More or less coils? What gives

[michael.i]

Hi there, Brand new to the board so this may have been covered somewhere already but...

I have seen stator designs in 6, 9 and some even in 12 coils, but I am not sure WHY you would want more or less coils? Is there a simple answer to this?

I am toying with the idea of building a wind generator and am starting to gather materials. I purchased 24 n50 2x1x.5 Neodymium Magnets on a wym, and now just have to figure out what to do with them.

So, any advise? I live in the southern interior of British Columbia in Canada, and my house is on the side of a mountain and I get a pretty steady wind most days.

I think I like the idea or a VAWT so I can mount it on a pole off of my roof instead of some massive tower mounted windmill with 10' Blades.

Any tips or suggestions appreciated. Also some info one my first question would be great.

Thanks and look forward to hearing from you soon

Michael Illingby
michael.i@me.com

[electrondady1]

hey mike, Ontario calling.
most of the alternators on this site use a 3 phase stator.
there is a required relationship of 3 coils for every four magnets.
so for your 24 mags you would need two mild steel disks 12" in dia.
and form a stator that contains 9 coils.
there are other configurations but that is the most common.

vertical mills are less efficient than horizontal mills,( 20%capture as opposed to perhaps 40%)
but esthetically can be more pleasing.

there are two types of vertical mills, drag and lift .
lift type verticals can capture about 30% of wind energy.

generally speaking, because vertical mills rotate at a lower speed
they cannot produce the amperage that a horizontal mill does.

a word of caution in regards to placing the mill on your house.
any vibration from the machine can be transfered into the structure .

[michael.i]

Ok, Cool. I appreciate the explanation between the differences there, Thanks!

My first question MAY have been typed in a misleading way.

What I meant to ask was this. In a THREE PHASE SETUP is 6 worse than 9 which may be worse than 12, 15 18 21 etc etc. I mean is there a reason someone may choose to use MORE coils in their three phase stator? It seems MOST go the 9 coil route, but why? why not go 18 or 21 or 15 even. Why stop at 9?

It would seem to me that the most BASIC Three Phase stator would have 3 Coils and 4 magnets, so why use more? I understand 1,33 magnets per coil rule. so, what does doubling or tripling that basic setup change? does each additional set of coils increase the voltage? amperage? this is what I am asking.

The number of turns in each coil determines the voltage, and the gauge and length determine resistance correct?

Get what I am asking now?

Adding more sets of three coils is doubling the resistance of each phase, but is it also doubling the voltage of each phase?


Confused, Michael.

[ChrisOlson]

It would seem to me that the most BASIC Three Phase stator would have 3 Coils and 4 magnets, so why use more? I understand 1,33 magnets per coil rule. so, what does doubling or tripling that basic setup change?

It has to do with the relationship of magnet area and the number of coil legs cutting lines of flux.

Example:  A typical 9 coil 12 pole unit might require 77 turns of wire per coil.  If you go to 18 coils and 24 poles it'll only require 24 turns of wire per coil, instead of 38 like you might think it would, which will give you less internal resistance in the generator and better efficiency.  This is assuming a flat coil arrangement.  If you use overlapped coils then you can use 12 poles with 36 coils, use 19 turns per coil, and get better efficiency yet.

However, most of the homebrew plans describe building flat coil arrangements for the stator because it's easy to build.
--
Chris

[imsmooth]

For a three-phase system the ratio of coils to magnets is fixed - 3:4.  You will have more if your rotor is bigger.  You can fit four magnets on a 6" diameter disc; you may fit twelve on a 24" diameter disc.  You would build a bigger rotor/stator if you are going to have a bigger prop for capturing more wind energy.  In order to harness the electricaly energy you will need more wire going through the magnetic field.  More turns of wire going through the field will allow you to increase the generated voltage and/or amperage.

[jaskiainen]

It would seem to me that the most BASIC Three Phase stator would have 3 Coils and 4 magnets, so why use more? I understand 1,33 magnets per coil rule. so, what does doubling or tripling that basic setup change?

It has to do with the relationship of magnet area and the number of coil legs cutting lines of flux.

