Crazy weather Spring 2011 combined with changes to the blade length caused a failure in the top of our wind turbine tower. When we brought it down we observed cracks in the vinyl-ester resin stator. It is time to make a new stator. Thanks to Mackenzie Thatcher we have more than enough copper to build new coils. The first stator mold was damaged primarily because the mold release was insufficient.
Stator mold I used 3/4 inch thick plywood for the top and bottom to help stabilize the mold, unfortunately the plywood had a warp I could not repair using heavy weights on top with the plywood spanning two saw horses. I then added the 2X4s to help straighten the wood. Reading the book again by Dan Bartman and Dan Fink from Other Power I realized the top was supposed to be round, no doubt to help keep the super sticky vinyl-ester resin from gluing the mold pieces together.
Stator mold Above is the next idea I had: Still employing the 2X4s to help keep the warped plywood flat. I don't know if you can see the small space in the front where the warp in the plywood is raised.
Stator mold – This side as well as the opposite side are lying flat against the center piece which is cut out in a circle for the resin to be poured into.
Stator mold – I was thinking I would screw the plywood to the 2X4s, but then I would need to counter-sink the screws and fill them afterward, as this bottom of this top mold piece is against the resin and needs to be perfectly smooth.
Stator mold – Carpenters wood glue and clamps are what I decided upon. I hope it works.
Stator-coils-fiberglass – While I worked on the mold I also worked on the stator coils. They have been soldered already except for the output terminals. I'll do those after I get the coils in position. The fiberglass is glued with Super Glue and pressed in place using the magnet separators, which are made from polyurethane which pretty much nothing sticks to.
Polyurethane is the material we prefer to use for the mold, but we could not find it at a reasonable price and we needed to get this project going.
Stator-coils-fiberglass – I used auto body working tools as weights. I still will need to shape the coils but first I need the coils to stay in place.
That plywood is from the first stator mold we built four years ago. See honey, it really does pay to keep seemingly worthless items around, hehe.
Friday,June 17 2011
Alrighty then, difficult as it was to get off the couch yesterday, after the extreme work day on the tower above Mora, sometime around 4:00 PM I did so. I may have jumped the gun, but that's the price you pay sometimes for pushing through what every day life throws at you. First I attempted to use the last part of a gallon of polyester resin from the first stator we poured. Unfortunately it was lumpy, so I poured it back in the can and moved on to the new gallon. I racked my nap-addled brain to recall how much hardener we used last time so as not to repeat that blunder, I re-read the directions. Yes, I read the directions. Then I reread them. I guess I really did want this to work.
Anyway, last time I supposed we didn't use anywhere near enough hardener because after 12 hours the resin wasn't set, and I picked the stator up to bring to Synergy Fest it began to leak out, whoops. I figured that it was the extra alumina hydrate power which acts as a heat sink that threw the proportions off. This time I figured it in, well actually I didn't really measure anything. I guesstimated the volume needed to fill the mold, poured that much resin in a coffee can. Adding a little over half of the powder I had left, yeah right another meaningless proportion, but hey it is what it is. Using a paint mixing paddle on my drill I stirred it up for a couple minutes, before adding the hardener.
The hardener directions suggest 1/4 ounce hardener to a quart of resin. Right there is half the problem. The hardener has a measuring cup, the resin does not. I hadn't calculated the volume of the mold anyway, so I guessed. Once one guess is thrown in, a second shouldn't matter a whole heck of a lot. Nevertheless, the question of how much hardener was biased by my previous mistake, so I doubled the amount, then gave it a few more drops for good measure. Those last few drops may have been over the top, but I'll not know until I try, right.
Last time the resin didn't harden even overnight, this time it was warming up immediately. Two part resins get hot when combined. So I call this a hot mix. Anyway, it was setting while I decided to open the mold and add one more coat of wax, because last time the resin stuck to the mold destroying it. The bottom line was the resin wasn't flowing well and did not penetrate the coils well,oh well, still it looks awesome and I am very happy I did it. I knew there might things that might go wrong, but I was trying to put indecisiveness behind me.
