Anotherpower.com Forum
Project Journals => User Journals => Oztules => Topic started by: oztules on February 20, 2012, 07:19:18 pm
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Stemming from an answer to Wolv regarding driving resistive loads:
Here is one experience I had with it. ;D
========================================================= from fieldlines some years back
Well I had sorted through the battery lot that I was given and found that I had 13 good ones. It was one of those blustery mornings and so I had the bright idea of "lets see what she'll do mister" type of thing going on in my head.
I had also pondered what to do with the excess power that the chainsaw blade mill seemed to be producing. I had read some of Daveb's posts on water heating... so I got the bright idea that I would use it as a dump load, and/or use the mill to heat up hot water.
The obvious conclusion was that in order to have reliable water heating, I would use the batteries to heat the water while the mill was charging. This would allow me to use say 5kwh to heat up some water, and if the mill was in reasonable wind, it would carry the load some of the time, and top up the batteries after the heating was done.... thats the plan.
So I dutifully fired up the mill, and proceeded to charge the batteries a 72v configuration from the 48v windings of the mill... It seemed to be putting in a fairly steady 10 or so amps, and so while it was doing that I hatched a plan to test the water heating idea.... funny how we think sometimes.
Armed with a plastic 1 gallon (4.5 litres) icecream bucket and a 4 ohm load, I wandered back to the battery bank and proceeded to fill the icecream bucket with cold water, and with the aid of two microwave transformer primaries, freshly stolen from two unsuspecting transformers, I put them in series, and threw them into the bucket of water. (The transformer primaries come out complete from the transformers with 6mm spade connectors, and were about 2 ohms each) I spaced them a few inches apart, and hooked them up to the batteries in series with an amp meter.
The 72v bank was now at about 80v, I hooked up the resistor (coils) to see what would happen.
I had forgotten that they were actually wire coils and was thinking only in terms of resistance...
You'd be surprised how fast they move together when you dump 80v@20A into two coils in a bucket....they were now tightly stuck to one another in the center of the bucket... I wiped the water from my surprised face ... they moved through the water very fast and smashed into each other erupting the water everywhere.... and I mused...oh well, no harm done... just frightened the hell out of me.
We were now putting about 1600 watts into the water. I shifted the mill input to the coil side of the meter. That way I could see how much the mill was putting in versus the batteries. ie no mill power meter means 20A into the coils from the batteries, as the mill gets some wind the amps contributed by the battery drop, and the meter moves towards zero.
A gust of wind came along and the meter dropped to zero, which meant the mill was carrying the full load, it then pushed the meter well below zero, with the meter hard on the stops, this means running the heater and charging the batteries.
It was at about this time I had the bright idea of dropping the batteries from the circuit, and see if the mill could do a reasonable job of driving the 4 ohm load by itself.
I repositioned the meter wiring to reflect this change, and the mill was putting out a nice steady 15amps or so.
By this time, the water was starting to get quite hot, and the wind a little stronger and it moved between 15 and 20 amps... all was going swimmingly.
Suddenly a larger gust came along, and the amps went up to about 25, and I got a little concerned, but it subsided as soon as it got up.... then it happened, a bigger stronger more lasting gust came along that just seemed to increase and keep increasing, the amp meter went hard over the 30A mark, until it was rammed up against the end of the meter, A quick look at the volts said 145,-150 the amps were well over 35A, and things were getting a bit interesting.
This lasted for an eternity (probably a minute or two really)... I dashed around the corner to see how the mill was coping... it was running perfectly, no vibration at all, no sign of trouble.... except the blades were just a blur.
I raced back to the batteries, to find steam pouring out of the icecream bucket, and hot water bubbling over the side.
At last the wind eased up, and I quickly re-attatched the batteries, which calmed the mill further, then shorted the 3 ph and the mill stopped nearly instantly.... it was over.
Luckily Zubbly's blade balancing method worked,... but the yaw didn't. Daveb was right about the furling part into resistors. It didn't look like furling.
So it was just (well) over 5kw into a resistive load in I would say a 30 odd mile per hour wind on a 3 meter pole. Now it is over it seems good really, but I didn't care for it at the time. The stator was absorbing around 500-600 watts (.39ohms in star @35A) the load was copping about 5kw (4 ohms) so the stator could have done this all day. The blades worked well, and I walked away with the mill all in one piece.
And that's how silly I can be....
............oztules
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If I don't make dumb, 'I should have known better' mistakes, I don't learn. :)
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geez, you could have at least used a five gallon bucket... ;D
great story!
