Author Topic: New build- 20 foot diameter variable pitch windmill  (Read 11784 times)

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windy

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New build- 20 foot diameter variable pitch windmill
« on: January 19, 2018, 11:17:00 PM »
 I am in the process of building a 20 foot diameter variable pitch windmill and may need some help in designing the stator and rotor. I have attached a file using the Axial Generator Calculator that was posted a few years back. Could someone look at this and let me know if this looks right.
 I will be using this generator for resistance heating only,(water and space heating). There will be no batteries or DC voltage involved. Controlling speed will be with a Arduino microprocessor  using solid state relays.
 The blades that I am using are the GOE 222 profile that I carved myself and read a few posts back that when using  the 222 profile, the stator should be wound accordingly.
 I designed the stator and rotor using Solidworks and used these dimensions in the file. I will be using 20 poles with 15 coils. Not sure if I have the wire gauge right.
Take a look and leave any comments or questions and will reply as soon as possible. When I get a little farther with the build, I will post some pictures.

windy
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midwoud1

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #1 on: January 20, 2018, 10:52:36 AM »
Hi  Windy.

There is a 20 foot diameter on a older  Otherpower  by the Dan's.

 7  pages  construction . Images seem to be lost, Reliable mill  work for years.

  http://www.otherpower.com/20page1.html

               

           

SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #2 on: January 20, 2018, 09:01:05 PM »
Hi windy!
It's been a while since we heard from you.  Glad to see you back.

Are these the same blades?  https://www.fieldlines.com/index.php/topic,147424.msg1019120.html#msg1019120

I looked at your spreadsheet.
Something I think we should discuss first is the load you intend to use, connected as resistance heating only.  I don't think that spreadsheet works for resistance loads.  In fact, resistance heating is so different from battery charging that I think we should discuss your resistance load in detail because it will have a lot of control over what the turbine does.

I remember Oztules hooking up a big turbine to resistance loads so let me look for that while you come back and tell more.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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windy

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #3 on: January 20, 2018, 11:44:26 PM »
SparWeb,
Thanks for the reply. Yes, those are the pictures of the blades that I posted 5 years ago. Wow, how time flies.

I planned on using three 3000 or 4500 watt 240 volt water heater elements, wired to three phase star configuration, to heat water in a hot water heater and when that gets hot enough, circulate the water through a heat exchanger in my ductwork to help with space heating. I could also dump excess heat into my heat pump ground  loop system in the fall of the year.

I looked at one of the online blade calculators and a 20 foot diameter blade is rated at 10kw @274 RPM. The Axial Generator Calculator show it to be 6.4KW @274 RPM. I am looking to wind the generator for around 9-10 KW@275 RPM.

There will be no offset on the generator. It will face directly into the wind using a tail. Speed will be controlled through the PWM terminals on an Ardunio Uno. The higher the voltage, the longer the PWM pulses are sent to the Solid State Relays which will increase the load to hold down the speed. I am still trying to figure out how to program it, but I think I can get it to work.  May have to ask OperaHouse for some help.  To protect the generator in high wind conditions, I plan on automatically pitching the blades out of the wind using a switch and timer, wait an hour or two and try again. At 250-275 RPM's, a linear actuator will pitch the blades so it stops rotating. That will be the only time the pitch mechanism is activated. I don't plan on using the pitch mechanism to control speed.

Does the generator resistance have to be wound to match the resistance of the load?

I am sure I will have more questions before I am done, but it will be an interesting project.

windy
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Royalwdg

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #4 on: January 21, 2018, 10:52:56 AM »
I have found that properly carved GOE222 blades have extreme torque capabilities. They will walk right through high electrical loads. If you are counting on slowing with adding loads you will probably be frying some stators. Blade pitching forward is a great idea for control.

SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #5 on: January 21, 2018, 12:53:21 PM »
Hi again windy,

Here's the Oztules story I remembered:  https://www.fieldlines.com/index.php/topic,129800.msg842966.html#msg842966

That was an ad-hoc test with 4 ohms in DC (after the 3-phase rectifier) hooked up to a 13-foot turbine.  He estimated 5kW based on 145v and 35 Amps.
He also says they were turning 450RPM which puts the TSR at about 7 if his wind speed guess 30 mph is right.
This sounds like an interesting point of comparison for your project.  Another important detail is that Oztules' 13-ft stator had about 3.9 ohms per phase in Star (not ".39" which I think it a typo) and he hooked it up to a 4 ohm load - the fact that they match was on purpose.

