Author Topic: F&P stators operate best with a constant current output  (Read 1803 times)

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DaveP68

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F&P stators operate best with a constant current output
« on: November 02, 2017, 04:02:56 AM »
For those who are curious about getting the maximum output power potential from an F&P stator (or any PMA) over a given RPM range.

Refer to the table below showing F&P stators supplying a constant current output with the voltage proportional to operating RPM.


The ohms readings that are shown in the table are only their for illustration of "the best load match possible". This relates to 'Load Adaptive Impedance Matching' which is the core operation of how MPPT (maximum power point tracker) works in inverters etc.

Please refer to the graph below that illiterates the power output of an F&P Stator increases in proportion to RPM.
10884-1

What this means in "practical terms" is all F&P stators (any PMA) want to put out a constant amount of current with a variable voltage proportional to RPM in order to maximize their output potential.

The strength of the magnetic field (magnets in the rotor cap) determines the optimum operating current. Changes of wire size 0.6 mm vs 0.8 mm vs 1 mm also has an effect on this optimum current value as well. The voltage range is proportional to RPM which again changes with wire size 0.6 mm vs 0.8 mm vs 1 mm, but this manly is due to the number turns per pole.

If we have no load (open circuit) the stator voltage increases in proportion to the RPM.

When the stator is run into a short circuit then we can reach the maximum output current with only a few RPM.

Refer to the table below on how wire diameter has an effect on the volts and current but the power outputs remain close to one another (100s 5% lower). Wire diameter 60s is 0.6 mm, 80s is 0.8 mm and 100s is 1 mm.


For the same RPM any 42 pole stators output power is 40% less for the same RPM as a 36 pole copper with black rotor cap shown above.

Here are photos of a modified Fisher & Paykel motor control module set up in a constant current mode used to test the stators.




This was how I was able to achieve such accurate results without having to play with different resistor values.

The big problem with connecting F&P stators to a battery to charge it, is once the terminal voltage of the battery is reached only the current can increase and the brick wall is hit so to speak!

A MPPT type inverter that allows the voltage to increase in proportion to the operating RPM range will work much better to charge batteries or Grid Tie applications.

Hope this is of interest to others, as this same concept should apply to any 'Permanent Magnet Alternator'.
« Last Edit: November 02, 2017, 04:06:59 AM by DaveP68 »
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XeonPony

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Re: F&P stators operate best with a constant current output
« Reply #1 on: November 02, 2017, 05:50:46 AM »
not sure if this falls under the wind category but guess a mod will let you know.
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Bruce S

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Re: F&P stators operate best with a constant current output
« Reply #2 on: November 02, 2017, 11:41:42 AM »
"Technically" it is not, BUT since this follows the discussion of one going up as a wind-gen.  :)
I don't see why it needs to be moved.
IF someone really complains we can move it then.

DaveP68, IF you need / want this moved to a different section any of the Admins or us lowly mods can make that happen.

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Bruce S

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OperaHouse

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Re: F&P stators operate best with a constant current output
« Reply #3 on: November 02, 2017, 12:48:55 PM »
I interpret that as this is open to the peanut gallery.  For many F&P are far and few between.  These LG motors are everywhere.  They tend to crap out between 8-10 years when for most it is not practical to fix.  They strip the plastic hub and the rotor assembly costs about $90.  Fine if a do it yourself which means you only need to know what end of the wrench to hold.  I got this washer free on craigslist.  Even with a stripped hub it would be easy to configure or pin. Believe the tub connects to the motor with a three leg spider ideal for a mill.

DaveP68

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Re: F&P stators operate best with a constant current output
« Reply #4 on: November 02, 2017, 01:50:59 PM »
This topic belongs here, as it relates to gaining the best power output from a PMA (F&P in this case) to be used on a wind turbine. Hence why it states down the bottom of the post MPPT. This information could be of use on Hydro, but as they tend to operate at a fixed RPM the constant current mode is less relevant.

This topic is also related to the discussion I started about "power factor correction capacitors" as the modified module described here was used to prove the power output potential with different setups.

The main point I'm trying to put across is PMA's are used on Wind Turbines and no matter what type is chosen to be used the information published here may be of use to gaining more power output, including LG stators.

Thanks Bruce for your endorsement.

