Efficiency

[Devo]

I am still a little confused on getting the best efficiency from a given prop.

I have a 5 foot prop with a single rotor 8 inches across & 8 1 x 2 x 1/2" neo's.

It works fine but my brother has given me a big steel disk & I haver more neo's so I kinda wanted to try this as a test but I thought I would ask the question first.

My cut in is around 300 rpm if I was to go with 20 mags on a single rotor or 2 8" disks (dual rotor) & used alot less wire keeping the same cut in & same thickness of wire would I end up with a prop that worked the same but put more of the energy into the batteries & less into heat or would it stall the prop? basically I want to run the same but convert as much of the energy produced from 10 to 18 mph winds into usable energy as possible.

(when one project comes to a stand still I work on another)......

Devo  

 

[Flux]

I am not surprised you are confused, it is a very complicated issue.

If it is working well now it is likely that the proposed changes will cause the prop to stall and although you will end up with considerably higher electrical efficiency you may capture less power.

Using 20 magnets on a single rotor or 16 on a dual rotor would seriously stall your blades for the same cut in speed.

Much depends on the tsr of your prop, if it is near 6 then cut in at 300 rpm is reasonable and what you have is likely to be a good match.

If you want best results in 10 to 18 mph winds, then if you are cutting in much below 10 mph your alternator is likely too slOW. If the prop starts to run away at 20 mph your alternator could be more powerful.

Unless you have wind speed and alternator speed measurements you really will not be able to make many decisions.

With the 20 magnet single rotor or the 16 magnet dual rotor you will seriously stall a 5 ft prop with cut in at 300 rpm. It would result in negligible increase in power and would be a waste of magnets.

Unless you are prepared to go to a larger prop then I wouldn't use more magnets.

By adding a second rotating disc with no magnets you can make the existing alternator more powerful and it will likely be a good match to a 5 ft prop.

I have done this on a machine with a 5'6" prop, set to cut in at about 6 mph for a very low wind area where it has to be silent.

If I halved the turns to raise the cut in speed to 10 mph it would run well clear of stall, be slightly noisy and produce far more power at 18 mph, with the tsr5 blades.

At present it operates best at wind speeds around 10 to 12 mph. If I forgot about wind speeds below 10 mph then it would be optimum at about 16 mph and that is the band you are looking for.

If you want more help I need prop details and winding details, but my advice is not use more magnets with the 5 ft prop. You may benefit from an extra magnet disc and a rewind.

If you want to use the 20 magnets to best effect put them on a single disc with a

rotating second plate and it will likely match a 10 ft prop over your desired wind speed range.

8 pole dual rotor should match about 8ft under those wind conditions.

Don't waste the magnets on the 5 ft machine and spoil its performance.

Flux

[finnsawyer]

If you want to experiment with the larger disk (how large is it?), you could try my alternator design as outlined in my diary.  It uses fewer magnets and more coils.  You could make an 18 coil 12 magnet version or a 12 coil 8 magnet version, for instance.  With the larger rotor one should also get a lower cut-in RPM for the same number of magnets.  But figure you need about a 16 inch diameter rotor for 8 magnets with my design.    

[whatsnext]

Have you or anyone else built an alternator with your design yet? Just wondering.

[finnsawyer]

Not as far as I know.  At this point I don't have the time to do it.  I am a bit taken aback by the conservatism I see displayed on this site.  Back in the seventies people were eager to try new ideas.  Not so anymore.  It seems to have become a "cookie cutter" world as far as wind power is concerned.  Doesn't speak well for the American spirit or the future of our nation.  I can't even engage anyone (and there are some fine minds out there) in a meaningful discussion of the merits of the idea.  I have indicated some of my insights about alternator design in my comments since posting the diary.  Someday I will update the diary.

[TomW]

fin;

 I am a bit taken aback by the conservatism I see displayed on this site.

I think it is more trying to steer folks away from expensive mistakes and pushing known functional designs.