Let's scale up to your 20-ft blades:
20^2 / 13^2 = 2.37 more swept area, meaning you can expect 2.4x more power under the same conditions...  12 kW.
I hope you're prepared for that much power.  In fact I think you should design your load closer to 15kW or more, so that it can withstand some "overshooting" as you tune the furling system.

When getting away from batteries altogether, the electrical system gets simpler.  All the AC-DC conversions go away.  The calculation you did, however is based on batteries and it won't be of much use.  Instead, you want to focus on combinations of wire windings that deliver the power, voltage, and resistance range you need.  These will trade-off with each other until you get to the combination that suits you.  The load you attach to the 3-phase leads should match, or have less resistance than, the alternator's resistance.  I expect the Star-phase resistance you should be aiming for is between 10 to 15 ohms.  Depending on the corresponding voltage range you end up with.  The line voltage will change A LOT with speed of the turbine, so abandon ALL notions of constant voltage that infects the minds of us battery-bound wind millers.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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kitestrings

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #6 on: January 24, 2018, 01:00:01 PM »
Quote
Another important detail is that Oztules' 13-ft stator had about 3.9 ohms per phase in Star (not ".39" which I think it a typo) and he hooked it up to a 4 ohm load - the fact that they match was on purpose.

I'm having, have had, trouble getting to these numbers to work - I'm missing something key.  The numbers for Oz's as you've corrected look about right.  I'll take one I know the properties for:

Ours is a 15' turbine.  In a strong wind we'll see typical peaks in the 4-5 kW range.  On a recent reading we saw 119VDC peak and 3,865w.  So, if my math is correct, This should have been at an RMS Vph of 49 VAC; 84 Vline.  If we have a balanced 3-phase load and 1.9 ohms we'd see 3,800w at about 26 amps; this seems about right (84 * 1.732 * 26 =).  And, we dump into a 3.4 ohm load bank.

If I calculate the stator resistance, however, I come no where near this value.  We have 2 in-hand, 14# CU coils.  They each weigh 585 g (1.28 lbs), and there are 4/phase.  This puts each coil at .065 ohms, or .26 ohms/ph; .52 ohms/line.

I get to similar numbers with Dan's 15'ter.  He had about 21-22 lbs. of copper, 3 in-hand #15, 5 coils/ph.  I'm coming up with only about 1/3 ohm per ph.  Is the the difference purely found in the (transmission) line resistance, or the effect of heat on the windings as the power increases?  What am I missing?

windy

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #7 on: January 24, 2018, 11:37:36 PM »
Kitestrings,

I see you are a bit confused too. I have been trying to figure some winding combinations for my idea and the numbers that SparWeb posted just don't seem to work. There is no way I can get that much wire in a coil to get to 1 ohm per coil and still fit in the stator. I posted a picture of what I believe SparWeb was trying to say. I found this formula on the internet.

My starting point is 10kw at 240 volts. 15 coil 20 pole generator using 240 volt water heater elements for the dump load. Could even go to 18 coils and 24 pole.

Wye connected:
10kw is 3.3kw between each phase to neutral
I through each 3.3kw resistor = 3.3kw/(240/1.732) = 3.3kw/138.57 = 24 amps
R = (138.57^2)/3.3kw = 5 ohms

Not sure what (between each phase to neutral) means. Does that mean to the star point or across the terminals.

Below is my sketch.
5- 1 ohm coils in series for a total of 10 ohms across the phases. What I can't figure out is if I use 12 gauge wire I would need 630 feet of wire to get a 1 ohm coil. 12 gauge wire is listed at 630 feet/ohm.

Any comments?

windy
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SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #8 on: January 25, 2018, 01:16:54 AM »
A couple of subjects to consider:
The per-phase resistance of a wind turbine alternator is set by many factors,
The sizing of a wind turbine alt for battery-charging is driven by different factors than when loaded by resistance heating,
Adding MPPT to the system means the alternator operates in-between-ish the two types of operation,
Battery-charge systems require rectifiers but direct resistance heating can work off pure AC,
I may have made a mistake myself...