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running away is my preferred option ...
and then maybe throw a few stones at it a bit later from a safe distance to shut it down ..... :P
great write up there indeed ... :)
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I would still stick by my first assessment that the resistance was changing as the elements were not staying cooled enough.
Also it seems very likely there was not nearly enough load to handle the mill you were driving with.
It may be possible to handle this by adding additional load as voltage rises with a controller monitoring such things.
Then you can keep it out of stall until needed?
Unless I am missing something completely, as far as I understand batteries they just naturally increase resistance as input voltage rises ( but decreases as battery voltage does ( to a point).
Where as resistive loads like nichrome acts in reverse as heat builds
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Hmmm how to put this.....
Ok, the figures of current and voltage tell us the resistance was still not too far from 4R, 150/35 =4 ish... so no I don't think so.
The coils must not get much over boiling point due to the massive energy needed to achieve state change from water to steam.
Without the water, then the temp would rise crazy, but you only need to quench red hot steel to see it drops to water temp very very quickly.
State of charge influences the battery impedance. dead flat... high impedance, mid charge, low impedance, fully charged high impedance to charge current, low impedance to load...
When flat, they lack ion carriers. When they convert lead oxide to lead sulphate, the h2so4 converts to h20. Pure water is a lousy conductor, so as the ions are very scarce at dead flat, we see batteries wont take much charge at all. As they do, they create more h2so4 (h3+ available to carry charge now.. hydronium ions from memory).. so the charge current comes up until there is enough carriers to make the reaction go well, and then we charge full bore.
When full, the active sites on the plates that can still accept the redox reaction are few and far between... we are charged now, and if we keep the voltage on the batts, they will finish off any left over sites (pbso4 to pbo and h2so4), but the rest of the current will dissociate the hydrogen from the oxygen. The current we see going into a full bank is really only that...... losing our water to h2 and o2. ... thats equalising, those cells still with active sites still charge and bubble, those full, just bubble.
(I think Chris knows lots more about this battery business than me)...
Nichrome does as you say.
..................oztules
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As far as batteries go, that is basically what I was getting at, I was just being more simple.
With the exception that they have a difference to a resistive load like nichrome.
Because is it not if you apply a higher voltage to them, given the same state of charge, the apparent resistance rises?.
As far as elements in small amount of water, I was looking for if the elements were heating to fast causing bubbles around the elements, and hot spots.. If you had more water creating larger water flows that would stay cooler, maybe this would not happen as quickly?
Also it does seem that if you had enough load it should keep it under control. If you short the alt, it does stop it, that is none the less resistance. Determining that load may be easy on paper, as we all know what looks good on paper, may not be true in real life. Teila and error might be the best way to get working numbers.
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W=E^2/R
Now my prop at 12 mph develops 350W, and the alt makes 48v oc so into the 4R load so that is 48x48/4 or 2304/4=576W
So at 12mph, 4R kills the prop.
At 24 mph the blades make about 3kw but the alt is only at 96v oc so 96x96/4=2304 watts. The prop now has more power then the load can take at designated TSR.
At 36mph the blades are making over 9000watts the gen should be at 144v oc so 144x144/4=5184watts
So we have gone from stall to way over power by 4000w. The prop will speed up until it is well off it's tsr,and power will fall... and the load will now match.
Can you see how far your resistance would need to change to make even a tiny bit of difference?
As the wind increases past a certain point we need to add load... and lots of it. squared function against a cubed function on a linear rpm.
That certain point here.......... would be about 20mph :the prop would do about 1600W. Alt about 80vvoc so 80x80/4=1600w
Any wind above 20 mph will give us too much TSR.... overspeed, and any wind below that will probably pull it to a stop after a short time.
Does that make sense now.
For the battery.
If we raise E and say R rises, then I (current) must stay the same..... E=IR
But in a battery in mid charge, if we could raise E by even only 2v, Current will go through the roof... so R must stay the same. ( in fact on a big bank we do not have enough power at our disposal to push it up 2 volts in one hit) .....If the resistance went up reasonably, we would have no trouble.
But that does not happen. Try and raise volts much, and current takes off. not R.... until we are near full or empty... then all bets are off.
Did I explain it right this time :)
..................oztules
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Heh that was a fun story to read.
