Assembling the Alternator

I forgot to take pictures of the assembling process so here is the atlernator fully assembled. It worked out pretty well. The stator coils are slightly offset like I thought, but not too bad. I will drill new holes next time it is disassebled in order to get the coils perfectly aligned over the magnets. It definitely is producing electricity judging from the sparks you get from turning it by hand and cancelling out the leads.
It was a bit more work than I thought to put it together. You have to be really careful so you don’t loose a finger between your wrench and the magnet rotors……ooooch these things bite hard!! You simply have to use jacking screws in order to bring the second magnet rotor down onto the machine. It is unbeleivable the kind of force these magnets can create. There is at least a couple hundred pounds of force between the opposing rotors so you can’t lower it by hand.
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Building the Stator Cont.

Time to fix up the stator. It had a bunch of air bubbles in it, so I taped up the edges and poured a bit more resin to fill them up. That worked really well as you can see from the images below. It still looks a bit patchy but it should work fine…regardless of how ugly it is.
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Next I drilled the 1/2 inch holes for the stator bracket so the stator can be hung on the alternator, and I drilled the 1/4 inch holes for the brass terminals lugs that you see below. Each of the terminal lugs corresponds to one of the phases in the 3 phase alternator and produces AC current slightly out-of-sink with the other two phases.
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You can’t really tell from the pictures but it turns out the copper coils were put into the mold just about a 1/8 inch to far to one side. This may cause a slight problem when mounting the stator later. I think it will be ok though. I may need to redrill the mounting holes or bend the stator bracket a little in order to fine tune it. We will have to see once it is assembled. I will not make this mistake on the next one for sure.
Anyway, the stator is done. This is definitely the most challenging part of building the wind turbine. A lot of things can go wrong and it can cost you a bit of money, so take your time and do it right. I think the coils being slightly offset is the first thing that I have done wrong so far and I hope it turns out not to be a big deal. We will see.

Building the Stator

I started building the stator the other day. This the stationary part of the alternator that sits between the spinning magnets and actually induces the electric current. It is what they call a 3 phase radial axis alternator and it has 9 copper coils and 12 magnetic poles. Of course, we have built two magnet rotors with 12 magnets each, one for each side of the stator. So it is a 12 pole alternator but it has a total of 24 magnets. The interesting thing about using magnets on both sides of the stator like this is that it increases the magnetic flux by a factor of 4. So it is a very good use of magnet material because you get 4 times the electrical output for twice the magnetic material.
Building the stator has been the trickiest part of building the entire wind turbine so far. You have to be very careful or a number of things can go wrong. Basically, you are making 9 copper coils (3 for phase 1, 3 for phase 2, and 3 for phase 3), wiring them in a star configuration, and then casting them into a do nut shape using vinyl ester resin. The stator will then look like a thin disk of copper coils that will be sandwiched between the magnet rotors. The do nut hole exists in the stator so it can slip over and attach to the frame that was built earlier.

I wound the coils using my home made coil winder that you can see below. The Otherpower book had plans for the coil winder too.


I then spent a lot of time soldering and heat shrinking everything together. It is difficult to get the coils spaced properly and all the leads soldered correctly and keep everything tidy. You have very little space to work in and are worried about shorting out a coil from all the bending and such. I didn’t do a voltage drop or resistance test or anything like that to test the finished copper windings so hopefully everything was done right. I won’t know until I put the alternator together. Take a look at the copper windings pics below. Oh, and thanks Jay for all your help with winding and soldering the coils. I bet you thought you would never see the day that I actually cast them in resin.

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It would be nice to build the alternator with the leads of the coils pointing towards the outer diameter of the mold so you didn’t have to risk any bad solders that are then encapsulated in resin. If you make one mistake you have ruined the entire stator at a cost of about $100 or so. I might try this alternative arrangement instead on the next one.

Next I waxed the mold and got all the resin ingredients together and measured out…

– 1 and 1/2 quarts of vinyl ester resin.
– 1/4 pint of fiberglass strand (1/4 inch long)
– 3/4 pint of ATH filler
– 1/4 ounce hardener


I decided to use the amounts above for a few reasons. I did not use as much filler as the book recommended because I wanted the mix to be less viscous so I didn’t have to worry about air bubbles being trapped in the mold. I also added a little fiberglass to add strength. I used a bit more hardener on this cast then with the rotors because it just didn’t seem to set without adding heat last time. Hopefully it will set in a reasonable amount of time. At this point it has been like 5 hours and it has not really hardened up much if at all. I’m going to let it sit over night and see what happens. If it looks the same in the morning then I am going to apply heat using an electric space heater. Anyway, here are a couple of pictures of it sitting in my garage. Notice the three copper leads sticking out of the mold.

