Why not put the alternator on the ground?

[justathought]

 First of all, hello everyone!

I'm Peter and I've been wandering around for a while reading mostly....not really lurking, I just never had anything important to say until now.

 All the home brew setups I've read about have the magnets and coils right behind the blades on top of the tower.

 Why doesn't anyone ever just run a shaft down the tower from the prop to an alternator on the ground?

 -It would have less weight up on the tower so you can use lighter construction.

 -Easier to raise.

 -You can make the alternator any size,weight or shape since it is on the ground.

 -The blades could be attached to a more streamlined hub.

 -No problems getting the power off the top of tower or dealing with lolly shafts and brushes.

 -Shorter distance to run the power to the battery bank(lighter cable less power loss).

 -Alternator can be protected from the elements.

 -Easy to maintain (no climbing or lowering)

 -You can install a brake or drag on the power shaft to prevent overspeed.

 A car rear end has very nice high speed gear sets to use to send the rotation down the tower.Properly built and designed it may even be more quiet.

 Has anyone tried this?

[Flux]

Yes Wesco or something similar tried it with a hydraulic pump for heating but they may have kept the pump at the top.

The gear box is best avoided but the idea will work, Not as easy as you think to bring a shaft 70 ft down a wobbly tower. Really needs a stronger and more rigid tower and looses most of the attraction.

I seem to remember someone in Australia doing it with a pumper windmill with a rotary pump at the bottom rather than the normal reciprocating rod.

Flux

[AbyssUnderground]

Wouldnt this also have some powerloss too?

[wooferhound]

Here is a story with good pictures of a guy that did it and ran a small car motor as a compressor at the bottom of the tower

http://www.fieldlines.com/story/2006/1/9/103933/9137

[smidy]

I kind of like hydralics, so wouldent it be able to put an hydralic pump up the tower driven by the prop and hydraliclines down from the top to a hydralicmotor at groundlevel driving the alternator, the hydraliclines can even be a part of the tower. anyone tryed this? is there much loses in hydralic transfers?

[finnsawyer]

The shaft running down the tower must have torque on it.  As the wind speed changes (gusts and such) driving the alternator higher, say, this torque will change over short periods of time tending to turn the wind mill out of its preferred direction causing a loss of power.  This means you will need a larger tail, which adds more weight or will need to anchor the mill, as the Dutch do.  You also need to consider the added friction losses due to the gears, bearings, and shafts.

[Experimental]

    Many years ago, we used both hydraulic, and also had a long shaft driven water pumper-- the shafts were surplus helicopter tail rotor drive shafts, with the helicopter bearing plates and worked quite well for pumping water !!

   The hydraulic set up, worked OK, but was driving a generator and unfortunitely, the gens we had, in those days -- Frankly SUCKED !!!

Todays PMA, would probably work quite well, and we used the Savonious type turbine,But many improvements have been made there too!!

    There were many loses, in both drive systems, but as the wind was free -- we didn,t care !!

  The generator, never put out much and the water pump worked quite well, from a shallow well..

We never tried a prop driven, as we had already tried many gear drive systems to change horizontal to verticle drive --- with nothing but problems -- so I really don,t like "drive, or gear boxes"!!

    Both these systems work, but with todays PMA,s -- as you have only one component moveing in the gen and a very high dependability factor -- shafts and hydraulics, seem rather redundant --- But, don,t let my thoughts stop you from experimenting -- that,s how things get invented and perfected !!

   Just want to add one thought to all this --- fewer parts, means, "less to go wrong" !!     Happy building, Bill H......

[smidy]

yes but you can avoid the torque if you have a pipe over the axel from the top that is fastened to the mill and the alt, so when the mill turns then the alt turns to. but you still then have the twist cable problem or brushes since the alt turns just like it dos when the alt is on top of the tower

[finnsawyer]

What I was getting at was the tendency for the reaction torque from the alternator to turn the windmill when the power to the alternator changes.  This is similar to the problem that exists in a helicopter if you don't have the tail rotor.  The entire helicopter will turn opposite to the blade rotation.  While the wind mill's tail will counter act this, it probably will not be sufficient.

[DanB]

Just to play the devils advocate...  

"-It would have less weight up on the tower so you can use lighter construction."

I expect the gearbox and the shaft would outweigh the alternator.  Plus, as was pointed out, the tower would need to be very rigid and the shaft supported very well by lots of  bearings.  We'd also have losses in the gearbox and all the extra bearings.

