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Construction of a 10 foot diameter Wind Turbine

Part 3

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Para Español, traducción de Julio Andrade.

Po polsku -- tłumaczenie Leszek Markiewicz


At the end of page 2 we had the machine pretty much finished except for final adjustments, painting and making the prop.


This is our last chance to grind any ugly welds down. After that we'll need to completely disassemble the machine and clean it carefully with gasoline or laquer thinner. We can then spray primer on it and paint all the metal. I prefer to leave the stator unpainted (I just think it looks neat when you can see the coils!) but we could surely paint it.


Then we can paint it up! Nothing left except the prop.


The drawing above shows roughly how I layed the prop out. It's not very scientific at all... though it certainly could be! It could also be quite a bit simpler... they could probably run with a straight 5 deg. pitch from root to tip and they'd work fine. The could also be tapered straight and not curved like I did these. I think you could even use fairly straight boards (no taper at all), put a 5 deg pitch on the front and an airfoil on the back and it would work OK. A *big* part of why my props look the way they do is for fun... the attempt to make them look nice! They could be much more angular and even simpler in design. I'm not getting into any science behind why they work... or how to design them. I'd suggest, for more information visit Hugh Piggott's website or take a look at Ed's page on blade design . The blades I made here work quite well, especially in low winds.. we are getting about as much power in low winds as we could hope for from a 10' diameter prop. The nature of the alternator is such that the 10' prop actually seems a bit underpowered in higher winds (like above 20mph). This results in lower output than you'd think in higher winds, but the good side of that is very safe, slow and silent operation. I like it that way! Most of our power is in winds between 7 and 15 mph and if we focus on that and forget about the rest of I think we do well.


We start with boards which are 5' long, about 7.5" wide and nearly 2" thick. I layout the shape of one blade, and cut that out. Then we have a template to trace around.


Pictured above, all the blades are cut out.


As per the drawing above, the tips of the blades are only 3/8" thick, and the root is full thickness. So quite a bit of material needs to be removed. Pictured above we are cutting off this extra wood on the bandsaw. We leave a bit of extra, just in case we make a mistake with the saw, it gets tricky ripping through the thickest part of a board this way, it's best to leave some room for error.


I used to think the saw, hammer, chisesl and power planer was the way to make a blade! After spending a bit of time in Hugh Piggott's seminar, I'm convinced the drawknife is the only way to go. At this point we have drawn lines so we know how far down to carve in order to get the proper pitch on the blade. With the draw knive we can hog wood off quickly and smoothly! About 15 min is required to rough out the front side of one blade. After that we clean it up a bit (though not much is necessary) with a power planer or a belt sander.


In the picture above I'm carving down to the line. This goes really quickly with a sharp draw knife.


To rough out the airfoil, First we plane (I use a power planer) the back side of the prop down so it's to the right thickness. (3/8" at the tips tapered to full board thickness at the root) Then I draw a line, 1/3 of the way back from the front (leading edge) of the prop, and use the draw knife (and power planer) to basicly carve it into a triangle. From here it's quick to use the drawknife and the power planer to make a nice looking airfoil.


The picture above shows the airfoil almost finished up.


I don't get too carried away with perfection on the blades... perhaps I should. It takes about a full day (8 hours) to get 3 blades cut out and carved. It could take lots longer if I wanted to remove every scratch and divot. When carving I try to do one operation on each blade, and move to the next one thinking this will help them all come out about the same. I use calipers to measure thicknesses on them and make an effort to get them pretty close to each other.

So once they are done, we need to put them together. The hub is made from two 1/2" thick plywood disks. On ours, the front disk is only 8" diameter and the back one is 10" diameter... more a matter of appearance than anything. I wouldn't go much less than 8". The larger the disks the stronger it will be. We lay the blades out on a flat surface, and measure from tip to tip ensuring that they are pretty much equally spaced. Hopefully they fit well together at the center! Then we center one plywood disk on them, and screw it down with lots of screws! At least 10 per blade per side I think. So once the first disk is screwed on the front, then we turn it over and put the 2nd one on. Once the blades are screwed together we can paint, or finish them. They must be water proof. For appearance, I stained the middle part of the blades. Once that dried I covered the whole blade generously (and repeatedly over a couple of days) with boiled linseed oil. I like the linseed oil.. it's easy, it doesn't chip off - and it's easy to wipe them down once a year if necessary.


So, there it is all finished up! The only thing left to do is balance the prop, hook up the wires, and stick it up on a tower! To balance the prop we simply turn it by hand. If it seems heavy on one side, we add weights to the other side (in or near the hub). It goes quickly. For weights we used lead pipe hammered flat and held it on with wood screws. If its a slight imbalance, sometimes adding washers to the studs can get it there.