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Well the mold did NOT appear to harden up much at all over night. I was not too concerned though because I knew from my experience with the rotors that I could just apply a bunch of heat in order get it to fire off. So, I let it set all day in the garage. It got up to around 95 degrees and then started to cure really well. It is about 7:00 in the evening now and it looks like it is well on its way to setting up. I’m going to wait a good while longer thought to make damn sure I don’t ruin the cast by opening it too early. I hope it turns out nice…or I’ll be a bit disappointed.

Well all’s well that end well. I ended up waiting another day before opening the mold. I took a bit of advice from the forums…

After a couple hours in the sun the mold (and my tester) was totally cured. I guess UV does work. Well my temperature gauge registered 107 degrees on the mold too, so that had a lot to do with it. Anyway, it cured up nicely even with so little hardener (about 1/2 %) but it did take some heat. I don’t think it would have ever cured without it. Unfortunately, there were a number of air bubbles but they all look like they are cosmetic and fixable. I am going to use a bit of tape around the edges and pour more vinyl ester resin into the hollow spots…maybe put something flat on top to smooth it out.

The mold was destroyed in the process of removing the casting. The bottom of the mold even pulled up a bit of the plywood. I think making a plastic mold is a really good idea. I would not do wood again. The stator does not “fall right out” if you are a mere mortal like me. The other guys are not mere mortals. And this was after 4 layers of linseed oil and 3 very thick layers of mold release wax. I’m not sure what else I could have done to make it release better.

Anyway, here are a few pictures…

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It could have been much worse. The stator did not crack or shrink and it looks pretty good. Not bad for my first stator I think. Hopefully, it can be cleaned up and more importantly does not have any shorts in the copper. We will see. I will put all of that into the next entry because this one is getting way too long.

Building the Alternator Rotors

I found some time last week to build the rotors. This step basically involved placing the magnets on the rotor plates, banding the rotors with stainless straps, and pouring vinyl ester resin in to fill up the space between the magnets.This part was actually really easy but it was a bit nerve racking because I hadn’t worked with any type of resins before. So, I was worried that the vinyl ester resin would harden too quickly or not at all. I read a number of horror storries on about people having big problems and it being a costly mistake. It turned out to work pretty well and so I am more confident now going into casting the stator.
Anyway, I had bought the magnets, 1/4 inch steel rotor plates, and the stainless steel rotor bands a while ago and started to assemble them last week. I heated up the bands with only a propane torch and was able to slip them over the rotor plates. The book recommends using an oxygen acetylene torch but it turns out the propane is hot enough. It was as bit tough to do this without assistance, simply because you have only a couple of seconds to slip the bands over the plates before they have cooled down and no longer fit. You have to be quick. This is really a nice way to band the rotors since you don’t have to bother welding, screwing, gluing or anything else like that. The bands are held in place very tightly simply from contracting around the circumference of the steel plates as they cool.


Well it turns out I banded the rotors before placing the magnets. That was a mistake. It was much harder to place the 12 very powerful magnets with the stainless steel bands in place because it keeps you from sliding the magnets on from the edge of the plate. It worked though with a bit of time and effort. Then I used a bit of supper glue around the edges of the magnets to temporarily hold them down. Next, I placed the 5 1/5 inch circular wooden “islands” in the center of the rotors using silicon caulk under them to create a seal. This keeps the resin from filling up the entire plate and running out the mounting holes. The book gives you a specification for these wooden peices. Make sure to put a slight inward angle all the way around the edge of the “islands” so they can easily pop out after pouring the resin. Mine broke because I had to pound them out with a hammer…not sure why. Below you can see the wooden “island”.
Next I had to cast the rotor with resin. I decided to do it pretty much to the specification in the book. I used a bit less filler but the recommended amount of hardener. I poured 3/4 of a quart of vinyl ester resin into a 2 quart measuring container and then added 3 cc of hardener. Then mixed it. This is half the amount recommended by the resin manufacturer, which is what the Homebrew Wind Power guys recommend. Then I added 1/4 of a quart of ATH as filler, so I had a total of one quart of material. Then mixed it. This is the total volume that the book says you will need for one rotor. Well, it turned out to be enough resin for both rotors and then some. Not sure what the deal is with that. I’m not too surprised though since I have seen them use plastic milk jugs and just estimate how much to use. 🙂


Anyway, after a few hours the resin had not hardened at all, so I got out an electric heater put the rotors up on 2 x 4s so there was airflow under them. The temperature got up to about 110 degrees with the heater so the rotors started hardening very quickly. I turned off the heater after it started to set and let it harden slowly all night. I think they turned out really nice because there was almost no shrinkage or cracking at all. They looked almost perfect without any sanding or anything. I might put a little caulk around the inner edge of the resin since there is a little gap where the silicon caulk squirted out from underneath the wood island during casting. Check them out below…