(You know it's going to be a long post, when I start with an index   ;) )

I gave the Oztules test as an example, but I fear I didn't provide enough context along with it.  Oz is brilliant and in his way he gives lots of information but when he's not in "teaching" mode he leaves a lot of things out (such as his inverter construction stuff).  I thought I'd filled the gap but not well enough.  Oz was hooking up his resistors after a DC rectifier, not directly to AC.  That throws a complicating factor into the mix. I tried to stay away from it before, but maybe I should have taken it on.  Since you, windy, aren't intending to rectify to DC that effort's probably wasted. 

So let's step back, and compare apples to apples:  Oztules was experimenting with a 13-foot diameter turbine, and pumped 5kW into a resistance load, so I scaled up by swept are and left it at that.  Kitestrings has chucked in more valuable numbers, also suitable, because he can also get 5kW from his 15-foot turbine.  His system is quite different, though, and we can't forget that his MPPT controlled system is set up to approximate the ideal wind power curve for his turbine - not to replicate ideal resistance load matching.  The power curve is similar, but it's not an apples-to-apples comparison any more.  But you are in the same ballpark.

When sizing up the swept are of blades, the exact electrical system doesn't matter yet, because you can work out what kind of power is coming in regardless of what purpose it's put to.  All you need is the wind power equation: 
P = 1/2 * rho * V^3 * Area * Cp.
rho at sea level is 1.225 kg/m^3
Area of a 20-ft blades is 29 m^2
Cp varies a lot, but safe to assume 0.35

For that size then, we can work out the power curve for various wind speeds:
10 kph - 0.1 W
20 kph - 1.1 kW
30 kph - 3.6 kW
40 kph - 8.6 kW
50 kph - 16.8 kW

That is mechanical power at the shaft of the rotor blades, available to drive the alternator if it will take it.
The alternator presents a load which is the combination of useful work and losses.
Power is lost to mechanical friction (ignore that for now) and to heating of the alternator coils (I^2*R).  The rest is useful power (I*V).

Next thing: The ideal power transfer from a source whose losses are mostly resistive, to a load which is also resistive, occurs when their resistances are equal.
That's why Oztules picked a coil with a 4 ohm resistance: it was a match to his alternator's resistance which was also 4 ohms.
(Again, ignore for now that Oztules had rectified to DC.  It does matter, but I think he didn't need to care because it was, after all, just a funny gag he was doing)

This is convenient because it makes it simple to figure out the resistance of the load - it just has to equal the resistance of the alternator.  If the alt is in Star, and the load is in star, then yes indeed, your diagram is spot-on, Windy.  What you've drawn is realistic, and a good starting point.  The terminology you need is that your alt is in "Star" or "Wye", and each "leg" has a resistance of 5 ohms.  If you measure across any of the "lines" you would get 10 ohms because you'd always get two legs in series.

Here's a diagram of several 3-phase hook-up schemes.  Star is the top left, and the NEUTRAL point is also called the "Star" point, at the middle where the 3 phases come together.


Yes it can be confusing if you don't stick to the terminology religiously.  Use a motor for an example: Usually the connection scheme inside a motor is is fixed, and you often don't have access to the insides of motors: it was built in Star, and it's always going to be in Star, so in that case you wouldn't take measurements from the neutral point.  You couldn't.  You can easily measure line-to-line, which is where the phases come out of the alt.  If you were troubleshooting a motor, you would measure voltage across the lines because you have those wires coming right out of it.  To measure anywhere else would mean to crack open the case.  If someone came along with a Delta-wired alternator, they don't even have a neutral point, so it would be pretty inconvenient for them to need measurements from a neutral point that they don't have.  So ignore the neutral point for measurements and calculations.

The phase resistance as you have drawn it is 10 ohms.  That's because 2 phases are in series anywhere you measure the lines. 

OK
This is getting pretty long and I haven't tackled half of it yet.  I will pick it up tomorrow.

I'll leave you with this: I know why you're talking about 240V, but that's not going to seem as important when we get to the end.  That's the tail wagging the dog.  Voltage will rise and fall with speed.  From 0 to whatever maximum you get at furling.  If you want the max to be 240 V then you will wind coils accordingly, but when the WT is in service you won't see that peak very often if you've done things right.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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kitestrings

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #9 on: January 25, 2018, 11:03:17 AM »
I think you meant "swept area" early, more importantly

Quote
The phase resistance as you have drawn it is 10 ohms.