I'm sure everyone has his / her own memorable moments like these. Of my own I think the furling failure on my 3.2m axial mill would be pretty high on the list. The winds were between 20-30m/s when it refused to furl and was pumping a bit under 3kW into my 12V battery bank... about 160 amps but the battery bank was at 18V at that moment :D, since the dummy load was not rated for that kind of amps. Ahh the smell of sulphuric acid..
Also pretty memorable was the first testing of the same 3.2m rotor, but poorly balanced on a 2m short test tower.. not having much clue what kind of power and speed it would be capable.. of course with high winds and a 45W bulb "surely providing enough load". I ran pretty fast when it started to sound like a helicopter jumping up and down at the same time.
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Yes Janne... when your new to high lift props.... life's learning curve is very very steep.
My first set of 8 footer blades were carved from the boards from a transport pallet.... not flash, but followed the proper curves as best you can with 4"x1" free timber.
It was with the naive knowledge of a three your old with bright eyes, that I screwed the boards ( now blades) to a triangle, poked them on a stout screw driver, and walked from the shed into the big wide world........ I was 47yo.
The breeze wouldn't even get them to turn on the screw driver shaft for a bit, then slowly it started to move.
I was fully in control, and completely nonchalant, as these seemingly harmless bits of wood started to turn in the breeze. A bit more breeze turned up, and they started to spin harmlessly up.... nothing. At this point I'm wondering how these things are going to power anything.... but we'll see if they can do any better.
Whilst thinking all these things and others like it, I'm oblivious to the fact that they have been slowly getting faster, and are now getting to the transition point where they are no longer drag driven but lift driven.
So I'm still daydreaming and disappointed at their performance...... and then there is that certain noise as they suddenly transform prom placid drag blades to fearsome roaring man killing weapons of doom.... they have taken off.
Now it must be doing over 400 rpm, making that unloaded prop roar, and I am rooted to the spot, with my fear ridden gaze transfixed to the propeller that only minutes ago was just a toy, and now was trying to kill me with every tiny move I made to turn it out of the wind.
The good lady wife, who had been wily enough to watch from a distance ,heads for the door of the house ( ostensibly so some one will be left alive to call 000 or 911).
By now I appreciated just what lift does to a blade. I appreciated that gyroscopic forces could cut my head or toes of... dependent on which way I turned, and that my life could well come to a sticky end right here.
Turning out of the wind wasn't an option, the wind was building .... and I was in trouble.
It was some minutes later that I recovered my composure as I had shuffled back sideways to the shelter of the shed, breaking off the wind.... I felt 97 years old.
I have done a lot of things in my time, but never had I been confronted with decapitation, or serious slashing.... by my own hand, and in my control with such surprise...... My life was on the end of a screwdriver with a roaring 8 foot slashing machine.... and it was my next move.
By gad I learnt a lot right there right then.
...........oztules
An adumbrate version of fear with a prop ;D
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Ok I have to admit it, I did almost exactly this same thing.
I had a smaller 6' 2 blade plus it was mounted well on a small generator and the head unit that was to go on the tower.
I was probably being a bigger idiot though.
I DID understand the gyroscopic forces from previous much smaller yard ordainment size windmills, and the likeliness of the spin up being rather fast..
Only I did it anyway, in over 25mph winds..
I was walking to put this thing on the tower when I got the hair brained idea to let the blade loose
That this was likely over 500 rpm in mere moments when I let er rip.
Thankfully I did have so much of the machinery there and the entire device was just heavy enough to aid in control but not to heavy to be unmanageable. I was able to move it to the point I could slow it to a stop , then grab the blade just as it seemed about to reverse.
Yup, never doing that one again, I learned something..
Or did I..
About a year later I had a 2 blade 8 footer up for a test
Maybe some remember the surprising output alternator I made from ceramic magnets scrounged from many microwaves
That was the bad boy that actually got me.
I had put this thing up with intention to see what it would do in real life and not just the bench.
I found out really fast that my magnet backplate was not up to meet the the forces involved.
Magnets were hitting the stator ripping it up pretty quick when I forgot to tie it down for the night.
I went out to try to rope the blade, and could not pull it off from the ground.. So,, with the fear of god I climb the tower and tried again.
Yup got it.. but it immediately got me too as repayment. When the rope caught the blade it turned right into me clipping my shoulder.
I was lucky to kept my head ( in all manor of speaking) and got away with only a really nice bruise and about 3 weeks of pain.