It would be unfair to just say "yeah, sure, try that" when it is relatively obvious it will be a failure. I don't do any building myself for several reasons but there are many things in the past I wish someone had pointed out the flaws in how I did them.

Plus not everyone is Alexander Graham Bell or Nikola Tesla. Even they failed many times before success happened.

Look back thru this site and you will see literally hundreds of silly, unworkable ideas and then look at how few of them ever reported any followup data, good or bad.

Anyway, we can simply agree to disagree but I call it as I see it. Sometimes just the way things are presented and the questions asked give a poor impression on the persons ability to think logically thru problems.

Say someone proclaims they are building a 30 foot unit and in the same post ask about glue types and how to work wood. I do not want him building within sight of my space. Same person may also make a note on how they "just learned" how to weld. Ditto the not near me please attitude.

Just an opinion.

T

[whatsnext]

Funny how none of us has any spirit when he's the one who won't even build his own mill. How hard would it be for him to spend his time and then brag about the results. He doesn't have to fly it, just build the PMA and spin it with a model T or something.

John...

[dinges]

"Back in the seventies people were eager to try new ideas.  Not so anymore.  It seems to have become a "cookie cutter" world as far as wind power is concerned.  Doesn't speak well for the American spirit or the future of our nation.".

But, but but...?

You aren't eager to try your revolutionary idea?

not so anymore, indeed.

a cookie cutter world indeed.

Doesn't speak well for the American spirit indeed.

So, put your money where your mouth is: build the design! That's what the Teslas and Edisons of this world did.

And yes, I know you are a very busy man without time to build it. So am I.

Before you start recommending your untested design to others, it would be fair to back it up by hard evidence that it works. Or, if you haven't got that, at least point that out when you recommend your design. And NOT after someone else asks whether your design actually works.... Doesn't reflect well upon the credibility of the person giving the advice.

To me, your generator reminded me of homeopathy: the less of everything, the better. Less magnet, less copper. I don't think it'll work very well. Oh sure, it'll generate SOME volts and watts, no doubt. It's hard to build something which doesn't when you throw in copper wire & magnets together.

But, I've been known to be wrong. And I'd love to be proven wrong. Keeps me sharp & modest. I need that.

But if you don't test out your ideas & theories (which, at the moment, they are. No more, no less), then don't recommend it, untested, to anyone to build. Or at the least, point out that your design is as yet untested. To me, that's only fair to anyone contemplating to build your design.

Just my opinion. But one I value highly.

And as far as conservatism goes: yep, that's me. Belts and braces for security. Politically in favour of the smallest state possible. Economically, same thing. Can't stand self-proclaimed progressive people or ideas. It's the same thing in science: you prove your ideas, or we won't believe you. And it's THAT (free entrepreneurial spirit; little gov't interference; scientific progression & testing) which causes progress.

NOT the barfing out of ideas.

</rant>

[finnsawyer]

I am sure you are quite well aware of the intricacies of Faraday's law.  Start with that when critiquing the idea.  As far as less of everything, that is not true.  You start with the same number of magnets, double the number of coils, and use a larger rotor.  That sounds like more to me.  As usual, it turns out to be a matter of inability to think outside the box.  Nor do I think one should not advance new ideas here.  The modern magnets and solid state devices made possible the 3/4 alternator design that everyone uses.  They also make possible the design that I have advanced (the 3/2).  Like any design it will have its trade offs.  One plus might be a lower cut-in RPM, a negative might be a higher resistance.  It will take a substantial effort (many trials) to determine what it is best suited for.  No one person can do it all without a substantial Government-University grant.  I don't have that.  But we have a large community of interested people here.  And occasionally someone asks a question like the one in the original post that might find its solution with this design.

