Anotherpower.com Forum
Renewable Energy Questions/Discussion => Wind and Hydro => Topic started by: bvan1941 on February 07, 2012, 04:16:15 pm
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"m12ax7" (in another post) today, made a comment about the difference in generator torque / impedance matching to overcome part of the problem. He rightly pointed out there were trade-offs too. It started me thinking.
Using "Alton's wind Speed Table" as a reference, I've been trying to figure out adequate Rotor size for my modest W/T project.
First of all I'm talking about wind speed between 9-20 mph !
I have observed that accepted concept for Rotor design/speed is to go with higher TSR (3) bladed rotors (for many sound reasons). Part of the (higher TSR ) reason is that they do, is there's not much power in the wind at lower wind speed and higher TSR Rotors need RPM's to develop the torque required by the load and in return, the generator creates, in meeting load demands.
Some recent innovativeexperiments have been made by well known Forum contributors.
Example : Chris Olsen has developed the "chain-driven transmission" then coupled that together with a Clipper and the MPPT Controller, with outstanding results. but He also demonstrated all this with a smaller Rotor!
Here's my proposal for reasonably more power in the 9-20mph wind band.
"Why not use a (4) bladed prop for more torque and use a "chain-driven transmission" similar to Chris's design for more Generator speed and power in the mid-range "normal" wind speed band."
I think the (4) bladed Rotor designed for good torque and medium speed would be have some inherent speed control as wind speed increases above the 20 mph range. "The analogy is high speed aircraft use a thinner wing for speed thicker wings cannot get to the upper speeds because of aero dynamic drag, but on low speed (STOL- SHORT TAKE OFF AND LANDING ), Aircraft they use this high lift design to their advantage."
Just a thought,
Bill
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"Why not use a (4) bladed prop for more torque and use a "chain-driven transmission" similar to Chris's design for more Generator speed and power in the mid-range "normal" wind speed band."
Bill, I think I would go with five blades instead of four. I experimented with a four blade rotor on a geared turbine for several months. It worked very will thru our typical lower wind speed summer. But I could never get it dynamically balanced. I fiddled with that thing every time I had a chance to try to get it so it wouldn't wag the tail on the turbine, but to no avail.
Going to five blades will make it a lot easier to balance.
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Chris
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Chris,
You are right I should have thought of that too!
It seems even numbered blades always seem to have a significant problem, where odd numbered blades seem to work out OK.
Bill
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Chris,
in view of your experiences with the S809 and GOE -222 airfoils, what would your preference be to a (5) bladed airfoil in the scenario of 9-20mph? or use another type? If so what do you recommend?
1. Would you give any thought for a much SMALLER (5) bladed GOE -222? Being smaller a diameter my thought would be that its TSR
would enable it to excel under heavy loads at the middle windspeeds. Wouldn't it work out to provide maximum power.
2. Would the GOE-222 be able to be controlled there?
3. If I under stand your previous statement about the S-809 airfoil, it would not start to "fly" until well into the upper half of the wind band described. This would apparently lose out to the GOE-222 there. Missing making adequate power in the lower half of the band of wind described.
4. Would your "chain-driven transmission" be a good fit for this scenario?
Just interested in your thoughts with all your trials and experience with airfoils and control at different windspeeds.
Bill
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in view of your experiences with the S809 and GOE -222 airfoils, what would your preference be to a (5) bladed airfoil in the scenario of 9-20mph? or use another type? If so what do you recommend?
If you want low wind, low speed, high torque power, definitely use the GOE222. The S809 has to RUN (and I mean at high speed) to make power.
1. Would you give any thought for a much SMALLER (5) bladed GOE -222? Being smaller a diameter my thought would be that its TSR
To get decent power from marginal wind speeds you need swept area. It's like the old saying in tractor or truck pulling engines - "there's replacement for displacement". If 575 cubic inches is good, 650 is better.
2. Would the GOE-222 be able to be controlled there?
Easily. With five blades it would never hit very high speeds, and hence have no problems with furling. But the torque would be tremendous in higher winds.
3. If I under stand your previous statement about the S-809 airfoil, it would not start to "fly" until well into the upper half of the wind band described.
No, the S809 works fine in lower wind speeds. It just has to be running much faster. It is a more slender, high speed, low drag, more efficient airfoil than the GOE222.
4. Would your "chain-driven transmission" be a good fit for this scenario?
Yes, it would work excellent.
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Chris
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Chris,
good info, will post if I'm going to incorporate any of these concepts. Those GOE-222'S are not cheap but it would a great experiment.
I would like to be able to demonstrate those
blades with a (5) blade configuration along with your "chain-drive" to maximize power made good in that powerband. I don't know if anyone has done that with Royal's light weight poplar blades. I think the "combo" would definitely improve performance for many people in low-medium wind speed areas.
(If money were no object !!!)
Bill
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I carved a set of GOE222's myself and it wasn't all that hard to do. I made them from spruce, roughing them out with a hand power planer, then doing final shaping with a custom-made draw knife and sanding. I think they're actually easier to make than twisted blades.
I've used both the poplar and ash blades from Royal Wind & Solar, and I prefer the poplar because they're lighter.
You could also use a conventional flat face airfoil like a NACA 4415. The 4415 is pretty fat and those fat airfoils make good lift at slow speed. But the GOE222 still makes more torque than the NACA 4415. On a slow turning rotor like that those GOE222's would be awesome because you can't fully stall them. The harder you load those down, the harder they pull. You get a set of them GOE222's lit up and you can short a strong generator and can't stop them. On a 12.3 foot three blade rotor I've seen torque from those blades that equals what a healthy small block Chevy can put out on the dyno.
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Chris
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Can someone who knows what they are talking about please post references or links to what these GOE222 NACA 4415 are in a posting so everyone don't just go... huh? oh well next topic..
Yeah, can Google it but how many will.
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Ok I'll do it ;D
GEO222
http://www.worldofkrauss.com/foils/435 (http://www.worldofkrauss.com/foils/435)
NACA-4415
http://www.worldofkrauss.com/foils/1694 (http://www.worldofkrauss.com/foils/1694)
I was going to post on S809 but worldofkrauss.com stopped responding with
Application error
Rails application failed to start properly
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Can someone who knows what they are talking about please post references or links to what these GOE222 NACA 4415 are in a posting so everyone don't just go... huh?
