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Construction of a 10 foot diameter Wind Turbine, page 2

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Para Español, traducción de Julio Andrade.

Po polsku -- tłumaczenie Leszek Markiewicz


When we left off on page one we had the stator out of the mold. In this picture we have stators for 3 machines. At this point I like to chip the extra resin off the inside and outside of the stator.


And, be sure to check out our book Homebrew Wind Power for more small wind power information!

Pictured above we've welded the stator brackets to the main chassis of the wind turbine. This is a good time to prepare the stator for mounting.


We line the stator up so it's perfectly centered around the wheel spindle. Since the stator is exactly 14" diameter, and each leg of the stator bracket is 7" long, the edges of the stator should line up perfectly with the edges of the stator bracket. We've drilled 1/2" holes in the stator bracket for mounting. We need to position the stator so that we can clamp it down, and then drill into it so that the 3 holes in the stator line up with 3 holes in the stator bracket. It's very important to position the stator so that we are not drilling through any coils! This is pretty easy to see, although sometimes it's helpful to shine a flashlight through the holes in the bracket so that you can make sure there is not a coil in the way. If we make a mistake and drill into a coil, odds are the stator will be scrapped and we'd have to start over again. Once the holes are drilled, the stator is finished except for wiring. The only thing left to do before wiring and being able to test for some output is to place, and glue magnets on the brake rotors.


Pictured above DanF is placing the magnets on one rotor. I usually do them one at a time. We'll actually be able to wire, and test the stator with only one rotor finished. On the first rotor, we need not pay careful attention to getting the magnets in any certain spot. The only important thing is that each magnet have the opposite pole facing out as its neighbors! So, They must go 'round the circle North, South, North, South.. etc. It get's a bit tricky... these magnets are very strong and a bit dangerous. You have to use very careful attention when handling them and be very careful that you handle only one magnet at a time, and keep the rest of the magnets away in a safe location. If two come together on a finger it hurts... it could possibly even break a finger!

So we put one magnet down at a time. The face of the magnet which is pointing out should always attract the out-pointing face of the neighboring magnet. I use playing cards as shims to keep some space between the magnets. Once all the magnets are placed down, we can use cards to measure the space between them, sliding them around and adding/subracting cards untill the gap between all the magnets are equal. In practice, for all these machines it seems like a gap as thick as 27 or 28 cards is about right, but this depends on the exact diameter of the rotor and the thickness of the playing cards. We call this "Hoyle's Law." Its about a 3/8" gap between the magnets. Once all the magnets are down, and the gaps are even, I like to put a bit of superglue around them to hold them there before removing the cards.

So now we have a steel disk, with 12 VERY powerful magnets around it! This is something to be very careful of. Keep it away from dirt, tools, metal filings, etc. -- it must stay clean and it must not be allowed to stick down to anything big and flat and made of steel or you may NEVER break it loose! It has enough magnetic force to squeeze a finger off should your fingers get between it, and that which it is attracted to. One must be very careful! We can't emphasize this enough! The attraction between a magnet rotor and a loose crescent wrench is enough to be extremely painful, or break fingers!


Once the magnets are stuck down to the rotor, we simply wrapped duct tape around the outer diameter, and made a cardboard insert for the center. (the cardboard insert is from a 6" cardboard tube which we modified to tightly fit the inside of the brake rotor). This creates a sort of dam, so that we can pour resin around the magnets and it doesn't leak out. Once that's done we mix up some polyester resin, add some talcum powder, and pour it in around the magnets. To tops of the magnets should be flat and free of resin, so we take care to clean them after pouring. After a couple hours the resin should be hard and we have one magnet rotor done. I mentioned it earlier, but it is important to be sure the rotor is free of oil or grease before pouring in the resin! It must be clean.


The wheel hub still has the original studs which used to hold the tire on the car. These are simply a press fit, and they are quickly knocked out with a hammer.