As far the historical reference is concerned, I stand by my comments.  People WERE trying all kinds of things after the first oil crunch.  Maybe it was just desperation, but at least they were thinking of new things.  In some respects I feel the area has gone backwards.  Exhibit A:  Making blades out of 2 by 10's or any 2 bys.  Back in the Seventies and before people understood that you needed substantial twist in the blades to get the best performance.

The Third Engineer      

[finnsawyer]

I think if you check you will find that I have mentioned my design to people that have asked specific questions or are looking for a solution to a peculiar problem, such as doubling the magnets (doable if you mount the magnets on studs so they can be moved around).  That particular issue could start with a 9/12 design, going to a larger rotor and my 18/12 design possibly followed by going to a 18/24 design.  There are always going to be people that want to try something different, and those are the ones I am trying to reach.  I have no problem with an individual using the 9/12 design if that suits him, but magnets are expensive and I feel that for a given number of magnets one can build an alternator that gives more output with my design with a lower cut-in rpm.  Time will tell.

[TomW]

GeoM;

The Third Engineer

HaHa.

A sense of humor is very valuable.

Cheers.

TomW

[finnsawyer]

Well, I know at least you read that comment.  Have a nice day.  I appreciate your insights.

[whatsnext]

Time would tell a lot faster if you would just make a little time in your busy schedual and show us how bright your idea really is instead of suggesting others waste their time on unproven designs. The whole point of this site is sharing of proven DIY designs. Yours is not proven, or even built yet. Lots of guys here use different designs, like windstuffnow, so it's not like anyone is 'locked in' to a cookie cutter approach. However, many want their mill to work the first time and unless you KNOW that yours will why keep suggesting it? You keep making totally unproven claims that your design lowers cut in and increases output but you are unwilling to just build one to show any of us that it is true. DIY meens DIY not Have Someone Else Do It For You. HSEDIFY?

John....

[dinges]

GeoM,

Yes, I've been bothered with Faraday in school several times. What I remember is that you need as big a flux change in as short a time as possible. I can't see how this could happen with your design. But I've never liked the reversed burden of evidence much.

I'm not really looking for an arguement here. But it's these kinds of comments that do the trick and make me reply despite knowing better of not to bother:

"No one person can do it all without a substantial Government-University grant.  I don't have that."

We're not asking you to design a new inter-planetary space probe. Build a simple stator or even a complete generator. Can even be a prototype setup

If that's asking too much & needs a government grant, I really fear for the future of America.

What happened to personal initiative & risk taking... Yes, in the '70s people seemed to have much more of that, judging by your comments.

The skeptic part of me tells me 'if you really believe in what you say, put your money where your mouth is. Don't go thinking up excuses for NOT building it, but just get down into the basement and start doing it.' It's not rocket science, and you don't have to take out a 2nd mortgage for it. But maybe I'm just overcynical.

[Devo]

Getting this bad boy back on track.... I have had plans on my back burner for a while to use an over sized rotor/stator as I have posted about before but filling the extra space with wire is just going to create more resistance & drop the efficiency(in my way of thinking) When I get around to doing one I will spread the magnets on a big disc this will hopefully let me use less windings to get the same cut in raising the efficiency.Much of the disc would be dead space instead of wire because I think if you fill the dead space with more wire you need more prop to drive it & get more heat , wasn't sure about more magnets but Flux's answer on that makes sense.

The trouble with the bigger disc the way I see it is it cuts into the usable wind area , probably a happy medium to be reached here, maybe we're at it with the standard rotor sizes & maybe we're not.

At anyrate thanks for all the input.

Devo

[finnsawyer]

Obviously, you do not understand Faraday's Law.  If you did, you would know that going from a 9/12 design with the same number and type of magnets with twice as many of the same coils (that is 18/12) interacting with the magnets at a greater speed (larger rotor) would result in a greater voltage at a given rpm when the coils are connected in series.  Keep in mind that for the 9/12 design only two phases (6 coils) provide output at any one time and their voltage waveforms are 120 degrees out of time phase.  With the 18/12 design 12 coils provide output at any one time and their voltage pulses are nearly in phase.  This is why I feel I can make the claims that I make.  Faraday's Law does not change.  The way moving coils and magnets interact is a given.  I invite anyone to debunk this design (the 18/12) based on Faraday's Law.

