general rule ... for a fixed rpm, bigger is betterer for more power. More rpm (speed increaser makes them smaller again)..... back to angular velocity I guess for fixed flux.

Things that get lost from time to time.....
Every turn of wire in the coil has it's own vectors with relation to the field changing in it's vicinity. All those vectors add up to the final emf in that coil at any time in the cycle.... in fact at top dead center, the total emf vectors add to zero.

With axials, the legs are not points, but spread across an area... all seeing the flux differently. So magnet size, leg width, hole diameter, coil height, area, magnet spacing all effect the outcome.....and the list goes on.... the only thing we need not worry with is the armature reactance. The synchronous impedance will be pretty close to resistance for our purposes.... and we know we need some resistance so the voltage can rise in the coils so the prop wont be in hard stall from the get go... or mppt.

We should know or be told....... that we cannot design an alternator on it's own. It is part of a symphony. All things must be taken into account if we don't use mppt, but we can build a darn good machine without it to.... but then it has to be part of a team.... not a solo player. Mppt takes the skill out of windmill design.

Personally, as an owner/builder of a few quite powerful axials, and a not so innocent bystander to a radial flux machine, now (hindsight is cool isn't it) I would want an iron cored radial any day of the week, even with (and I WANT) oodles of armature reaction (Flux rolls eyes).... and ferrite magnets (eyes roll again).

Still the best, toughest by far, bullet proof home powering mill I have been in contact with is the AWP HV transformer coupled unit with the rewind we did for it.

That thing is fairly well matched, and burn out proof (thanks to the reaction component)... and the magnets don't degrade either

End waffle

..................oztules

Edit:

I just can't get excited with efficiency when I'm not paying the bill for the wind.
Stator efficiency  for finding the watts lost for the sake of heating I have to be interested in.
System efficiency pales into insignificance compared to matching the items to the wind.
Paying for fuel makes it a whole different ball game.
   

[bob g]

Oz
thanks for the input

to add a bit more and to explain maybe a bit better my motivation for asking questions

things like efficiency come up in the ongoing discussion, and i will ask questions regarding same, realizing of course efficiency might have little to do with the topic at hand. however ...

this is part of my learning process, which is ongoing as it should be. i often learn more from the journey than i ever will from the destination.

just as one would likely learn to weld, use a plane, and use epoxies in making a mill, they are all ancillary to the design discussion.

sometimes there are little things that might not apply in a particular discussion, but turn out to be a significant puzzle piece to some totally unrelated topic sometime down the road.

if you know what i mean.

i asked Chris about how he calculated efficiency, not because i am particularly worried about the efficiency of an alternator, i just was interested in how he came to his conclusion and the process.

i also understand your assessment, and it is not only valid but a good one, that we ought not get all caught up in a single facet of a multifaceted problem. windpower is certainly a multifaceted problem, where a total system view should be the prevailing concern. this would include all the compromises that must be considered.

as you so well stated, getting caught up in one area of concern to the exclusion of all others is likely to be the wrong road to travel when it comes to wind power.

having said that, i don't want to do that, nor would i support anyone else doing so.

this discussion is one of theory generally, which i tried to be upfront about in the original posting.  realizing of course most folks aren't heavy into theory and avoid its discussion to a very large degree. some folks actually get all pissed off when such a discussion comes up, and i am not sure why, but i accept the reality and deal with it as best as i can.

it takes all sorts to make the world go round.

sometimes i wonder if hugh's development and promotion of the axial air core alternator would have been so widely accepted so quickly had he been just another joe schmo on the forum, rather than a man that had considerable experience and an almost cult following preceding him.

i wonder had he been just another guy with an idea or theory that was somewhat radical compared to what everyone was doing in the diy wind game, what the discussions might have been on the forums? my bet is he would have been met with stiff resistance.

i also wonder how folks would respond to him now if he were to post some theoretical discussion on the forum's, would folks be so bold as to confront his questions and assertions? 

i would hope so!

thanks guys, i appreciate everyone's comments

bob g

[Frank S]

thank you Flux that is what I was hoping someone would confirm for me.
 Bob G; I find myself off in a field so far away from the accepted norm so much of the time that at times I can only enjoy a good discussion based on theoretical impracticality
 
OZ; When the subject of large diameter came up I started thinking only of radial I've looked at the various large axial generators and could quickly see what someone said a long time ago they simply do not scale up beyond certain sizes very well.
 but a radial design you could in theory construct one to reach right around the equator admittedly it would be a nightmare to decide how many phases or series of coils per phase but the possibility is still there and the technology to construct it does exist although it might take several years of the total GDP to build it even though the planet is rotating it would still have to be considered the stater but the rotor would only have to rotate about .01% slower to produce an obscene amount of power
 Yes I can think of the ridiculous 

[Flux]

I think Oz has summed the whole thing up extremely well.

