Vertical Axis Wind Turbine Alternator

Interesting, hope you are documenting it, and would share your progress with us.

But I do not think you are using the correct terminology.

such as;

to short the alternator field in order to slow down the turbine

Braking is a waste of energy, you would want to draw off that energy.

No, I need to brake the turbine. We have 35 mph winds here almost daily, such that overspeed will be a problem both where structural strength of the turbine is concerned and where overproduction of current is concerned.

I have designed a mechanical furling device for the Lenz-type VAWT (my design is a variation), but I want to experiment with both methods with this first turbine. I have a further design in mind, you see.

Thanks, though.

No, I need to brake the turbine. We have 35 mph winds here almost daily, such that overspeed will be a problem both where structural strength of the turbine is concerned and where overproduction of current is concerned.

I have designed a mechanical furling device for the Lenz-type VAWT (my design is a variation), but I want to experiment with both methods with this first turbine. I have a further design in mind, you see.

Thanks, though.

I'd consider shunting the braking current to a resistive element in a water tank. Trying to capture some of that excess energy as "hot water" might be worth the added effort. Just make sure you have a working pressure relief valve for safety.

Thanks for the response.

I propose to do just that - and a couple of things more. First, however, I am building an experimental unit with which to test conditions here (high winds, murderous heat and humidity, air full of debris (we live two hundred yards from a WalMart - which in South Texas is like living next to a landfill), and more.

I'm wondering if anyone here has any ideas concerning methods by which to wire a stator brake on my generator. I'm also studying ways to put several turbines and their alternators on line, which will require that I synchronize them.

Thanks, though, for the prompt input - everything is much appreciated.

With such a high and constant wind speed you should consider designing the blades to match a generator that will take full advantage of the conditions.

I have only built a 8ft (2.4m) dia HAWT and used a furling tail on it so that the blades are turned away from the wind and that prevents overspeeding.

Increasing the number of blades (spines) would decrease the speed. Adding a transmission could also work.

Depending on your ambition, this is something I would like to see someone do. CVT continuosly Variable Transmission.

How would a CVT help in a wind turbine? My idea is that if the transmission is in its highest gear so to speak, it wouldn't allow the turbine to spin and this would represent the fastest wind speed. During low winds, the gear would be in the lowest gear, allowing the turbine to spin freely and generate power. This would solve all the problems of not being able to start during low winds and eliminating overspeed while providing continous power. The turbine slows down automatically as the wind speed approaches it's design limit.

With this one, you could actually use the speed of the turbine regulate itself.

Bicycle transmission.

Adding a transmission could also work.

have to keeo in mind the stress put on the (spines), Since this is 'homebuilt' one may want to consider the having a less aggressive pitch to the blades,

making a variable pitch may be too complex (costly)

Thanks! I have, however (and as I've remarked elsewhere here) built into my design a way to control turbine (angular - rpm) speed by controlling blade pitch. It's very simple, but it works. I want alternative methods of braking in case future modifications of my design make other methods necessary (a much scaled-up design, for instance).

Greenja, thanks for the comment. Unfortunately, I am a retired seventy-three year old retiree who lives on a fixed income and works with only the tools he has in his garage in a very small town in Texas. I am severely limited, in other words.

More, the VAWT I have designed is so in order to suit all the conditions here. I have, for instance, to mount the turbine on my roof - there is nowhere else available (despite the truth of everything everyone is telling me about the need to use a horizontal axis turbine and put it a hundred feet or more above the ground). The design is my own, based on the Lenz turbine found on the Internet, but equipped with furling blades and other modificaitons.

It also happens that I am also a survivalist, one who gets huge emotional reward out of the proof and knowledge of his own resourcefulness. While men - especially the young - in this country have grown up used to the idea and the fact that everything is available and easily bought (just pick up the phone and call somebody), I need to know that I can make do and take care of myself with whatever is available to me. It's a little like the airplane races in which I used to participate, races designed to carry the greatest load the greatest distance in the least time at the lowest expense. I want to depend upon me, nobody else.

Thanks, though, for the reply. It's appreciated.

That's an interesting idea, one I will think about when I have this experimental unit completed. The only trouble I see is cost: I want to do this in as simple and inexpensive a manner as possible (see my remarks elsewhere here). The furling design I've included in my turbine does what I need to control angular speed of the unit mechanically and with very little extra expense (about twenty-five dollars, matter of fact). So far, I've built everything - turbine and blades, stator and rotors, and several model turbines and test instruments - for less than a hundred dollars. I've use only the WorkMate bench I have in my garage, and tools contained in a tool box I carry in my trunk on trips, plus a couple of things I bought to build and install the HHO booster I have on our car.