Sorry. The NACA airfoils were developed by the National Advisory Committee for Aeronautics for aircraft wings. They were never developed for wind turbines, but they work well at about 32% efficiency, and they're easy to carve.
All the NACA series airfoils are designated with the first digit describing maximum camber as percentage of the chord. The second digit designates the distance of maximum camber from the airfoil leading edge in tens of percent's of the chord. The last two digits designate maximum thickness of the airfoil as percent of the chord.
The GOE airfoils were developed by the Gottingen Aeronautics Research Center (now the German Aerospace Center) in Gottingen, Germany. The GOE222 is a time tested airfoil that has been used on wind power systems since the early 1940's.
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Chris
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Does,
anyone have any personal experience they would like to share with (5) bladed wind turbines? Do they really make more power than the conventional 2/3 blade versions?
I know some have talked about high speed blade versions having worked for Ametec type conversions, but I was thinking more of the 8'-10' diameter rotors with homebrew or motor conversions in 700watts(+) category.
Bill
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If designed PROP-erly ( ::) ), they should make 'the same' power regardless of the blade count.
It mostly comes down to matching the PMA.
More blades turn slower (in typical designs).
Less blades turn faster (in typical designs).
Here is a servo motor.
It did not need speed, it needed torque to keep out of stall. (or bigger blades, but I'm not exactly in an enviroment for bigger blades).
My quickie solution was some seriously short wide blades made to ZubWoofer angles.
It worked well, except the flimsey blades bent back and started to flutter, at about 14~16 MPH, IIRC.
Made 60~75W a few times when I was watching.
Seems like the dia is about 31.5", though I call it 'Ugly 30'.
G-
[attachimg=1]
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anyone have any personal experience they would like to share with (5) bladed wind turbines? Do they really make more power than the conventional 2/3 blade versions?
No, they don't. Going from two blades to three, you can extract about 3% more power from the swept area. Going from three to four you lose power. The more blades you add, the more power you lose due to drag and aerodynamic efficiency problems.
There's a reason most of the commercially built very large turbines have three blades. The reason involves both economics and efficiency.
The advantage to using 5 blades vs three would be very low wind startup, high torque available at low wind speeds, a slow turning, very pleasant, quiet running machine, and probably better power production on slow wind days when a conventional three blade rotor is trying to get up to speed but a five blade can extract power from what little wind is there.
The facts still are, that once you get a three blade rotor up to speed and making lift and power (usually 6 mph or so for most), you will not match it for efficiency with any other configuration of blade numbers.
"Low Wind Power" is a fallacy. A 10 footer at 6 mph @ 30% efficiency will make 28 watts. Assume a 10 foot turbine @ 28 watts 24 hours a day, 365 days a year. You will generate 245 kWh.
Put that same turbine on a site that averages 12 mph and now you generate 2,303 kWh in a year - 9.4x more power from an increase of 6 mph in wind speed.
A five blade turbine like you describe can make some useable power on a marginal site, and will probably do better overall than a conventional one because it will make power when the conventional one won't in the poor wind conditions. But don't expect even a very large one to come close to what a conventional 10 footer can do on a good wind site that averages 12 mph.
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Chris
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Seems there are some misconceptions here.
The number of blades make no difference to the CP of the design.
The number of blades makes no difference to the tsr of the design. (can be the same for any number of blades)
There are no efficiency differences between blade numbers at the shaft.
If you go to a blade calculator (say altons) and plug your tsr, blade number and diameter in, the rpm and power at the shaft is the same for all wind speeds with any number of blades..... so thats the theory.
In PRACTICE this is not so easy to achieve. If you do do the above exercise, you will find the blades are impossible to actually build and have any strength when you get to high blade numbers.... they are so thin to achieve the same high TSR we expect with say 3 that supporting the force on them is no longer trivial.
Luckily, some folks (such as here: http://old.windmission.dk/workshop/bladenumber.html ) have actually built and operated 12 bladed designs, and achieved measured CP in the reigion of 0.47. Thats not too shabby at all.
If you only buy pre-made blades, then the more you add, the lower the TSR and the higher the torque, and all the things mentioned by Chris will come to pass...... but if you design for a TSR and build to those specifications (if possible) then blade number makes no difference.
Commercial mills didn't miss this. Two blades are cheaper to make for the same TSR, but wobble, and have their own problems. Three blades solve all those problems.... even though it is 50% dearer to make.... so they make these. Making three blades to go as fast as the 2 blade design is structurally significant, so they settle for a slower three blade with a bigger gearbox
5 blades for a given TSR offer no more power , no more ....or less speed, no better CP, TSR or any other advantage other than they will cost more to make, and be structurally weaker for the same TSR as a three blade version.
If we want more torque on a practical scale, we add more of the blades we have that are strong and available..... and we find lower speed operation, and higher torque.....but ONLY because we didn't change the cord and the pitch.
What we see and measure can lead us to the wrong conclusions if we dont fully appreciate what is really happening.
The most important factor is MATCHING THE LOAD to your blades, and blade count will make no difference..... loading will.
If you chose 5 blades of a three blade design, you will get more torque at a lower rpm, but you will need a much bigger alternator to match it physically (more magnet and copper and steel) for the lower rpms.
...............oztules
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That 5 blade idea came from ebay sellers?
ebay is not a good place to do blade research. You knew that.
It always amazed me they could claim 5 of those bent metal (slow) blades, or 6 or 8 of the Air-X knock-offs, would somehow make "more power" on an Ametek considering most peoples problems with Ameteks seems to be their 3 blades are not fast enough. Slower blades will not help if the PMA needs a higher TSR.
It all comes down to matching the blades to the PMA.
A slow 5-blade set of whatever 5 the guy happens to make for all his 2,3,4,5,6 and 8 blade sets may be fine on one PMA (like that Ugly 30),
but it won't make any power if it hardly ever reaches cut in RPM on another PMA (or treadmill motor).
Should be able to find out how to make a 2 blade, or 5 blade, of the same dia, that match a given PMA.
I just saw Oz posted, mentioned Alton's free calculator.
I like windstuffnow Ed's $5 download calculator.
A calculator lets you change things and see the impact of what is what.