 "-Easier to raise."

Not if what said above is true...

 "-You can make the alternator any size,weight or shape since it is on the ground."

weight may be a small issue, but size and shape isn't really.  We dont build the alternators a certain size or shape because they're on a tower - we build them a certain size/shape and weight so they can do the job of converting the mechanical power  from the blades to electrical power.  They'd be the same, on the ground - or on the tower I expect.

 "-The blades could be attached to a more streamlined hub."

I think the hub would have to be similar - the way we attach the blades is not a compromise based on the alternator.  The only consideration is strength at the root.  So the hub would probably be the same either way.  If we're worried about 'streamlined' we could build a nose cone in either case, but I'm not worried about that - I'm pretty sure that's a none issue although some disagree.

 "-No problems getting the power off the top of tower or dealing with lolly shafts and brushes."

I think a wire running down (or even slip rings) is lots easier than supporting a heavy shaft - I don't think a real problem exists there.

 "-Shorter distance to run the power to the battery bank(lighter cable less power loss)."

A small issue for some folks perhaps - especially when running very low voltages but again I expect gearbox/bearing losses would far outweigh a little line loss over the length of the tower.

 "-Alternator can be protected from the elements."

We can do that on the tower top too - although I'm not sure that's been a problem for anyone yet.  I admit though, there wouldb e some fun things about having the alternator on the ground.

 "-Easy to maintain (no climbing or lowering)"

I think you're talking about lots more to maintain actually - bearings, shafts/gears.  With a PMA, there is nothing to maintain other than bearings (assuming the alternator stays together which I must admit I've had some problems with lately).

 "-You can install a brake or drag on the power shaft to prevent overspeed."

I dont think a brake or drag is a good way to prevent overspeed - there are better ways which we incoorporate.  It would make a mechanical break for 'shut down' a bit easier though.  

Forgive me - I'm always resisting change and love to play devils advocate sometimes!   A bad habit sometimes. Just putting fourth some thoughts on it all.  I think it would make things much heavier, less efficient, and more complicated.

[Stonebrain]

I think it there are some complications if you

try it with a hawt:

1. the torque-problem
   
2. rather complicated yaw-transmission to vertical shaft
   
   

think about a vawt.

none of these complications,but there are others.

cheers,

stone

[Vince]

I've seriously considered this, as I have a rather tall barn that I could put large collar bearings at the top and bottom of, and the majority (or at least half) of the shaft would be inside.

With a VAWT, there would be no need of a gearbox, and it would be very light at the top.

[whatsnext]

This is the perfect place to say "less is more". I really hate being the class naysayer around here but if more of us would look at reducing parts instead of trying to make things somehow better via increasing the parts count a lot of these questions could go unasked.

John...

[TomW]

John;

Excellent point!

Off the main topic so apologies to the original story poster.

I once read someplace, probably online, that perfection [in attaining the required result] is not achieved when no more can be added but when no more can be taken away. I think that can apply to this field of endeavor as well. This position is likely not held by everyone and certainly not by some on this forum. I said this once before and it was apparently misunderstood by one poster who seemed to take it personally.

Lots of what I think of as overthinking the plumbing lately which i suppose in some ways is good. Anyway just had to chime in here as an observer and non builder so my opinion may not count or be taken seriously.

Ok thats it for now and this is not in reference to any individual just an observation from the peanut gallery. Now out to see if I can get that conversion to spin by force of will with no wind.

Cheers.

TomW

[CG]

Probably the best example of placing the generator close to the ground, for ease of maintainance and a reduction of weight on the rotor head, was the Andreau, Enfield Cables Co. turbine. This was a turbine rated at 100kw and tested in the UK in the mid 1950s. The power was transmitted from the blades to the turbine by pnuematic transmission. The blades were hollow with holes at the ends; as they spun centrifugal force threw the air out creating a pressure drop, more air was sucked up through holes in the bottom of the mast, in which the generator was placed. But unpressurised air is not a good transmitter of energy, and the turbine did not reach its expected performance.

The turbine was taken down and re-errected in North Africa, where it worked until it was destroyed in a storm in about 1960. This French designed and British built turbine was quite large for its day, and although considered a failure, every now and then a new version is suggested, the latest is by a Hungarian who thinks he can improve the performance figures.