If I spend a lot of money, in short, it will take me forever to compensate for the cost with whatever I save with what I've built.

Thanks, again, though.

Resistive breaking is easy and efficient, but has to be adapted to torque, so a variable resistor is necessary,

install a safety device if water is near boiling,

this may be a mechanical brake to stop the rotation,

or a change in the angle of attack of your turbine-blades (or may be some other change in flow field and turbine efficiency).

Pure mechanical breaking to generate heat is possible too with a conical geometry with constant gap to be adjusted to necessary torque (viscous torque only, no wear).

RHABE

Thanks, RHABE, for your input. You have zeroed in exactly on the reasons for my question. We have tremendous winds here continually, such that changes in size, design, and all the rest require me to think of both mechanical (furling) and electical (resistive) braking might be necessary. With a small - four feet high or so, like the one I'm building - turbine, I'm pretty sure the furling device I've got will do. With a bigger one, or with a series of turbines together, I may need to brake using both methods.

I'm trying to stay as simple as possible, the reason for my question here.

Finally, I'm not sure (I happen to be a self-taught engineer) what you mean with your last sentence. Do you refer to the turbine blades and furling, or to stator and rotor plate gapping? It happens that I'm driving myself nuts, doing the math to estimate effect of separating or approximating the rotors and stator. What is meant by "conical geometry" and conical geometry with constant gap?" Do you refer to the transmissions someone (you?) mentioned here?

Anyway, your remarks are most interesting - I hope you will explain (and make more comment).

Thanks again.

You need to make a big tube (somewhat larger than the Turbine), supported above the VAWT and when the winds get too strong, you lower it over the VAWT and reduce the amount of wind reaching it.....in the worse case condition, you could cover it 100% and stop it completely....it does not need to be closed at the top end.

Your suggestion is excellent, even if I have already considered - and experimented - with that identical method. I plan to use a method exactly like that when removing the unit from service for repair, for adjustment, or what have you.

Any ideas about braking the outfit by shorting the alternator (stator, of course) field?

Thanks again!

I think that shorting the stator windings will probably damage them by over heating....it might be a method to slow it down so that you can lasso it and hold it tight!!! But I would only trust a good mechanical system like the tube described in my post #9....

A big VAWT without that could simply get dangerous in high winds....in fact, I would automate the tube's deployment, in case you are not around when the wind gets up.....

I would not ever trust a mechanical or any type of electrical brake.....

Very astute observations, and I agree. These are the problems with which I'm attempting to deal with my design. Keep in mind, though, that I have constraints imposed by environment, availability of materials, money, et cetera.

The I have built a four feet by three feet turbine and intend use four or five of these instead of one big one has to do with concerns having to do with a big VAWT and the highs winds around here. I have, as I mentioned above here, experimented with a "sleeve" in which to incrementally shield the VAWT "wings" from the wind. The thing (as does the automation you mention). complicates installation problems enormously, however, and seems when in the "undeployed" condition to be even more likely to become a victim of the high winds.

I'm also, incidentally, experimenting with a simple wing arrangement to move in front of the VAWT and break up or divert airflow.

Keep in mind that I'm looking for the simplest, while most effective (I've been a argent devotee of judo all my life) way to do what I need. Technology, especially the mindlessly "anything that's different and will sell to the booberie" kind, is like our government - all but always ineffective when really needed, and costs hugely disproportionate sums to repair when it does.

Thanks, though, your comments are sincerely much appreciated.

This is getting to be an interesting blog, thanks for starting it.

I like your idea of having more than one, but smaller, that appears to be a good idea, you still get power while repairing one and the forces involved are several powers less than with a single large one......really sensible.

Hi again -

Yeah, that's how I see it. What comes next should be most interesting, and lots of fun. Es soll immer besser gehen, nicht wahr?

Thanks again for your interest. Und tschus!

Good German too!

Vielen Dank!

Absolutely right:

shorting the windings (both stator or rotor windings may be existing) will dissipate the power in the small resistance of these windings. Overheating and failure to result within seconds to minutes.

Protection system: I would use two independent ones as failure may be costly and dangerous.

A simple one is a mechanical brake (underwater it can dissipate a lot of power until dry) that is actuated by a centrifugal mechanism.

