Slowing a wind machine in a storm

Connect additional resistances in parallel across the output terminals as the speed begins to rise and take them off when it begins to drop?

There exists an automatic braking system for conventional water pumping windmills. Try putting your hands on one.

With this system, the weathervane turns and makes the mill's turbine stay parallel to the wind, anytime the winds blows faster than advisable.

I will try to find the information for you, but I am not sure I will be able to do it.

Thankyou I will look into both.

But the extra load - why not another alternator - the savonius has great torque?

are there any functional ideas out there how to attach more than one alternator to a shaft ?

I Know fewer blades are faster in VAWTs but what about fatter (I think thats called a high Reynolds Number) blades?

Braking a horizontal shaft wind wheel is explained at www.southx.co.za (reefing)

The site seems to be down. I will try and explain

The the centre of the wind-wheel is offset from the pivot on the tower.

High wind will therefore try and swing the wheel out of the way.

The tail fin will always point away from the wind.

With the wind wheel at an angle the area facing the direction of the wind is smaller (circle vs ellipse).

The leverage caused by the bending (between wind wheel and tail) is used for braking.

This cannot work with a vertical spindle wheel.

The big power generation turbines use tip braking, which basically stalls the airfoil to slow it down ( but they also use disc brakes as well.) Is there some way to stall your airfoil, or perhaps turn it 180 degrees (so it wants to reverse rotation) it might work. With the 180 degree idea, you would have to clock speed and apply a brake at low speed or it would slow down and the spin back up in the other direction...

Thank you very much. What about a centrifically launched chute?

I don't think a parachute would solve your problem. Once released it would 'hang' on the downwind side and cause additional strain on the system.

Extendable vanes would also cause more force because of the additional face to the wind.

Fixed adjustable guide vanes around the wheel might be the best solution.

Raising a sleeve like structure around the wheel (reducing the exposed area) can also be considered.

Can the pitch on the wheel be changed?

A generator charging batteries switching in as soon as the speed exceeds limits may also work. Can it be fixed?

Stopping may produce more forces than slowing down.

Can you post a sketch for better understanding?

I feel that provided the structure is strong enough, you need to "Shield" the rotor from the wind in some way. I am sure that it could even be done mechanically with a little thought.....I have some ideas, I will post them if any of them appear to be useful next week....

The way this is done is "shorting" the generator.

You will need a brake to bring him to a standstill as this shorting/braking can only be used for a limited time.

Generator suppliers must be able to lell you which current can be allowed for which time.

without the use of a brake.

This is a contradiction in terms.

You could switch in a short ciruit load at a certain wind speed that would slow it up.

A centrifugal brake is the simplest way.

Each half of the rotor could be spring loaded so it swing out and stops collecting wind above a certain rpm.

Why not a brake? That's simpler than deploying parachutes, and it's probably cheaper.

Otherwise, a simple governor mechanism may do the trick. See Flyball Governor.

Why not just augment the unit so that you can change the pitch of the blades to not catch as much wind. this can be controlled by a mechanical means with a clutch. which will or can be acted upon by the wind.

more wind=more clutch. more clutch =more angular pitch closer to direction of air flow. as the wind blows harder the stationary mechanism of the clutch will apply some braking tension while at the same time turning the blade pitch to catch less wind. kind of slows it down gradually and when the wind begins to subside it gradually releases. Conversely you can use a throw out bearing type mechanism that would not apply any brake force but simply alter the pitch of the blades

I hope this does not sound to idiotic

We are talking about a Savonius Windmill I believe, but I do not like the shorting out of the generator/Dynamo, or brakes, all are subject to possible damage and a runaway Windmill......my ideas on this are as follows:-

See also the following link on Wikipedia:-

http://en.wikipedia.org/wiki/Savonius_wind_turbine

The Turbines look a little like this (taken from Wikipedia)

May I suggest that with a little careful modification, using weights that swing out when over speed is achieved, that viewing from above that this:-

(Black spot is the spindle and center of rotation)

Turns into this:-

...and then it locks itself in this manner as otherwise it would oscillate between open and closed as it slowed down and speeds up again......

Of course, with even better mechanical preparation, you could use it to maintain a constant speed of rotation in any wind above a certain minimum.....then you could actually generate MORE current in a high wind!!! Or even generate 3 phase using the right equipment......constant controllable speed of rotation is a must for the AC versions, so giving a constant 50hz for europe or 60hz for many other countries....

I personally feel that this could be easily developed and although this type of Turbine is not as efficient as normal propeller methods, it does have an appeal with its simplicity of mechanical design.