I have indicated that my suggestions are directed to those who have gone beyond the first windmill stage.  Why can't you accept that?   It is also news to me that we should only consider "proven designs".  That is not how I have perceived the intercourse one finds on this site.  People are always asking for suggestions and thinking of new ideas (to them).  I suppose I could have waited and built a prototype and then sought a patent, if I lived long enough.  I decided instead to give it to the community, which seems to be a lot more conservative than I expected, not to mention a certain amount of hostility.  I guess I expected attitudes similar to what I saw in the Seventies.  Still, there are a lot of experimenters out there. Who knows what they are doing.  I just hope anyone trying the 18/12 design will present their results here.

[finnsawyer]

"Yes, I've been bothered with Faraday in school several times. What I remember is that you need as big a flux change in as short a time as possible. I can't see how this could happen with your design. But I've never liked the reversed burden of evidence much."

Take a look at my other comment on this thread of today.  There's no point repeating it again.  It gives my take on how Faraday's Law relates to this.  Basically, one would use the same size magnets, same size coils, same gaps, etc., and a larger rotor.  The result should be more voltage at a given rpm.    

[whatsnext]

Who cares? More voltage at a given rpm would require using a bigger prop. If you are going to do that you could easily increase your rotor diameter and just double the number of coils. That would do everything your design does without the wasteful coil shape. The problem people have with your design has nothing to do with the phasing of the coils, the cut in speed or anything else. The problem was that your coils are shaped in such a way that they are very wasteful of wire and therefor have unnessisarily high resistance. Do you really think that is the most efficiant coil shape for what amounts to a single phase alt?

[finnsawyer]

Still not thinking out of the box, eh?  Let's start with the voltage or more precisely the cut-in voltage.  If you want the mill to cut-in (get 12 volts at say 8 mph wind), and all your getting is 10 volts, you have a problem, as was the case with a recent posting.  So, a higher voltage with the same number of magnets (keep an eye on the bottom line) can be desirable, nor does it mean a larger prop.  The size of the prop is a POWER issue (voltage times current).  Also, with the 9/12 design, doubling the number of coils also means doubling the number of magnets (that pesky bottom line again).  Actually, my design operates between the original 9/12 alternator and your 18/24 upgrade with a lot of design options.

"The problem was that your coils are shaped in such a way that they are very wasteful of wire and therefor have unnessisarily high resistance. Do you really think that is the most efficiant coil shape for what amounts to a single phase alt?"

Again, you are not going beyond what you see.  The shape of the coils is determined by the shape of the magnets.  To get the most flux the magnets will be sized such that they completely fill the coil centers.  I showed the sizes as I did in the diary to make clear the timing of the pulses and explained that in an actual alternator the magnets and coils would be sized as usual.  The most efficient wire to coil area would be for circular coils and magnets.  The best voltage generation, however, would come from wedge shaped magnets, which would give a higher rate of change of flux.  Of course, wire size is fixed, so the coils must deviate somewhat from the ideal wedge shape.  Alternator design has a lot of trade offs.  Don't get hung up one aspect of the design process.

I hope this helps you focus on the real issues here.    

[finnsawyer]

Sorry about hijacking your posting, but I feel I need to respond in many cases to avoid confusion on the part of other readers.  As far as adding the copper is concerned, I think the real issue should be the cost of copper per cubic centimeter versus the cost of magnetic material.  Doubling the number of coils will double the amount of copper, but it doesn't have to be the same size wire or the same number of turns.  With my design you should expect something like a factor of four increase in voltage with the same number of turns on the coils and the larger rotor at a given rpm.  Well, one can reduce the number of turns and increase the wire size or simply make the coils smaller with less turns of the same wire.  Is this beginning to sound more like art then science?  Please note that the ultimate rotor size will depend on the coil size.  Smaller coils means a smaller rotor.