That's when you can see a 5 blade setup, with 6" from the tip being only 1/128" thick, and getting thinner, is not a great idea on many PMAs.
3 blades is easier to build the blades. (2 or 4 can have balance issues, 5 is just more precise and need to make 5 instead of 3!)
G-
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Thanks oztules for your posting. That sums it up real nicely.
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Ghurd, yes I liked the windstuffnow Ed's $5 download calculator. and bought it some 7 years ago..... but now I use linux
I used altons, but felt that Ed deserved a "donation" because he was an inspiration.
I use altons now as it is web based, but Ed at windstuff now inspired a lot of the things that have transpired since. He is a great innovator and deserves attention.
... and thanks Janne...... it is as I see it.
..............oztules
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oztules,
A lot to digest. Considering the components (one has), the area's wind band, picking a correct rotor to match, may not be very apparent! Blades with approximate TSR's of 5-7 it would seem to require significant rpm's / wind speed ( + 9-14mph?) to develop the necessary torque to make any real power made good.
The more I think about "matching the load to the blades," what comes to mind is "how many amps do you want to see for a wind speed, based upon knowing the rpm's gen. has to make for the amperage desired (on a 12v system as example). This brings me back to figure what wind power is available at that speed and what blade can provide the required torque. A sobering moment for me was to accept that my avg. wind speed falls below12mph. Most gens. need to be turned at least +200-400 rpm for any significant power into batteries. If one has a 24v system the problem seems to get worse to "match the load/ rotor" equation (in this scenario).
Example for clarification:
In this scenario I would have opted for GOE-222 blade for raw torque under load and possibly a up-speed transmission for gen. rpms
to put acceptable amperage in the batteries. Is this your definition of matching the blades to the load?" Anyone in this type of may think "add more blades to maximize the torque" once the rpm's to the gen. was established.
Bill
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oztules,
I forgot to add that in choosing a higher TSR blade would not allow the blade to "fly enough" to make the required torque and the necessary rpm's for the gen.
Bill
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Hello!
I've mentioned before that I've "got no dog in this hunt", I live in a low area with a ridge right next to me, would require a 150 ft tower and that's just not going to happen.
But I still often read these threads and try to absorb some knowledge, and I've got a question about this subject (matching blades to alternator/generator). If one is designing a system from scratch, shouldn't one match blades to generator and generator to load?
Wouldn't it make sense to have all three Blades/Generator/Load variables matched at the same time? I understand that there are electronic controllers available (to match generator to load), but some sound pretty pricey. If one keeps the generator to load matching part of the blades to generator matching process could one save $$ over all?
Or is this out in left field?
ax7
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Any power helps the battery.
Can you put the turbine on the ridge?
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@m12ax7
From my understanding matching over the entire range and conditions that the batteries/load may be could prove to be difficult.
I gather the biggest problem is that the match is almost always the worst it can be when the need for power is the greatest. This of course is also generally when there is the least wind.
I'll leave mathematical explanation to someone more qualified to do so, maybe oztules?
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12ax7
Yes thats the ticket. The best, simplest and cheapest way to make power is to match the blades to the alt and the alt to the batts..... easy when you say it quickly.
The competing interests are diametrically arranged against us all the way.
1. We want least resistance to keep the I^2 losses to a minimum...... but less resistance means more stall sooner.
2. We want voltage to rise in the stator as rpm increases.... but the batteries present a non-dynamic load for the most part, and try to pull the blades off their nominated TSR
3. We have a linear relationship of wind speed to RPM.. but a cubed (theoretical....in practice perhaps closer to squared than cubed I think) power curve... so cubed to linear problem.
4. we want power in low winds.... but there is precious little there to get.
We need to balance these concerns as best we can, and taking into account what we have at hand..... a big ask.
bvan1941.
Don't be fooled by the smoke and mirrors. You can have high torque, or high rpm, but only both in high winds.
Think about it some more. If you sacrifice rpm for torque.... thats all you have gained... and a bigger alternator.
If you sacrifice torque for rpm, same deal... and a smaller alternator ........you lose one to gain the other.... but the net gain is nil.
So if you add more of the same blade, then torque goes up, speed goes down... net gain nil.... but a bigger alternator.
Power is power. emf is the rpm, amps are the torque... WATTS= AMPS TIMES VOLTAGE ..... increase amps you must decrease voltage for the same power..... same as power = torque times rpm for the same power. You can shuffle the figures all you want, but if you win on one, you must lose on the other..... and we need both.
If we have a 100 hp tractor and a 100 hp car... both have the same power. The car may do 90 mph, the tractor20 mph, car 1 tonne tractor 4 tonne. Tractor motor long stroke low rpm, car over square, high rpm.... still the same power, but both cant do the same job. One is MATCHED to the plough, and one to the highway.... notice the high torque low rpm unit is heavier than the high rpm, low torque unit??
Thats matching the load.
We want maximum rpm we can muster... so 3 blade tsr7... and easy to carve and strong profile.. if your in a poor zone, then consider twice the diameter for a normal zone, and you may get something useful.... but you MUST furl early too.
Gearbox adds another unnecessary layer of cost and complexity. So too does an MPPT. If we spend that all on magnets, we will be able to build a much much bigger machine.... and nothing describes the power of a mill more than diameter.
If I read Chris right, the 3.8 was around the same for mild winds as the mppt special 3.2m machine. My 4m machine would probably be more again with 5kw bursts at the top end.. size really matters in lower winds. Build it big, and the torque you crave will be available. For mine only 300 watts@12mph, for 3.2m maybe 200w.
Visitors.... must go.... later
.........oztules
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If we have a 100 hp tractor and a 100 hp car... both have the same power.
To throw a different monkey wrench into the works, they use different hp rating systems on cars and tractors. The car uses the SAE method, the tractor uses the Nebraska rating.
Some years back we had a IH 806 gas rated at about 96 hp. The engine tossed a rod and put a hole thru the block. So we got the bright idea of putting a 175 hp small block Chevy in it with a transmission to gear it down to the 2,600 rpm the tractor engine ran at. I put a Woodward belt driven governor on it to govern it at 4,400 rpm, upright headers - it was really cool and sounded nice. We put it on the blower and found out that 175 hp Chevy didn't have even CLOSE to the power the tractor engine had. It lasted about 6 hours on the blower and the small block threw a rod.