Example:  A typical 9 coil 12 pole unit might require 77 turns of wire per coil.  If you go to 18 coils and 24 poles it'll only require 24 turns of wire per coil, instead of 38 like you might think it would, which will give you less internal resistance in the generator and better efficiency.  This is assuming a flat coil arrangement.  If you use overlapped coils then you can use 12 poles with 36 coils, use 19 turns per coil, and get better efficiency yet.

However, most of the homebrew plans describe building flat coil arrangements for the stator because it's easy to build.
--
Chris

Like Chris said there, You can use less turns of wire per coil and therefore you can use heavier wire in your stator wich gives you less resistance and more output from your genny.
There is also a "limit" how big your generator should be. If you buy lets say 80 magnets and use 60 coils then what you get is expensive and heavy generator. Hope this clears things a bit.

[michael.i]

This all helps a lot. The information in this hobby is overwhelming to say the least. The strangest thing I have found so far is that there is no perfect setup. It is basically just setup the turbine, see what it does, then "Try" and build the right alternator to go with it to handle your needs.

Sorry if calling this a hobby offends anyone, but to me this is a hobby.

I will bother you all with more questions later. Thanks.

Michael Illingby

[ChrisOlson]

It is basically just setup the turbine, see what it does, then "Try" and build the right alternator to go with it to handle your needs.

Well, I can do better than that.  I already know you got N50 1 x 2 x .5 bar mags.  You tell me what size and type the turbine rotor is, how big the tower is, what the average wind speed is at that tower height, and I can get you pretty dang close, within a 1/16" of air gap adjustment, on the generator design.
--
Chris

[jimovonz]

Well, I can do better than that.  I already know you got N50 1 x 2 x .5 bar mags.  You tell me what size and type the turbine rotor is, how big the tower is, what the average wind speed is at that tower height, and I can get you pretty dang close, within a 1/16" of air gap adjustment, on the generator design.

Thats a pretty impressive claim! Are you saying that you can accurately model any setup with 1x2x1/2" N50 mags? Is that any pole count/magnet rotor diameter/coil size/coil thickness/turn count/wire gauge/phase count/air gap/blade profile/blade diameter/design TSR/transmission wire gauge/battery voltage/battery size? Does it extend to other size/shape/strength magnets? I'm sure there are a few of us who would be interested in how you go about that.

[ChrisOlson]

Thats a pretty impressive claim! Are you saying that you can accurately model any setup with 1x2x1/2" N50 mags?

I can get it very close.  I've built enough turbines, and run enough generators on my test stand, using those magnets, and recorded the build and performance data with blades ranging from 7.6 up to 13.1 feet, flat face and S809 airfoils, so that I don't have to take a stab in the dark.  I also have enough experience building generators with N35 and N42 wedge mags to get you pretty close with those too.

I don't follow the homebrew plans, I design and build my own stuff.  You can search the board if you want and find probably a half dozen different turbine/generator setups I've built and posted here, and that only covers a portion of them.  Michael needs to know, having never built one, that it's not a crap shoot matching a generator to its input power and load.  And that's what those of us who have the experience are here for - to help those that don't.  If Michael decides to build an OtherPower 10 foot or something from the plans, then I can't help him because he's going to get what the plans give him.  If he wants to build something of his own design, and doesn't know where to start, then I can help him design something that will actually work using those magnets that he bought.
--
Chris

[jimovonz]

So for instance you could predetermine what the performance difference (say x%) would be between a given alt with a 10 foot diameter blades and the same one with 11 foot diameter blades? Or perhaps the same blade size but with different design TSR? How does this model of yours work? With so many variables to consider you must have some sort of spreadsheet or similar to handle the permutations? Can you give us more detail of how you correlate all these variables to allow you to determine the optimal configuration? I have never seen even the most experienced here on the board making a claim such as yours - to be able to pre-determine the best blade match to a given alternator to within 1/16" airgap for an arbitrary system based solely on the specification. From my experience, even determining the flux in the gap is a bit of a crap shoot without doing some measuring using the actual magnetic assembly. Coil size and shape also play a big part.  As far as the aerodynamics of the blades go, best I've seen is an assumed Cp at some fixed loading. I have not yet seen anyone here on the board apply a variable blade Cp (based on loading) to produce an actual output curve of a complete system. All this is needed to give the best possible match. As I said, I'm sure I'm not the only one interested in how you achieve this. Please give us more detail of your method.