I think you meant "line resistance" here, 5 ohms is the indicated phase resistance; two in series 10 ohms L-L, but otherwise I follow and can see we kept you up late here Spar ;)

I'm sorry if I've complicated it with my system, it just saved me from looking back at other alternators because I know our specs/details.  Our is MPPT and it is battery charging.  I've just always had trouble understanding why the calculated resistance for a given alternator was seemingly so low compared to what would be the matching balanced 3-phase load that it could support.  I suspect that one of the variables, and you may get to this, is whenever we look at AC we have a reactive component to consider, and what we see/measure, or "apparent power" (VA or kVA) is related, but different from the "real power" (watts or kW), and I assume there are losses in both the MPPT conversion (there's certainly heat to dissipate from the FETs) as well as in the rectification with battery charging.

Back to Windy's project - I recall someone posting a few years back on direct, wind to dhw project for a fairly sizable turbine.  Maybe you recall.  When I have a minute I'll search it.  Lastly, I've found this to be helpful among some of the tools and calculators I draw from:

https://www.watlow.com/en/resources-and-support/engineering-tools/3phase-delta-wye-calculator

Best, ~ks

kitestrings

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #10 on: January 25, 2018, 11:08:09 AM »
I think the posts that I was trying to recall were by Dave B.  Windy, you might take a look as he had an 18'-ter that was direct-tied to water heating IIRC.

SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #11 on: January 26, 2018, 12:48:23 AM »
Hi Kitestrings.  My bedtime used to be when the bars closed.  Now... not so much.

Good catch, I did use "phase" where I meant "line" but I hope my added emphasis through the rest of the post was enough to clear it up.

I've been looking for DIY turbines running heaters, too, and not finding many.  I know I've seen plenty over the years, so really it's my fault not using the right search terms or something.

Big picture: don't worry too much about reactance and stuff, it's not a big thing and just adds confusion. 

Windy,

I have to introduce a new piece of terminology - the technical term is "Electromotive Force".  EMF.  A generator that's producing electricity is creating an EMF, which is literally electrons motivated by magnetic force.  It's what produces the voltage.  Is EMF = Voltage?  No, except for one case, but they are both measured in volts.

The only time when EMF = Voltage is when current = 0.  This is known as open-circuit and when you measure the voltage across the lines with no current, you are also measuring the EMF.  Once current starts to flow, though, the voltage you measure drops, even though the EMF is the same.  Voltage drops are caused by resistance, as Ohm's law shows us.  You could call this "back EMF" but I would rather not.  That term is much more useful in motors.  The same thing happens in our alternator but we really don't need special terms for it.

So, time for an experiment.  We couple our alternator to a motor so that we can drive it, and measure the electricity that comes out.  Let's say our motor is big and not bothered by the load the alternator might put on it, and the motor turns at a fixed speed.  No matter what load the alternator applies, this motor won't slow down.  So, we flip it on and leave the alternator's wires unconnected.  The alt is running open-circuit now, so if we put our voltmeter on the leads we get a high voltage and we are also measuring at the same time the EMF.  If we speed up the motor, the EMF goes up.

Next, for the sake of demonstration, we connect a very high-resistance load to the leads of the alternator.  I could pick a number from the air...  1 kOhm.  While picking numbers, let's say the resistance in the alternator is 10 ohms, and the EMF we measured was 300 Volts.  Then the current that will flow in the alternator's wires is
(300V) / (1000 ohm + 10 ohm) = 0.30 Amps. 
The voltage that we measure on the alternator's leads won't be 300V any more.  Instead it will be (10 ohm) * (0.3Amp) = 3 Volts -> 300V-3V=297V.
Nothing dramatic is going to happen because this is a puny load on our alternator:  I^2*R = (0.3A)^2*(1000ohm) = 90 Watts
Meanwhile, inside the alternator, only 0.9 Watts of heat will be shed off.  The power input to drive the alternator is just 91W.
As an aside, since we are experimenting with a motor with a fixed speed, our drive motor didn't speed up because we made it drive a tiny load.
Wind does not behave this way.  It behaves the opposite.



One more run of our theoretical alternator.  This time, same alternator with its 300V of EMF, and 10 ohm stator.  Now we hook up a 10 ohm resistance to its leads and see what happens.  Same calculations:
(300V) / (10 ohm + 10 ohm) = 15 Amps. 
Voltage measured across the leads:  (10 ohm) * (15Amp) = 150 Volts -> 300V-150V=150V.
Note how the voltage across the leads is dropped exactly in half!
Now the power is much higher:  I^2*R = (15A)^2*(10 ohm) = 2250 Watts
Since the resistance in the alternator is the same as the load resistance, then the heat shed by the alternator is ALSO 2250 Watts.
The sum of the two is the power input required: 2250+2250 = 4500 Watts.  Lots of power (not enough for a 20-foot diameter turbine though.  But you can scale up the numbers until they work for a 20' turbine.

