Recasting a Stator

[Boss]

Good Morning

After the pep talk I gave yesterday, and the wonderful posts and pictures from Fieldlines of other people showing off their handiwork building small wind turbines,  I felt I had better get on the ball and do something constructive with my time.  Hard and harsh as reality sometimes can seem, I began by searching each of our cold, dark and snow drifted out-buildings, locating parts and supplies for building wind turbines. Perhaps adversity was responsible for our success. All the while I was searching for the magnet templates I was controlling emotions about the lack of a major tool. How were we going to move the mechanics tool-box over to the new work shop, without the hitherto trusty Ford pick-up? "One piece at a time," I supposed, in not so much of a muttering old man tone. Except for the snow and the rough driveway, we could separate the boxes, and roll them the 150 feet. I do have the WVO trailer I can pull with the Trooper, which just needs the tire aired up...

If this, then this,  is how the morning was going. If it wasn't for the fact that I kept finding useful and inspiring goodies for the wind turbine work shop. Well, most of the stuff is inspiring and as it worked out even one distressing find proved to be inspirational. There in the corrugated tin shop, just beyond the reach of the drifting snow was the first casting of the turbine stator, still entombed in its plywood mold. Instead of disregarding what was considered by me to be the first major failure and breaking point of the Las Tusas Ranch wind turbine building effort, I grabbed it, and hauled it up to the new workshop. After all, as I thought about it, it was our intense efforts and subsequent failure with the stator that pushed me forward in the realization that we needed a proper workshop.

I continued to look for the aluminum magnet templates. It's mildly irritating that I recall putting them someplace, specifically, but they weren't there. Truth is, they weren't in any of the places I thought I put them, lending me the freedom to trust that I really had no idea where or when I moved them or where I  put them. Well, the day was full of work-arounds, some emotional, others purely spatial in nature. To a successful,  work-at-home person, the trick to dealing with adversity and obstacles it perseverance, and quickly dismissing negative thoughts. I find myself thinking, "Okay, forget about why I don't have something, the important fact is, I don't have it. How can I accomplish the task with what I do have?"

Sometimes it is better to switch to a different project to keep moving forward. Looking for the magnet templates kept me looking for stuff pertaining to the wind turbines. Absolutely, some stuff wasn't going to turn up on the morning I decided to make the leap from building-a-shop, state of mind, to realizing it was done enough to get back to what we were doing eight months ago.  As it was, I toyed with the failed stator turning it over and over wondering what it looked like inside the plywood mold. Not sure why I never ripped the mold apart. Possibly because I find it stressful tearing things apart that so much attention and hope went into. I dug up an image of the stator when we were building it prior to the Synergy Fest, in April 2008.



stator coils and mold

Nice and neat then, after nine months of sitting in the weather it didn't look so good when I picked it up yesterday.



Stator

The stator was pretty messed up. After Kevin and I peeled the plywood away, one sliver at a time, a less deformed casting than I imagined emerged. Perhaps it was only a matter of time before I let go of the notion that the mold itself was a waste of time. All I had to do was change the way I thought about it.  We were going to need to build another mold. The question is when, before we could move ahead?



stator

After we cleaned off the miscasts and garbage normally associated with casting resin we continued with the inspections of the stator. What made me think it was totaled was the delamentation on one edge. This happened when I picked up the mold on the morning of Synergy Fest and noticed the resin hadn't dried over night. Foolishly I set it back in place, but what I should have done was put all the clamps back on it, before we left for town.



stator

The result of tipping the mold, not noticing the liquid resin coming out, was gaps in the stator, more on one side than the other. After tests assured us that the coils were intact and showed the same values, we worked out a few scenarios for repairs. Lucky for us Jackson showed up with his vast surf board building and repair knowledge, adding it in with ours. Most of my experience with resin casting came in the form of a class I took at NMHU. Except for the seminar at OtherPower in Colorado none of us worked with vinyl-ester resin, all our experience was with polyester resin.  It turns out vinyl-ester resin sticks really good, which explains why it wouldn't come out of the mold until we destroyed the mold to release it, and only then after the plywood was softened by nine month outdoors.



