Specific coil winding question...

[fcfcfc]

Hi:

Most of the PM disk alt's I have been looking at for reference for my VAWT, are lower voltage, 12,24,48 etc for charging the associated battery banks. Has anyone built one of these for input into the higher voltage wind grid tied inverters which often require 100 to 250VDC input..??.. If so, what wire size decreases and winding increases have you settled on through experience, to obtain the higher voltage but lower amperage values required..??..

Thanks...

.....Bill

Just like everyone else, you likely need to build a test coil to determine the turns needed. Regardless of the application.

[fcfcfc]

To anonymous comment made to this post:

Your answer seems unlikely since;

1. Everyone would be reinventing the wheel over and over again, negating the reason for a discussion board in the first place, which is information and education exchange.

If you don't want to share the info or don't have it, just say so directly and please identify yourself. There is no reason for cloak and dagger is there....

.....Bill

[DanB]

Bill - it will depend on the size/geometry of your alternator, the magnets (size, grade).. the rpm you plan to run at etc.

If its a VAWT (direct drive?) it will likely be running pretty slow...   You give no detail though.

Basically - voltage is directly related to the number of turns in a coil (double the turns double the voltage).  To get double the turns in the same space you need to use wire with half the cross sectional area.  Roughly speaking - any time you go up 3 gages (AWG)of wire you'll have half the cross sectional area.  Past that - with the information you provide there is nothing else that could be said to help.

[TomW]

Bill;

Well, excuse me, but, as supported by Dan below, the statement was actually an attempt to point out it is often necessary to figure out on a case by case basis.

Your question is vague to say the least. It also shows that you did not research very deeply because this coil relationship is often covered here. With the bottom line generally being the "test coil" advice for systems not following the "normal" designs. Jumping on the VAWT bandwagon places you firmly in the non standard camp, especially direct drive. So don't blame me for stating the obvious.

Having been a member since '04 you should be aware who does editing here so the anonymous editorial comment complaint is petty and baseless.

Good luck with it.

T

[fcfcfc]

The question was not so much what I am doing but a reference to the lower voltage (12,24,48) gens that are talked/referenced in detail in various places, as to whether anyone has built a higher voltage one more "geared" (no pun intended) towards the synchronous wind inverters which often have about 5 times the voltage requirements. The answer I was expecting would be something like, "it is the same design as the 48VDC stator except we drop from an #14AWG to an #18AWG and increase the turns from 65 to 200 - 250 etc. all else being the same... the voltages we got at various RPM's are graphed at   ...some URL". That was the kind of thing I was expecting if someone had made one. If NO ONE HERE has made one, then obliviously that info is not available, and a reply like, "we have not made a gen to interface with those inverters so we don't have any experimental data, etc.., etc.." again something like that.. instead of.. gee, you just have to make a test coil like everyone else...

That comment just didn't seem appropriate....

I am normalizing for 1 RPS with the design I have been playing with, that would give a wire speed through the field around 100 IPS for a magnet circle of 34", air gap no bigger that 1/2", using the 1" x 2" x 1/2" N40 mags... I have allot of ideas I have been toying with including not even using wire for the stator.. I am looking at everything as possibilities as well as my own creative ideas

.....Bill

[oztules]

Bill,

I suspect that you will be despondent with the replies thus far..... So I'll attempt to explain why no realistic answer is available to your query.

If for example you were to build the standard Danb 10' hawt, your question can be answered fairly simply. If you use the same setup as the 10 foot danb, and it says to wind T turns of D diam wire for 12v, then for 120v you would just multiply T turns by 10. this would get you to 120v.... question partly answered. For the wire diam, you need to think that you need 10 times the turns in the same space, and so would calculate the smaller size accordingly....or you could increase the rotor diam to get more space between the mags and not reduce the thickness as much.... and calculate accordingly... I'd wind a coil of the 10X turns at best guess thickness and see if it fits..... problem solved.

However with out the baseline of the original mill you wish to change, it becomes a "how long is this piece of string in my pocket" type of thing.

The vawt complicates things further as no-one knows how big, what gearing, what mags, how many etc etc. so you can see there is no answer for you until you get a VAWT that actually works, and you have some fair idea of it's revs, torque (for probable gearing up) etc.

If you had a 12v VAWT that worked, you would simply multiply the turns of that mill by 10 (or whatever volts ratio ( volts wanted/volts original) you were after) and decrease the wire size to fit your winding space.

So how long is this piece of string I'm holding up..... see the difficulty now?

