Author Topic: 20 Ft Wind turbine (Read 3365 times)

Sue Karber · « **on:** March 14, 2006, 11:18:59 PM »

This is my first posting. I have been watching for several months. In the past I have built a 5 ft turbine with a induction generator with chain drive transmission. The turbine worked fine but the generator made little or no power and at times consumed power. I have been looking for a direct drive alternator or generator that I could build and I believe the axial design that is used here is it. I have 32 neo mags 3"x1 1/2" x 3/4". I have planned to build a 20 ft turbine with 3 blades 14" at the base and 6" at the tip with 6 degrees angle of attack at mid blade and 3 degrees at the tip. The alternator will be three phase dual rotor using 5/8" thick steel disks, 48 volt dc charging into a battery bank, with a 12 coil stator wired in star configuration 5/8" thick. I have a 6000 pound rated trailer wheel bearing. I have constructed a coil winder & have wound my first coil with 2 in hand #13 mag wire 70 turns. The reason for the #13 wire was to lower the resistance and to avoid stator over heating ; however I find that to make everything fit around the stator my rotors will have to be 27" in diameter. I will be putting all this on a 40 ft tower made from 4 1/2" pipe with guy wires (5/16" cable). Before I fire up my plasma cutter to cut the rotors I want some advice from the board, am I on the right track or am I fixing to make high priced junk. A little help from Nando, Flux and DanB would be appreciated, but anyone would be welcome to make comments. Thanks ahead of time for all comments. Harold & Sue

willib · « **Reply #1 on:** March 14, 2006, 06:17:54 PM »

sue & harold , looks to me like it will fit in a 12.56 " disk.

wanna see the drawing?

fanman · « **Reply #2 on:** March 14, 2006, 06:20:28 PM »

hey sue

fanman here, it sounds like you are on the very right track here, ive made a 16' axial flux just lately and its working great, one or two words of insight would be make it as strong as possible in all respects, which it sounds like you are, and make sure your cut in is fairly low for that big blade, somewhere around 65, 70

rpms or so, if your wind site is above average kick the cut in up a bit to say 90 rpms that will help eliminate the stalling effect. i found the best way to build anything is to take in all the information you can,and make your best desicion, everyone on this board is very helpful and extremly knowlegable, make sure you post alot of pictures eh? good luck

Nando · « **Reply #3 on:** March 14, 2006, 10:47:19 PM »

Sue:

Such diameter wind mill will be producing a lot of more power if the generator is designed to produce high voltage at peak RPM.

For this a MPPT controller will be needed and as well an ELC for wind mill protection.

Depending on the generated voltage and the winding phase resistance the power dissipated by the generator can be set to 10 to 15 %, lowering the generator dissipation by 35 to 40 %, and the power delivery could rise to about 35 to 40 % additional of the expected power if the generator is treated as a 1/2 power wind mill.

Nando

Flux · « **Reply #4 on:** March 15, 2006, 01:17:49 AM »

Sue

The turns and wire size seem fine for 48v but the magnet rotor diameter seems excessive.

I suspect you are thinking to use a thin stator. Those 3/4" thick magnets will take a stator about 1" thick with those turns and i would have thought you should get it in a diameter of 20" although I would be tempted to increase it to 22".

I think you had better confirm your stator thickness before we continue discussion, but in general you are close.

Flux

picmacmillan · « **Reply #5 on:** March 15, 2006, 07:15:48 AM »

hi sue/harold..

i am building a17' turbine now..the stats will be in on the stator by the weekend(just soldering it up today..) ..everything you putdown as data seems at first glance to be correct..

my stator(and yours should be about 5/8" thick..(.625)..my stator is 20" diameter so yours wont be much bigger, if at all..in fact i could have put a little more wire in there if needed..

i used 69 turns of #15 wire..i am not totally sure if 70 turns of #13 is the correct number of turns..you may have been looking at danb's test coil he used.not sure and i apologise if i am uninformed here..that could be an issue

another kind of primitive thing i do is i squeeze my coils in the vise when i am finished just prior to putting them into the mold..i put a thin piece of wood on each jaw of the vise so the metal vise doesnt scratch the coating off the coils..this doesnt hurt anything as i have done this on all my turbines so far.the main reason i do this, is because i have a real hard time fitting my finished coils into the room available usually...