[ChrisOlson]

So for instance you could predetermine what the performance difference (say x%) would be between a given alt with a 10 foot diameter blades and the same one with 11 foot diameter blades? Or perhaps the same blade size but with different design TSR? How does this model of yours work?

I don't know if you're looking to pick an argument, or what.  Like I said, I've gained enough experience building generators using those identical magnets to get Michael within a 1/16" of air gap adjustment on a design if he wants to build something that's not in the book.  If you want to try to convince yourself and everybody else that it's a mysterious crap shoot getting a match that works, that's fine with me.  If Michael wants my help in figuring out how to build a generator using those magnets that will match what he wants to build he can email me - my address is in my profile.
--
Chris

[electrondady1]

ok, ok, before the pissing contest starts you guys might want to re read the mans first post .
where he mentions he wants to build a vertical mill.

mike, the mags you have purchased are popular and are used in a lot of alternators in this forum.
a vertical mill is a very different animal than a horizontal

you must first decide on a drag or lift configuration or a combination of both.


 

[kurt]

i win!

[frepdx]

Hi there, Brand new to the board so this may have been covered somewhere already but...

I have seen stator designs in 6, 9 and some even in 12 coils, but I am not sure WHY you would want more or less coils? Is there a simple answer to this?

That's a good question - the answer is whatever works for you

The 'recipes' you find are built around commonly available magnets and materials. Use enough magnets and coil turns to match the power from your mill.

A twelve pole, 9 coil arrangement could be re-worked to a 4 pole, 3 coil arrangement with the same materials; use three magnets at each pole to give it three times the area, and re-size the coils to match. Then it turns our to be a packaging exercise.

[ghurd]

Something I did not see mentioned is frequency.
If all else is the same, like total magnet surface area and volume, same turns per phase, etc,
then more poles will make more voltage.

The faster the magnetic field changes, the more volts are made.
G-

[frepdx]

Here's a formula that's been floating around (i think it's Hugh's formula);

Turns per phase = 17000 x (System V, V +1.4) / ( Cut in speed RPM) / (Flux in Tesla) / (total area of magnet face in square inches)

Note that the number of poles isn't needed.

In my earlier example going from three coils per phase to one coil per phase and tripling the pole area, you'd have to also put all the turns in that one coil. I think that would take care of Ghurd's point above.


Ref: http://fieldlines.com/board/index.php/topic,137269.msg904942.html#msg904942

[jimovonz]

I don't know if you're looking to pick an argument, or what.

Not at all. You made an exceptional claim. If you can do what you say then I am truly interested in how you do it. Predicting the performance of a 'lift' type turbine (HAWT or VAWT) has long been an interest of mine. However, if all you are going to give us is 'from expereince' and for all intensive purposes pluck number out of the air then I will not be so impressed. All I am doing is asking for more information.

[electrondady1]

decreaseing the number of poles is a step in the wrong direction
 with vertical mills,frequency already suffers.

it's quite possible to use all 24 mags on one disk, say 24 "dia., and an other24"rotor (with out mags)
turning in sync as a flux return path.
but i don't think it's quite as efficient.

mike, i've been doing a world survey, what did you pay for your mags?

[frepdx]

decreaseing the number of poles is a step in the wrong direction
 with vertical mills,frequency already suffers.

doesn't matter, as long as you keep the same (cumulative) pole area and the same (cumulative) number of turns.

http://fieldlines.com/board/index.php/topic,137269.msg904942.html#msg904942

Turns per phase = 17000 x (System V, V +1.4) / ( Cut in speed RPM) / (Flux in Tesla) / (total area of magnet face in square inches)

Note that the number of poles isn't needed.

[ChrisOlson]

doesn't matter, as long as you keep the same (cumulative) pole area and the same (cumulative) number of turns.
Note that the number of poles isn't needed.

Well, you're right, but.........