This was shown in an earlier drawing on page one. Once the studs have been knocked out with a hammer, we replace them with 10" long pieces of 1/2"-13 allthread. The new 10" studs are held to the wheel hub with a nut on each side. We need to leave about 1" of thread sticking out past the nut on the back side so there will be room for the brake rotor and one more nut on the back. When tightening these studs to the wheel hub, I like to get them really tight and use plenty of locktight (super glue works well I think). These may never be removed again, so we don't want any chance of them coming loose!


In the picture above we are placing the back rotor on. One has to be a bit careful, as the magnets will attract the hub. Sometimes it's easier if one person holds the hub securely while the another lowers the rotor down over the studs. It should fit on nicely, and well centered. The wheel hub itself is only very slightly smaller than the inner diameter of the brake rotor, this helps keep things nicely centered. Once it's on there, we again use locktight, and tighten it down with 5 nuts. There is no real reason the back rotor should ever have to come off again.


This shows how the back rotor fits over the wheel hub. Had we not turned out the center hole on a bit larger, the hub could not have fit through like this as the rotor was never designed to fit on in this way. Now we only need to tighten 5 nuts over these studs and locktight them.


In this picture we've put the wheel hub, and bearings, and back rotor onto the rest of the wind turbine chassis. At that point we can rotate it and make sure all is flat and centered. Then we use the 3 6" long pieces of 1/2"-13 allthread, with 4 nuts on each piece to fasten the stator to the stator brackets. The stator will be adjustable in and out with nuts. It should be set so that it run pretty close to the magnet rotor and so the gap between them is the same all around.


Once we have 1 magnet rotor, and the stator mounted, we have everything we need in place to wire, and test the stator. Output won't be quite up to par with only one rotor on, but once wired we will be able to test each phase and know that the alternator will work. First step is to strip the ends of each wire on the stator. I find the easiest way to do this is with a propane torch. Heat the ends of the wires till the enamel burns off, and then rub off the ashes with sandpaper untill you are left with nice clean copper.


There are 9 coils, and this is a 3 phase alternator, so each phase consists of 3 coils in series. Hooking 3 coils in series per phase is the first step, and the drawing above should explain this. Each coil has a start lead, and an end lead. Each phase has 3 coils which are 120 deg apart around the circle. Usually I'd pick one, keep the start lead free (this will be the output from that phase) and then hook the end of the 1st coil to the start of the next, and the end of that coil to the start of the next, and the end of the last coil will be the output. Once those connnections are made you can test that phase with an AC voltmeter. It should be easy to see at least 10 volts with a good spin by hand, even with only one magnet rotor on. In the picture above, you'll see that we have 6 leads coming out, labeled A, B, C, and X, Y, Z. I've always made this for 12 volts, and we have always wired it into Delta. For 12 volt operation, we'd hook X to A, C to Y, and B to Z -- and these connection points would be our 3 output leads for the 3 phase output. At that point we can bring those connections out to some kind of terminal... I use 3 long brass bolts with copper washers and nuts. This makes for easy connection to the line. We should now be able to give it a spin, and use our AC voltmeter to measure between any 2 of the 3 terminals and see good output. (just like before, a good spin of the hand should show 10 or more volts AC).

There will be a drawing further down which explains how to make use of this 3 phase output for battery charging.

I suspect (though I've not tried it), that this would make a fine 24 volt machine if we wired it into the Star connection. In that case we'd just tie ABC together and the output would be X,Y, and Z. This gives us about 1.7 X the voltage at any given rpm, and I believe it would be fairly appropriate for a 24 volt system. It is hard to say if it would be better to go that way, or simply use finer wire (AWG 17 perhaps), twice the number of windings in the coils - and stick with the Delta connection. I think either approach would work if the goal were to charge 24 volt batteries.


At this point we have the stator wired, soldered, and you can see the 3 brass screws we used for terminals. I like to take some epoxy at this point (once all the connections are tested) and glue the wires down around the edge of the stator to protect them, and keep them from vibrating. DanF is building a cowling around his stator to keep the wind from vibrating the solder connections.