also because of the big magnets you are using( i am using these also), there will be some cancellation at the innermost ring of the stator anyhow..dont worry about losing a bit of power...you will be getting lots of it anyhow..worry more about getting the coils to fit in the mold.....

further, i have a serious reservation about making the stator as big as you suggested..at this point the stators 20" in diameter are starting to melt at 400 degrees farenheit..i believe from a technical standpoint that the moment(distance) created from where the stator is bolted to the inner edge of the stator(where this is no support), is too long already, any further would make the stator even weaker...the heat created and the linear expansion of the wire make the stator curl, which leads to contact with the magnets and total failure....in a nutshell you dont want that.....so,as stated in the other posts..your stator doesnt need to be that big...your figures are wrong...you can squeeze them a bit in the vise if needed, and a larger stator will result in failure due to heat and warpage..hope this helps..i will post some pictures later on todays....good luck...pickster

Flux · « **Reply #6 on:** March 15, 2006, 07:28:16 AM »

Just found your stator thickness, 5/8".

At that thickness your cut in will be slow with 70 turns. You have some choices. You can reduce the number of turns and that will get it in a smaller diameter than 27" or you can increase stator thickness and keep turns the same and again reduce disc diameter. Finally you could increase stator thickness, keep turns the same, use thicker wire and keep the large disc diameter.

The last option may pay off but I have no experience of this wide magnet spacing approach and from tests I have done for jerry lately you may find that you may have to do it by trial and error. The emf will be the same but waveform changes may reduce the effectiveness of star connection.

Not an easy choice, the thick stator is more rigid and stable but heat transfer will be worse than the thin one.

If you have wound the coils then you may decide to proceed with the big discs and open the gap to suit, otherwise I would be tempted to increase stator thickness and bring the magnet rotor diameter down as long as your hub is not a factor in needing the larger disc diameter.

Flux

Flux · « **Reply #7 on:** March 15, 2006, 08:00:56 AM »

Pic.

Your wire size is very small, I wouldn't have considered less than 2 in hand #15. I think Sue's winding is nearer the mark but with a thicker stator and rotors about 22" diameter.

I think you are more likely to have a burn out due to small wire than a larger diameter stator. Personally I think these stator temperatures are crazy and burnout is inevitable, just a case of when. I think Dan's trouble started with the rectifier fault and the original rating would have caused long term failure but it may have taken years to show. At the rating after increasing the air gap life was bound to be short.

I would go for a very low resistance stator and either live with drastic stall as a means of protection or add line resistors and dissipate the most of the heat outside the stator. It is a shame that furling is a crude and not precise process and if it worked as it should in theory then life would be a lot easier.

It would be difficult to work reliably at these high temperatures with true class H insulation everywhere. I have no idea what polyester is rated at but it does put up a good fight and I suspect it is better than normal epoxy ( neglecting special epoxy motor varnishes).

What was adequate for 8ft machines a few years ago is being pushed well beyond the limit for these large machines.

Flux

dinges · « **Reply #8 on:** March 15, 2006, 08:45:46 AM »

I agree with Flux here.

Also, PIC, when you say that 'a little loss is not much of an issue'. It's not much of an issue in a 'small' genny. However, 10% loss (don't know if this is accurate guesstimate; 90% efficiency I'd consider to be pretty good) of 6000 W is 600W. That's a lot of heat. Your stator is ofcourse a bit bigger too, but not proportionally, I think.

I think absolute priority is having a low stator resistance, i.e. as thick wire as humanly possible. And when designs are getting this big, I'd probably cast-in a little thermo-sensor as well. It gives you the option to monitor temperature, or just ignore if later temperature of stator isn't an issue at all.

About a year ago, when I started reading this board, the maximum seemed to be 14-15 foot. Nowadays 17ft is the standard upper limit, and there's already talk of 20ft. Wow... I wonder where it'll end.

