Hi SparWeb
"Welcome to the group. Awesome credentials; pretty soon you'll be the mentor."Thanks! I hope that maybe someone will glean some info from my experiences over the years. Even after all these years, I'm still learning. Good stuff, what other hobby can you have that keeps the mind moving in so many ways?
"Tilt-up furling has been done a few times by small WT manufacturers, Parris-Dunn comes to mind."Yes!
I love that machine! I have a 6V one that has been on display in my shop for eons now. Great little machines. If I recall correctly, they built up to a 12 footer. LOVE the old Pre-REA turbines. Been a collector for years and have a small handful of Winchargers and such.
"Nothing against the cast axial stators but under your weather conditions.... The Axial-flux design as per Hugh Piggott is a specialist at medium wind speed ranges with the advantage of the ability to "tune" for manufacturing variations. I don't think an axial will address your problems."Here are some of my thoughts- Yes, the axial alts have their weaknesses, overload being a major one of them. A very large number of the failures I've had have been mechanical. For the electrical / overloading end, I'm planning on having my machine being fully furled by about 20-25 mph. I've got the frame all welded up and it has an offset from the furling pin of about 6 inches (plenty in my experience). The rotor is pre-canted to a 10* angle vertically when in it's normal "home" position to help with the onset of furling. Fully furled, the rotor will be at 80* from horizontal. Springs will help in holding the turbine in it's normal running position and to increase the resistance to furling as it progresses. I'm not too worried about the peak power that I get out of the turbine as the higher windspeeds are always less common and I'd rather have the machine produce what it will up until the 20-25 mph range and then just "get out of the way and hide" when winds increase beyond that. Probably 65% of the time our winds are below the 20 mph range, but when it decides to get windy, it usually does in a big way. 40+ mph for 3 or more days straight is not uncommon. I actually held Ventera's 24 hour production record when I was testing their 10 kW machine for Elliott Bayly at my home and hit 294 kWh to the grid in one day. I'm not looking for a cure-all with the axial, just something that I can build in my modest shop and not dish out another grand when it blows up.
I'm winding my stator up as we speak. 75 turns of #13 are going into it (24 V machine). I'm fudging a bit from Hugh's and the Dan's plans as I'm also using a 1750 lb. axle which incorporates a bigger hub (5 on 4.5), leading to a bigger center hole, leading to more room for copper. Hopefully the equation equals a bigger cushion before meltdown. My main objective has been to make the thing as mechanically stout as possible. The furling pin is an 1.5 inch tube, .25 inch wall with greaseable needle bearings in the ends of the tube and thrust bearings on the ends between the uprights. The whole frame is .25 inch plate and already weighs more than the XL.1 it will be replacing. The children's story of The Tortis and the Hare comes to mind here. -Wait, maybe that's because I just read it to my 2 year old...
I know it's a bit ugly at this point, but here's where I'm at with the frame:
"Further thoughts on a bullet-proof turbine for extreme wind speeds and possibly very strong gusts is to have NO furling at all, and design for stall regulation..."One of the windfarms that I oversee is a group of 750 kW NEG Micon turbines. These machines are stall regulated. No furling, no pitch adjustments, no nothing. They have the blade angle pre-set to stall at a peak power and they have to live with it. Here's the problem- stall works up to a point. This winter, we were experiencing some extremes. 25-40 degrees below zero and 50+ mph winds were very common all of January. The month's average windspeed was well over 10 m/s (over 22 mph). These Micon turbines were constantly faulting out on errors because they were overproducing and stall was not setting in and holding on as it should. These 750 kW turbines were hitting well over 1 MW during these conditions. Some of them even peaked at over 1200 kW. From what I've found, stall works, but only to a point, and then the rotor will start to overpower the load. If you push the limits, stall will break free if the conditions warrant. And, that would be a time that I would desperately regret not having furling. This is also the exact reason I plan to incorporate a pull cord of sorts to furl the turbine manually from the tower base and not rely on dynamic braking. -There's no better way to stop a turbine than to get it out of the wind. They figured that out nearly 100 years ago.
More to come as things progress...