As second one I would use switchable resistive heaters to provide additional electric power.

Complete shielding of rotor by a movable big tube may be not storm-proof: what is the maximum wind-speed to survive? How often is breakdown by high winds accepted? Will any insurance pay? What about damage to others from free flying parts?

RHABE

Thanks (again) for your interest.

It happens that I'm using a permanent magnet-type alternator. I'm interested in braking the turbine by stator shorting only as a supplement to the mechanical turbine blade furling I've designed and will build into my experimental unit. Obviously, assuming that I understand what you mean about "dissipation of power" in the stator windings, I will want to control current and other results of the method in order to assure current and heat stay below potentially damaging levels, and I was interested only in determining whether anyone might have better and simpler methods of shorting the stator field, in order to lessen just what I think you must mean.

I'm finding that everyone with whom I discuss my project suggests things that increase complexity far beyond what I want. A mechanical brake, especially one underwater or cooled by water (I'm wondering how I would do that without adding enormously to the size and weight of the device I want to put on my roof) is just too complicated to be practical for my needs here.

Regarding your third suggestion - that of "switchable resistive heaters" - I'm afraid I'm not sufficiently knowledgeable to know what you refer to or mean. What is a "switchable resistive heater," how does it work, and where might I find one to try?

Using conventional data regarding force of the wind, a movable tube seems impractical. Once again, any device employing such an arrangement would not only increase complexity of the unit prohibitively, it would require structural stength and concomitant weight far beyond what I want to put on my roof (I have to install, service, and repair this thing by myself). As I indicated earlier here, I propose to take the VAWT out of service by slipping a canvas tube over the turbine blades. I did experiment mentally and on paper with a series of rings that might be raised successively into shielding position, but that also is prospectively far too complicated, unwieldly, and therefor impractical.

As it stands now, my VAWT design envisions (having done the math) maximum wind speed of thirty-five mph. My concern for higher winds - including the hurricanes that pop up around here continually - is the reason I'm researching braking and furling methods. More, I've decided upon a design that lets me simply remove the whole unit from the roof (it will not even be bolted to the roof, being held in place by congruency of shape and easily managed guy wires) in event of forecast winds exceeding my design speed. That's another reason I want to keep the device as simple - as light and manageable - as possible.

Liability for damage resulted from high winds comes under "act of god" legally, and is not a concern in this case. More, "due diligence" in design and installation basically negates any tort liability exposure otherwise (of course, in the U.S. anyone can literally sue anyone for anything; I might be sued for damage to the view above my house or because VAWT are unsightly to persons employed or otherwise beholden to oil companies. I've thought of that, too.

Good observations, however, and much appreciated. Any ideas on ways to short the stator most effectively and efficiently?

Hi,

your generator will have a current limit - look at the specs or test the coil temperature rise by dissipating electrical power in the coils and measure the temperature rise (by rise in resistance with 0.4%/K). From the insulation of the wire you have the permanently allowable temperature, thus the allowable power dissipated in the coils, thus the allowable current.

Attach either a current measurement into your electrical circuit (very small constant resistor) and switch into the circuit (relays from a car if low voltage, from 400V systems if higher voltage) additional heaters. These shall be selected according to voltage and current, thus power.

Heater elements from washing machines may be suitable - usually 1 to 2 KW at rated voltage (110 or 220V). If 1 KW at 110V this is 9 amps and 12 Ohm.

You can make any resistance yourself by taking a stainless steel (or titanium) wire or ribbon and first oxidise this in a flame or by current heating and then coating twice with a good epoxy or embed in a ceramic cement. (Good for low voltage generators.) The alloys that are used for thermocouples - if available in near 1mm thickness or as sheet material - are a very good choice too.

Decide how to limit maximum speed: speed is proportional to generator voltage so a voltage comparator (look into the electronics course that is going on at the moment to learn more if necessary) can be set to switch if your generator's output is above ( for a second or so) the limit. Switched comparator will switch the first resistive heater. (May be one only depending on the range of wind-speed you are thinking about.)

RHABE

RHABE, this is just great, and I thank you very much. It happens that I've just assembled the rotors and stator I built myself, and am ready to assemble the VAWT blades and components I've also built. Once I've tested the turbine and discovered its rpm in local winds (that and other operation parameters), I'll start building a charge controller and start testing that. All your suggestions are clearly useful: I'm teaching myself electrical engineering, the result being that you've suggested several things I probably wouldn't have thought of. SUPER!