Wind turbine stator in the rough –What I wound up with is by observation,a perfectly flat stator. I noticed that the mold was bending with the strain of six "C"clamps squishing the top to the bottom. I simply backed the clamp pressure off until the mold flattened. I see a marginal penetration of resin to the coils. I think I can repair that with a thin coat of polyester resin. Most likely I'll trim it up and try it out on the wind turbine to see what type of output I get,before calling this stator a success. In the above image you are seeing the bottom of the stator. Obviously,the reason it popped right out of the mold is the resin didn't penetrate the lower layer of fiberglass.
Other side of wind turbine stator in the rough - This is the top. I applied the top piece of fiberglass after pouring the resin. It was setting because of the extra hardener I added. Right,that stuff really works. If practice makes perfect, then after a couple more stators I ought to have this process figured out,well, better figured.
All in all,I am delighted with the results. Just the fact that I got this pour done pleases me. Certainly there will be consequences to not getting the resin to penetrate the coils. The alumina hydrate along with the resin act as cooling agents. Making the stator is a complex process, with quite a few variables. I'm looking forward to the next one.
With renewed hope,
June 21st 2011 adding new pics and stuff to the new stator project
This is a dry run to see what the stator looks like in relation to the magnet rotor. First thing was centering the stator on the hub
stator-1-magnet-rotor – I had to figure out a way to adjust the stator laterally. First I tried to file out the holes but there really isn't room on the stator because the coils and the mounting holes are very close. Then it occured to me that I could bend an offset in the mounting bolts which are made of All-thread. I did a rough bend in the vise hitting first one side then the other, leaving four nuts in place to protect the threads. As usual the first off-set bend wasn't enough, so I went too far on the next two, one of which you can see in the above photo. I'll need to straighten that one a bit.
stator-1-magnet-rotor-front – Above you can see that centering the stator with the off-set all-thread worked well enough. There isn't but about a 1/16th of an inch clearance so it had to be pretty close to not rub.
stator-1-magnet-rotor-side - the next adjustment was getting the stator back against the magnet rotor evenly. I'm pretty happy with this gap. The magnet rotor isn't real true so I can only get it so close before it wobbles into the stator.
stator-1-magnet-rotor-close – the gap on this one side I have the magnet rotor on is around a millimeter- with play of half that all the way around
stator-1-magnet-rotor-top – looking down – A multimeter showed exactly the same readings from each terminal to the next: 20 VAC spinning the hub by hand fast as I could.
This morning I'm trying to get a little done on the turbine, while I'm washing a batch of biodiesel
Stator back on after adding a pint of resin to fill in the voids from pouring too-hot last time.
Gap looks much better than the first stator
I thought I better check the grease on the bearing, good thing too. It was ready
Next on my hit list is figure out how to work around the Blacksmith shop's misreading blueprints and making the jacking holes larger instead of smaller than the all-thread holes
Updates July 16th 2011
I did a rough sanding on the blades that Kevin Murphy made on a CNC router, They are pretty thin, I hope the wind doesn't tear them up right away.
Looking down from the tip, you can see the curve. Kevin says, he hopes this helps keep them off the tower
He has beautiful curves. Next time I will get him to leave more material to aid in finish sanding
These are very slender blades
Above the blade is up against the last set we made on the CNC machine
I've got the blade held next to one of the six foot blades from the last set
Very artistic, I hope they hold up
again such a lovely shape to work with
I like the Cedar wood, but it isn't nearly as hard or heavy as the douglas fir of the last set Again this photo shows the curve
Stator clean up, sigh
A couple of the blades together
At the same time as I was sanding on the blades I used a pneumatic orbital sander on the stator to get it flatter. I got a bit carried away with the last finish coat of vinyl-ester resin
I am getting happier with the look and feel of the stator, but I have to say to the newbies, try and get it better to begin with, clean up takes way too long when we're sloppy
I did the first trimming of the inside circle cutup for the hub with a crappy little auto body rasp. Then I figured out to use a rough sanding disk on a air tool
I don't remember what you call it but there it is the sanding tool