If you take a 12 pole 9 coil flat stator three phase unit and double the number of poles but leave the number of coils the same, it takes half the number of turns per coil to get the same voltage.  However, that configuration won't work for three phase, nor will it work for IRP because of canceling problems due to the poles of the same polarity passing both coil legs at once.

So let's say this 12 pole 9 coil unit has 50 turns of wire per coil.  If you cut everything by one third - 4 poles and 3 coils - but triple the pole area, then it requires 150 turns.  But if you drop back to three coils and 4 poles leaving the pole area the same it requires 454 turns of wire to get the same voltage you had with the 12 pole 9 coil.

Getting back to what I said when I first posted on this thread, if you take this same 12 pole 9 coil and increase the number of poles to 16 and the number of coils to 12, it now takes 28 turns to get the same voltage.  You increased the number of poles and coils by 1/3, using the same pole area, and it takes only 56% of the number of turns of wire in the coils.  You double everything to 24 poles and 18 coils and now it takes only 13 turns of wire to get the same voltage as the 12 pole 9 coil unit with 50 turns.

Refer to what ghurd said about frequency.  Low rpm direct-drive turbine generators run at too low of frequency the way it is.  Increasing the number of poles and coils in the right relationship increases efficiency of the unit pretty dramatically.  Since frequency is also related to rpm, 12 pole direct drive generators are best suited to high-rpm turbines under 10 feet in diameter, although they can be used on turbines up to 13 feet in diameter if you use more pole area with wedge mags or similar.  They won't work very well, if at all, on a VAWT unless you use some sort of step-up drive to increase the rpm of the generator enough to get decent efficiency out of it.
--
Chris

[vawtwindy]

how do you arrive "total area of magnet face in square inches"?


_{Turns per phase = 17000 x (System V, V +1.4) / ( Cut in speed RPM) / (Flux in Tesla) / (total area of magnet face in square inches)}

[electrondady1]

it must be morning in India windy,lol
length times width times number of magnets

[michael.i]

mike, i've been doing a world survey, what did you pay for your mags?

I bought them off of eBay for $169 + $45 S&H magnetsforless

[michael.i]

Well, I can do better than that.  I already know you got N50 1 x 2 x .5 bar mags.  You tell me what size and type the turbine rotor is, how big the tower is, what the average wind speed is at that tower height, and I can get you pretty dang close, within a 1/16" of air gap adjustment, on the generator design.
--
Chris

Yea, I was thinking about going to a vertical so that it would be less of an eyesore, no tail needed to keep it pointed into the wind etc. however, I am open to Windmill style if you think it is superior to vawt.

Also, Chrisolsen, thanks for the offer to help, I will gladly accept your help. I just ordered an an anemometer from eBay to get some numbers on wind speed and so forth first. I will post what I get in a few weeks once it gets here.

Can we talk more on why someone would use a VAWT if if Windmill style is so superior? This is another thing that I couldn't find anywhere. Cheers

[electrondady1]

horizontal axis wind turbines have evolved to the point where there output is predictable.
 thanks to Hugh Piggots research, the Dans contribution and all the contributors to this site over the years.
but strangely enough, the idea of a vertical mills still crops up in spite of the fact that they are inherently less efficient.
i just like the way they look.

[ghurd]

I believe VAWTs suffer from too much salesmanship.
Read the stuff published by people selling them.  Most of it is twisted (pun intended) or just wrong.

A lot of newbies want to build a VAWT "because it is easier".
I think it is a lot harder. 
Just balancing them seems impossible for me.  If any of my (poorly done) attempts spun up fast enough to do any charging, they would have torn themselves apart by then.
G-

[Bruce S]

Can we talk more on why someone would use a VAWT if if Windmill style is so superior? This is another thing that I couldn't find anywhere. Cheers

Another reason could be that for Urban stuck people, H-mills are a no-go, BUT V-mills can be considered as lawn art since their rotational speeds are usually much much slower with regards to "S" style V-mills.
Knowing the limits, a person can design one to be useful.
Windtsuff ED has done enormous amounts of testing had has built some very good units.

Cheers
Bruce S