Now we need to prepare for the 2nd magnet rotor. We have no magnets on the rotor yet, so it's somewhat safer to handle. I take the rotor, holding it backwards (so the magnetic force of the back rotor doesn't grab it too hard), and see if the 5 holes in it line up nicely with the half in studs. Usually it doesn't, because the studs bend around a bit when we tighen them to the wheel hub! But this test gives us an idea how far off they are.


Carefully measuring from one point on the stator, we try to get the studs as straight and in place as possible. I use a long piece of 3/4" pipe to bend them around as needed. During the bending process we can re-check alignment with the other brake rotor. In the end, we want the other rotor to fit on there easily, and on center. Again, it's important to hold it backwards right now, because there are no nuts yet on the studs to keep it from being pulled into the stator by the force of the magnets on the back rotor.


Once the studs are straight, we can carefully measure exactly where to put nuts that will hold the front rotor out just barely away from the stator. The nuts are about 1/2" thick, and our magnets will also be 1/2" thick. In the end (as per the drawing on page 1) we'll double nut here, but for now a single nut will do. We have to put single nuts on each stud, and they need to be placed carefully so that the rotor will sit flat on all 5 without wobbling. I measure all this very carefully! When we're sure we have it right, we hold the front rotor very carefully in such a way that it would be impossible for our fingers to get caught between it, and the stator! - Because -- The force of the magnets on the back rotor will grab this front rotor and pull it down with some force! This will be much more dangerous once the magnets are installed on the front rotor, but even now it goes on with a bang! If the nuts are adjusted properly, then there is a small gap between the front rotor and the stator. It should turn freely and there should be minimal wobble. This part will be off again, so we can make adjustments later if necessary.

Now we carefully make marks so that we know exactly where to place the magnets on the front rotor. This is fairly important and has to be done carefully. Wherever we have a North pole on the back rotor, we must have a South pole on the front rotor! (so they attract each other). I usually make two marks just to be sure... marking the location of 2 magnets 180 degrees around the circle. I mark the back rotor, and the front rotor, and then it's very important to mark 1 stud, and one hole on the front rotor. After this, the front rotor must always go on the same way, so that the same stud always goes through the same hole. It doesn't hurt to use a file to make some of these marks, as we'll be painting it in the end and it's easy to lose marks made with a pen.


The drawing above shows how the magnets must be aligned. Again, once we mark the front rotor, and place the magnets we must be sure it always goes back together this way. Since there are 5 studs, and 5 holes in the front rotor... it would be easy to reassemble the alternator improperly if we don't make good marks and line things up whenever the alternator is assembled.


So now we can remove the front rotor again. It should pull off easily by hand at this point, although levers could be used if the magnetic force is too strong. Down the page a bit we'll be making a wheel puller so we can remove this once all the magnets are on... perhaps we should have made the puller earlier! Once the front rotor is off, and we have made marks laying out where North and South poles need to be, we can place down 12 magnets on the front rotor and cast them in there just like we did on the back rotor. This time the magnets must align with the marks perfectly!

Once that resin sets up, we need to prepare the alternator to mount the front rotor. First we need to double nut the studs. If the gap between the blank rotor and the stator was good before, it should be good again by adding 1 more nut (which adds extra thickness and compensates nicely for the thickness of the magnets). We should measure very carefully again and double check! A little wobble in the front rotor is OK so long as the gap between it and the stator stays almost exactly the same all the time. A bit hard to explain, but we will be balancing things, so as long as the wobble only puts things out of balance at this point were OK, but if it results in the gap between the magnets and the stator changing, then the nuts must be re-adjusted. The nuts should be adjusted perfectly... We can have the propellor wobbling up and down a tiny bit - as we can balance that out with weights, but we can not have it wobbling back and fourth very much. A small error at the center of the alternator could result in a large wobble at the tips of the prop which could be bad. So we measure the nuts very carefully, and double and triple check before putting this front magnet rotor on.