I'll leave it to you to try the same calculations for different resistances - it always comes out with the highest power when the resistance of the load matches the generator's resistance.  Notice that I haven't mentioned the connection in Star yet.  That's because it hasn't mattered yet.  If you connected a 3-phase alternator to a 3-phase load both in Star and did all the same measurements you'd get the same thing.

Another thing worth noting is that the voltage measured line-to-line was a step in our calculation, but not really the driving force in the machine.  It's also dependent on the resistance load you hook up to it.  It still matters if you're connecting standard water-heater elements as your load, since their ratings are for standard 240VAC, but most of the time the wind isn't blowing like mad, so your heating elements will only be exposed to dozens of volts to 100 V or so.


How does this help us design a wind turbine alternator?  Because EMF is driven by the speed of the alternator.  When doing open circuit tests like in our experiment above, we were measuring EMF at a specific speed.  Let's say it was 100 RPM.  Then we had 3V/RPM of EMF.  If we have this much EMF on the leads of our alternator, then we can work out some facts about the coils inside it.  This is still just an example.  Play with the numbers until you find the size that's right.
Since you drew 5 coils per phase, then our line-to-line EMF is composed of 5 coils on one leg plus 5 coils on the other leg, out of phase, on those lines.
So our EMF can be broken down per coil:
3 V/RPM = 5*(E_coil) + 5 * cos(60deg)(E_coil) = 0.4 V/RPM/coil

And since we already worked out that our alt has 10 ohms per phase line-to-line, then each coil is 1.0 ohm.

This is enough information to roughly size the coils, choose the wire gauge (to handle the current), and the number of turns (to get the EMF).  A few spin tests to confirm the calculations are right.
Since you've got 20' blades, there's no way this guesstimate is powerful enough to hold them.  In my post yesterday, I showed that he wind power in the blades will be more than 16kW in a stiff wind, and having some margin of safety means the alt should actually take in about 20kW or more before getting too hot.  Ultimately, heat often kills these things, and while strong winds are an excellent way of dissipating heat, there are a hundred details that can either improve or worsen this.

Well it's late again.
There's more to say about matching wind loads to electrical resistance loads, starting with "they don't, not easily".
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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DanB

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #12 on: January 26, 2018, 09:57:29 AM »
Hi  Windy.

There is a 20 foot diameter on a older  Otherpower  by the Dan's.

 7  pages  construction . Images seem to be lost, Reliable mill  work for years.

  http://www.otherpower.com/20page1.html

LOL ~ the 'new' Otherpower page is rather over my head and I don't go there much...
For stuff like this I often use internet archive (the wayback machine).  All the old stuff is there.


               

           
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #13 on: January 26, 2018, 06:08:21 PM »
The only thing about this link to the page, none of the images are working

windy

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #14 on: January 27, 2018, 02:44:35 PM »
SparWeb,

Thanks for the information. I didn't realize there were that many different 3 phase wiring diagrams. Next question. Which diagram would be the best to use. I can build the generator with 6 connection on the stator if that would give me more options.

Another question I have is, is there a formula to figure out how magnet material is needed for the rotor. I planned on using 40 N42 neo magnets (1.5" x 3" x 3/4" thick).

windy
I don't claim to be an electrical engineer. I just know enough to keep from getting electrocuted.

SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #15 on: January 27, 2018, 04:15:52 PM »
Star is probably best, but it's up to you.  Here's a website that taught me a lot about it:

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/three-phase-power-systems/

There's a lot to read there.  A lot of the stuff I have been talking about comes from there, so you might as well read it from the source!

You can estimate magnet size and wire choices with the spreadsheet you posted before.  You just have to cut out the stuff that's geared to battery-charging. 
Taking a second look, the first sections are great...  Section 4 chooses the battery voltage you don't need... keep it for now because it's tied into the calculation above that finds "RPM/volt" and voila - that's the EMF I was talking about before.

