Vertical Axis Wind Turbine (VAWT) Under Construction

hi, I'm going to build this kind of wind turbine myself, I have made some calculation but I still dont have a clue on building alternator w/ cut in speed at 60 rpm. can you give me some info about it? pls send it to my email, Im very thankful.

regards, andi (from indonesia)

Hi Andi. I'm still figuring windings and cut-in speed myself. I haven't gotten my turbine perfected to the point where it will spin safely at 60 rpm, and until I get it working properly, I'll put worrying about the alternator on hold. The cut-in speed, or windspeed at which the alternator begins to make sufficient electricity to charge the batteries, depends on several factors, Of course there is the efficiency of the turbine (the aspect that's giving me problems right now), the strength of the magnets, number of poles, and number of windings in the coils. Many alternators of this type are designed to be 3-phase with 12 magnets and 9 coils. In such a set-up, every fourth coil is wired together in series.

So what you could do to estimate of the output of your alternator is build the entire alternator except the stator. Then make one coil of 100-200 turns and mount it temporarily between the two magnet rotors. Spin the rotors at 60 rpm and measure the voltage produced in the coil. If your battery bank is 12v, then you will want a coil that produces from 2.8 to 3.3 volts. Adjust the windings in your coil until you reach that voltage. The (very approximate) formula I will use for my 12 magnet, 9 coil, 2 rotor, 3-phase alternator is: X*5.1=output voltage, where X=the voltage of one coil. Perhaps more knowledgeable folks will want to weigh in with their opinions.

I haven't gotten my turbine so I feel safe sitting next to it at 60 rpms to measure the voltage it puts out, but I'm fairly sure the 53 windings per coil is only about a third of what it should be. I'm going to make a new stator, and will be more methodical in my calculations. My "test coil" will start with 200 windings.

Good luck with your project. Keep us informed of your progress.

Very Good. I think u admir all support. All the best to u. Contact me. Gnaneshwar

Thank you for the kind words, Gnaneshwar. I have made quite a few changes in the design and hope to put them on the web log soon.

I like your design and the air foil’s but it doesn’t look vary sound if it was to be in a high wind but on the other hand I can tell from the airfoils that it is meant fore low winds

if the turbine rotates at low rpm’s and has sufficient stork you should try experimenting with a gear system fore your alternator

http://www.windstuffnow.com/main/vawt.htm http://www.windstuffnow.com/main/darrieus_type.htm

um my suggestion’s on improving your turbine wood be to extend the pool connected to your alternator and support it from the top aswell as the bass but you will have to design a new frame O.o um if that is to taxing you cood extend the bare and support it with 3 pool’s and cables that should give you an idea on how effective the rig will be in a high wind it should help you keep the rig more stable < but I think your problem is that your wind foils are to heavy and me not be the same weight cozing it to be unstable in high wind’s I don’t know how to be any more help

Gary, you raise an important point about strength and stability in high winds. The most recent incarnation of the rotor passed the wind test last week with flying colors. It freewheeled in 50mph winds and gusts that were considerably higher. The solar panels did not fare as well. They were completely smashed to bits, but that's another story.

There were three issues with this VAWT. First, the temporary stand was not able to keep the unit upright in a high wind. It tipped over once and there was quite a bit a damage done to one of the airfoils. I replaced the airfoil and weighted the stand down with about a ton of rocks at the base, and now it won't move.

The second issue had to do with the strength of the junction of the airfoils and the rotor. I used some hardened steel tubing, like bicycle frame tubing, that runs through three of the ribs and the end of the rotor arm on each foil. I changed the rotor arm from wood to rectangular aluminum stock. It is so strong now, I think I could hang off the end of the rotor and let it spin me around. I haven't dared try that though :~)

The third issue has to do with rotational speed. It starts to spin with the slightest breath of air, but it just won't go fast enough to generate a suitable voltage for charging batteries. I'm debating between shortening the rotor arm or gearing the alternator up with a chain and sprocket assembly.

Another thing to try is to replace one of the airfoils with a counterweight. I've recently learned the most efficient airplane prop designs are based on a single blade and counterweight. Maybe it would work for a turbine too.

hallo im a student at aruba. we was making a model figur VATW about 37cm lengt of the blades and 8 cm high.we made it out of sodacan.do you know what material is good to make the bigger one

Hi Sergio, If you want it to be strong and permanent, I recommend using aluminum sheet metal. For smaller temporary models, why not try making it from cardboard. Good luck!

with this model howmuch electrical power was available to charge the battery

Ninan, I have not yet gotten to the point where it makes electricity. There are many many factors that influence electric output. A few are, rotational speed, distance between magnet poles, number of magnet poles, strength of magnets, size of airfoils, number of windings, thickness of wire in coils, and of course, windspeed. I was hoping it would make a couple hundred watts in a good wind, but I am still a long way from that.

i`m just intrested abaut vawt...