Hope that helps ease the pain a little

........oztules

[TomW]

oz;

Well said and probably won't be misconstrued as withholding information or unfriendly.

Cheers.

TomW

[DanB]

Right...

well again, it does depend on rpm, magnets etc.

I am curious about this myself actually - I have somebody who wants me to build a small machine to be wired to the windy boy inverter.  Wiring the stator is easy if you have a starting point - again, the voltage produced will be directly related to the number of turns in the coil and the rpm.  So you can look at existing designs I expect and extrapolate what you need.

Im more concerned about the windy boy inverter and its issues - I should probably start a new post/see if there's much that this community has to offer.  I know they're happy to take about 140 - 400 volts or so, but Im not clear on how to protect the machine if the grid goes down - or...  how to protect the inverter from over voltage.  I should probably email the company.

[vawtman]

Hi fc

 Check out these vawts from a story i did awhile back.

http://www.fieldlines.com/story/2007/6/14/17915/4819

 Has oz stated its hard to match the load.

 Once you get the turbine built you will probably need to do springscale tests on it.

 Ive been struggling but not givin up.I have the 32in wheel on a testbed and when all the mags are on it im going to experiment with coil design.

 Its been a harder process than i imagined earliar on.

 Good luck to ya.

[fcfcfc]

Hi:

Thanks for the reply. I do understand all these issues, although from my question you might think I was a professional chef perhaps, who woke up one morning and noticed the neat whirly thing on top of the office building and thought, hum.. those look interesting.

Actually I am more like the kid who from when I was the height of a standard countertop, and going forward was doing things like building 1.5 million volt Tesla coils from scratch, 15,000VAC spark gap radios, a 10watt CO2 laser from scratch including all pressurized gas mixture equations,  a salt crystal at Brewster's Angle, ground and drilled the exit mirror, my own dark room since I was high school photographer, capacitor driven high intensity pulsed magnetic field coils for magnetization, low and high explosive Chemistry and just about every hard science you can think of excluding bio and associated areas, not a favorite.

Anyway, all I was doing was searching for a baseline that someone might have had on the higher voltage side with these style gens. The VAWT really is allot simpler then the HAWT's since over speed, cut in speed, optimal speed etc. issues are not there or greatly simplified, since a VAWT's maximum torque is technically at zero RPM although of course no useful "work" is being done.

There is a huge difference between Physics and applied Engineering and most of the differences are learned through experience. Just trying to shorten the road a bit....

Thanks again..

.....Bill

[fcfcfc]

Hi: Thanks, yes I have seen that site. I think though the link below has one of the "slickest" engineered VAWT's. Its very close to what I want to build with the exception of the thin aerofoil baffles at 120 Degs I want to use to intensify.

http://www.youtube.com/watch?v=q9flSPAdOLk

When starting looking at this idea to do this, which has not been very long, after looking at the disk gens I felt the following:

I liked the neo PM's for field and the overall simplicity of the design.

I did not like the efficiency and the coil layouts because there is too much "dead" wire and times when the coils "fight" themselves, though I am sure they are trade offs for ease of building. I came up with the idea of what I now know is called wave winding (Wind section "VAWT Helix" post) to reduce the "dead" wire although you really aren't getting rid of a cross over its just that the overall usage of the wire works out to be more efficient. In my wave winding I zigzag around every one of the 72 magnets. The three phases are on each magnet so there are no coils so to speak, and really one can use any number of magnets. At no point does any phase fight itself. Still I was determined to improve the design since it was going to be a bear to build. I got the idea after much thinking (still doing that) that maybe it can be done more efficiently without wire. I know you are probably think I am nuts but my grandfather was a successful inventor and I just can not help thinking of these things when I encounter a problem. Anyway, I was thinking of how printed circuit boards were made and then saw the bit on how they had 1/8" aluminum water jet cut to place the magnets on the rotor. So for magnets 1" x 2" x whatever and a 34" rotor, the stator is built by taking, as an example, 20 thousands copper foil and stack 45 sheets on top of each other, 34" x 34" and water jet cut a rectangular zigzag in the form of the stator diameter circle. The zigzags are 1/3" wide and have a 1" cut out section between each leg and end up looking like something you would hang up at a party. They have a cut in them of course for the start and end with longer legs to connect to. You lay them in the ring, phase one first foil, then slip clockwise 1/3" and lay the next one (they are all identical) which is phase two and slip the third one down 1/3" more clockwise for phase three then repeat the process building up all 45 foils. In the end you have 15 foils for each phase which you then just attach in series giving you 15 x 72 = 1080 legs for each phase and a copper conductor cross sectional area equal to about #11AWG square magnet wire .0083 square inches. No wasted air space between wires, all legs and cross conductors are identical!! You could even on the crossing zig zag dead copper, play with making it wider (less resistance) or narrower (smaller mag foot print) to optimize performance. And yes, you have to spray or laminate or both some insulation material between the foils so they don't short of course... add resin and compress the stack... Just another idea of mine if you can visualize this...