David
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Bruce S

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Re: F&P stators operate best with a constant current output
« Reply #5 on: November 02, 2017, 02:17:01 PM »

Thanks Bruce for your endorsement.

David
David;
Not an endorsement, merely a 2 cup of coffee decision.
 Knee jerk reaction would've had me move it to Controls, as this is indeed using controls. However, I was taught by some of the original Admins here (TomW, Wooferhound, Gary, Ross) and a slew of others; to look at the big picture, let some things have a semblance of continuity.   

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Bruce S
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DaveP68

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Re: F&P stators operate best with a constant current output
« Reply #6 on: November 02, 2017, 10:35:10 PM »
I interpret that as this is open to the peanut gallery.  For many F&P are far and few between.  These LG motors are everywhere.  They tend to crap out between 8-10 years when for most it is not practical to fix.  They strip the plastic hub and the rotor assembly costs about $90.  Fine if a do it yourself which means you only need to know what end of the wrench to hold.  I got this washer free on craigslist.  Even with a stripped hub it would be easy to configure or pin. Believe the tub connects to the motor with a three leg spider ideal for a mill.

I would like to get an LG stator and run it through the same test rig that I use for the F&P's to create the same data tables and publish them on here. I know that the LG product is far more common across the globe so more likely easier to get hold of than the F&P's I've got.

Thanks for reminding me to look out for one that has been scrapped.

David
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kitestrings

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Re: F&P stators operate best with a constant current output
« Reply #7 on: November 03, 2017, 06:54:33 AM »
Our Siemens (Bosch) washing machine is probably the closest I’ve gotten to one of these things, so bear with my questions here.  I’ve followed Dave’s related discussion here and on TBS forum.  It looks as though you’ve gotten the theoretical potential for a given pole count, size, configuration thoroughly vetted.  Not with-standing the limits of the drill, lathe/drive that is used though, I’m having trouble picturing a turbine that can come anywhere near the  bandwidth of rpm needed achieve the potential limits of the alternator.

If I somewhat randomly select a starting point….let’s say a 12’ (direct-drive) prop with a TSR of 6.  So, starting in a ~7 mph wind we’re spinning maybe 100 rpm and, by Klemen’s “good turbine” (30-35% of Betz IIRC) estimates we might see 68 watts; somewhere near the low-end range of your table.   These are obviously at best estimates, but used to illustrate my (forth coming) mental block.  So now if we’re to get the available capabilities out of 36-pole, 60s we need to run upwards of 5x this cut-in speed.  Our 12’ prop is cable of some 10w/ft^2 at a mere 18 mph…but at 18 mph we’re already operating at a TSR of nearly 12, and most of us with rather not be around it.

If I go back to my washing machine, I envision a ‘calm’, quiet turbine running at the speed of the wash cycle, and the theoretical potential of the alternator comparable to the high-speed spin cycle.  With gearing and/or MPPT we might more practically get nearer the sweet spot.  I’m not questioning your methods.  I’m just trying to understand whether, even with this knowledge, we can get even close to a practical load match that will at best let us pick more than narrow band-width of the overall potential.

~ks

DaveP68

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Re: F&P stators operate best with a constant current output
« Reply #8 on: November 03, 2017, 09:18:40 PM »
Hi ks

Thanks for your input and interesting question relating to adding stator to a 3.66 m (12') set of blades with what you say a TSR of 6.

Running the numbers through myself it would only require 2x 36-pole, 60s stators with capacitors added to get an output power 1.5 kW at around the 300 RPM range.

Refer to the graph below for the actual power output from a single 36-pole, 60s stator with normal output and with capacitors added.
10890-0

The capacitors are a bit small on stator in the above test to get 750 W at 300 RPM but it wasn't too far of it.

When the capacitor values are selected correctly a peak output gain of 2.5 times the maximum expect RPM can be reached. Example 300 RPM we can expect to extract up to 750 W from a single stator. I have reached a gain of up to 2.75 times at around 600 RPM but that's spinning a bit too fast for most wind turbines.

With say a 7' (2.15 m) prop with a TSR of 7 we could easily run a with a single stator with a peak output of say 1.5 kW at over 600 RPM. As we go above a 10' prop just add more stators to the shaft as we know the prop has the power to drive them.