But I'm afraid that the design is being pushed to its very limit here. There are limits to scaling things up. Looking forward though to hearing updates on that 20footer!

BTW, Sue & Harold, I assume you are aware of the Nirvana machine at Hugh Piggot's website?

Succes,

Peter.

BigBreaker · « **Reply #9 on:** March 15, 2006, 10:40:24 AM »

There are resins designed for high thermature and high thermal conductivity. We just aren't using them yet.

Once you are using resins that trnasmit heat, you can also start to dump that heat in a variety of ways. As it is now though... the heat is mostly trapped. Not good.

nanotech · « **Reply #10 on:** March 15, 2006, 11:56:06 AM »

Has anyone thought of using computer CPU heatsinks molded into the epoxy/resin on some of these larger machines?

I'll try to describe it in words without resorting to TurboCAD....

When you wind your coils and set them in the mold, could you not place a CPU heatsink directly onto the coils, and then fill the mold with the epoxy/resin? That way any heat developed by the coils would be transfered to the heatsink, and then out throught the heatsink to the air. The benefit of this is that the heatsink would be doing its most work when the most cooling effect is available, ie; when the most heat is generated is when the most wind is coming over the heatsink.......

I mean, Dinges was just talking about a 600W dissapation requirement, and my current CPU creates 105W of heat. So if you've got 9 coils (low number, I know) each with a heat sink capable of pulling off 105W of heat, you're 50% ahead of the 600W requirement there. Even more so with a 12 coil system.

Just an idea for all you folks building these monsters......

kitno455 · « **Reply #11 on:** March 15, 2006, 12:21:39 PM »

uhm- embedding a big chunk of aluminum into the stator is a REALLY bad idea. just think of all the eddy currents in that thing, it would stall the prop. i guess you could try it only on the outside edge, but we are already looking at a pretty good temp. diff. in the radial direction. the stator would probably end up looking like a belleville washer.

allan

Nil · « **Reply #12 on:** March 15, 2006, 02:42:05 PM »

What ever happened to the "Nirvana" machine anyway. I found a link on the scoragwind page, but there was not a update on it.

Also, has there been any issues with overheating a converted motor? I know Zubby was fairly certain that the way the motors wer built would allow good cooling of the coils. Also in the conversions you dont have the casting to wory about, just the coils and the steel.

Anyway just some questions to draw this off topic.

DanB · « **Reply #13 on:** March 15, 2006, 03:34:38 PM »

yes - I expect (hope) Pickster used 2 strands in hand of #15 wire... a single strand would have very hgh resistance for that machine.

willib · « **Reply #14 on:** March 15, 2006, 03:50:48 PM »

any in particular in mind?

Sue Karber · « **Reply #15 on:** March 15, 2006, 06:26:59 PM »

Is this a great board or what. Thanks to all for your comments this is exactly what I was hoping for. Yes I will post some pics as I build, but I do not build at the speed of DanB so be patient. Thanks again Harold & Sue

picmacmillan · « **Reply #16 on:** March 15, 2006, 06:29:55 PM »

hi all thanks for looking out for me..

just a misprint on my part..i am in fact using 2 strands #15 wire , not one..not sure if i didnt state that, but sometimes my brain is slower than my typing fingers..

i think everything i have done for this turbine has been researched and looks to me like it will run fine..in my application if i get 4000 watts, that is plenty more than i need...so wasting some power to cancellation isnt an issue in my case...

i use 7 kwh of energy at my place now..obviously having this much energy isnt needed, but sometimes i like to leave my place for extended periods of time and we heat only with wood...we have no oil furnace or anything so electric heat will release me from being a slave to a wood stove 3 times a day..and more than all of this..building these things is the most fun at any hobby i have ever had...the challenges that come along with learning as we go is far more gratifying than any lab i had done while taking mechanical engineering in school..anyone who has been in this field knows the labs are rediculously mundane and irrelevant....