Can't wait to get started (if I have questions, I trust that I may feel free to ask).

Thanks again!

Dead shorting the alternator windings will almost certainly destroy them. Speed braking through an appropriate resistive load (full on or PWM controlled) is only ONE part of a safety system. You should also include a mechanical brake and, if possible, a method to "spoil" the blade aerodynamics.

Many home-built HAWT's are designed to pivot away from the main wind flow if wind speeds become dangerous.

http://www.otherpower.com/turbineplans.shtml

is just one example that seems to limit excessive RPM while still producing power. Not sure how to accomplish this (simply) with a VAWT.

Aside from injury, you don't want to see all your hard work self-destruct when the first storm rolls through!

Good Luck!

I'm having a second look at the idea of using water for a brake on the turbine. That might not be as complicated as I first thought, and I thank you again for the suggestion. Have you any ideas concerning how you would do it? Design turbine torque is 2.28 hp (i.e., at 15 mph windspeed and 200 rpm - where I want to hold the latter).

Returning to the question of shorting the windings, if shorting the stator field will slow the rotors and shed power, why wouldn't the system then be self-regularing? Current is being generated by rotor RPM (torque, actually), such that as the "drag" induced by the stator slows them, current would diminish accordingly. Or am I perhaps overlooking residual current - capacitance in the field?

I pose the question merely because it strikes me as an interesting one. I've been elated at having found a site wherein useful discussion can be had (unlike, invariably, the political ones), and I'd like to hear from the members here even more. It happens that I've already decided to make the turbine's speed self-regulating with a VAWT blade design (another of my own variations on an existing design, this one known as the Princeton Sailwing, and my small model tests indicate that it's a winner). I'm also in the process of designing (and acquiring related parts and wherewithall) a simple charge-controller which includes provision for dumping excess into a secondary load or loads in order to prevent over-charging of my batteries.

But I'm also thinking about future development, and plan to experiment with a separate - attachable to the system I'm already building, i.e. - electrical brake. I might make a smaller (perhaps) secondary alternator (they're both easy to make - meaning I can do it here in my garage with the facilities I have - and cheap) just for the purpose of slowing the turbine. So - again - why wouldn't the stator and rotors of my permanent magnet, three phase (star winding configuration) alternator be self-controlling? Or were we talking about an alternator with a battery-excited field winding (which, incidentally, occurred to me after our last discussion)?

On, yeah - and while I don't want to sound boastful, I'm a self-taught engineer, such that I understand most technical terms and the math related to the physics of electricity. Everything and anything anyone might be good enough to contribute will be much appreciated, in other words. And thanks in advance.

You can brake with your alternator shorted.

But with simply shorting the windings you will dissipate the power (torque times rotational speed) in the windings. These have bad cooling and will quickly burn.

No good idea.

So think about 1 Ohm winding resistance and 1 KW power: near 32 A (amperes).

What is the rated current of this alternator?

Put a resistance of 10 Ohms in the circuit and calculate yourself by Ohms law and power equals resistance times square of current how much power is distributed in the windings and how much in the added resistor.

RHABE

I can't be sure yet, because I don't have the dratfangle I've designed and am assembling up and running, but my math calculations expect 65 Watts at 14 Volts = 3.3507 Amps.

As my VAWT exists now, I have eighteen AWG gauge wire doubled, sixty-five doubled wire turns per coil, nine coils between twenty-four Endymion magnets. Output suggested above is at about 115 rpm of a four feet tall VAWT with three feet diameter. The stator plate has twelve inches diameter, the rotor plates eight inches.

Were I too build a brake like that mentioned - a unit separate from the main (power producer) one and smaller - I would perhaps use a smaller winding, heavier wire with less turns. That one would be used simply to slow the turbine. The trouble is that I would probably have to synchronize the two alternators, and add complexity I'm trying to avoid. I'm just doing mental experiments, and hope in that regard I'm not wasting your time.

And thanks again for your interest so far.

P.S. my last I haven't, by the way, calculated how much torque I'd need for the second, electrical brake. I've also been wondering about putting two power-producing alternators on the same turbine, so I'll have to do that, I suppose. I have a second VAWT design that looks super promising - I've just finished mailing myself a "postal patent" - one that with the same general size will develop considerably more torque. If my math isn't screwy, the scale model I had on the roof suggest the full-size outfit would generate a full horsepower and 28 ft-lbs of torque at 200 rpm.

If my math isn't screwy (which it sometimes is)>