Matt's 15' diameter wind turbine had some problems after the high winds last weekend. Actually, I believe this problem started about 6 weeks ago, when Rich and I were up there and it was making a loud 'clunking' noise. At that time, we shut it down. Matt came home and we turned it on... and the noise was gone - so we let it run for another 6 weeks. After last weekends high winds (which it seemed to handle fine) - it started making a similar clunking/scraping sound on Sunday night. So we shut it down and got around to dropping it on Friday Morning.
(this was adventurous because we dropped it during extremely high winds!)
Even though the winds were high, it came down nicely and the landing was uneventful.
Perhaps this explains it. We suspected something like this when we started finding stainless nuts at the base of the tower. We'd never put lockwashers around the stator and the nuts at the stator brackets came loose even with lock washers!
One of the studs that held the stator in fell completely out!
My bet.. is this one fell out 6 weeks ago and it's been running with only 2 studs - that would explain the weird noise and why it stopped.
Ok... this is the last time I'll put one up without a bushing or bearing at the top of the yaw bearing. Although it still seemed to yaw, and furl fine while up on the tower, once we lowered it - it seemed as though somebody had welded the machine to the tower top. The machine wouldn't budge - I finally had to use the 7.5' long tail as a lever to break it loose, the crowbar I used in the picture above wouldn't budge it. The top pipe of the tower had cut into the thick washer at the top of the yaw bearing deep enough allready, so that it locked itself on the tower top.
There it is, all taken apart. The stator is fine - barely scratched, which is amazing. The noise was from the studs scraping on the back of the plywood hub that holds the blades together. I believe this has been running quite loose for a while now. This machine is really effective in low winds, and it's pretty much either making power, or shorted out - so there is almost always current flowing through the stator if it's turning. When there is current flowing through the stator, I believe it 'self centers' itself between the magnet rotors because the coils are repulsed from the magnets on both sides. Kind of interesting...
I think this thing rattled apart partly because of... poor use of hardware, and vibration. Since this alternator has the magnets fairly close together - the sine wave has tall narrow peaks, and it vibrates a bit more than most 3 phase alternators. (nowhere near as bad as a single phase machine though) We put it back up yesterday. Same hardware - but this time we've got lockwashers on the stator, and locktight on all the nuts. We put a throwout bearing (from a volvo) in the top of the yaw bearing - it was a perfect fit in the 2.5" pipe. Although it was not a problem, we also improved the tail stop for the furled position by mounting a rubber motor mount to serve as the stop. It's back up for now, and seems to be working nicely.