Not that it applies to the topic, but thought I'd throw that out :)
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Chris
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ostules,
maybe I just "saw the light" --- It is in your opening statement, when you said- "you only have high torque, or high rpm's and you can only have both in high winds."
If I hear you correctly, without correct wind speeds, you cannot have high torque or high rpm's -- either one!!!
Those of us that don't have the necessary winds---we're just having conversation about wind turbines and we can try to get enough swept area to have fun. Just get the rotor stopped before it gets to runaway speed, when we get serious winds!
Guess I"ll call my dog in and get back in the truck----LOL
Bill
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bvan1941
It's more than that. Poor winds are exponentially worse than good winds. The power drops out at a staggering rate. Mine at 12mph may do 300 watts, at 30 mph we could do over 5000w if we use transformer switching, or drove a resistive load....
Keep that in mind.
Now for design in low winds, (any winds) we need to balance ALL the competing difficulties. All are inter-related to each other. Utopia is running at design TSR, not stalling the blades and converting all their power into the batteries.... simple.
In low winds this is easier than catering for the whole range of winds, as we can cheat a bit.
Assume for a moment, that 400 watts was the limit, and we never expect more than 12 mph. Put simply, we could build a big rotor tsr7 diameter 4m 3 blade. The rpm will be low, so we wind the coils with lots of turns, lots of coils and lots of smallish magnets.... we end up with a big stator that has high resistance..... everything we usually try to avoid like the plague.
In this case it will be ideal. The high resistance will give great flexibility to the blade set, the large stator will keep cool thermally (400w over say 250 sq ins of cooling area 18" diameter stator). If the resistance is too high, we will lose all the power in the stator so we can't go silly, but you can see that we can play with the variables too get what we want...... but it must furl or burn up when a real wind comes.
Cant have everything. In stronger winds, we need to pay much more attention to the resistance, as we have lots more power to overcome it, so we start aiming for 1 ohm star stators, and early furling, if you have my wind, you aim for .5ohm stators or less because we have the wind to drive them right up the scale.
As our expected power changes... so too do the magnets size and strength. With bigger blades, comes more torque, power and less rpm for a given wind speed, so the alternator will be much bigger, and use as much magnet as we can cram into it, and as much copper in the winding window as we can jam.
Gearboxes give us another way to increase the rpm, and get the alternator size down.... it offers no more than that, and with some losses, but with induction motor generation into the grid a 14:1 box will make it work, and nothing without it. For Chris, allows decent power from weak magnets in a smaller unit (easier than say 28" rotors), and it was a way cool exercise to compress the alternators size.
You must think of all aspects at every stage. Don't go up a blind alley trying to optomise any one part, they all need attention at the same time. It really is a symphony, and it must all work together to get a decent result.
If you optomise the alt (zero R) you will stall at cut in, if you optomise the torque (TSR<1), you won't get to cut in, if you optomise the rpm (tsr12 etc) you have no torque when you do get to cut in.... they all need to match each other.
................oztules
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Gearbox adds another unnecessary layer of cost and complexity. So too does an MPPT. If we spend that all on magnets, we will be able to build a much much bigger machine
Afraid I have to disagree with this. It's not unnecessary, it's not costly, and not all that complex.
When I first started looking at gearing from an engineering standpoint, I was able to build a small, high ouput generator with better performance than a direct drive 16 pole for a 3.8m machine. The cost in 8 magnets (at that time) alone more than paid for what it cost me to design and build a decent gearbox for it. Plus it allowed one thing you cannot do with a direct drive turbine - design a very efficient generator and match it to the blades using the gear ratio to put both the rotor and the generator at their peak at the average wind speed on your site. And at the same time allowing lots of headroom at the top end to prevent burnout because the greatly more efficient generator doesn't dissipate as much heat in the stator.
Later I used the concept to build a ferrite magnet unit that's relatively light and small and runs up to 100 volts.
The gains from both far exceed ~5% loss in gearing. Attempting to accomplish that without gearing is what adds cost and complexity.
Same with MPPT - it's not unnecessary. I once thought it was. But after learning about it and actually building a turbine for it and flying it, there is no way you will match a turbine that uses it without adding considerably more expense and complexity to the machine than the controller adds to the overall system.
Just wanted to point out that nothing is ever "unnecessary" in engineering - it's all in the design. When you start looking at a design and set a performance goal, but can never reach that goal because the things that make it possible are discounted as "unnecessary", you are merely limiting your design choices and not thinking outside the box.
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Chris
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Yes it's all in the design.
There is very little I can agree on here.
Your costs are through the roof compared to mine. I built 2 x 4 meter units for the cost of your black box. Either one will probably out perform your latest 3.2m unit.
They have run for 4 years or so, and only some magnet rot to show for it. They run in winds I can hardly feel on my cheek, and in low winds will certainly whip a 3.2 and in high winds I try to keep them less then 2.5kw.
With a stator change and a boost converter (or cap bank), they would sustain 3kw or more without stalling the blades too much at all (curves match much better with 16mph cut in)
There is no extra cost, little/cheap extra complexity..... just simple stuff.
If we were to look at a single swept area as a maxima, then your arguments would be more justified. I am happy though to not match perfectly through the range, and just make it bigger if more power is required. Blades are near free, steel is cheap, a few more magnets (go to 16 per plate) is not terribly expensive ( I have heaps of 50x15 n50 and 50x12.5 n45).
But I also have a big milling machine, lathe, brake press (60 ton) guillotine etc. Making a gearbox is not the issue at all.... simple stuff even on a remote island...... but why would I try to stall the blades.
I also do a lot of power electronics, so that would not stop me either...... so I don't mean complexity as in I cant do it or understand it, I mean not needed if you just want to make real power.
There are lots of other ways too. The AWP up on the hill is 3.7m It can do easy 24-35 kwh per 24hrs. It is ferrite, no gearbox, radial (ok I rewired its 90 coils from 1kw to 2kw) It runs at 200-500 volts, transforms down and drives the battery bank (48v). 7 years without problem after we ironed out the manufacturing defects that the Africans built into it. ( poor electronics we rebuilt, poor fibreglass blades, and terrible tolerances in the machining and shocking yaw system and woeful furling ).... but it's redeeming feature is the armature reactance that stops it from burning up no matter how fast it runs.... so it runs flat out day after day 1000 feet above the surrounding land.... sort of built in load matching/limiting
So we don't need to do other than match the load as best we can in direct drive mode to make usable power..... unless we feel the urge to build the interesting stuff because we can, but it is not necessary, and adds cost/complexity to the unit. The gearbox is a useful idea, but it is still likely to introduce stall with neo magnets I would think, which can already stall a design without speed increase.