I get these stators in big numbers for free so I'm not worried about trying to limit a set up to just 1 unit.

These F&P stator(s) do require MPPT on the output to get the best results.

I set up the stators on Fred's (flc1) 3 m (10') prop wind turbine. It can output about 2 kW around 400 RPM in 22-24 mph of wind.
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OperaHouse

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Re: F&P stators operate best with a constant current output
« Reply #9 on: November 03, 2017, 09:58:22 PM »
Still scratching my head. LG states the maximum power in washing is 280W.  That over designed and sustainable?

DaveP68

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Re: F&P stators operate best with a constant current output
« Reply #10 on: November 04, 2017, 05:10:17 AM »
Hi OperaHouse

Are referring to the power consumption of the washing machine at 280 W?

The Fisher & Paykel washing machines have around the same power consumption rating.

I have run a stator up to 2 kW at 1770 RPM on a VFD with no over heating, didn't even get that warm. The circulating currents in the windings are only about 1.15 Amps AC so total heat dissipated across 36 poles is about 65 W so not much considering it's size. The F&P rotor caps have fins to circulate air to cool the windings.

Check out this YouTube video below of 4x F&P stators each producing 2 kW continuous output power which is sustainable.
https://www.youtube.com/watch?v=jb67RtSmav0
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electrondady1

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Re: F&P stators operate best with a constant current output
« Reply #11 on: November 04, 2017, 06:48:37 AM »
slick

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Re: F&P stators operate best with a constant current output
« Reply #12 on: November 04, 2017, 04:06:57 PM »
Proper job...
Robin Down Under (Or Are You Up Over)

kitestrings

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Re: F&P stators operate best with a constant current output
« Reply #13 on: November 04, 2017, 06:41:48 PM »
Cool vid., and one I think I'd seen before - maybe something you/someone posted to TBS - and I hadn't realized then that these were F& P alternators.

Dave here's my disconnect.  You say,
Quote
With say a 7' (2.15 m) prop with a TSR of 7 we could easily run a with a single stator with a peak output of say 1.5 kW at over 600 RPM.

The Betz limit of a 7' turbine at 22-24 mph is 1,200- 1,500w, but we know based on typical efficiency levels that we're unlikely get more than 700-900w at this wind speed, and then we have line losses to where ever we're going.  Again, not questioning the power potential from the stator, just whether we can load-match a prop to get it, and do this over a broad enough range.

Not trying to rain on you.  It's all quite interesting, and I've enjoyed seeing what you've done with flc's.  ~ks

MattM

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Re: F&P stators operate best with a constant current output
« Reply #14 on: November 04, 2017, 07:10:33 PM »
So are capacitors picking up the ebb and flow of electrons that normally would be turned to heat as they circulate in the flux fields, or what is the theory here?

joestue

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Re: F&P stators operate best with a constant current output
« Reply #15 on: November 04, 2017, 08:04:47 PM »
So are capacitors picking up the ebb and flow of electrons that normally would be turned to heat as they circulate in the flux fields, or what is the theory here?

The reactive current increases the flux density in the air gap which means more volts per hertz. This increased voltage pushes more current into the battery/load.

SparWeb

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Re: F&P stators operate best with a constant current output
« Reply #16 on: November 04, 2017, 09:16:45 PM »
Hi Kitestrings,
In answer to your previous question, about prop matching, the details are important as you can see.  One thing that helps the mental block is to convert the tip-speed ratio into angle of attack of the blade tip.  Then it gets easier to see what's really happening to the blades (from stall to runaway) which I find easier to picture in my mind.

Take an airfoil profile whose angle of attack at stall is 15 degrees.  Let's use it on a wind turbine whose TSR is 7:
TSR comes from the ratio of blade turning velocity to incoming wind velocity, Vr/Vw=X
Draw that as a triangle, and each is one side of the triangle, and the relative wind is the hypotenuse.
In other words...
if X=3 then for wind=10mph a 6' blade will turn 70 RPM
if X=7 then for wind=10mph a 6' blade will turn 160 RPM
if X=14 then for wind=10mph a 6' blade will turn 320 RPM

While doing trigonometry, we have the ratio we need to find the angle of the incoming wind:
atan(1/X) = atan(1/7) = 8.1 degrees
Okay, the blade is designed to work at TSR=7 or 8 degrees angle of attack, but if it runs unloaded, the thing spins too fast...
atan(1/X) = atan(1/14) = 4 degrees
And if the generator load is too great, then it's forced to turn slower...
atan(1/X) = atan(1/3) = 18.4 degrees
That angle is greater than the airfoil's stall angle, and the blade will be stalled. 
The stall actually starts near the root and works its way out so this blade is deeply stalled when forced to turn so slowly.