I can't figure it out from there.  The rest of the spreadsheet relies on the look-up tables on sheets 2 and 3, and they look a lot like calculations extrapolated from somebody's own machine...  I wouldn't use any of that stuff since figuring it out will be harder than just working it out on your own.  You should chop out the 2nd and 3rd sheets, erase Section 8, and keep all of the calculations above it.  The rotor power in section 8 is out to lunch, so you won't miss it.

One thing I noticed in the spreadsheet that you posted is that the coil thicknesses are calculated to be 1.5 inch thick.  The air gap between magnets would have to be about 1.75 inches because you can't expect a 1/32" clearance between rotor and stator to work on such a large alternator.  But the coils are too thick anyway - the flux per pole is getting low with the magnets so far apart.  As a rule of thumb, keep the air gap roughly equivalent to the magnet thickness.  For a 1" gap, need 1" magnets.  Not a hard rule, but if you play with the numbers in the spreadsheet you'll see the flux drop well below 1 Tesla as you move them apart.  I tweaked them and got better coil sizes that match better the magnet size and has a higher flux through the gap.  These numbers look pretty realistic.

The spreadsheet also does a good job of re-calculating the amount of wire as the flux gets stronger, so I'd keep that, too.  That's pretty handy.  It also does a second calculation for Delta at the same voltage.  Like I said, in your machine the voltage won't be constant but it's still worth seeing how much thicker the coils will be if you want to connect it that way.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #16 on: January 27, 2018, 04:34:18 PM »
Something else I wanted to talk about:

Matching the power the rotor blades need to keep the speed under control to the speed the alternator runs at for the same power...  that's the design trick.  When doing resistance heating, the matching of the power is tricky.

The hard thing is to abandon is the concept of "my turbine always turns at # TSR because I designed it to".  It won't run at a constant TSR. 
No fixed-pitch wind turbine runs at a constant TSR, although the MPPT-controlled ones come close.  Instead, think of TSR as the ideal point, and you want to design the WT to run at the ideal TSR at your site's average wind speed, and let it run at different TSR at other wind speeds, within reason.

I've attached a graph to demonstrate with.  It's based on a bunch of back-of-the-envelope calculations which I tweaked until I had the lines in roughly the right spot.  FYI it's based on a 20' WT rotor and a stator whose Star resistance is 2 Ohms and has an EMF of 70 volts/RPM.  I haven't checked if that's realistic or not but it "feels right".



On the graph, the red line is the wind power curve with CP=30%.  The dashed lines are the alternator power curve assuming different TSR.  If the ideal TSR is 7, then the WT power curve crosses the alternator power curve at XX kph wind speed.  At lower wind speed, the TSR is much lower, and vice-versa at high wind speed.  As long as the furling system stops it from seeing full wind power at high wind speeds, then it will stay under control.

This is not radically different from a battery-charge power curve.  In fact it's not that different at all, except that below cut-in, the WT can spin at high TSR but there's no power in the wind so the speeds are still pretty low. 
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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windy

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #17 on: February 01, 2018, 11:17:00 PM »
SparWeb,

In your last post, you stated "FYI it's based on a 20' WT rotor and a stator whose Star resistance is 2 Ohms and has an EMF of 70 volts/RPM." That seems a little high. Did you mean .70 volts/RPM?

Still reading and calculating.

windy
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SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #18 on: February 02, 2018, 12:08:14 AM »
Quote
...That seems a little high. Did you mean .70 volts/RPM?

Yup!  You are right.  The lesson: check all calculations - even the know-it-all guy makes mistakes, too.

Huh... did you notice that's the same typo Oztules made?  At least I'm in good company...
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joestue

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #19 on: February 02, 2018, 02:14:43 AM »
with a resistive load there is no chance of burning up the generator using scrs to modulate the power output if the generator is sized correctly.. for 100% direct connection at full load from generator to load resistor.

Quote
how magnet material is needed for the rotor. I planned on using 40 N42 neo magnets (1.5" x 3" x 3/4" thick)

that would depend entirely on what wind speed you intend to run it at continuously and whether or not you intend to rely on manual breaking.

the problem with matching the generator resistance to the load resistance, is that with a single load resistor, using scrs to modulate the power, the efficiency of your generator remains at 50% all the time. the cheapest way around this is multiple load resistors. so if at full load the generator resistance equals the load resistor, then at half the windspeed which is 1/8'th the power, the load resistor would need to be 3 times the resistance of the generator, which means the efficiency of the system has increased from 50% to about 75%.
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #20 on: February 06, 2018, 11:08:49 PM »
Still trying to figure out the coils in the stator. Haven't  had much success with that. Starting to see why it's difficult to match alternator to resistive loads. May have more questions later on.