Other factors affect things just as much as the alternator.

Your wind regime and what you want the power for is also a big factor. In a high wind area efficiency as such is of little importance and worrying about 5W on a low wind day probably doesn't matter.  On another site those 5W could be the difference between managing or running a generator.

With free fuel true efficiency matters little as long as you have enough power and the thing survives and this largely accounts for the different attitudes to design. The stalled neo axial machine does a good job in low winds and in high winds most people have full batteries and don't seem bothered. Others will find ways to use every available watt and use every load available rather than dump from a full battery, it is here that better results in high matter.

As always an interesting discussion and it is good to revie things as ideas and technologies change.

Flux

[ChrisOlson]

sometimes i wonder if hugh's development and promotion of the axial air core alternator would have been so widely accepted so quickly had he been just another joe schmo on the forum, rather than a man that had considerable experience and an almost cult following preceding him.

It's hard to say.  I like the air core axial because the faster you turn one the more power it makes - and never "kicks back" with any core reactance.  Oz likes the core reactance because he feels it makes the venerable radial design "burn out proof" (which it really doesn't - I've seen plenty of burned up radial iron core generators).

The air core axial can be built to be incredibly efficient, has zero cogging problems because there's nothing in the core for poles to be attracted to - the only "bad" thing about it is that it makes relatively poor use of magnetic material.  And that's why (outside of Gordon Proven's designs) it was never adopted in the commercial generator world.  For wind turbines where zero cogging and zero core losses are desirable, especially for lower wind speed performance, it's a natural match.
--
Chris

[oztules]

"Oz likes the core reactance because he feels it makes the venerable radial design "burn out proof" (which it really doesn't - I've seen plenty of burned up radial iron core generators).
"

It really does if it is designed to do so.
The AWP using ferrites can run all day short circuit, and still be perfectly happy. The F&P can run short all day, no damage or any sign of damage.

It all comes down to design. If the back MMF is focused by the laminations, and the magnets are just ferrites, there is a big chance the amp turns in the coils will repel the magnetising field to current limit at a temperature that is non-destructive.

The ones you have seen burnt up likely used neo's to squeeze out a bit more LV current. It is very much harder to get enough amp turns to repel the magnetising field enough to keep the temp in check against powerful fields..... It will still current limit somewhere, but it may be still destructive.

Thats why I like the HV stuff, the current is very low .. only a few amps in the AWP for 1kw, and it limits at around the 5A -6A mark. Not earth shattering current, but at 500volts, it does not need much current to develop the power required. When it current limits, this one puts out around 2000W. I rewound the 90 coils so it is a bit different to the normal ones, they would limit at around 1.5kw..... just need the blades to be held on well!... it is no stall machine, it runs free.

The synchronous impedance is nothing like the resistance in this instance, and resistance has  very much less effect on calculating the performance of this stator, whereas resistance pretty much defines yours. In the AWP etc, the impedance of the stator is not just resistance, so you can't calculate the losses the same way.
If you drive voltage through a resistance, you can work out the watts lost, the current present and all is fine, with reactances.... lemme see...OK... try this...

If you measure the input to your welder, it may be a few ohms (or less). If you calculated as you do for your mill windings it would look like this.
V=240, R=2.... so current in the winding is =V/R or 240/2 or 110 amps at 240 v.......... clearly this does not happen.
So are all your results  wrong??

No not really, but your problem is not having to take in the effects of impedance. Here that will be a function of the cross sectional area of the laminations, the frequency, and the turns.... and we find the welder with no load is only drawing magnetising current, not 110 amps and is closer to 3-4A Your air coils are so low inductance, that they don't count even at the much higher frequencies your using compared to the 60 hz welder.

Can you see the difference now?

It is all about matching components. Just because it's commercial, does not mean they were all designing for the same outcome.