A Vee pulley(s) could be used to connect it to a car alternator(s) with very little effort indeed....either underneath or above (or both!!)

One could even design a double version on one axis (each at 90° to the other to increase efficiency further) to allow a middle pulley to be used for power take off......

I hope that this promotes some further interest for yo'all!!

I see what you mean now.

I think if you were to make something like a governor with sliding levers on it and weights as you mentioned it could be easily attainable as you suggested.

Nice thinking,

A lock is even not necessary: the rotor will limit its speed and can supply power through the storm (interesting when you rely on it for pumping the excessive water a hurricane delivers)

The system is a kind of speed regulator, when no power is taken the speed will go up and the rotor closes.

How do you call this: the andy governor?

Why not?

I anticipate that the two halves on on tiny racks, with the pinions on the main shaft and a pair of weights with a spring in between to set the speed by reducing the size of the cup, pushing the racks in and out.....once I am really finished with working, I aim to knock up something say 2 meters long and about 50 cm diameter when fully closed.

I am wondering if the change in opening or closing will give dynamic balance problems.....or not.....?

My eventual aims are to drive one or more car alternators to charge batteries, also later to try and make 3 phase unit at 50hz, with a really good frequency control.....whether this will be achieved by a mechanical governor or not is another question I have!! ...to answer I mean!

I like this style of windmill for its simplicity for the home builder, even though it is not the most efficient.....

As long as the parts are equally weighted and remain symmetrical balance should not be an issue. Where you will get into problems is if things wear over time. You may then need to balance it occasionally..

But I do that with steam turbines, and gas turbines, and motors so why not??

Thats what I am talking about Andy

Have each rotor piviting on it's inside vertical edge. Have the outer edge held in postion by a spring....too much wind will push it back against the spring causing the air to spill out radially (also it won't spill into the other rotor anymore) this will slow 'em down and would be relatively simple to implement.

Del

There are newly developed transmissions for wind operated generators continuously variable transmission is coupled between rotor and generator so as generator rotates almost constant throghout the veriable wind speeds , just like that used in scooters lawn movers but in opposite mode . also you can design your blades(wings) to be controllable when in motion you can change the angle of inclination of blades for slipage or coverage , or you can add centrifugal breaking to your installed system so as at certain(above) RPM these breaks engage and slow down or stop . But it is unwise to waste already generated energy in that fashion that feels precious were we talk of recovering waste energy , energy efficiency , fuel saving & conservation , pollution and likes. You can try to store & restore the excess amount of energy in batteries or supply to grid by control electronics , if you are protecting your system from excessive winds that are to strong to damage your equipment than you have take it differently , try caging , shielding .

All your suggestions and recomendations are noted, appreciated and are now the object of my obsession. Thank you so much. You folks are a wealth of information. I have plenty of options to explore. Keep them coming.

The design is premature to provide a sketch.

Please supply pictures and notes as you progress for the rest of us, we were all born nosey!!!

Sure Andy. Thanks.

I have great respect for those who offer assistance to us amateurs who have a passion for sustainables.

In this area I too am an amateur.

Hi, y'all--

Your drawing of a Savonius rotor, Andy, is different than the one I saw in some early solar and wind power journals back in the early 1980's. The ones I saw had two or three long thin blades held between a top mount and bottom mount on the central vertical axis. They were longer than the distance between the two mounts, so they followed a curve similar to the catenary of a bridge cable. It is quite possible that both designs have been given the same name.

If the one that Corneliusvansant is speaking about is the blade type instead of the barrel type, another method may exist for stopping the turbine. If the mounts are able to move further apart, the area of the wind's path that the rotor is cutting will be reduced, so the rotor will draw less power from the wind. I believe that the blades of this type of rotor are made with one side a little longer than the other, which is what makes them catch the wind and provide the turning torque. This probably will also impose a limit on how far apart the two mounts can be moved.

Since this type of blade furling motion is directly working against the force of the wind, it may be very hard to do. The alternative is some form of braking mechanism which slows the rotor to a stand-still and is strong enough to hold against the force imposed by a hurricane. Scary.

Regards--JMM

The drawings I showed are of a Savonius type, the types you are describing have various other names. Look at this link, it gives all the different names, you can click on them and see a drawing...

http://en.wikipedia.org/wiki/Vertical-axis_wind_turbine

Andy,

I really appreciated the link and tone of your reply. I was describing a Darrieus type, and was also wrong about the need to have a strong brake to hold it once it is not moving--it "does not self-start, even in strong wind speeds".

Thanks--JMM

Don't worry, be happy!

Nice to have "met" you....