.....Bill

[finnsawyer]

As I recall, Vawtman was planning to use 60 of the same size magnets with a 32 inch rotor.  In that case his coils would need to no more than 1.8 inches wide.  That puts the magnets .4 inches apart.  That's pretty close, and with coils even only .5 inches long you can still expect a considerable loss in flux through the sides of the coil before the flux reaches the iron behind the stator.  You can reduce the flux leakage by moving the magnets farther apart, but this means using fewer magnets and coils.  But the coils can now be larger with more windings.  So, when a coil is exactly centered over a magnet you have more flux through more turns, which tends to increase the average voltage.  But it takes longer to pass from one magnet to the next, which tends to decrease the average voltage.  We can do a calculation assuming the flux doesn't change if Vawtman decides to use 56 magnets and 42 coils to see if there is any hope here at all.  In that case the coils can be 2 inches wide (or very close to it).  The number of turns has increased by 20%, not bad.  But it takes 7% longer for a coil to pass from one magnet to the next.  So we expect an increase in the average voltage of 12%.  There are .933 as many coils per phase.  So, the net increase in voltage per phase for no change in flux would be 4.5%, not very much.  With the drop in leakage flux it should be somewhat greater.  But note that this minor increase has come at the cost of more than a 20% increase in copper and resistance per coil, which is offset slightly (7%) by one fewer coil per winding.

In your case with the 34 inch diameter rotor you could use 60 of the magnets with the 2 inch diameter coils.  But in order to ensure the results you want or to establish whether they can be achieved, you really need to do the testing that TomW has suggested.

You might have had better results if you had asked for people's experiences in building alternators to have cut-in at 60 RPM.  It always helps to focus in on the most important aspect of the problem, which I take to be the cut-in RPM.  Given a good design for say 12 volts you can then scale it up to your desired voltage.

[finnsawyer]

If you are going to put 72 magnets on one 34 inch rotor they will be 1/8 apart.  The leakage flux will be severe.  That is, much of the flux will bend from one pole to its neighbor without ever reaching the iron backing the stator.  The upshot is that the upper foils or windings will see very little flux for the V 'cross' B term, which I believe you are focusing on, to give any voltage.  This is a drawback of the wave winding.  All three phase windings must occupy the space that normally only one winding occupies.  In this case all three windings must fit in 0.5 inches.  While it is true that each winding interacts with the magnets in its own space, how can you bring the windings down close to the magnets in the desired order, particularly when using foils?  If you do the obvious and have one winding close to the magnets and the others above that, they will have different induced voltages.  You can interleave the foils and connect them at the ends to balance the voltage, but still the individual foils farther from magnets will put out less voltage.  You also need to isolate the foils electrically, which will use up some of the 0.5 inches.

I'd like to know how and when the coils "fight" themselves.  A diagram would be a great aid.

[fcfcfc]

I went and typed a whole bunch of text regarding your comments on gap etc., very specific, and when I inserted the pictures it wiped all the text out. I am not going to retype it. Bottom line the 1/8" gap you suggest I am left with is wrong. The average gap will be .4" not .125". Leakage should not be bad at gap = almost magnet thickness.

Voltages are no different in the foil stack than in a regular coil. Some legs in a coil are close to the field and some are not. Same with mine. It averages out.

The voltages are induced in the vertical legs not the cross overs...

I am out of time for now....

[fcfcfc]

Hi:

I attached some drawings above of the foil idea. I lost all of the text and did not have time to put it back in the detail I had originally. I can certainly reduce the number of magnets to increase the space. I could widen the foil from 1/3" to 1/2" or 3/4" which ever worked out to fill up the space or just keep it the same 1/3" width and add 2 more phases. 5 phases would be a bit smoother wave form and my number of legs would increase even though the number of magnets would decrease. To try it at four phases I would need to increase from 1" to 1-1/3" width for the windings. Going from a magnet separation of .4 to .8 makes each magnet take 1.8" in a circumference of 100.48", so 100/1.8 = about 56 magnets. I wonder if it would be worth it to put 1/2" x 1/2" by 2" magnets with the fields going sideways repelling the two magnets they were between, laterally. The back side of the main magnets would be attracted but the front side closest to the coils would be repelled and opt more towards the more attractive opposing magnet through the coil. Kind of a field deflector if you wish.