Yeah, now that the wife will learn the real truth of how I got that. I'll see if she still lets me keep playing with this stuff. :-\
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not long after putting up a small mast for the machine ..i had to re adjust the cables in the turnbuckles after things "bedded in".....i had the winch still there , so i decided to let the whole thing down ...(test run kind,of)
before disconnecting the extension piece on the main winch stay i got into a bit of a muddle with the shackles ....did i loosen this one or that one ...where is the big one and (most important ) why is the dog looking at me like that ?
so i was really standing there holding the main stay in one hand with the mill (luckly very slightly of vertical) for an instant ...... a good day to have no wind .... ???
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Sounds like a touch of ADHD there lol
I can relate.
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In another life...
I went into a 35 MPH curve at about 90 MPH on a 1976 Heritage softail. Proved a couple finer points of physics. You cannot slow down much at that speed with a few seconds of warning. Muddy fields can be almost as hard as concrete. And the fact that I think I can operate a motorcycle MUCH better than I actually can!
Once the bike kicked out from under me (bailed out) I imitated a bean field luge run for a couple hundred feet feet first. Beat the hell out of me but mostly damaged pride and trashed leathers. No clue how I avoided the barbed wire fence on the way into the field but I think I went over it.
I didn't quit riding motorcycles until after a drunk guy in a van changed lanes and actually ran right over me. I didn't get up and walk away from that one and it was my last motorcycle ride on the street. It still hurts daily. :o.
I did the thing with a 2 meter 3 blade prop holding the "test pole mount" in my hands with the turbine screaming and trying to yaw. Luckily the wires were hanging off the alternator so I just puinched them together with my left hand and it slowed enough to get it out of the wind against the gyro forces.
Tom
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The most stupid thing "I ALMOST DID" was to post about the most stupid thing I did do!
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@m12ax7
Should we be looking for a body then, or the money?
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Mark..... which was.......
ever talking about water wheels....
or was it something else?
..............oztules
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@m12ax7
Should we be looking for a body then, or the money?
There are NO videos or pictures (or living witnesses), so I KNOW NOTHING!
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Mark..... which was.......
ever talking about water wheels....
or was it something else?
..............oztules
Well.. I didn't think the waterwheel idea is/was all that stupid, ambitious maybe.... but not stupid.
and the other... mum's the word!
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Far from the most stupid thing I've done - merely "one of the stupid things I've done recently"...
Had been balancing and painting my old 2.8m (10') prop. It was outside, and was just on a fairly flimsy, lightweight support to allow me to turn it freely to balance, and turn while painting...
(http://house.albury.net.au/06jan2007/000_0118.JPG)
Just a very mild breeze - barely enough to blow the paint fumes. So I'd taken off the stay so I could turn the blades to make it easier to paint.
The breeze picked up a bit, and before long it was a moderate breeze, probably 10mph or so. I thought I'd just let it turn a couple of times and see how it looked.
I didn't expect it to spin up anywhere NEAR as quickly as it did. On needle-rollers it was very free... and the blades are solid fibreglass - several kilograms each. In seconds it was far too fast to stop. It was such a flimsy mounting I didn't dare risk trying to turn it out of the wind (gyroscopic forces would likely have just broken the pin off).
Blind panic set in, I lost skin and got quite bruised, but brought it (just!) back under control by trying to grab hold of the blades back at the root and slowing it down fractionally, and moving slowly out along the blades until I could get it under control.
Never again. Nup, no way.
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i've never spun up blades in the "hand held position", but i did have an interesting experience not to long ago.
i decided to work on a junction box while it was still hot. five wires in, five wires out. AC hot and neutral, DC + and - and a ground. somehow i managed to shock myself with the DC - and the AC hot. worst part is it was in one hand, and out the other. it really jolted me, and i shock my self often at work. it took a good half hour before i started to feel normalish again.
lesson learned!
adam
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Okay, I'll admit to using a putty knife to pry out a fuse out of a 3 phase fuse/disconnect switch (440v). It was for loading dock door, door fully up and there was a raging blizzard outside. The arc flash blinded me for about a half hour, in which time I stumbled around (a large furniture factory and I was the only one there, IN THE DARK, about 1 am) thru two buildings to locate the tools needed to remove the master link from the drive chain. Had to balance the ladder at the edge of the loading dock (about a 5 foot drop) while the blizzard blasted into me. The temp out side was about 15 and the humidity INSIDE the building was held close to 70%, so what snow didn't cover me was made up by the buildings humidity turning into snow/ice.
