What comes up.......

[fritzblitz]

During the last few years I have 3 windmills running following Hugh Piggott's Scoraigh design. Both with rotor diameter of 2,4 m ( 8 ft), one of them 3 phases, the other 5 phases. Both are running so far without problems, furling securely and braving severe winds and even storms.

The reliable 8 foot machine

Encouraged by that, I went and built a fourth one,

Diameter 3m (10ft)

Disc 350mm (14 inch), width 10mm ( 3/8  inch)

Offset 130mm ( 5   inch)

12 magnets 40 grade 46/30/10mm ( 1 1/2 /1 1/8/3/8   inch)

9 coils, 55turns, diameter 1,7mm  14/13 AWG/3 phase generator

Gap 2,5mm ( 1/10 inch)

Stator thickness 15mm (5/8inch)

Tail length 1,5m      ( 5  ft), weight  0,5 kg less than the original construction

Distance windmill to battery: 100m ( 33   ft), cable 16mm ( 5/8   inch) aluminium, strand

Normally, this is a low wind region, except of several stormy days in autumn and spring, so I made the tail lighter than the original.

Well, it ran perfectly and really brought watts, but later in  the same day I put it up a strong wind came up (20-30m/sec), the ampere meter showed 40 and above. And the short circuit failed to stop it! The machine ran away like crazy, there was no way to stop it. Eventually, a part of the stator dropped down, miraculously not hitting the blades. The tail jerked, but did not influence the direction of the rotor, the mast shook. The rotor ran on, through the whole night, and we hoped the wind would stop to give us the chance to catch it, but in the afternoon the second part of the stator loosened, and because that part was fastened to the rectifier with the cables, it finally hit the blades, the shock brought the tower to fall and everything came down in splinters except of the rotors with the magnets which were unharmed. What a disappointment!

Stator mold with coil -placement

10 feet machine test  open voltage at 600 RPM

Mounting the generator to the tower top

Last correction before the start

Notice the windmill far right, half of the stator is tangeling behind the blades before it eventually fell down

Burn out syndrome: the rest of half the  stator

High RPM self destruction, the upper half of the Stator still clinging to it's place

Sparkeling coils....

......producing burnout smoking

Down to earth again

The magnet fixation was very strong they all kept in their place! Notice the coils between the rotors!

Trying to analyse what had gone wrong, I suppose that the rotating speed of the blades was so high that these centrifugal forces disabled the furling system. Even though the tail jerked up, it was not able to move the blades out of the wind once they had a certain speed.

[Flux]

I haven't studied this in detail but several things come to mind. firstly I don't consider 12 magnets per disc to be adequate for a 10ft machine unless you can furl it safely in quite low winds.

From your pictures you have not used a lot of the available winding space so you have thinner wire with more resistance than it should have had.

The two factors would give you a machine that will not stop with a short circuit in high winds. Your furling failed and it went head on into the wind as these always do if the offset is too small.

When you lost control the only hope you had was to leave it running and as it was doing over 40A you would probably have had to let it run open circuit. I don't know whether it would have survived that on over voltage or over speed. If you had extra batteries available you may have saved it working into a higher voltage but messing about with battery connections under those conditions is not something to undertake lightly.

If furling fails and you have no back up method of stopping it then disaster is almost certain.

I am now completely convinced that if you use Dan's style prop then an offset of 1/2" per foot is not enough. With Hugh's faster prop with tsr 7 it may be ok.

Normally low wind areas are tricky as it may take you a long time to find that it doesn't in fact furl and if you find out during a storm then it's disaster.

I don't seem to be able to get it through to people that lifting the tail is no true indication that it is furling. Unless the prop moves far enough edgeways on to the wind to actually see the power drop in a high wind it is not furling and you can't be sure it is safe. Tail weight is only relevant to the power you get out when furling, if the offset is too small and it seeks the wind it will run upwind without a tail and you have no control over it.

I discovered this a long time ago but fortunately I have never built a big machine without alternative ways of stopping it.