This machine is going up at a neighbors house. (one of the fellows who helped to build it) We'll be building a 30' tilt up tower from scraps we found around. 30' doesn't seem very high, it'd be nice to go higher! - but, we're working with the resources available here. He's also quite clear for hundreds of feet all around except for a couple trees which should only be a problem on occasion. Pictured above is where we decided to put the base of the tower. It's a big piece of granite coming up from the ground. We drilled several 1/2" holes into it with a hammer drill. The brown piece of steel I-Beam will serve as a mount for the pivot which we'll be making from pipe. We liked this location, because we are able to find large granite rocks also to use for guy wire mounts! We do those the same way, drilling into the rock with a hammer drill, and pounding in rebar with epoxy to use as a guy wire mount.


We pounded pieces of rebar into the rock, with epoxy, and welded the I beam to them so that the I beam is perfectly level. This makes for a strong base. Normally with a tilt up tower, one would choose to have level ground. In reality - especially in the mountains, that's wishful thinking! If we did have level ground, we could count on the side guy wires to hold this tower rigidly while it was being raised and lowered. In this case, we may be able to count on one wire to help - but the base needs to be strong enough to be nearly free-standing in raising and lowering.


For the tower we have found 36' of very heavy duty handrail from something or other! One side is made from 2" pipe, and it's welded to another side which is 1.5" pipe. We'll use one section for the tower base, and the other for the jin pole. Pictured above Tom is cutting pieces off square and we're preparing to weld the tower together.


In this picture you can see the tower as we're starting to assemble it to the base.


We welded more pipe to the top of the tower to get a full 30'. This picture shows roughly how it all goes together.


Here is another shot of how the tower looks before we raised it. At this point, we can assemble the wind turbine on the tower. A 10 gauge extension cord is hooked up to the 3 terminals on the alternator, and it runs down through the washer on the top of the yaw bearing (the part that slips over the tower) and down the tower pipe. At the bottom we have a locking 3 prong plug so that it can be unplugged, and the wire untwisted should that be necessary. From there we bring the line into the batteries. This particular installation is nice, because Tom's battery bank is in his little power house which is only 8' away from the tower base! So we'll have very little line loss.


So we have 3 wires, with 3 phase AC coming into the battery house. The diagram above shows us how to either use individual diodes, or bridge rectifiers to turn this 3 phase AC current into DC current useful for charging batteries. From there we may go straight to the batteries, or incorporate a shunt regulator in the system.


We pulled the tower up with a truck and a chain. It went smoothly! At the time of writing this page, the machine has been up for about a month. It turns in the lightest of winds and seems to make 10 amps in practically the lightest breeze. In higher winds it speeds up some and makes reasonable power, although again, I think the blade could be a bit larger if we wanted more power from the machine, especially in higher winds. As it is, you can never hear any noise from the blades and it's making good power when we need it most! (7-15mph winds) It seems were getting a good 100 watts around 10mph, which is quite reasonable for a 10' prop. We probably see about 500 watts or so at 25 mph and maybe 700 at 30 when it starts furling out of the wind. 500 watts in 25 mph is a bit less than we'd hope for from the 10' prop, and I believe it's because the alternator is a bit too powerful for it. A larger prop could still cut in nicely at 7mph and have the power to bring the alternator up to speed in higher winds. As it is, our alternator produces 12 volts DC at 110 rpm. If our 10' prop runs at a tip speed ratio of 7, we could actually be hitting that speed in about a 5.5mph wind! So it seems reasonable, that if we wanted more power from the machine, an 11 foot prop would be appropriate... although it would work the machine harder and heat up the alternator more.

So, we could run a bigger prop I think, but for safety, quiet, and peace of mind I'm quite pleased the way it is. Tom used to conserve power, he only had 200 watts worth of solar. I believe hes got well over twice the power he had, especially in winter. Since we installed this he's usually turning the machine off early in the day as he cannot seem to use enough electricity! It's been lots of fun.

I've tried to cover most of the details about building this. I'd strongly suggest that anybody considering such a project first do a bit of homework!

Check out these pages....

Hugh Piggott's website! This machine is very much along the lines of his design and his plans are the main inspiration.
Windstuffnow for lots of useful formulas, 3 phase alternator education, ideas projects and plans.
Our Discussion board, because this sort of thing is mostly what we talk about!
The Caboose Windmill page is an almost identical machine we built earlier in the year. There's less detail, but it might be useful!

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This page last updated 2-20-2012

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