Hi Tom, I've just finished reading 'Windpower Workshop' by Hugh Piggott. An alternative alternator design he talks about is an 'Axial' or 'Air Gap' design (as opposed to the more common 'Radial' design). Advantages include no 'cogging' and minimal starting torque. They also look easier to build than a radial alternator. A thought that struck me when I looked at it was that you could use a large diameter 'axial' design with an increased number of magnets and/or coils and that this could be a better way to get things moving quicker than using gearing (which is lossy and prone to mechanical failure). Could be worth a look - I'll be keen to hear how you go, as I've also got a VAWT project on my list. Cheers, Chris.

Hiya Chris. The axial design is what I have chosen. It can be quite effective using dual rotors that have magnets on them. The stator is fixed between them and has properly sized and spaced wire coils. The problem I've had is I just can't get the thing to spin fast enough to generate voltage sufficient to charge the battery. I could correct this problem in a variety of ways, e.g. increase the number of windings, use more powerful magnets, decrease the air space between the rotors, gear up the rotors, or decrease the diameter of the rotor arms. Since this is an alternator that makes AC, I also thought about making a transformer to step up the voltage. Each method has its weak points. I've elected to begin by adding a chain and sprocket assembly. The first gear ratio I will try is 3:1. The unit is in the shop right now undergoing alterations.

One more lower transfer loss option - increase the stator diameter. Yea, you'll get a funny looking waveform in testing, but the flux delta will be steeper while the magnet passes and net more voltage.

It would take a little bit of work on the mount, though.

Thanks, Sean, for reminding me of this option. Of course, increasing stator size would also require new matching rotors.

i think the blades have too much cord for high speed you have made most of a wing reduce the core and cover top and bottom and it should fly!

I have windmill with rotation sailes.

http://gau.psp.efos.hr/DesktopDefault.aspx?swidth=800&sheight=600&DocumentI D=1997

Dave, the blade profile is as it should be. This design by no means adhears to conventional aerodymaic "wisdom". thinking about an aircraft wing will distort your view of whats happenning as airplanes don't fly in tiny circles.

Improvements will be made but I doubt the profile will adopt a more winglike shape.

I am also thinking about building this kind of of VAWT when I have done al research of what type of alternator i needed and so on. I want to make a 1kW version and was hoping it would not be to big.

What kind of wind speed have you seen and at which rpm did your machine rotate at certain wind speeds?

Ed's smaller version rotated with 240 rpm at 17 mph. Do you get the same kind of rotation speed with an upscaled version?

Hi, As my final school project I am building a VAWT having 2m Dia. with 3: 2m * 2m sheet aluminum & composite blades using a modified verson of a Rahai airfoil profile. Full 3-D Cad models have been created. Stress analysis as well as CFD have been partially comlpeted.

We are now on to materials selection. I however have no experience in bearings selection as well as the electrical components needed to generate power. I would like to get a flanged bearing unit that will support the axial load from the weight of the blades as well as radial loads from the wind. Do you have any ideas, what kind of bearing are you using?

Regards, Adrian QC, CA

Thank you, Adrian and Peter for your comments. The VAWT is nearing a new stage of completion and I hope to have a new blog entry updating my progress soon. I'm building my second stator (the first didn't turn out the way I wanted). According to my coil tests, I expect the 3-phase stator to produce about 20 volts rectified dc when the rotors are turning about 20 rpm in a gentle breeze.

Rotational speed is a function of windspeed and rotor diameter. Given the same windspeed, a small diameter rotor will turn at a higher rpm than a large diameter rotor. It is like the spinning ice skater who speeds up when arms and legs are drawn together. Because this VAWT has an almost 4 foot diameter, I had problems getting it to spin fast enough to generate a usable voltage.

Peter, you can get a very rough approximation of how a rotor such as this VAWT will rotate by applying this formula: RPM = windspeed / circumference where windspeed is measured in feet per minute and circumference is measured in feet. Since circumference is pi times the diameter, maybe you can visualize how increasing diameter will result in a slower rpm.

I have finally gotten some promising results that I will be reporting on soon (hopefully!). As a preview, the VAWT now uses a chain and sprocket to increase the rotational speed of the rotors. The VAWT turns very easily in a 7-8 mph wind while spinning the rotors at about 60 rpm. The 9 coils in the new stator are #18 awg, 200 turns, and each phase (three coils wired in series) can turn out 13 volts at that speed.