So, I don't expect to sway you at all.
I won't knock you for doing what you have done, quite the contrary, but I would not encourage anyone else to do it either.
If I were to use a gearbox, it would likely be on an induction conversion, but even that smacks of shooting yourself in the foot just to test out the first aid kit
As you said it is all in the design. For me good design is doing the required job with the simplest fool proof system. The wind takes no prisoners over here.
................oztules
Edit. I have never understood why people on these boards don't use transformers in their design. Microwaves are cheap (free even here) and plentiful, and can provide mountains of laminates to build very powerful transformers...... but no one else seems to do it. Even quiet day/ heavy weather tap changing would yield surprising performance differences..... including your headroom. It is easy to double the current in the bank while decreasing the current in the stator on windy days. The AWP would never see more than about 7 or 8 amps in the stator while delivering 38 or more amps@55v.
The stator from the AWP:
[attachimg=1]
Ferrites in the AWP:
[attachimg=2]
Another ferrite unit I built only 1.5kw or so
[attachimg=3]
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Your costs are through the roof compared to mine. I built 2 x 4 meter units for the cost of your black box. is not terribly expensive ( I have heaps of 50x15 n50 and 50x12.5 n45).
That's my point too - I can build 4.2 gearboxes for the price of 32 of those magnets and get at least of good of performance from the machine using ferrites as you can, spending all that money on fragile and corrosion-prone neo magnets.
As I stated somewhere else, the same principles that apply to solar panels wired in high voltage configurations with MPPT apply to wind turbines. After trying the MPPT and putting a few weeks on it I've decided I like it. I got 20 kWh from that little 3.2 meter machine last Thursday at an average for the 24 hours of 7.9 m/s. The wind died down a bit on Friday and it only made 13.6 kWh. But it still matches the bigger 3.8 meter machines in lighter winds and beats them handily at anything over 6.5 m/s.
So no, you won't sway me. I'm not a first time turbine builder either :)
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Chris
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Interesting, the best I can get those ferrite that you use is $330 for 30 magnets over here.... I only paid about $1000 for 100 of the 50mmx12.5mm neo over here. More recently bought 50 bigger ones from china through a member here for not much more/unit.
Power for power the neo's are way cheaper here than the ferrite. .... that nails it for me.
I have now got 20 litres of west systems epoxy. The original ones were potted in resin (f/glass) as was the tradition at that time.
I have learnt my lesson, and the next time they will be better protected from the marine weather here.... probably another three years away yet.
I was never going to sway you any more than Flux and Dan and Hugh couldn't sway you on single phase and magnet/disk copper usage (I agree with them on those points), so we'll just have to agree to disagree. But on a price basis the ferrites are a non starter for axials here from the look of it. ... never mind the mppt and gear box.
I would like to explore the ferrites in a iron core configuration again though. I am a big fan of armature reactance. Although I can beat the AWP easily with headline figures, it's idiot proof current limiting is a worthy feature..... but I still have a hundred or so of the neo's to use up first.
The other problem I now have is the solar panels I built put out more power than we can use.... so the windmills are of less and less value as the days tick by. Solar got 26kwh the other day, and another 18.6 today.... harder to justify the mills existence we only use 11kwh/day.
On another subject, ( your earlier reply ) I dumped a chrysler car slant 6 into a dodge 7 ton truck, but I used the auto transmission as well. It survived another 7 years in that configuration. Over here we use kilowatts for car and truck power... the same things here. 100kw is 100kw The only non-power hp rating I recall was the rac rating in hp for registration purposes.... but that was bore x stroke x no of pistons I think.
........ oztules
Edit I think we may be thread hijacking here re-reading this waffle.... sorry folks we'll leave it alone i guess.
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I'd just like to add a bit on the horsepower ( calculation ) thing. 100 hp is not 100 hp as it seems. 100 hp at 2200 rpm is 202 lbs/ft of torque at that 2200 rpm. The ' same ' 100 hp at 4400 rpm is ~119 lbs/ft of torque. To multiply the torque, a gear box is need and with the losses through that box, the higher rpm will not produce the same " HP " at the wheels as the low rpm torque engine.
I believe you nailed this one with perfect examples for sure Oz. No replacement for displacement for sure. Oh wait except BOOST, COOL BOOST at that. Ha Ha.
Tractor = Linear hp = Force x Velocity / 33000
car = Rotating hp = T x Rpm / 5252
car = Rotating Torque = HP * 5252 / RPM
The tractor is draw bar hp most likely. And the car, well most likely at the flywheel before drive line losses. But, who knows how it is in other states.
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Interesting, the best I can get those ferrite that you use is $330 for 30 magnets over here....
Yes, that is interesting. I've been getting them for $113 for a box of 60.
I was never going to sway you any more than Flux and Dan and Hugh couldn't sway you on single phase and magnet/disk copper usage (I agree with them on those points), so we'll just have to agree to disagree.
That's right. What some folks fail to realize is that I don't follow the book. I don't even refer to it. In all that discussion over single phases and magnets/copper I still hold the trophy for building the most powerful ferrite magnet generator, with sustained output capability of 60 amps @ 30 volt without overheat in a 78 lb package. And since then, on the last three I've bumped the rating to 78 amps @ 30 volts continuous by winding them with 12 AWG, and still keep the stator temp below 135 degrees F on a sustained bench test without any extra cooling air blowing on the generator.
Folks tend to get so hung up on book theory that they fail the see the forest for the trees sometimes. My goal was to build the smallest, lightest, and most powerful ferrite generator that had ever been built in the homebrew world for a 3.8 meter turbine. I didn't give a hoot about what the book said, number of phases, or magnets. And I accomplished it. And I duplicated it 6 times on 6 other machines after that and every one of them is flying today.