All things are open here, at least for my project...

.....Bill

[wdyasq]

Bill,

I am going to make a suggestion. I suggest you build a small version, as close to scale as you dare of you proposed VAWT. Also build a Proney brake and a bit of data collection stuff. This will give you an idea of what MAY be available power wise.

You are venturing into an uncharted area. There is no data on the type of mill you propose. Once you get some data, there are folks here who MAY be able to help. But, it is hard to give good advice without some sort of base.

Good luck on your project, I'm looking forward to seeing data on a successful homebuilt  VAWT large enough to be more than a toy.

Ron

[fcfcfc]

I have been thinking of that myself which is the way I usually end up doing things anyway. A small scale gen, 8" OD will probably be very necessary also, especially if I do the "foil" thing rather than using wire. Its probably going to be a long time though because I have so many things that NEED to be done, its not even funny. My main RE focus is in solar thermal, which is where my business is at. Wind turbines have always been of interest but have taken a back seat from reality... I get a decent amount of sun but not much wind... Very spotie... but present...

Thanks....

.....Bill

[DanB]

A few comments.

RonB started a new post about the helix VAWT, I've seen that before (actually - I have a few 'favorites' of 'unworkable stuff' in my youtube account 'otherpower' and it's in there)...

While I can't say that VAWT you posted the video to might not work or be well desiged, their claims about output and hype on the website is totall unrealistic.  They either have no idea what's going or they're decieving people in my opinion.

I've played a bit with wave windings and it's been done before/discussed a fair deal here over the years.  I have a feeling you'll actually wind up with higher resistace and more 'dead wire' in the alternator than you would with more conventional designs.  

I don't care for the foil idea either - it may workout OK if you run at very low frequency (very low) but otherwise I think that such wide conductors will have severe eddy currents induced in them.  If you're relly worried about cramming as much copper as possible in a small space you might look into square magnet wire and do something along the lines of what SamoaPower is doing (look up his diary).  I would take a simpler approach and probably just build a slightly larger alternator.

[finnsawyer]

I did err.  I divided by two when I shouldn't have.  Of course, your magnets will not be parallel.  I computed the magnet gap at a minimum radius of 14.5 inches to be .26 inches.  While the average gap may be near 0.4 inches, you be should be aware that the parts of the magnets that are closer will have more leakage flux.  And you also do not understand the true nature of the leakage as it pertains to the coils or windings.  Think of the flux as leaving a north pole and spreading out like a fountain.  But it is a peculiar fountain.  The flux either can go into the stator backing or bend around and enter the neighboring south poles.  This 'flux structure' continues symmetrically around the rotor.  There are two consequences of this behavior.  The flux gets weaker with distance from the rotor and some of it will be parallel to the rotor during part of its path.  When the flux is parallel to the rotor there will be no voltage induced in either a coil passing by or your wave winding.  Also the flux that does bend around causes a loss in the flux flowing at right angles to the rotor with distance from the rotor causing a reduction in induced voltage for coil turns that are farther from the rotor.  What becomes important here is the value of the total air gap versus the separation of the magnets.  You are going to have air gap somewhat in excess of 0.5 inches versus a magnet separation averaging 0.4 inches.  That is a recipe for large leakage flux losses.

The main problem that I see is that each of your wave windings must overlap at the inner and outer radius.  This means each wave winding can be only 1/6 inch thick to fit in the half inch space.  So, at best each winding reacts to only 1/3 of the flux, while in the usual construction each coil reacts to all the flux (assuming no leakage in each case).  All this to save a little copper?  According to your diagram your windings would be about 0.3 inches wide (actually less since the magnets are not parallel), not much different than what you would get with standard coils.  

[fcfcfc]

Hi:

Thanks.. Yes I have been thinking about the whole first paragraph relating to basically, flux where you don't want it, etc., etc.. A possible work around would be to go six phases and cut the width to 1/6" reducing the eddy and self induction issues. The other thought I had specifically on side by side magnet leakage, has anyone played with getting some 1/2" x 1/2" x 2" neos and placing them on their side, that is, North and South parallel to the disks and opposing the poles they are next to. This would tend to make the opposing poles on the other rotor more appealing and draw the back main magnet flux more into the steel directly behind it as well. Another way to say it is the top main magnet pole face gets pushed away from the deflector magnet, the bottom main magnet pole is attracted to it.