One other thing.  Just because an alternator can provide more power than the prop can provide doesn't doom its use.  You can match it to the prop by controlling the amount of current you draw.  Of course, once you have it and know what it can do you have the option of a new prop.      

[whatsnext]

There really is no reason to "think outside the box" because alternator design is very old science. You can prove that the many here who think your idea is silly wrong by simply building one and proving us wrong. Until then you will get these exact replies every time you suggest someone else should build your unproven design.

John.........

[jimovonz]

"The most efficient wire to coil area would be for circular coils and magnets." Would not the most efficient setup be long thin rectangular magnets (long in the radial direction) such that the wire linking the two legs (which is inactive and is basically 'dead resistance') is minimized and the amount of wire in the legs under the magnet (actively producing EMF) is maximized? Rectangular coils maximize the amount of wire running directly perpendicular to the path of the magnet.

[finnsawyer]

No, flux depends on the area of the face of the magnet.  Next to circular a square shape is the most efficient, that is, it has the shortest circumference for a given area.

[finnsawyer]

So now there is no new science.  Seems to me I heard that before.  Closed minds can only think in circles.  Step aside and let those who want to advance this area do so.

[whatsnext]

Advance away and THEN tell us how smart you are. Without data your advancements look weak.

[jimovonz]

No arguing that a circle encloses that greatest area for the shortest circumference. However in our situation that is not the only consideration. To maximise output the copper over which the magnet passes need to run perpendicular to the path of the magnet. A circular coil only gives you that at two points, everywhere else you are loosing out. Square (well actualy wedge shaped for our axial flux alts) magnets/coils with a high aspect ratio would make the best use of the stator space, maximise output and minimise dead copper(resistance).

[finnsawyer]

Without understanding any technology looks weak.  By the way when was that alternator/generator technology set in stone?  Was it circa 1800, 1900, 1950, 1975, 2000?  I believe any reasonable person will realize that significant advancements were made around many of those dates.  Technology doesn't stand still.  Just because you don't understand something doesn't mean it has no merit.

[finnsawyer]

Actually Faraday's law doesn't care about the shape of the loop (or its size for that matter).  It relates the voltage around the loop to the time rate of change of the flux, which we want to maximize for the greatest voltage.  The length of the loop or wire becomes important when we want to maximize current in the wire (or output power).  The circle shape still gives the least wire length and least resistance for the greatest flux enclosed.  It may be, though, that the rate of change of the flux is not as great for the circle versus a wedge of the same area in a particular design.  That becomes a design consideration that probably would have to be settled by trial and error and a sizable outlay of money and time.  Personally, I don't think it matters that much for people using this site.  Either type of magnets should work fine.  I may be wrong though, in which case I am sure those with experience will set me straight.  

I believe you are basing your comments on the "V cross B" version of Faraday's Law, which is actually equivalent to the other form discussed above.  Using it is another issue.  I would just like to point out that for a circular loop passing over a magnet the V cross B term is actually non zero for most points around the loop, meaning that most points on the loop contribute to the voltage developed around the loop.  The resulting voltage, if you could calculate it, will be the same as for the time rate of change of flux method.  There is, after all, only one type of electromagnetic phenomenon.  Note that with the "V cross B" method you only get a net voltage around the loop if the two sides of the loop experience a different value of magnetic field.  For such a condition to persist the flux within the loop would have to be changing (the coil is moving onto or off of the magnet), which is consistent with the other form of Faraday's law.

[whatsnext]

It get's carved in stone around here when someone shows that a design will work instead of just flapping their gums at it. In the amount of time you've spent posting about an unbuilt design you could have easily built a small single coil test version and shown us all what a great idea it is, or isn't. Until then you havn't done squat.

John...