I think you have a few options, you can reduce prop diameter and keep the same offset and this will probably suit your magnets better. Alternatively you can try to get more copper into those coils and increase the offset and see if you can keep the 10ft prop with better low wind performance but with a furling scheme that will control it in high winds.

With those magnets and a 10ft prop you may never be able to rely on short circuit braking to stop it or hold it in a high wind but if it furls then as long as you leave it running it ought to be ok.

I expect people are fed up with me keeping on about offset and wind seeking, few seem to want to accept that this phenomenon does occur but I see evidence of it and stator failure here regularly.

A furling scheme that works on one machine in one area may not work on another with different line resistance and other factors in another area. Ideally we can copy a proven design but even if it is proven few will copy everything exactly and it seems that changes to the prop more than anything else affect this wind seeking issue.

I have never had trouble with an offset of 1/2" per foot but I have never built stall regulated machines and I don't build my props the same way. I originally thought it was ok but I have had to change my mind over the years. I was originally convinced the trouble was excessively heavy tails but I now think it is wind seeking.

I feel particularly sorry for you as with several successful machines you were probably convinced that all would be well, this still remains a black art.

Flux

[jaskiainen]

Hi Flux!

It seems to me that the magnet rotors have survived from disaster, but

how about the magnets? From the pictures it seems to me that the temperature

have been quite high? How much magnetization is there left?

[Flux]

I share your worry about the magnets but I am reasonably hopeful that they may be ok.

There doesn't seem to be much evidence of the coils bursting and rubbing the magnet faces, that is what normally causes enough heat to destroy them. There will have been a lot of heat in the coils but with the wind I doubt that direct radiation will have heated the magnets enough to destroy them but there were a lot of demagnetising amp turns floating about and it wouldn't have needed a lot of heat.

I would suggest a test coil to check that the magnets are still ok. The fact that they are still in place may be an indication that they are still reasonably strong.

I really hope he gets away with the magnets, he needs a bit of luck after this.

Flux

[dlenox]

fritz,

WOW - sorry for the problems - but thanks for the terrific pictures and narrative!

Dan Lenox

[Janne]

Sorry to see this happen.

I also know how it feels to see the furling system prove to be ineffective in a storm, but I was able to get away from it by shorthing the phases. I thought it was furling ok, since it was lifting the tail, and even seemed to drop the output while "furling" but when the first real storm hit, it wasn't limiting the output at all. The rotor was heading into the wind regardless of the tail.

It will be interesting to see, if we will ever get to the bottom on the causes of the seeking phenomenon. So far it seems the only certain thing that causes seeking / bad furling is low offset.. but then again some commercial machines get away with very little offset, and furl properly.

[Junkie]

Wow, I've never seen a failure that looks like that!  At least you have the other mills to compensate until you get it flying again.

[Flux]

Yes indeed some commercial machines have very little offset and furl ( Bergey does but it virtually shuts down when it does).

Another that I won't mention survives but I think it does so because the alternator reactance limits below burn out current.

The Bergey blades are probably the reason for their ability to work with low offset, I believe that if you fit different blades it fails and goes head into the wind.

I think if you hit peak power and peak thrust at furl point things work much better. If you are in stall when the thrust starts to lift the tail you are not controlling by turning from the wind alone and if it breaks through stall the furling point either disappears or moves to a wind speed above burn out point.

Flux

[taylorp035]

Thank goodness you didn't get hurt.  I always stand in front of my windmills when it gets really windy.

I almost hurt my self pretty badly once by making the mistake of mounting an 8 ft windmill to an aluminum step ladder.  Not only did the quick grips fail, but the 40mph wind was too much for my self and my brother to push the ladder forwards.  Luckily when the blades shattered, they went up and out instead of backwards.  The blades flew about 150 ft.

I have a storm coming towards my house tomorrow with expected sustained winds of 41 mph, so I hope to get out today (5-10mph winds) to test my new windmill.

[MagZ]

Hi Flux,

I have a 10ft machine using the 48 volt heavy duty stator setup and went with a 6 inch offset which seems to do the trick 'so far'... I am in a very high wind area and I must say it is scary to see and experience when you get those really extreme gusts of wind. I have been toying with the idea to put an electic control right on top to pull the tail and the alternator into complete furl position. I have 2 anemometer runnig all the time for data logging and both units allow me to set a max for gusts or windspeed that can trigger anything from dial out to solid state relay.