Adrian, I would love to see some pictures of your project as you progress. The bearings on which my rotor turns started out as old riding lawn mower deck bearings. They are really very good bearings that are easy to mount on a frame. They were free at the local repair shop. The down side is they are an odd size and every other component had to be machined to the right size adding expense, since I had to hire a machine shop to do the work. It would have been more economical for me to buy new standard size flange bearings and a stock spindle to fit them. A good source for these is a place called surpluscenter.com I went to them for the chain, sprockets, spindle and flange bearings to support them.

As for the electrical components, most wind turbines are suited to a low speed three phase alternator made with two rotors on which permanent magnets (often 12) are mounted. Between the closely spaced rotors is a stator holding coils of enamled "magnet" wire. The balance of # turns per coil, coil width and thickness, wire gauge, and distance between the two magnet rotors determines the electrical output. The higher the output, the larger your airfoils must be in order that they will overcome the resisting forces created when current flows through the coils setting up magnetic fields that are opposed to the magnetic fields of the magnets on the rotors. -tom

Hi again,

Thanks for your explanation of rpm versus wind speed! Now I can plan what diameter I am going to use on my PMA. I am planning to buy a one instead of making my own and concentrate on getting the VAWT really good instead. Will a third wing lower the rpm and in that case will the torque then increase?

Could you explain how the wind attacks this typ of VAWT (lift/drag)?

The wings should be open for maximum effect, or?

I was thinking of letting the wings be able to move around an axis instead of being fixed. What do you think of that idea?

Regards, Peter

Peter, My first attempts at a VAWT used three airfoils. I was pleasantly surprised when I tried a two-wing rotor and it actually worked better than the 3 wings. I had heard it would have trouble starting, but that is not the case with this design. I think the improvement has to do with reduced solidity, a concept more suitable for HAWTs. Basically two blades are less mass that has to be pushed around so it's less resistance for the wind.

I am no expert on airfoils and lift baffles me. I'm told that this design relies on both lift (which it gets from its long trailing edge) and drag (which it gets from the cups). Ed Lenz, who originated the design in a three-wing version characterized it as being a slow rpm workhorse. I am inclined to agree. It catches gentle breezes, but does not spin wildly in high winds.

I don't think I would want to experiment with moveable wings with this size and shape of airfoil. They are so large and massive, there would be huges forces to manage if the wings could move.

Today my new stator was put in place. I have not yet connected the rectifier. Early indications are promising. 15 vac on one phase at 30 rpm in a 6-7 mph wind. -tom

Nice!

How about ribs cut out of polystyrene sheets and then make the skin with the kind of shrink poly used to wrap boats for winter storage.

I have made a smaller version only used the shrink poly used to insulate window in the winter.

Good to see lots of interest in VAWTS.

Geoff

If we build a bigger scale windturbine( 3m high by 1.5 m diam.) , that let's say should substain winds of around 36km/h. Don't you thnik there will be way too much vibrations. And at this kind a speed, the massive profile of those type of blades will slow down the turbine and create a stall effect ?? What do you think about my opinions ??

I think you could scale this up to a much larger size. My present VAWT is 8 feet in diameter and uses 6 foot blades. It has survived winds of 80 mph. As size increases you have to worry about centrifugal forces during high winds. A weak spot of this turbine is where the blades join with the rotor arm. If your blades are 3m, you will want to make sure they are rigid enough to withstand the centrifugal forces as well as the force of a high wind trying to topple the blades over. Study the construction techniques of small metal aircraft wings. I don't believe stalling will be a problem in a VAWT of the size you describe. To the contrary, you will be very surprised at how easily the blades turn. My VAWT now has a 5:1 chain and sprocket on it to allow the alternator to run fast enough. It starts turning in a 5mph wind. Before I put on the chain and sprocket, when it was running direct to the alternator, it turned even when you could not feel the wind on your face!

I am wanting to build a VAWT similar to yours as well. My plan for the electrical end of it is to have a large disk at the bottom which will help to support the wings. This disk will have 3 alternators arround it which will run on friction. This wil provide a very high gear ratio with minimal energy loss if my plans are correct. Have disks on the top and bottom should also reduce the tip votex losses as well. I haven't begun construction yet so we will see what happens when it gets running.

I have ventured into this area as well. A a sailor and pilot I know something about lift. I believe you have the metal on the wrong side. The "top" part of the wing is the one that needs the surface, not the bottom. Think of how the sail of a sail boat works.