I have another design question. What would be the suggested length of the tail and surface area of the tail. I seem to remember years ago that the tail length should equal the blade length in feet and the tail area should be equal to the diameter of the blades, in feet. Those dimensions were for windmills that were offset and had a furling mechanism. I presume that the tail length was from the blade to the end of the tail.

My design won't have any offset or furling so I am not sure if that design would work for me. If anyone has any suggestions or comments, it would be greatly appreciated.

windy
   
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SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #21 on: February 07, 2018, 10:22:06 PM »
With tails that fold to furl the turbine, the balance has to be struck at the right wind speed - not to fast, not too slow, Goldilocks.

You've probably got a lot more latitude to make the tail the way you want it.  Do you think there will be much turbulence?

I've noticed that my turbine follows the wind pretty closely, but it also suffers from turbulence because the trees have grown (too much) since I built it.  When a gust drives it to yaw left or right, I can tell that it slows down.  This could be due to the oncoming wind changing direction - not flowing in parallel to the axis - but when I consider the math I'm not convinced:
Cosine(0 degrees) = 1.0
Cosine(10 degrees) = 98%
Cosine(20 degrees) = 94%

So I'm not losing much when the wind shifts the incoming angle around.  So I think what's really going on is that the angle of attack of the blades is being changed on each side - getting lower on one side and higher on the other side.  Lower angle of attack on one side isn't bad, but higher angle of attack on the other side probably creates a lot more drag and slows the RPMs.  Just a vague theory.  Basically what I'm saying is that I don't think this particular performance issue is due to the tail.  I thing the tail on mine does its job fine.

I don't see any harm in keeping the formula - though I think it's pretty conservative.  The Dans don't use 20 square feet of tail on their 20's.

My turbine diameter: 8 feet, tail area: 6 square feet, tail arm: 6 feet.  It furls at the wind speed I want it to furl.
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #22 on: February 24, 2018, 11:22:09 PM »
Still trying to figure out the coils in the stator.

Here is my stator design.
24 Magnets 1.5" x 3" x.75" thick
18 coils
Width of coil leg-- .75"
Thickness of coil leg-- .70"( air gap)
54 turns #12 gauge wire
58 feet/coil
12 coils=696 feet
#12 wire=629 feet/ohm
345 volts EMF @ 275 RPM's
1.25 volts EMF/RPM
Star connected
Calculated line to line generator resistance--1.13 ohms

It was mentioned in an earlier post that the generator resistance should be in the 10 to 15 ohm range. I have tried different wiring and wire gauge combinations, but there is no way I can get that much resistance in the generator coils. Should resistance be 1 to 1.5 ohms? I even tried 1" coil legs to try to increase resistance, but that didn't help much.
Am I missing something?

Comments?
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SparWeb

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #23 on: February 25, 2018, 09:47:53 PM »
When Oztules used 4 ohms for his 13-foot test, I think I moved my estimate the wrong way for your 20-foot turbine and started working with 10 ohms.  I can tell that's wrong now (credit Kitestrings for pointing it out).  You want less resistance per phase than 4 ohms, so I think you are going in the right direction.  Maybe too far.  See if you can get closer to 2 or 3 ohms.

My coil geometry calculations match yours. I estimate the coil to be a bit thicker than 0.5", so an air gap of 0.70" is good for clearance between each magnet face and the stator.  I also get 1.1 ohms per phase.  That seems too low.  You also have a lot more EMF than I expected.  It would make your alternator too powerful, and the blades would run slow and stalled most of the time (TSR ~ 2).  Safe enough, but far from ideal performance. 

Are you using a spreadsheet like the one from Olsen you started with?  I found some mistakes in it before... maybe there are others I didn't find.  This is why many folks make test coils as they go - the calculations don't mean much since it's metal that goes up on the tower, not numbers.  I tried extrapolating from the resistance and EMF you have, but something's not right.  One or the other needs to change to make a sensible machine that fits a 20' rotor.
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #24 on: March 06, 2018, 10:57:53 PM »
SparWeb,

Thanks for the reply. 2 ohms seems easier to work with. I have to admit that I was using the formula that I posted previously. Was using it more to find the coil shape. I did some more recalculating and came up with this design. I am also attaching a  picture of the coil design.
 