You want to match a generator to the blade in this example?  Then pick a point, say... 200 RPM and Dave's generator can generate 200W without and 250W with capacitors.
The output comes from a mechanical efficiency of the generator of roughly 50% NOT KIDDING DAVE :) so need to have 400-500W mechanical input on the shaft.
If the blades run at a Cp of about 0.30 (you'd be doing well) then the incoming wind power needs to be between 1330-1670W.
With blade radius 6 feet as said before, diameter is 12 feet.  The wind through the swept area needs a velocity of 13-14 mph.
Check the TSR with that wind speed, radius and RPM... X=6.4 which is not bad at all.  We have a match.  With or without capacitors doesn't matter much.

Walk a little further up the power curve....

350 RPM:  350W without capacitors, 700W with them
mech efficiency will be less, 40% so we need 875/1750W shaft power, respectively.
Same blades so same Cp:  2900W/5830W wind power through the disk
wind velocity through that swept area has to be 17mph without / 22 mph with capacitors
That means the TSR that it will run at is actually X=8 without caps  or X=7 with them

Not bad at all.

Hard to extrapolate from the data at hand, but you can see the TSR getting higher as the wind speed gets stronger and the turbine turns faster.  This is where the matching comes in and apparently Dave's got a scheme that improves this match by keeping the TSR down closer to the design speed in higher winds.
« Last Edit: November 04, 2017, 09:24:04 PM by SparWeb »
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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DaveP68

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Re: F&P stators operate best with a constant current output
« Reply #17 on: November 05, 2017, 12:12:18 AM »
Good work both ks and SparWeb and agree with most of what you have outlined. Like the level of detail as I can forget to put in some important bits from time to time not intentional.

But on the he efficiency of the F&P stators "correctly load matched" it's >80 % and at this stage don't personally have an accurate way to validate my numbers, but know of others that have.

With a battery operated cordless drill I took an input power reading from battery to the drill and then measured the maximum output from an F&P stator and I get 62 % peak power transfer. Now what the "unknown factor" within this 62 % power transfer is the efficiency of the drills motor. It won't be anything above 90% and probably more closer to 80 % itself.

Another thing I outlined earlier was an example of a 7' prop on a wind turbine using a single F&P stator being able to peak out at say 1500 W. What I didn't state was how much wind this would require or what the peak RPM would be, did state it would be above 600 RPM. If it got lots of wind above 24 mph this power output could still be a possibility.

I think a Cp of about 0.30 on smaller wind turbines is not a maximum figure. I know for a fact that Fred's (flc1) wind turbine using GOE 222 blades and F&P stators as the PMA's is doing up to 0.45 at times (sweat spot you might say).

Can agree that using Cp of about 0.30 is a very good guide to use and if you do better than that, it's a bonus  :)

Check out the overall performance of this Hitachi 2 MW wind turbine with a peak Cp of 0.489 and that is everything blades the lot!
http://www.hitachi.com/products/power/wind-turbine/performance/index.html

At the end of the day a lot of you have built wind turbines and I haven't, so very much in the shadow of those that have. Talks cheap and action speaks louder than words as they say...

Still plan to get a wind turbine of my own up one day, but in the meantime these F&P stators are very impressive in what they can do and easy to modify into different configurations to suit various set ups etc. As stated get them in big number for free to play with, hence the interest and wanting to shear some data with other like minds :)
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kitestrings

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Re: F&P stators operate best with a constant current output
« Reply #18 on: November 05, 2017, 08:51:59 AM »
Spar,

Thanks for that explanation.  Very helpful.  I understand what TSR is and how it is calculated, but I didn't know the relationship between TSR and the angle of attach - which I've now added to my "tools" spreadsheet.  Thank you.  A related question though...if we have a twisting cord/pitch blade, where along the blade would we expect this relationship to be most accurate?

