long coil question

[joestue]

see post #18

I agree with Lumberjack 100%

[fcfcfc]

Hi: I think all the initial questions are answered to my satisfaction. You raise an interesting point about the optimal curve to represent saturation/desaturation. With 1" x 1" x 2" neos, half used as main and half used as blocking, the distances traveled by the legs relating to the field would be, starting at zero flux traveling 1/2" to the max flux area across the max flux area of 1" then traveling 1/2" more to get to zero flux. So, over the cycle, 1" is spent in sort of stable flux and 1" is spent traveling either towards zero flux or away from zero flux. 50% "stable" 50% "changing". Thinking of the "standard" 3 phase gen here, a very small percentage of the "time" is spent in the max flux area COMPARED to the time spent in the changing flux, zero area. This is mostly due to the distances separating the magnets. So the question arises in an air based stator where iron core latencies in the magnetic field saturation/desaturation, magnetization curves etc.. are not present, what is an optimal relationship between time at zero and time at max field and in between..??..

[ghurd]

The down time is needed for a 3 phase.  Not enough down time will cause problems due to inductance.  See Flux's diary for some things that are related.

Ed's 'alt from scratch' with overlapping coils gets more copper active a higher percentage of time.

Might find something here,

http://www.fieldlines.com/story/2004/9/4/145716/3657

G-

[electrondady1]

it's called a hijack casual traveler.

fcfcfc turned the discussion to his own ends

and muddled up the ansers.

it is one of the major flaws with this forum.

and when some one in the future tries a google search on coil or magnet lengh

they will need to sort through it all.

.

[Lumberjack]

I tend to refer to the time a coil passes from the leading edge of the flux to when it reaches the trailing edge as dwell time. It is a combination of magnet width and the speed it is traveling.A second related consideration is latency or the lag time needed for the wire to react to the change in the feild.

Optimum is the point where the coil is in the flux long enough to react and reach its full potential. If you were to plot the relationships you would likely get a bell type curve. Unfortunately it is almost impossible for us to optimise any one design and get it perfect. Even microscopic variations in the construction change the result and then there is the fact that we do not make any real effort to control the speed of the generator. Everything considered there is no real way to predict the actual output untill the complete genny is actually flying.

Personally I believe that for a working generator reliability should come first and should not be sacrificed for a little bit more output. If anything I suspect the reason the normal design usually works well is because it does not generate as well as it could. Bear in mind that the more power you make the more heat is also created and so you end up with thermal limits in addition to all the others. I guess what I am suggesting is that a little less then optimal is better in the long run.

One of the biggest issues I see rather then coil sizing is magnet usage. Copper inspite of its expense is usually cheaper and more forgiving then the neo magnets we use. I have scrapped several designs simply because the magnets cost way to much. While I was impressed by your research on the blocking magnets when I priced it out I decided (for me) that it was more efficent to simply upsize the magnets a bit and keep them spaced out....

Dont limit your thinking to only three phase. Most of the time you will be converting to DC so the actual output is not limited to any number of phases. You can just as easily use 5 phases or more so long as each phase is rectified to DC. Most of my research points to using 6 to 9 separate phases as a better use of wire. Each coil can output less but the combined output appears to be much higher  

[TheCasualTraveler]

     Oh, I don't mind the twists in the discussion, I don't think it was really off topic. Actually I thought it was neat that my naive question brought about so much discussion. I think a novice reading will see the discussion for what it is and realize it will take more research to find answers. I only wish I understood half of it....

     But wait! I saw in the news recently that they have filmed an electron in motion, here it is...

<<<Scientists have filmed an electron in motion for the first time, using a new technique that will allow researchers to study the tiny particle's movements directly.<p>
Previously it was impossible to photograph electrons because of their extreme speediness, so scientists had to rely on more indirect methods. These methods could only measure the effect of an electron's movement, whereas the new technique can capture the entire event.>>>

     Now that we've got em on film were going to find out for sure just what the little buggers are up to in our coils!

[fcfcfc]

Hi: Thank you for your thoughtful comments... I will keep plugging away until I think I "have it right". The magnets do get expensive. I am in the $1300 dollar range for my layout, which now is at 150 - 1" x 1" x 2" N42's. I have to do more analysis on the time in and out of flux, of the designs that are already out there. A good point on the speed issue. I am trying to design this "whole thing", turbine and all for a low turbulent wind area, so 5-15MPH will dominate in my design although I have to of course handle the occasional 60 MPH gust and the one in five year sustained 30 to 50 MPH left over hurricane winds, which can last 24 to 48 hours.... so reliability and survivability are key...

[Lumberjack]

I know FCFCFC... I live on the other side of the mountain from you in Benton :}

[fcfcfc]

Hi electroD..

I didn't HJ this thread. My questions just went to "the core" of what it means to have a leg longer or shorter in relation to the side or non productive wire. In short, if length, in and of itself with all other factors being equal, got you nothing than long thin magnets would not make sense. In fact the shorter the better would be the case. But the reality is as the length goes up on the leg, all other factors being equal, the voltage goes up which to me makes sense. Its just that there are many other factors in play along with length that make the optimal design point not as simple to come by as we would all like!! At least I like simple, although you would never know it from my posts...

Have a good one...

[finnsawyer]

I hadn't see this comment before.  The thread got away from me.  It's probably impossible in a real situation to impose the conditions that you state.  To fit in more copper you would need to make the coils longer.  This in turn makes the overall air gap longer, which then requires stronger magnets.  Unfortunately that does not guarantee that the flux density would stay constant as the greater air gap would probably mean a greater than proportional increase in leakage flux.  A dual rotor would give the best result as far as leakage flux is concerned.  The end result is that voltage would probably increase by a lessor percentage than the resistance due to leakage effects.  But the maximum potential power output would increase by a greater percentage (V^2/R).  The whole problem comes about because the column of flux passing from magnet to stator backing loses some strength as it passes through the stator.

Have you checked out this link?  The theory of operation presented there may be of some help to your understanding.

    http://www.fieldlines.com/story/2006/4/21/16237/9933