So in all that ordeal of people telling me what I'm doing "wrong", I have yet to see somebody put their money where their mouth is and match it or exceed it. It has to be less than 14" in diameter (overall including the stator), weigh less than 78 lbs, be able to develop 1.8 kW continuous on a 24 volt system without overheat, and be easy for homebrew folks to duplicate.
So folks need to understand that that's where I come from. I spent 19 years working as a mechanical engineer in one of the most competitive businesses on earth before I got burned out. Businesses like that hire engineers that not only think outside the box, they don't even recognize that the box exists. And that's why nobody is going to sway me. I get these "visions" of a design concept and I have to build it and test it. And when I do it I'm on a mission and casual observers might think I'm nuts, but they don't see what my goal is.
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Chris
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I believe you nailed this one with perfect examples for sure Oz. No replacement for displacement for sure. Oh wait except BOOST, COOL BOOST at that. Ha Ha.
Yeah. Actually my main toy is not even wind turbines. No "cool boost" here - 280 psi @ 650 degrees F with 9 quarts of water injected @ 2,500 psi every 10 seconds at each intake port and the bottom two pressure stages just to control the fire.
[attachimg=1]
[attachimg=2]
The tractor is draw bar hp most likely. And the car, well most likely at the flywheel before drive line losses. But, who knows how it is in other states.
The automotive industry has used SAE, SAE net, insurance method, and about a dozen others - which ever happens to look good in the sales propaganda. Tractors are rated by usable power measured on a dyno at the PTO and drawbar in the Nebraska Tests under a very stringent set of rules. Even so, some companies like International Harvester tried to "cheat" by running some of those older tractors like the 806 diesel with a D361 in it at 1,130 rpm on the 1,000 shaft for their "factory rating", while the Nebraska Test requires 1,000 rpm. It sold a lot of tractors with the bigger "factory" number though :)
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Chris
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I believe you nailed this one with perfect examples for sure Oz. No replacement for displacement for sure. Oh wait except BOOST, COOL BOOST at that. Ha Ha.
Yeah. Actually my main toy is not even wind turbines. No "cool boost" here - 280 psi @ 650 degrees F with 9 quarts of water injected @ 2,500 psi every 10 seconds at each intake port and the bottom two pressure stages just to control the fire.
(Attachment Link)
(Attachment Link)
The tractor is draw bar hp most likely. And the car, well most likely at the flywheel before drive line losses. But, who knows how it is in other states.
The automotive industry has used SAE, SAE net, insurance method, and about a dozen others - which ever happens to look good in the sales propaganda. Tractors are rated by usable power measured on a dyno at the PTO and drawbar in the Nebraska Tests under a very stringent set of rules. Even so, some companies like International Harvester tried to "cheat" by running some of those older tractors like the 806 diesel with a D361 in it at 1,130 rpm on the 1,000 shaft for their "factory rating", while the Nebraska Test requires 1,000 rpm. It sold a lot of tractors with the bigger "factory" number though :)
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Chris
And there you go again. Damn hp rating of 1000's if I remember right. Nice
Let's see, 5000 hp at 6000rpm is 4376lbs/ft torque. Heck, I guess we can build a turbine for 5252rpm and the hp and torque would be the same. But, I'd love to watch that tractor pull.....
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oztules, Chris and all-
Lively point and counterpoint discussion. I've learned more and got a good reference to reread. Not worried about the "hijacking"
diversion, it happens.
Balance, in designing ones project and the components in the project makeup, are important.
One thing that stands out after all this discussion(and many others) is that, there's a point where picking a rotor that delivers the requirements that give good low-med. speed torque/rpm's to do the job, may be large enough to seriously worry about controlling the "beast" IF THE WINDS BLOW HARD FOR A WHILE. Above worrying about burning the gen., we've got a very large rotating mass going ROGUE 40' + in the air.
Many times in discussions, control of the rotor ( lack /fear of ability to control) MAY LIMIT a potential design.
Experienced builders cite rotors overcoming any furling control. Some are pretty close to approximately 500 rpm's when that happens. Others with larger diameters don't specifically cite any rpm's but, when the winds get above approximately 25-30mph clearly indicate the rotor to staunchly face into the wind and overdrive/power the system.
No matter the rotor size, it is a concern that is being overcome by builders using several ways to combat loss of control.
Clearly you(oztules), utilize the inherent design of the Induction motor to self limit gen. power when rotor overspeed happens.
(you and m12ax7 also mention the use of transformers to trade voltage for lower system voltage and much more current.)
Chris on the other hand has upped the gen. efficiencies (minimizing stator losses) using a transmission and limiting the size of his rotor and as he says limiting to under +/- 500rpm's-- for positive control! He has been using the MPPT controller advantageously too.
Midwoud1(sorry if I don't have Handle correct)- He has approached rotor problems by blade pitch control of his own design. He may have to tweak some things, but has made significant gains and demonstrated success at this juncture.
By asking these questions many small problems have been clarified for me. I have been reading the forums and over the past few years and building all parts of my small systems, experienced a number of things +/-.
All of these approaches are certainly credible and some can be achieved by a number of us, with some help by the original innovators!
I think much more can be achieved using the forum, learning how to overcome problems, bypassing failures and achieving significant improvements, because of our innovative members. thanks for the in-depth discussion.
"The wind shows no mercy" --oztules One to remember!
Bill
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Chris on the other hand has upped the gen. efficiencies (minimizing stator losses) using a transmission and limiting the size of his rotor and as he says limiting to under +/- 500rpm's-- for positive control! He has been using the MPPT controller advantageously too.
That being said, on smaller rotors it's pretty easy to control them in really strong wind with a good generator. And I'm comfortable with them doing that.
On larger rotors I would tend towards a variable pitch prop. I have built and experimented with a couple variable pitch props on smaller turbines in the past and found no real benefit. After 5 meters in rotor diameter, or so, I would incorporate it into the design. I suppose this could be construed as once again adding another layer of cost and complexity, but I feel a variable pitch prop would help me get the most from a larger turbine, and have it be reliable. I feel that waggy-tail furling has its limitations and is not a good method of power control with larger machines. Even Bergey realizes that and they simply unload the turbine if the furling fails to hold it within reasonable power limits. But the Bergey's PowerFlex rotor is designed to be able to run up to 119 mph wind speed unloaded. Few homebrew turbines can do that.