Regarding the overall post, I look forward to seeing more.  My skepticism stems more from a gut feel, which is that if we cut-in at a given rpm, and we're looking for something over roughly 3x that speed before we furl, tilt, brake, or pitch blades, or power-yaw...we may have something that no one in the yard wants to be around.

I'm secretly starting to want my Siemen's washer or (F& P) dishwasher to fail just so I can play with one of these.  Please don't tell my wife.  ~ks

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Re: F&P stators operate best with a constant current output
« Reply #19 on: November 05, 2017, 11:24:20 AM »
Some meaty subjects today.

One thing called Reynold's Number bites us in the small wind turbine field.  The scale of our turbines means they have a very small Reynolds Number; between 100,000 and 500,000 when turning full speed, and much less when getting started at cut-in.  This drastically hampers real-world performance.  The Megawatt monsters operate at RN in the millions so they can develop CP up to 0.5 no problem.  We're not so lucky.  Not only does Reynolds Number reduce the efficiency of our blades, but they also restrict the Lift/Drag ratio they can develop.  Choosing a GOE 222 airfoil helps, because its family was designed to operate at low RN.  But even so, its L/D at low RN is still reduced.

To gain the advantages of a low-RN airfoil, you need to maintain a fidelity to the airfoil profile of approximately 1% error.  When the chord of the blade is 6 inches, that means that the tolerance on the carving/molding job must maintain +/- 0.06".  The aluminum extruded blades that Dave has (posted on the other thread) are probably better than that, which is great, but note that the trailing edge of the extrusion is NOT a knife edge like the "theoretical perfect" GOE 222 airfoil.

KS,
I could have extrapolated the TSR figures up and down in speed. 
Looking at the bottom end, before cut-in, consider what the generator load is there: practically zero.  So until the turbine comes up to cut-in speed, its almost running unloaded.  Air drag on the blades is the greatest part of resistance.  As a result it is free to turn at a very high TSR.  Like 15 or 20.  My 8-ft turbine cuts in at 150 RPM and has enough inertia that regular fluctuations in wind speed of +/-5kph don't change the RPM very much when it cuts in.  The wind speed is roughly 10kph but I don't know for sure.  That makes a TSR between 7 and 14.  Roughly.

At the high end, well I don't know much about the F&P's-
Despite hearing about them for a long time, I have not seen clear power curves from a conversion.  Dave has, but I've been looking and not turned up any in the past 2 weeks re-reading old threads on the Backshed.  Dave, if you could point me in the right direction...

My own experience is that the efficiency goes down as it runs faster.  This is because of I^2R losses that grow with the square of the current, but the output power grows only in a straight line (V*I).  The input mechanical power required to keep the generator turning increases as you turn faster.  It does not increase as quickly as the wind power through the blade disk increases, but it's close.  Here's a mind-bender:  The MORE inefficient the motor, the BETTER the match will be.  At least that's the case for my generator.  My own conversions are sturdy beasts that don't shine in the efficiency department.

When people brag about how efficient their generators are, they are also pointing out that the input power curve is close to a straight line like the output power curve is.  That's a problem for matching blades to the generator, because the wind power curve is nothing like a straight line!  It's a subtle irony but does not often matter.

Dave's last posted output power curve is quite different.  With capacitors the output power is not a straight line at all, and without capacitors it is a straight line.  Now I hope you have a better appreciation of why I'm so keen on seeing an input power curve!  The effect could be a very close power match with the blades, but there are so many other things going on that I'll only believe it when I see it.

Here's the generator power curve that I developed using a lathe to drive the shaft, and clamping a beam to the casing to measure torque:

OUTPUT POWER


INPUT POWER
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kitestrings

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Re: F&P stators operate best with a constant current output
« Reply #20 on: November 05, 2017, 12:03:23 PM »
I watched the videos you linked to on this set-up.  You were in it deep, and having entirely too much fun; much like Dave appears to have done with these F &Ps.

Regarding the blade angle of attack relative to TSR: okay so at a given station, we would have a known diameter, we know the speed so we could calculate the TSR, and with the atan(1/x) relationship we would also know the angle; that makes sense.  How do we know at what angle, for a given airfoil the prop will stall?  In your example 18 degrees was too steep, but how did you know this?