And yes, I had the time to blindly grope my way to find the needle nose/screwdriver BUT NOT THE TIME TO GET A FUSE PULLER.
I was probably 17 (still in high school), my only excuse.
At least there were NO witnesses!
And that's what I'm willing to admit to!
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Well a few years ago a mate asked me test out some of his curved plywood prop setups, they were setup on 3/4 thin walled pipe and a couple of flimsy pipe clamps onto the blades. The blade diameter was 3 metres and 4 blades, for a few weeks they did a good job with a F&P washing machine motor as the genny then one night a gale came thru and the missus said to go look at the wind genny as it is sounding pretty loud. Anyway 1/2 way up the shed the blades decided to let go bigtime and one went flying straight past me landing down the hill about 50 metres away from the tower. That was it for me I went back into the house and said I aint going out there until morning to pickup the pieces. The wind was that strong it bent the 2" water pipe above the guys to a 45 degree angle and the blades must of hit the tower. I did find the pieces of 3 blades but that 4th blade was no where to be found. About 4 months later my son brought me the blade and said he found close by the shearing shed which is close to 150 metres away from the tower. Now the house is inbetween the shed and shearing shed so I was damm lucky those flying blades didnt take out my solar array.
Well it just goes to show if a guy asks you to test out a set of blades beware and make sure you ask why aint YOU testing them.
Cheers Bryan
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See... that why you make wooden ones ( just don't use knotty pine like I did... live in fear)
.....oztules
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For "Off Grid"...
There was a factory made chinees CFL looking lantern. Users told me it was nice.
Step 1. Do something about the 8(?) D cells.
Step 2. Design, build, install, Dremmel tool, etc, the thing.
Step 3. Try it with 36" test leads to a 7AH 12V SLA, which it was modified to hold.
Click the On switch.
Magic Smoke.
Not the regular kind of Magic Smoke.
This was the Extra Super Magical Smoke kind of Magic Smoke.
I am talking about LOTS of smoke coming from inside a screwed together assembly.
So, naturally, gotta get to where that Magic Smoke is originating from.
Grab the screwdriver.
Interchangeable bits screwdriver, with the #2 Phillips installed.
OK, that does not fit in the deep #1 Phillips hole where the screw is.
Where is the #1 Phillips tip?
I have no idea.
Just had it a second a ago.
After 5 seconds? 10 seconds? Whatever.
The smoke is getting thick.
No #1 Phillips bit anywhere to be found....
Pretty sure this silly thing is gonna burn my house down.
Wholley Crap! What do I do now? Flee for my life? Abandon my home to the eminent catastrophic flames? Grab the family photos on my way out?
I reach down... and unclip a wire from the 7AH battery.
Problem solved.
G-
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In the 1980's, Mother Earth News "Book of Home Made Power" had a picture of a man that had just carved a 2x4 prop. He was holding it into the wind to demonstrate how simple it is to build a wind turbine to produce electricity.
I have to wonder how many folks here saw that same picture?
That photo came to mind just as I finished my first 4 foot diameter prop. That was a neat experience while the prop was spinning up. Then I wondered, who had whom? I stood there for what seemed like two birthdays until I could turn it out of the wind. I had a nice shiny screwdriver afterwards, new knowledge and nothing bruised or skinned. My lucky day!
Could the prop spooling up in your hands have caused this insane addiction to wind mills? ::)
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Could the prop spooling up in your hands have caused this insane addiction to wind mills?"
I'm sure your right Philb..... certainly burns it's antics into your mind.
..............oztules
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As the wind increases past a certain point we need to add load... and lots of it. squared function against a cubed function on a linear rpm.
Oz, that's a good description of the problem trying to control turbines with resistive loads. It's also what I've found out playing with my voltage clipper on my Classic controller. I already burnt one clipper to a crisp and had to regroup and re-think how to do it. Using a really big load with PWM is the only way I've gotten it to work.
Once you get a turbine into over-speed they refuse to furl for some reason. Even making well over "rated" power, they refuse to furl. Not exactly sure what causes that. But my little 3.2 meter will furl fine at 30 mph if I got it lugged down 450 rpm. Let it run over 500 rpm and it don't even attempt to furl even at 45 mph putting out over 4 kW.
It has something to do with this windseeking thing that Flux talks about. I never believed in it. Flux always told me he had a turbine once that the tail busted off from. He witnessed that turbine in overs-speed, with no tail on it, hang dead into the wind and just scream. Since I've now seen the same thing, I believe in it. But what causes it leaves me at a loss.
