Posted: 03:37am 19 Apr 2006

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hello

instead of having the conventional windmill that sits up and has the tail to spin around so that the fan is always facing in to the wind. i was thinking of having the alternator facing upwards, that way there is no need to worry about the wires twisting around the mast, because the alternator can be set in place and only the fan would move.

my question is, if i use a car alternator for the windmill, how long would it take to recharge a car battery?

Posted: 04:14am 19 Apr 2006

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How long is a piece of string?

Depends on the state of charge of the battery, the turbine, the wind, construction (bearings, condition of them etc), condition of the prop, air temperature and humidity (ie, density).

If you were to use say, a 60 amp alternator, with a decent wind and good turbine etc, and were able to actually get 50 amps OUT of it (you would have to excite it so that would sap some of your power), and you had a reasonably good condition 100 amp-hour battery that was half charged, it would take about 1 hour to "recharge" it assuming the battery was 100% efficient.

To get it fully charged would take about an hour and a quarter, depending on temperature.

YMMV, E&OE!

Posted: 08:18am 20 Apr 2006

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what do you mean by excite it?

Posted: 10:23am 20 Apr 2006

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Car alternators don't have permanent magnets.
They require some power to create the field. This *MAY* come from residual magnetism, and then from the alternator output itself, but usually comes from the cars battery.

Posted: 02:13pm 20 Apr 2006

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so i would be better off having a permanent magnet motor as my alternator. ill have to have a look around for old washing machine motors, how would they go?

also, with the horizontal windmill design where the fan looks like a ~ how do u keep the fan steady, all that spinning could make it flail around especially at the top.

Posted: 10:41pm 20 Apr 2006

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Yes, thats right, unless the vertical axis wind turbine is on a very stiff axle you need to support a top bearing somehow.  You can do this with two (or more) posts and a horizontal beam or by some sort of guy system.  If you use guys you need a thrust bearing at the top.

I have seen one used for pumping water.  three posts that may have been utility poles.  Cross beams near ground level supporting the rotor which consisted of two sets of 44 gallon drums cut in half, then the shaft went through the upper bearing (which was supported on cross beams) and was extended to carry one pair of halves cut from a 12 gallon drum. He had a truck axle and diff at ground level, the vertical shaft looked like 3 inch water pipe and the upper bearing was three or four ball races bolted to the beam so as to run against the outer surface of the pipe.

 It had been running for about 20 years when I saw it.

Posted: 02:25am 21 Apr 2006

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I believe vertical axis wind turbines usually turn much slower than the horizontal types but on the other hand they have a lot of torque. 

Because of the generally cumbersome shape of the VAWTs they are (or seem to be) always mounted near ground level so if you are building something like that monster I described you need to protect it against unwary people, kids and animals getting injured by what is really a quite powerful machine.

I think you can expect to need some method of gearing up to run your alternator, belts, chains, gears etc of which I think belts would be the easiest.  At least with the VAWT you can have all this mechanism at or near ground level where it is safe to attend to as required.

Posted: 05:42am 21 Apr 2006

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is there anything wrong with putting a VAWT up high? if not i would like to put one up high.

it would be better to have the ~ shaped ones because you can fit more of them in the same amount of space.

Posted: 09:17am 21 Apr 2006

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rossw mentioned that there advantages and disadvantages of using a vawt or hawt.

could someone list these disadvantages and advantages?

Posted: 11:48am 21 Apr 2006

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guiding ropes could be put at the top of it to keep it from flailing around, and a pole coming up next to it for it to attack to could also work. building them wouldnt be cumbersome because i can build them on the ground and then put them up and i have access to a cherry picker. :)

im thinking that i could build a dozen of these windmills to power all sorts of things.

what are the disadantages and adavntages of either a vawt or hawt setup?

Posted: 07:41pm 21 Apr 2006

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I have never really compared the disadvantages versus advantages of the different basic types, however I can make a few guesses.

Firstly, the size of the machine.  The effective size of the horizontal axis system is the area swept by the blades, this is the area from which the energy is being extracted.  A vertical type needs to be at least as big to extract the same energy from the same wind.

Vertical types are pretty much drag machines whereas horizontal types have some degree of aerodynamic advantage from the shape of the blades. No doubt efficient aerodynamic shapes could be designed for vertical turbines too but most practical designs seem to be simple curves of plywood or sheet metal.  So even if the vertical type is as big as the area swept by the blades of the horizontal type it cannot extract the same energy from the air flow.

The vertical type has half the turbine doing the work while the other half is turning against the wind causing drag,  horizontal types have all blades working at every point of their cycle.

Not to say that vertical types are all bad though.  For a job like that water pumper I described an effective vertical turbine can be easily made without too much technical design work and using material that might be easily to hand.

Vertical types of the drag variety (e.g. the simple ~ shape)  have good starting torgue. However once aerodynamic blades are designed for a vertical turbine the starting torque may have to be sacrificed.

There are  really highly efficient vertical designs like the 'egg-beater' style but they have to be motor started or they have a simple drag turbine on the same shaft to get them going, the drag turbine is on a clutch which allows the main turbine to spin up much faster than the drag turbine.

Without aerodynamic design the drag type can never spin faster than the wind blows.