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Chris
But, I'd love to watch that tractor pull.....
Watt - I got a whole bunch of videos that, someday when I get time, I have to get off tapes. Somebody else took this one from 2007. Don't remember my distance - it was either 288 or 298. Whatever it was, I won.
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Chris on the other hand has upped the gen. efficiencies (minimizing stator losses) using a transmission and limiting the size of his rotor and as he says limiting to under +/- 500rpm's-- for positive control! He has been using the MPPT controller advantageously too.
That being said, on smaller rotors it's pretty easy to control them in really strong wind with a good generator. And I'm comfortable with them doing that.
On larger rotors I would tend towards a variable pitch prop. I have built and experimented with a couple variable pitch props on smaller turbines in the past and found no real benefit. After 5 meters in rotor diameter, or so, I would incorporate it into the design. I suppose this could be construed as once again adding another layer of cost and complexity, but I feel a variable pitch prop would help me get the most from a larger turbine, and have it be reliable. I feel that waggy-tail furling has its limitations and is not a good method of power control with larger machines. Even Bergey realizes that and they simply unload the turbine if the furling fails to hold it within reasonable power limits. But the Bergey's PowerFlex rotor is designed to be able to run up to 119 mph wind speed unloaded. Few homebrew turbines can do that.
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Chris
But, I'd love to watch that tractor pull.....
Watt - I got a whole bunch of videos that, someday when I get time, I have to get off tapes. Somebody else took this one from 2007. Don't remember my distance - it was either 288 or 298. Whatever it was, I won.
That puller is awesome. I'm afraid that now I must see it in action, first hand. We have nothing near that much fun around here. We have a few pick-up pullers around and give them lots of glory but..... You know I'm sure what I mean. Thanks for sharing that video.
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Bill,
Be wary of implications based on statements based on "New Facts".
G-
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bvan1941..
Your statement ....
...Clearly you(oztules), utilize the inherent design of the Induction motor to self limit gen. power when rotor overspeed happens.
(you and m12ax7 also mention the use of transformers to trade voltage for lower system voltage and much more current.).......
although is certainly true, I'd like to mention that my comment about using a transformer was about "matching" the {impedance} output of a servo motor that is being used as a alternator/generator, to a load. Along with the understanding that one is selecting the servo more on price and/or availability. As an example, I found my servo in the junk and paid scrap price for it ( think I paid about $4.00 for my 7.5KW servo)
When one is building their own generator and are winding their own coils (and doing it correctly) they shouldn't need to use a transformer to match impedance or step up/down voltage or current.
ax7
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m12ax7,
Got what you mean. I too had envisioned using other than a self-made generator for my project. So that was prompting my question about matching impedance via transformers. Do you have good results with your set-up?
Thanks,
Bill
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To all,
In trying to figure out what power I can expect with my new project, I have used "Alton's wind speed chart" to roughly calculate what power the wind has at speeds under 24mph and what rpms can be expected also.
(Don't hold my following figures to be exact, there's a small amount of extrapolation I did. I tried to be conservative.) The following numbers are what I come up with:
Avail. Approx.
wind speed Wind power Rotor speed
10 mph= 120w= 200rpm
15 mph= 380w= 300rpm
20 mph= 950w= 400rpm
23 mph= 1400w= 450rpm
Taking into account the efficiencies and inherent losses read about, it's troubling figuring out how to get significant power under 20mph.
I'm not sure how some people are getting so much power from their systems. I know there's aggregate figures and the add up. I know in my area the wind isn't steady enough. maybe I'll have to move to the great land of the winds --- are the numbers I came up with valid for avail. wind power and rotor rpm projections?
Bill
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Those figures look fair for about 3m machine for my money. As I alluded to in an earlier response, power is in high winds, not much in the low winds.
Here we have winds, and consistent winds. You know where these winds blow as all the vegetation leans away from the prevailing wind direction. If you don't see this in the native flora... you havent got real wind.
Little mills put out good power in high winds, medium machines put out useable power in reasonable winds, and big ones put out useable power most of the time.......Nothing describes a mill like the SWEPT AREA.... no smarty theory, no cool bananas electronics, no fancy profiles... big is better..... and bigger is better still.
The 35 footer I play with from time to time, drifts in and out of cut in at about 2000-5000w.... and is going well at about 35kw... the 55 footer is much better still. In a decent wind they can do 70-100kw. Simple induction motors with gearbox, grid tied. No pitch control, fixed blades, old irrigation 3 phase motors for generators..... no class at all.
But you must have wind for all sizes..... it's just that the bigger they are, the better they seem to do with low winds.
..................oztules
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I wonder what the difference would be on a wind site that averages 6 m/s between two 3.2 meter machines that operate at 34% efficiency vs a single 5 meter machine that can only average 25% efficiency?
Actually I already know the answer. The big one loses even though it's got more swept area.
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Chris
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Yes, the answer is simple, and you are correct.
But the cost differential is laughable.
A 5m machine of 25% is cheap to build. A 34% 3.2 will all the gadgetry is hyper expensive. Two towers, two controllers, two dump systems, 2 sets of bought blades ( you claim home built blades are inferior ) 2 clippers and the list goes on.... and more real estate to put them on.
$500 gives me a 5m machine.... 22-27% depending on how I match the blades to the expected wind regime .......your up for $1600 for mppt, before you even start to build your two machines with their two towers, and two sets of blades, and two sets of clippers..... and they will probably fail within 8 years anyway.
I haven't seen inside these things , but I suspect you will find a reasonable sized cap bank suffering ripple. They will fail by design... just like batteries will. The KOH will eventually cause failure as in ALL modern electronic stuff with PWM power stages instead of the old reliable transformer.... from your computer , your dvd recorder, satellite transciever.. you name it. It cannot be gotten around. I think the best that the worlds very best manufacturer can possibly guarantee is in the 8 year range. Electrolytic caps are most fallible, and you will do well to keep them as cool as possible to prolong their useful life. They will last 16 times as long at 60C than at 100C.
The electrolyte is the main cause for the lifetime being limited for the cap. It must continuously modify it's electrical characteristics at the dielectric layer, and a combination of self healing and drift through the seals will sap the electrolyte down. Heat will make the electrolyte less viscous, which will actually help lower the ESR. The current flow is mediated by the ionic nature of the KOH, and as the ESR lowers, higher current may be seem in the caps.