Kevin

We used fancy duct tape to contain the liquid resin. One concern was non-uniformity in thickness of the stator. The side that leaked out resin was a millimeter thicker. After squeezing the delaminated side with a couple of "C" clamps convinced us that the thickness issue was tolerable. we began mixing vinyl-ester resin along with the hardener and heat sinking talcum power.



stator

Here the "C" clamps squeeze the fat side of the stator. The proof will be in the pudding as they say. We need the stator to be of uniform thickness because the distance between the spinning magnet rotors influences alternator output efficiency.



stator

Here you just make out the coils in the semi-translucent vinyl-ester resin. Actually I think what stands out most is the tape around each edge of the coils. A lot of effort went into placement symmetry of the coils, well one thing is for certain, our first stator casting ain't pretty, let's hope it works well enough.

Next projects for the wind turbine are laminating, either Western Cedar like the guys at Other Power showed us, or go with the locally available Douglas Fir. While we gearing up for building the blades, I'm figuring out what to do about the fact that E-trailer sent us mis-matched axle and hub sets. I went online yesterday and learned that I had ordered a matching set, so either the bearings are wrong or their part numbers are.

Alrighty then

[Jon Miller]

Hello,

Shame about the original casting outcome but good job on the repairs there.  Im sure if there is a slight increase in the air gap, that it could be balanced out by shortening the blades slightly.

All the best with it.

[oztules]

Good stuff Brian. Due to interference from a certain dog, my stator was a shambles as well, but you'd be surprised how well it still works, even being about 3mm thicker than it was supposed to be, and ugly as sin.

 The stator from hell is in here : http://www.fieldlines.com/story/2008/8/18/83321/8140

............oztules

[Ungrounded Lightning Rod]

We need the stator to be of uniform thickness because the distance between the spinning magnet rotors influences alternator output efficiency.

The two aren't related.  The MAXIMUM thickness of the stator (actually the highest points on opposite sides) sets a minimum for the gap, but the physical gap is controlled by the spacing of the rotors and unchanged whether it's passing over a thick or thin part of the resin.

Remember:  With a stator that has no magnetic core the magnetic gap is the space between the magnet poles, not the space between the poles and the stator.  The resin has essentially the same magnetic permeability as air, not the orders-of-magnitude higher permeability of iron.

The main problems you might encounter with a nonuniform thickness to your casting is strength issues and uneven cooling of the coils.  The former should be pretty obvious if it's enough to be an issue, while (with no parallel-connected coils and wired Y) the latter just means you have to set your furling to limit the current in the most-insulated coil.

[Boss]

We had a major biodiesel Isuzu Trooper failure to deal with since the last post so I didn't get to work on the re-cast stator until this morning. The turbo charger blew on my work truck. I'm a WiFi installer and the prospect of being without my work truck was devastating. However unlike the shop at OtherPower I did want a garage door on our new shop, so we pulled the Trooper in and replaced the turbo in one day. I love the new shop.



Lots of sunlight and natural warmth from the south facing windows

This time we used more hardener in the polyester resin and the resin set up nicely. We must have messed up the proportions the first time around. I used to tell my  customers back in the day when I owned a VCR shop, "Yes, you can service your VCR on the kitchen table, but better results will be attained on a work bench."How true this is, the casting came out so much better working in the shop.

You might notice the poor spacing of the coils in the translucent resin. We will do better on the next one. what you can't see is that the thickness is uniform, not perfect, but close enough, I think.

My buddy is working on the blades and reportedly has two sets ready. So that part is looking up. I also wrote to E-Trailer and told them of the mis-matched bearings, axle and hub, they advised me they will supply the proper bearings. This will be done at  my expense because it was during the Spring that I ordered the hubs and I lost the receipt.

Next on the hit list will be the magnet rotors. We had a local welding shop build the steel disks from 1/4 plate. They did a lousy job, but then this is the first wind turbine we are building outside of the Other Power workshop, so we hope they will work well enough. They match the five hole hubs (which was also my screw up) bought from E-Trailer, so we'll use them. Everything about this first wind turbine is working out the hard way. This is part of the learning experience, what can ya do, but keep at it, until it is right?

 

[Boss]

Sorry for the bigish image  of the Trooper, is there an edit function, I'll resize it