On the bottom para though, I am not sure you understand the winding exactly. Lets say with 45 sheets .020" thick and 1/3" wide, you have 15 layers for each phase one next to the other. Between the magnet faces your thickness never exceeds 15 x .020 (not taking into account here insulation etc). Now on the cross overs outside the magnet faces you will have "stacking" up to 45 x .020 thick but that is fine because the rotors themselves are not 1/3" or 1/2" apart but more like 1.34 to 1.5" because each magnet is 1/2" thick, so rotor (steel) separation is 1/2" + 1/2" + magnet air gap". In short you can pretty much have any width you want on the outer cross over, within reason. It doesn't effect the height.

Actually the major problem that I can't solve on the foil idea apart from all the possible flux issues is a practical one. To water jet this pattern one time in a circle for all the sheets requires the copper stock to be about 2 inches bigger in its square size than the largest magnet circle. In short, 45 sheets of .020 copper 36" x 36" would require Bill Gates money since most of the material is wasted.

Most likely, end of idea.... I tried to think of a way to bend a straight pattern of the same in a circle but there are to many mechanical issues and the associated time as opposed to a nice neat circle that you just drop in place.

.....Bill

[DamonHD]

Hi,

I'm rather late to the party on this, and so I'm sure that I'm missing a crucial point or five, but just in case not...

Why couldn't you use flexible circuit board?  They can be bent into any shape you like, multi-layered, etc...

Rgds

Damon

[fcfcfc]

Hi:

Actually when I was looking at the whole idea I had, which was wire not foil or sheet copper at the beginning, I got square #12AWG 200 DegC sample wire from MWS. Nice stuff and almost equal to the cross sectional area of #11 Round, about 11.2 AWG I think.

The appeal to be able to drop in whole layers is very nice, even if you narrow the material and double the thickness. But the only way to preserve all the "lineups" is to add phases rather than more to each phase, unless you just go thicker with the magnet gap. And for a 1/2" air gap you can only go about 60 sheets at .20 because even though each phase only has 15 sheets thick through the magnet faces, the cross over thickness represents all 60 sheets, 1.2" plus insulation thickness..

As I mentioned on another post, I think the practical cost issue on the copper, due to most of it is wasted kills it....

Glad to see a VAWT area. I will have to take a look....

.....Bill

[fcfcfc]

Hi:

LOL!! No, these parties never end, even if you want them too... so no such thing as late...

To summarize way to much text, mostly on my part, one of the possible concerns is eddy currents in the conductor. In short, a circle or round conductor is the most desirable because it has the maximum cross sectional area with the smallest possible parameter. This is relevant because the greater the surface area of a conductor in relation to its cross sectional area the greater the possibility of eddy currents or wasted energy into more heat. The perfect conductor would be infinitely small in diameter with no resistance (a-la superconductor). All current produced in it will flow in only one direction because no matter what two points within the material you pick (assuming material in a straight line) the direction of that line and all the others must be the same. It is the reason they laminate cores in transforms. It limits the creation of eddy currents in the core. Did I say in short!! Anyway, the point was made if the conductor strays to far from a circle or square shape, the risk rises on loosing all you might gain to eddy currents... I am guessing that you probably don't want to go more than a 5 to 1 ratio on thickness to width. That might be conservative but I would have to dig in and find the formula that relates to such at a particular frequency. The higher the frequency the worse it gets...

How thick is the copper in the board material..??.., plus I can not imagine it being cheaper than just plain copper sheet which is cost prohibitive. The wasted material is the practical problem I can not seem to solve, to name a few...

.....Bill

[DamonHD]

Hi,

Well, if you get the boards made, it is possible that the board manufacturers already recycle the etched copper, or apply it another way such as by printing/laying it somehow for example.

So there is no necessary relationship between board area and 'wasted' copper cost to my mind...

Rgds

Damon

[fcfcfc]

Hi:

I think it is an interesting thought but I think the Cu in PCB's is usually only a dozen or so microns thick, no where near enough for the current capacities of this application...

Thanks though...

.....Bill

[wdyasq]

Bill,

I have used PCB material with thickness from "1/2 ounce" to "3 Ounce". I have seen, but not personally used 10 ounce and 20 ounce material.

Just keeping the record straight, the knowledge honest.

Ron