In the picture above we've put the front rotor on, and basicly the alternator is done. Putting the front rotor on is not necessarily easy or safe the way I do it! Perhaps better would be to weld a bracket and a nut onto the inside of the front rotor so we could safely lower it down. The force between these two magnet rotors is fantastic! What I do, is carefully hold the front rotor up, and line up the marked hole with the marked stud so I know its close to the right position. Then, quickly, I place the rotor on there so that it's resting on top of the studs! This is a bit tricky, because the magents are attracted to the studs and unless things are fairly well centered the rotor will be pulled into the studs and I have to pull it off and try again. This could be resolved if we used stainless steel allthread studs, but I'm not sure the extra cost and difficulty cutting stainless warrants it.

Once the rotor is sitting on top of the studs slightly skewed, I can then rotate it a bit so that it lines up with the studs. It's very important to hold the rotor in such a way that there is NO POSSIBILITY that fingers could get caught between the rotor and the stator! I then start lowering the rotor down over the studs, and very quickly the magnetic force will yank it from my hands and it will be sucked down onto the nuts which hold it into place! Again - a jacking screw in the center of the rotor would improve this operation a good bit, I think it's well worth the time to do so and will next time! As it is, this bangs on with gobs of force and sounds a bit like a gun going off when it comes into place. Without a jacking screw or a wheel puller, it will be impossible to remove! At this point, we can rotate the alternator. The gap between the front rotor should remain the same as it rotates (none of that sort of wobble is tolerable). Again, a bit of up and down/side to side wobble could be balanced out... it means we didn't get the studs quite straight probably. But wobble that changes the distance between the stator and rotor must be fixed with the adjusting nuts.

I've really not had much problem with either though, the worst being less than 1/16". If all looks good, then we know it's well adjusted and don't have to make any changes. We'll take it apart 1 more time for painting. If all doesn't look good, we keep disassembling it/putting it back together until it does! In either case, at this point we can turn the alternator and check output. At 60 rpm (1 revolution per second) we should see about 6 volts AC between any of the two terminals on the stator.


Above is a drawing of the wheel puller as we made it. This doesn't do much to help peaceful lowering of the magnet rotor I don't think, it's not stable enough, but it does pull the rotor back nicely so that we can get it back far enough from the back rotor to safely remove it by hand. It might be better to weld the 3.5" steel part of the puller to the inside of the front rotor, this way it might be easier to use and it might serve well to lower the rotor back on easily. If I were going to do that, I think I would upgrade to thicker steel and larger allthread just to be sure nothing could bend.


In the picture above we are hand turning the alternator and testing for output.


I didn't get many good pictures of this, but above is shown the notch in the tail pivot which sets the stops for the furling system. We like to weld a bead around it to strengthen it here and hopefully prevent cracking. The drawing on page one shows this to some degree. The notch must allow the tail to pivot around so that it's almost perpendicular to the wheel spindle on which the alternator rotates during furling (in high winds) and it must stop it just a few degrees PAST being parallel with the same wheel spindle. Check out the drawing on page one, as it shows this somewhat.

To determine the location and size of this notch, we first weld the short 1" pipe to the tail boom, and place it over the pivot on the windmill chassis. We simply move the tail boom into the normal running condition, and mark it - then into the full furled position and mark it. We can then cut the notch out. In practice... we may not get it quite right the first time. Some adjustment may be required and we'll know after we raise the wind turbine and observe if it's running square with the wind or not. Sometimes it's easier to adjust the size of the tail than it is to adjust this notch, but... with a welder, and a grinder, we can add and subract metal here as needed. Initially we want to get it as close as possible.


Pictured above we have 3 machines very nearly finished except for tails, paint, and props. The tails we'll put on here by welding brackets of 1" wide, 1/8" thick steel bar stock near the end of the tail boom. Again, the tail boom is 3/4" pipe, 5' long. The tail itself will be made of 3/8" plywood, and will be about 5 square feet in area.


Here we have the tail brackets, and the tail on.. all finished up except for paint and a prop! We'll get to that on the NEXT PAGE.


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