here, we learn every day..we interact with each other and help one another along the way..and hopefully we make a friend or too which is a bonus....it is rare to see in industry, but quite common on this site for folks to look at what you are doing(like they did above for me), and help us when they see something that doesnt sound right and this ensures we build good quality machines, and look out for our well being in the process...if you can beat that, i'll buy some myself ..i got my 17' machine stator done tonight and will send the information on it tomorrow,....cant wait.....thanks men(and ladies)..pickster

paradigmdesign · « **Reply #17 on:** March 16, 2006, 09:09:55 AM »

The only thing I would change is the 40' tower, turbilance is a important factor as the size of the turbine goes up, and unless you are located on something flatter than a corn field, 40 feet will have alot of turbliance. Sounds like a solid design, blades seem appropriate for what you are looking to do.

What is the wind class (average wind speed) where you live?

nanotech · « **Reply #18 on:** March 17, 2006, 12:10:29 AM »

I wonder if there's a ceramic heat sink.......

Hrm.

ghurd · « **Reply #19 on:** March 17, 2006, 06:04:53 AM »

Beryllium oxide ?

G-

dinges · « **Reply #20 on:** March 17, 2006, 07:28:17 AM »

Try Plutonium perhaps?

BeO is extremely toxic. I'd be surprized if anyone could purchase it. If I could, I wouldn't want to work with it (saw, grind or sand).

I'm assuming Ghurd is joking here. I hope?

Peter.

ghurd · « **Reply #21 on:** March 17, 2006, 08:02:19 AM »

Thanks Peter! I did not know it was that bad.

(Yes, I know where to buy it)

DanB · « **Reply #22 on:** March 17, 2006, 01:42:31 PM »

Im working on something along those lines and I feel like Ill be pushing my luck with 40 of the same magnets. You're planning heavier wire, but Im wondering how youll fit so many turns if you keep your magnets reasonably close together - assuming youve got 16 magnets per rotor, and 12 coils. With that many magnets, I would be inclined to have smaller disks (around 18" perhaps) - and I think youll need to use finer wire and a smaller blade than 20' diameter. Unless Im misunderstanding your plan..

I think you have the same # of magnets as I used on the 17' machine, and some benifit could be gained by using larger rotors than I did for that machine. I expect the coils should be similar, you can probably squeeze in two strands of #14 with larger rotors - I expect a 17' blade would be reasonable.

Sue Karber · « **Reply #23 on:** March 18, 2006, 08:54:42 PM »

We live near Kingfisher, Oklahoma. The wind data from the Mesonet says we have an average wind speed at 30 ft of 12 MPH and that our winds come from the south or the north most of the time. Assuming you've never been here it is extremely flat. Thanks for your comments.

Sue Karber · « **Reply #24 on:** March 18, 2006, 09:04:07 PM »

Thank you for taking the time to comment on my post. It is highly valued. Perhaps I should scale my machine back a bit. We always love your posts. Thanks again Harold And Sue

oztules · « **Reply #25 on:** March 18, 2006, 09:24:33 PM »

Heat sinks in continious duty can only transfer heat from one place to another. Once your ceramic,aluminium,plotonium or whatever type heat sink has sunk its heat, where is it going to put it?

Being embedded in an insulating material (epoxy or other resin) once it absorbes the initial heat load, it has nowhere to transfer it. In your computer, a fan disappates the heat from the fins to the surrounding air, how can this be accomplished in an encapsulated environment?... and thats not worrying about the eddycurrents in a conductive heat sink.....

You already have excellent heat conductors in the stator.......the copper. But it can't get rid of the heat either.....because of the insulating properties of the resins.

It would appear that without solving this heat problem, that the upper limits of this technology may be getting nearer. Using electronics to give better efficiency will push the problem back a bit, but sooner or later it will re-appear, as we always want more...and more ....

slightly bewildered......oztules

BigBreaker · « **Reply #26 on:** March 20, 2006, 10:57:38 AM »

Checkout DanB's article testing resins with talc and aluminum. Silca additives among others can also help.

Resin is typically sold by its use rather than a formula. A quick googling for casting resin should get you your answers.

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Author Topic: 20 Ft Wind turbine (Read 3365 times)