The ripple forced on the caps by the buck switching (superimposing the switched DC on the background DC) is the culprit. It cant be gotten around, any more than the evil death of batteries can't be gotten around. Both systems can be designed to be less abusive to the batts and caps, but only by never discharging the batts too far for too long, or keeping the ripple to a very low level so that the caps electrolyte gets an easier ride.
The estimated lifetime can be empirically guessed at by the use of temp time graphs from the various manufacturers. Temperature and voltage will help accelerate the degradation of the electrochemical characteristics of the capacitor .
So you have built in death in your 2x3.2, and expense I can't comprehend. Living where you are in contact with the current manufacturers helps, but where i am... forget it. It would cost $500 just to send it back.
So I won't be swayed by bells and whistles either. I still applaud you for doing it, but I would still caution anyone else particularly if they are not in the USA to either build their own, or stick to tried and true methods.
I'm not sure the comparison was useful.
...............oztules
Edit: It is interesting to contemplate what will happen on about 5-8 years hence with all the grid tie inverters that are out there. They have been installed in this country extensively over the last 2 years or so.... there must come a time where they are all going to fail together. The cap failure rate is a bathtub graph... a sample will die within days, then drop to a long period of only scant random failure, then toward the expected life end, it will rise up again very steeply then taper off. There will be piles and piles of grid tie units on the tip.... will be interesting times indeed.
I suppose to ones mounted on the sunny side of the houses will go first.
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I think the comparison is useful because efficiency is as important as size. Cost, for me, is really no object. I got a brand new 80 foot Rohn SSV tower laying in my machine shed that I haven't put up yet. I'm enjoying the smaller very efficient turbines because they really don't need to furl until the wind speed gets up to 15-18 m/s where they finally overwhelm the ~84 amp limit into the battery bank plus the clipper load. They don't take NEAR as much tower as a bigger machine does. The wiring to wire them up is cheap - all it takes is 10 gauge down the tower. The rectifiers don't get hot.
Splitting out your incoming power sources into several smaller ones vs one big one makes it easier to manage, improves odds for higher survival wind speeds, and redundancy. Imagine if they tried to make a Boeing 747 fly with one huge engine strapped to the roof vs four smaller ones hanging under the wings.
There's a lot of things I like about the smaller very high-performance machines. Not to mention that they're WAAAY fun to build :)
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Chris
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hope this is on topic ... :)
i,d go a bit further with the issue of home made blades ....i think you can actually compete very well with the commercial blades ...it,s a matter of personal choice i guess..
its pretty easy to "knock" up a constant pitch , constant chord ,no taper wood blade....that,ll work just fine
now... if you have extra time on your hands , (and your a bit nuts) you can use a blade calculator and make the non linear twist ,graduated chord , taper blade .....you can even feather the trailing edge to a razor point if you wish .... :)...get a ultra smooth leading edge etc....
going after these traits might seem a bit extreame ....but the side effect often overlooked (i think) is that you get a stronger quieter blade .....
if you really want to get certified you can play with winglets at the blade tips ....and yes it has to be fun ..... :o
the best part is your in controll of your own machine ....you can replace the parts , if you need too
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Oh, I'm not going to knock homebrew blades. If you're skilled enough you can match the commercial ones. After all, somebody has to build the commercial ones too. It's just that I'm pushing Cp .40 with those S809's. I like that airfoil and it's really hard to carve it. It was designed by the NREL, specifically for wind turbines, to be forgiving of dirt, ice and roughness on the blade surface. They run fairly quiet at high tip speeds. And I like the glass blades because glass never soaks up, or gives up, moisture or changes weight or density with age.
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Chris
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hi Chris.... :)
yes ....that airfoil seems almost impossible to carve....and moisture content in wood blades can throw out balance a little .....
buying commercial blades seems tricky .....theres so much iffy stuff out there
sorry for going of topic a bit ... :)
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Chris,
I agree that the design of the S-809 blade takes sophisticated equipment and to evaluate the foils ability. The part of your statement that has some error in it is the belief that "fiberglass is impermeable to moisture(water)! Wrong--- fiberglass is actually just a big sponge without a waterproof layer applied and chemically bonded to the fiberglass.
In fact if one were to look at raw fiberglass under a strong magnifying glass or microscope. one would see thousands of holes in the material. (The holes are microscopic gas /air created in the mixing and chemical reaction of the resin catalyst mixture). The only thing that keeps boats or anything made from fiberglass watertight, is a very thin layer on the outside that's called"gelcoat."If the people in this forum would cover their fiberglass with "gelcoat" when they take the stator out of the mold, they wouldn't have moisture get in and start the delaminating of the fiberglass. Another little known fact when dealing with fiberglass (polyester,vinylester,epoxy resins), is all resins bought off the shelf, has liquid wax mixed into it. This is what make the fiberglass "smooth to the touch," otherwise it would be "sticky" to the touch and stay that way for quite a while.
When applying "gelcoat" to "cured fiberglass" one MUST LIGHTLY SAND OFF ALL THIS OUTER LAYER OF WAX that comes to the surface during the curing process in the mold. Gelcoat can be put on by brush, roller or sprayed, your choice. Two coats applied immediately will negate the required sanding necessary if allowed to dry between coats. This procedure also applies when building up multiple layers of fiberglass as well. Unless your using resin without wax already mixed in the resin, the "rule" is apply successive layers before the curing is complete (meaning, while the previous layer is still "tacky" and before the wax rises to the top of the fiberglass).
Just trying to help (Thirty years of fiberglass work repairing boats !!!)
Bill
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Couple notes on applying a gel coat..
This stuff is rather dangerous, you MUST have the correct equipment and respirators, or risk serious health problems.
Another possible solution is a couple step process. I have used a thick polyurethane paint, like a bed liner ( Herculiner ).
I strain out the rubber pieces, then use it for boat bottoms etc. As polyurethane does not hold up well to UV, there are additional polyurethane
compatible coatings meant for this problem. Downside in this is this turns into a relatively thick coating, but it works well for at least a decade, and is much less toxic and expensive to apply. Gel coat is relatively thick also, so the results may be comparable.