Regarding your mind bender: wasn't that the reason that in many of the axial direct-tied (to a fixed battery voltage) designs they intentionally added line resistance to improve the match at lower winds?

~ks

SparWeb

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Re: F&P stators operate best with a constant current output
« Reply #21 on: November 05, 2017, 04:28:44 PM »
Oh yeah.  I got all excited about the power comparison.  Forgot to say anything about spanwise TSR.

The TSR does mean "TIP speed ratio" but you can see that you can use the ratio at other points along the blade.  So take a measurement part-way along the blade, call that the radius, and solve for TSR again.  BTW, that's why I call it "X" instead of TSR because the math works at any point on the blade.  The scientific papers use the greek symbol Lambda, but I don't have a greek keyboard.

The X that I worked out above was for the tip:
"if X=7 then for wind=10mph a 6' blade will turn 160 RPM"

but we can work it out at any point along the blade
X = (160RPM)*(6ft) / (10mph) * {some conversion factor} = 7
X = (160RPM)*(4ft) / (10mph) * {some conversion factor} = 4.6
X = (160RPM)*(3ft) / (10mph) * {some conversion factor} = 3.5
X = (160RPM)*(1ft) / (10mph) * {some conversion factor} = 1.2

Next work out the incoming airflow angle based on these:
@ X=7.0; atan(1/7.0) = 8.1 degrees
@ X=4.6; atan(1/4.6) = 12.3 degrees
@ X=3.5; atan(1/3.5) = 15.9 degrees
@ X=1.2; atan(1/1.2) = 39.8 degrees

This is why blades should be twisted.  If the blade pitch was flat all along then the root of the blade would be stalled all the time.  In fact, this is the case for extruded blades like the ones Dave has (but don't tell Dave).  The root just runs at high angle of attack all the time, and with even moderate load, it can start to stall.  That doesn't matter much, because it's the outer 1/2 of the sweep of the blades that really generates the torque and the power.

By putting a twist in the blades, the airfoil can still meet the air at an angle with a good angle of attack.  The blades I made have a 20 degree twist, but they're pretty extreme and not a lot of people bother to do it so drastically.  My motor conversion has a cogging torque to overcome, so I'm happy the twist is there to help get started from the "locked" position when the blades are at a standstill.

Lots is written about airfoils and their characteristics.  More than necessary. 
This website just crunches the numbers rather than make extraordinary claims:
http://www.wolframalpha.com/input/?i=NACA+3512+airfoil&rawformassumption=%7B%22F%22,+%22AirfoilAngleOfAttack%22,+%22a%22%7D+-%3E%2215+%C2%B0%22

Very few airfoils can handle an AoA of 20 degrees.  If they do it's usually because they have very blunt leading edges and a lot of camber, in which case they have sacrificed something else to get the high stall angle, such as increased drag or pitching moment, like the GOE222.  Since pitching moment doesn't bother us much with wind turbines, the GOE 222 has merits.  For carving from wood, I was quite happy with the NACA3512 because I could make 80% of the face completely flat.

To your last question, yes I think that's true.  Another term that can be used to describe an alternator is "stiffness" which roughly means how quickly the power curve goes up with increasing speed.  If the thing cuts in at 100 RPM and by 200 RPM is generating 2kW, then that's very stiff, compared to another alternator that also cuts in at 100 RPM but at 200 RPM is only generating 200W.  Your genny, by the way, is pretty stiff and that's why it responds well to your MPPT scheme.  If you didn't have the MPPT then you might be using some resistors to flatten out the power curve a little, too.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: F&P stators operate best with a constant current output
« Reply #22 on: November 06, 2017, 01:07:14 PM »
Our blades IIRC go from about 2 degrees at the tip to about 15 degrees at the last three stations nearest the root.





There's been quite a bit of discussion here on the diminishing returns of going after the area nearest the hub.  It'd be interesting to see what a the difference would be between the practical that most people carve and the ideal if you could put the two in a wind tunnel.

SparWeb

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Re: F&P stators operate best with a constant current output
« Reply #23 on: November 06, 2017, 06:51:02 PM »
Your blades are fine.