I was thinking of using a small electric actuator like you would see on a steerable dish, except way smaller. Sometimes you can see the shorter ones used for snowplows on pickups.

Any comnments that you might have. Maybe you can also describe your safety net that you have build in. If there is anyone else that is using an overide... or has a good idea - why not share it and describe it or maybe even a picture would be nice.

I think the alternator itself the design has been very well perfected, but a great deal needs to be done so that all that work - does not go up in smoke.

I am in the process currently to build 2 more 10ft turbines and I really want to put some more effort into furling and an emergency override. I have to stick with 10ft max, because in my area windmills are not very much liked and the bylaws are horrible.

yes, I do live in the country....

Thanks in advance for all input!

Cheers, Manne

[fritzblitz]

Hello flux,

I am very grateful for your immediate and throughout answer. Thanks for investing this big amount of time and trouble to analyze my troubles.

It really seems to be a kind of "black art". But obviously not all of it. And good advice inevitably leads to more questions:

Test coil: I am able to realize that, but what shall I compare the results of my measurements to as to know whether or not the magnets still are ok?

Next try blades: As I have to make new blades anyway (and I love making blades, today I made 3 complete ones!), I have the option to make them a smaller diameter. I prefer the DanB-method , because it is a bit easier to make them. But what diameter should  I choose? If I got you right, you make your own blade design, am I allowed to know what it looks like?

Stator: I cannot change the number of magnets (if they are still working), but I have to make a new stator.  What size of  wire should I take and how many turns? And how should they be connected, star or delta?

Other means of slowing down the machine: I will install a disk brake this time. I know there are models existing, but I could not befriend me with any of them, so I have designed an individual one. If it will be working as I think it should, I will write about it in a separate posting.

Well, thanks again for all the hints, especially that regarding setoff and rotor relation. I think you point to something crucial there.

Best regards

Fritz

[Flux]

This business of having a back up shut down scheme is a trick one. Inevitably it adds complexity and in some ways violates the KISS principle.

I am sure you could use your servo motor satisfactorily but it does open many new areas for failure. I have used something similar but at ground level actuating a manual shut down.

Several people here have managed to incorporate some form of brake as a back up but it needs a bit of ingenuity to get a control wire to operate it,

I use schemes to turn the tail at right angles to the wind to stop the thing and again the messy bit is the linkage that converts the pull through 90 deg to do this.

It is effectively a mechanical slip ring that lets the machine rotate without winding up the control cable and it then converts the pull to a suitable direction to turn the tail to full furl.

I find it very difficult to draw these mechanisms as they sort of have to be drawn in 3 dimensions to show how it works. I am not sure if I could manage to post pictures at the moment even if I could draw it.

The ideal fail safe mechanism would shut the machine down if the stop cable failed, one of my machines does work this way but it has a strange furling scheme ( in fact most of mine have). This particular one has the tail gravity controlled to furl and the control cable holds the machine into the wind. By adding more weight to the control it raises the furling speed. To achieve this I have had to resort to slip rings so that the control cable can hang down the centre of the tower. In many ways I prefer not to use slip rings but if built properly they are ok, in the hands of most people they are a disaster.

The other machines with no slip rings have a sliding sleeve round the yaw tube, pulled by the control cable and a flange on this sliding tube works a bell crank that revolves with the turbine head and pulls the tail to full furl. It works perfectly well but the sliding mechanism needs greasing about once a year in our nasty climate. in dry areas it may work for years without attention.

The scheme was used in a similar way on many wind pumps and was also used on the Lucas Freelite and I have to confess that is where I got the idea from. I think the little Winco used a similar idea to apply a brake. I wouldn't use a brake in our climate but in dry areas it should be fine as long as it can stop the machine and hold it stopped, any half measures will burn out very quickly.

In some areas it seems fine to let machines run through a storm but unless the thing is up in very clean wind things can get very turbulent indeed and tails start wagging about and even if it furls properly a gust will often catch it in the wrong directions until it sorts itself out again. It is probably safer in the end for things to be shut down under these conditions.