24 Magnets 1.5" x 3" x.75" thick
18 coils
Width of coil leg-- 1.37"
Thickness of coil leg-- .55"( air gap)
115 turns #12 gauge wire
103 feet/coil
12 coils=1242 feet
#12 wire=629 feet/ohm
.91 volts EMF/RPM
Star connected
Calculated line to line generator resistance--1.97 ohms

I would like to build a test coil, but would like to have an idea of what the coil should look like before building.

windy

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windy

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #25 on: March 09, 2018, 08:18:57 PM »
Royalwdg,

Can you recall the specifications of the stator that you used with your 18' diameter GOE 222 blades that you mentioned in a previous post.
https://www.fieldlines.com/index.php/topic,149385.0.html

I'm trying to design a stator for resistance heating using a 3 blade-20' diameter GOE 222 blade. Hoping for 10000 watt output at 274 RPM. Just curious if my design is close to yours.
 
Thanks,
windy
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #26 on: March 09, 2018, 10:15:10 PM »
Hi Windy,
There's no way for me to check calculations while I'm away from home on a trip, but I'm happy to see you are still making progress with it.  I agree there is a lot of value in making an estimate before winding a test coil - if it turns out you can't re-use the wire, then at least it is worth it for the information you get.
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #27 on: March 14, 2018, 08:27:08 PM »
I'm using a pair of 16 ga. wires 52 turns. 28  3/4 x 1 x 2 magnets on each 20 inch dia x 1/2 inch magnet rotors.  21 coils mounted in epoxy disk with a 1/8 inch gap on each side.  Cut in is about 80 rpm for 48 volt battery bank. That is about a 60 mph tip speed. That is where this profile really starts to hit it's power band. The flyweight gov pitches blades forward at about 275 rpm.  This arrangement is working well for battery charging and dump loading to 3000 watts per phase resistive room heaters.

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #28 on: March 19, 2018, 09:21:54 PM »
Royalwdg,

Thanks for the info. Every bit helps. One more question. Are your resistive heaters 120 or 240 volt?  I presume they are 240 volt.

windy
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Re: New build- 20 foot diameter variable pitch windmill
« Reply #29 on: March 21, 2018, 07:40:07 PM »
120 volt. 2 in parallel per phase

kitestrings

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #30 on: March 23, 2018, 08:59:33 AM »
Hi Windy, Dave,

Sorry I haven't had much time here, but a few comments, questions:

First, if you are doing variable-pitch I would recommend that the default position - on loss of power, control signal, etc. - be that the thing fully furls, or that you have a secondary fail-safe.  Midwoud & mbouwer have been doing a lot with the variable pitch approach.

275 rpm seems really, really fast to me for a 20' rotor.  I know Dan normally designs intentionally for a lower TSR; leaning toward an alternator that is over-sized a bit relative to the prop in the typical range of winds (8-20 mph).  Not that it shouldn't be able to hold together, but I would think that the predominant winds would be such that you don't play in that range much, and that the turbine might be a bit noisy if it isn't feathering before that point.

I would think you would want some sort of PWM or controller strategy like Joe was describing to allow for a quasi- load match through a wider range of speeds.  IIRC your design input is for something like 28 mph, which is quite high.

Is a single strand #12 CU enough to handle the peak output, plus some safety margin?  I know you are at a higher target voltage, so I don't have as good a feel for this, but most of the designs I've seen have two or three strands of ~#14-15, something like that.

Good luck & stay safe, ~ks

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #31 on: March 23, 2018, 06:31:58 PM »
2 strands of #14 is ~ the same as #11...

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Re: New build- 20 foot diameter variable pitch windmill
« Reply #32 on: March 23, 2018, 11:01:13 PM »
kitestrings,

I plan on using an Arduino Uno and PWM to control the speed up to a preset rpm. I designed a centrifugal switch that engages the linear actuator to pitch the blades forward if it over speeds. The blades will hold in this position for a set amount of time and then try again.  That's my secondary failsafe.

The stator is still in the planning stage. I was thinking that using a single #12 wire would make for a tighter wound coil instead of 2 in hand #15 which would make it easier to wind. I need to wind a test coil before going any farther.

My idea of having a higher target voltage was so I could use a lighter gauge wire to increase the resistance in the stator and still hit my target of 10 KW. All just ideas at this point.

windy
I don't claim to be an electrical engineer. I just know enough to keep from getting electrocuted.