There's more to setting the twist than that (there always is).  There's also an inflow rotation that is induced because the wake downstream is given a rotation by the drag.  This induced vortex is strongest at the root of the blade, and makes a big difference on the angle of attack.  Above I calculated the inflow angle at 39.8 degrees at the root.  If I had considered the vortex, it would have reduced that by about 10 degrees.  But the math gets pretty heavy.  I just remember finding out about it a long time ago, when I tried to do all the calculations for my blades myself, and carved them with too much twist, before discovering this for myself.

It should come as no surprise that this has been studied to death.  A small sample:

http://nrel-primo.hosted.exlibrisgroup.com/primo_library/libweb/action/search.do;jsessionid=E3F404D37D46DAE14E84176DF4C1537D?fn=search&ct=search&initialSearch=true&mode=Basic&tab=default_tab&indx=1&dum=true&srt=rank&vid=Pubs&frbg=&vl%28freeText0%29=wind+turbine+blade+element&scp.scps=scope%3A%28PUBS%29%2Cscope%3A%28NREL_INTERNAL%29&vl%28870446075UI1%29=all_items
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

SparWeb

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Re: F&P stators operate best with a constant current output
« Reply #24 on: November 06, 2017, 06:56:02 PM »
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

DaveP68

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Re: F&P stators operate best with a constant current output
« Reply #25 on: November 07, 2017, 12:56:27 AM »
This information you chaps are publishing here is like gold nuggets to a novice like myself.

Check out this YouTube video re a 3.2 m (10' 6) prop using GOE 222 blades.
https://www.youtube.com/watch?v=iBiUAvnr5sA

Take special note of data logged from 3:41 onward. The claim is 920 W from 20.9 kph (13 mph) of wind.

Doing the sums on these numbers those GOE 222 blades have to be 96% efficient and the PMA 100 %! So much for the Betz limit of 59.26%...


One thing called Reynold's Number bites us in the small wind turbine field.  The scale of our turbines means they have a very small Reynolds Number; between 100,000 and 500,000 when turning full speed, and much less when getting started at cut-in.  This drastically hampers real-world performance.

Nice blades ks and from a renewable source too.
There are realities that if you do not accept, will lead to frustration because you will be spending time on wrong assumptions and the results cannot follow!

SparWeb

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Re: F&P stators operate best with a constant current output
« Reply #26 on: November 07, 2017, 01:04:15 PM »
Dave,
Fun video.  Thank you.
Gotta think critically about the value of spot measurements and hand-held video documentary like this stuff. 
If people make opinions with polar opposites "truth from god" and "damned lies" then we won't be able to talk reasonably about what we really see in videos like these.
Two ways to look at this comparison test:  Absolute figures VS comparison figures.

Running two turbines side-by-side like that, which seem to be identical models of Exmork, is a great way to get COMPARISON data, and I'm going to watch it a few times for that alone.
Collecting data with identical dataloggers, with Davis anemometer kits clamped onto the towers makes the comparison of data even more clear.  This one is convincing.

Using that info, however, to make absolute calculations of the performance gets you in trouble.  There's no reason to believe that the wind speed at anemometer height is the same at the turbine hub height.  It could be 50% more.  It could vary more often.  The site looks turbulent - you can even see some trees.  Tower 2 with the basic Exmork has an anemometer without a wind vane.  The statement that turbine 2 is not following the wind is based only on comparison with the anemometer on tower 1.  Which is waggling back and forth the whole time.

I have a Davis anemometer, and it doesn't flap around like that in any wind speed.

Back to the video:
How much blanketing of turbulence was on turbine 1 vs turbine 2?
How tall are the towers?  What obstacles to the wind are in the area?
The video maker points the camera at the logging screen to show both outputs simultaneously at about 6:00 and holds it there for a minute.
There is something wrong with the turbine on the left - either it's been shut down or its furling is not properly set.  That could make this an unfair test.
Looking at the numbers themselves, why is this thing whipping about so fast?  400RPM at 30kph wind for 11' blades?  The new blades seem to run at TSR=9.

The cheap Exmork turbines are terrible machines.  I've seen the aftermath of an Exmork blade explosion.  Any change to an Exmork is an improvement!
If the guy who put the new blades on is expecting the Exmok furling tail to protect his blades from overspeed, I can't guarantee how long it will last in wind like that!
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024