A machine that furls properly and shuts down or a brake switch should be ok to shut down or leave running. The big snag if there is no back up comes if you develop an electrical fault and loose the alternator connection, it can't be stopped and with no load furling will probably not come into play until it reaches a frightening run away speed.

Flux

[fritzblitz]

Wow, what a lot of response on the board! Thanks for the encouragement and sympathy, there seem to come more of them down as I realized they were. I always thought it was only my bad luck caused by my limited understanding of electrodynamics and aerodynamics!

Thanks to all of you!

Fritz

[Flux]

If you make new blades then I suspect you will need to keep between 8 and 9ft. I really think you need more magnet for much bigger.

I make my blades very similar to Dan but they are not as wide or as thick ( I only do it as a hobby and wood is costly). My blades probably are nearer tsr7 and I personally consider the inner third useless so I won't use wide thick roots ( just thick enough for strength). I am sure this does change the seeking behaviour. You could probably consider my blades as being similar tu Hugh's over the outer 2/3 but simplified as Dan's to run out to the root dimension without large chord or twist.

If you work back from your winding calculations to the voltage for a single coil and make one as before you should get the same voltage at the same speed. If the magnets are down you will get lower volts. I certainly wouldn't chance it if there is much loss in flux as you are short of magnet anyway.

In theory they could be remagnetised but it needs a capacitor discharge scheme with large capacitors and high voltages, not normally practical for attempting at home but if you are competent with high voltages and have some capacitors it may not be impossible. Ideally you need a big thyristor to connect the magnetising coil but  a big switch and a fuse in circuit may work as long as the circuit doesn't ring. I am not really advising you to try but it may save the cost of a set of magnets.

It seems as though your cut in speed was ok before so going to a smaller prop should be ok . You may be able to manage with a few less turns with the faster prop. I would choose a wire size such that you fill all the space, the outside of the coils should just about touch and you can squeeze the holes a bit triangular if needed to get a bigger size in the centre part of the hole doesn't loose you much if it is a bit smaller than the magnet.

Flux

[fabricator]

I hate to kick a guy when he's down but, the structure seems light for a ten foot machine.

[ibeweagle]

think thats bad look at my posts or pictures from 4 years ago or more stator exploded on 12 footer design for stronger generator now have it worked out the thiner the stator the more cooling it has also went to 16 mag per rotor look at you tube under ibeweagle to see cheers hope you get some ideas and get it back up wish I had pictures of it bolwing up but the blades did seervive and used the tail and rope to stop it from free weeling

[Dave B]

 Sorry for the accident and I wish you well on the rebuild. I'd like to comment on and thank you for posting this as well as the great photos.

 For any one still wondering about the rotors and securing the magnets etc. this is a perfect example showing that properly securing the magnets with a quality adhesive can take some major punishment with no loss. Also, look how by not casting the magnets there is very little potential for cracking and holding moisture leading to rusting and eventually the many failures that we have seen in the past.

  Just my observation and a confirmation to me that I will always secure the magnets with a quality adhesive and proper perperation of the surfaces. I won't trap them by casting them in potential water pockets when the temperature changes and the rotors flex and all that good looking stuff between the magnets cracks. (the rotors do flex)

  Thanks again for sharing your failure and great photos that we all can learn from. You'll lhave this back up again soon I'm sure.  Dave B.  

[Dave B]

Looking at the photos again it appears that you may have some type of pin(s) at the outter end of the magnets ? All the better as far as securing the magnets, I'll repeat again it's good to see how well they stayed fixed in position after all this punishment.  Dave B.

[imsmooth]

Flux,

If the prop is seeking the wind, what is keeping the tail up in this condition?  Wouldn't the face of the tail be in the wind and pushed back?

[fritzblitz]

It is very consoling there are some positive things to see, too.

You are right, the magnets kept in place. But I did not only glue them in place, I fixed them with roll-pins as well. But I will open a new thread for that (Magnet fixation without casting) for there are some pictures going with that and it will be a bit too big for this thread here.