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Chris
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It has something to do with this windseeking thing that Flux talks about. I never believed in it. Flux always told me he had a turbine once that the tail busted off from. He witnessed that turbine in overs-speed, with no tail on it, hang dead into the wind and just scream. Since I've now seen the same thing, I believe in it. But what causes it leaves me at a loss.
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Chris
If I had to guess I'd say it's gyroscopic forces. 20+ pounds of wood and metal spinning at 1000 RPM or more is a whole boatload of kinetic energy. The rotor disk has more energy keeping it stable than the amount of energy in the wind trying to push it off axis. Trying to furl just by pushing it off it's axis isn't going to work very well, you'll need some sort of cyclic control on the blades similar to a helicopter rotor, using it's own energy against itself.
Kevin
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Another posibility:
3.2 meter rotor @ 2000 RPM is a little over 1200 FPS tip speed, Mach 1 is 1100 FPS. Weird things happen with air at transonic speeds. Subsonic airfoils don't behave normally, something called control reversal is a real problem. Chuck Yeager lost elevator control at near Mach, the airplane had a "full flying tail" meaning pitch trim moved the entire horizontal stabilizer to make trim adjustments. The only way he got it under control was to use trim, not the normal elevator control. Modern supersonic aircraft still use this same control method of moving the entire tail.
Perhaps something similar is happening on the turbine at very high speeds, instead of drag pushing the rotor off axis the blade are producing lift towards the wind instead of the normal away from wind direction. Essentially it's in equilibrium pulling the turbine forward as much as the wind is trying to push it back.
Just the crazy random ideas going through my mind as I'm half asleep...
Kevin
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Perhaps something similar is happening on the turbine at very high speeds, instead of drag pushing the rotor off axis the blade are producing lift towards the wind instead of the normal away from wind direction. Essentially it's in equilibrium pulling the turbine forward as much as the wind is trying to push it back.
Both that, and the gyroscopic forces make a degree of sense.
Be pretty easy to tell - if the prop follows the wind quickly, it's more likely the latter explanation. If it wants to stay as it was, then gyroscopic forces seems more likely!
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I think it has to be aerodynamic forces causing the problem with no furling at high rpm. Gyroscopes tend to precess. And the heavier the rotor, and further it is from the yaw axis, the greater the precession force is. Theoretically this should make a right hand turner/left hand furler (viewed from upwind) tend to precess to the furl side. But if you calculate the precession force, it is so minute that it is impossible for it to be a factor.
The moment of inertia of a turbine rotor is quite large. And because of this it will tend to resist changes in its state. But it will never firmly plant it in the direction of the wind and refuse to move, and even follow the wind when the wind changes direction, as Flux has described. There is no way that can be described with any of the engineering math I ever learned in college and practical application.
I believe it is purely aerodynamic. These offset head tail waggers are pretty much unknown in the commercial world of wind power except for a few examples like AWP (designed by Hugh) or Bergey. And Bergey recognizes that there are times when "excessive power output" can happen with the Excel. So I dunno.
There was some dude on Fieldlines that had a big grant and a wind tunnel. He wanted somebody to design a turbine for him with this grant money. I tried my damnest to get him to let me use that wind tunnel, and he even said he would let me use it. Except after that, the guy evaporated or something and he forgot all about me and my wind tunnel time I was supposed to get.
If I could've gotten a slot in that wind tunnel I would've had a turbine loaded up in the truck and heading to where ever it is in a matter of a few hours.
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Chris
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"But it will never firmly plant it in the direction of the wind and refuse to move, and even follow the wind when the wind changes direction, as Flux has described. There is no way that can be described with any of the engineering math I ever learned in college and practical application."
Chris, I had reason to drop in at the larger turbines near town yesterday. I was called to look at a yaw motor (3/4Hp 14:1 reduction box and then more gearing to the head).
That was simply bearings had exploded (nearly 30 years )and the bits shot into the windings and killed it... not what this is about actually.
What took my attention, was that I had the yaw motor in my hands, but the mill was drifting in and out of cut in 1-5kw.... (panel next to me)but there was no yaw... as I had it.
I thought I was working on the next mills motor, but it was the mill above me (control room at base).
I questioned the owner, who said that provided the wind did not change direction rapidly, the mill would stay directly into the wind and follow it... producing power all the time......... weird science. I didn't believe Flux many moons ago, but have seen it with mine, and now with a biggie ... its true for sure.
...................oztules