Vertical types have the advantage, although rarely implemented, that they can make use of wing walls to get much better performance from prevailing winds. In this system a solid wall is built close to the turbine and angled to direct more of the the prevailing wind into the turbine.

In some respects comparing the simple drag type vertical turbine with a horizontal type which has aerodynamic blades is like comparing the effect of a kite (which is traditionally just a flat surface) with the aerfoil of an aircraft wing.  Bear in mind though that Southern Cross and others built thousands of water pumpers with just flat blades, they just had lots of blades to compensate and of course they wanted torque at low RPM for the water pump.

As I said, these are my guesses of the pros and cons,  I might be wrong on some (or all!) of them.

Posted: 09:41pm 21 Apr 2006

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I've built a few VAWT's and HAWT's, both have thier pro's and cons. The comments above are pretty spot on with what I have found. The HAWTS need a lot of attention paid to blade design and strength around the hub/root area. They are technically more dificult to make, especially blade profile and angles. But they are light and compact for their swept area, so easy to man handle and get up on the mast.

However, they need clean air, that is wind with stable direction. My new place has very turbulent winds, I'm on the north side of a hill, and most of the wind comes from the south east. So my HAWT spends a lot of the time turning around to face the wind. This is why I started on VAWT's

A VAWT has a large surface area. I have made a small lift type VAWT, but the fact that it wont self start turned me off. I made a  Lenz design windmill, its 1200 high by 1100 wide from memory, and attached a F&P motor. It did work, easy startup, but I had a problem I didn't think of before hand, noise. The VAWT has a large surface area, big wings, and the F&P makes a lot of vibration as it rotates, so this vibration was converted into a very loud drone. Sounded like a motor bike. This noise could have being reduced with dampers and some redesign, but I ended up converting the windmill into a water pump, and its worked well since then. I also have a small Sandia Labs design savious windmill, sort of a modified S. It works VERY well, and I would like to build my next big windmill on that design. I plan to use aluminium sheets on a steel frame to make the wings. Total size will be 2400mm high and 2200mm diameter, and it will drive a couple of big servo motors ( no vibration ).

I should add that my ground level Lenz windmill is almost always running, where my HAWT on its 7 meter mast is almost always stopped!

I agree that I think the reason most VAWT's live on the ground is their large size and weight makes them a lot harder to get high on a mast. And you would need a stonger tower.

I really think it depends on your location. If you can get into clean air, a HAWT works well. If you location has turbulent winds, like a yard in the city, or the back of a hill, a VAWT is better. VAWTs also work well at ground level. But HAWT's run at higher RPM, so its easier to extract the power, where a VAWT offers low RPM torque, so you need to gear them up.

Off topic, but I often hear on "Field Lines" how its bad to use any sort of gearing to step up the windmill RPM. But the big wind farm windmills do just that, using gear boxes.

Glenn

Posted: 02:44am 22 Apr 2006

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youv mentioned names of certain types of windmills, but i dont know what these different designs are;
   lift type vawt
   lenz design windmill
   sandia labs savious windmill
what are these things?

also, a hawt has a tail fin to make it spin around to face the wind, so why are hawts not so good for turbulent wind?

Posted: 06:12am 22 Apr 2006

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Without being rude.... "Google is your friend".

For that very reason... if the wind swings, the whole turbine assembly for a HAWT has to swing around. This takes time and there's lots of lost energy potential.

A VAWT doesn't need to - it can take wind in any direction without needing to adapt/adjust.

And for "turbulent", we mean swirling, variable wind, not just "wind that swings around a bit". Turbulent air can have dramatic changes in direction in seconds, unlike a larger "clear air" mass.

Posted: 06:30am 22 Apr 2006

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Makourain

Have you made any experiment windmill nor have one setup and go ??? How about show us any photo of your windmill gen ?? 

Dwyer the bushman

Posted: 09:51am 22 Apr 2006

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i did google those names and didnt have much luck, google wasnt too friendly in this case.

and also, i cant post a photo of awindmill iv made because i havent made one, thats why im asking all these questions so that i can make one. without mistakes that is.

Posted: 10:29am 22 Apr 2006

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"He who has never made a mistake.....

     ..... has probably never made anything."

Posted: 01:07pm 22 Apr 2006

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Hey Makourain.

You can find my Sandia on this page http://www.thebackshed.com/Windmill/photos4.asp. Left side. There is also a copy of the original plans.

The Lenz design is there too, other side of page. I later build a big one, http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?T ID=60&PN=1 

I can see your starting the same way I did with windmills. Some of my early ideas seamed to make sense to me then, but now I look back and I think "You dill, that wont work" My first big windmill had a set of 5 1 meter long PVC blades on a hub. I laser cut a big sprocket to suit a push bike chain, and this drove a smaller sprocket on a old 12v car generator, thats a generator, not an alternator, it was about 50 years old. The gear ratio was about 5:1. I set it up on a test stand and moved it into the wind. I was sure it would work.

It didnt. Made heaps of noise, chain kept falling off, stuff all output power. It never made it to the top of a tower!

One of the best ways to get started is to build a smaller windmill, like a stepper motor windmill or small induction motor conversion http://www.thebackshed.com/windmill/AssemblyA.asp

Its a big learning curve, but its fun and an addictive hobby.

Glenn