I had hopes that your experiments with the ferrites would give us some protection via the armature reactance, but due to the coils not being able to focus the back mmf, I could see no real current limiting benefit other than it would naturally match a bit better than the stiffer neo's....

I do like the core reactance, as you can design around it to some extent, and have a very robust performer... not too different to your units, but with smaller ferrites, much less copper, and direct drive, and no real power electronics.

We can't just look at the alternator and go for raw power, most times we need to look at the system to get the desired result.... or go raw power and mppt.


We need to look at the whole package and how the limitations are imposed, how we circumvent some, and live with others...it's not simple if we dont go mppt.


...............oztules

[ChrisOlson]

Can you see the difference now?

Yes, I actually already knew the difference.  And you can do the same thing with an axial.  I short circuited tested a ferrite generator being driven by a hydraulic motor and it proved to be "burn out proof" as well.  So there is some bending of flux that takes place even in an air core.

The iron core radials that I've seen burn have mostly been Chinese built ones with a neo rotor.  But I have also seen some of the old Whisper 1000 and Whirlwind turbines burn out stators.  And they had ferrite rotors.

But typically, with axials, the resistance has to get very very high (like short circuit) before they will exhibit reactance type tendencies.  Otherwise pretty much the faster you spin them the more power they make (up to the temperature limit of the winding).
--
Chris

[fabricator]

I've always ascribed to the "Efficiency? Who cares" school, the wind is free, the parts to build an alternator and a tower to put it on are not free, but if you build anything close to a Dans design or a Piggot design or an Olson design and pair it up to mppt efficiency really don't mean squat.

[DamonHD]

Where 'efficiency' may matter is where you don't have a lot of space and are restricted in the size of equipment you can put up; more likely in terms of roof space for solar on a small plot like mine, but could show up as a limit turbine height and diameter too.  Thus you care about efficiency per unit area of your ground space...

But I general I agree with you, the fuel is free.

Rgds

Damon

[bob g]

to me efficiency matters

it matters as a function of size, of weight and of cost.

it all depends on ones perspective and design philosophy i suppose.

bob g

[Frank S]

When I hear a lot of talk about efficiency, what I am mostly hearing is only 1 aspect, when the talk is about AE/ RE it's the output
The output is not the all-powerful end all to end all result of a machine. It is merely a byproduct
Far too often in a wind generator the factors get turned upside down trying to squeeze the last joule of available energy out of a given design at the expense of longevity and serviceability.
Simplicity cost and weight are large contributors to poor overall design; Cost being the worst of the 3
Things do not have to be overly simple to function perfectly well nor do they need be extremely complicated. Too often a generator is constructed ‘TOO' simple only to require a higher complexity of electronics on the other end. Conversely the mechanicals can become so complex in an effort to simplify the electronics weight drives up the cost un-necessarily. Over simplification also drives up the cost of the electronics as well
 AS far as weight goes to me that is only something to be concerned with when there is so much of it that the ground supporting it cannot hold it upright for a given sized machine that is, obviously one would not chose to have a generator weighing 10,000 LBs that is only going to produce enough energy to charge a couple of batteries.
 I would by far rather have a generator that weighed 1000 LBS capable of turning out a continuous 4KW with a 12KW spike overload running in 15 to 20 MPH winds @ 40 to 45 & efficiency, if it was going to provide trouble free service for 40 years running with minimal electronics. Than a 150 LB machine that may be capable of churning out 4KW @ 94% efficiency, in perfect conditions with complex electronics, if I was going to have to service or preform almost daily tweaks to keep it from damaging something
If I have a large enough machine or machines to handle whatever I could throw at it/them, and am in a good wind area I would not be the least bit interested in a huge storage But I would want my machine to produce Stable line voltage for use the Inverters supplying power from the bank would only be for emergency backup and slight momentary overloads
 What I would be or am thinking of is  20 to 35 KW with 3ph 415v output  I have virtually zero use for split ph 120 but should I require it it is easy enough to step down
 When I set up my bank it will be 48v or higher and would almost be tempted to use one or more scavenged systems out of a Toyota Prius with its 288v nominal
http://toyotapriusbattery.com/

[fabricator]

You need to buy a grid tied Jake and a good inverter/charger to keep your batteries charged to run critical loads during an outage, I think Chris has an extra one laying around.