Another new 12 foot diameter turbine

[DanB]

Last week our friend George S came up from Indiana to build most (everything but the blades) of a 12 foot diameter wind turbine.  It's much the same as others we've made but some things are different.  Here are a few details about that project which includes some basic testing on the alternator.



Normally for a 12 foot diameter 48 Volt alternator we have been winding the coils with 70 turns using 2 strands of AWG 16 wire in hand.  usually there is a small gap between the coils, which is not ideal in my mind.  This time we wound with 68 turns using two strands of AWG 15 wire in hand.  These were a 'close' fit but a bit too fat.  In the picture above you can see a coil, with the number 3 in the middle... and a line below that.  That line is the outer path of the magnets and the edge of the hole in the coil (at the bottom) should meet that line... so the coil is too fat.



By actually gluing the two boards down to create a sort of 'from' - and pressing / 'whacking' the coils into the form, we got them to fit perfectly.   Once we assembled this stator, the coils all fit perfectly in their place and they are touching one another on the sides.  There is very little room to fit more copper in this machine.



Pictured above are the powdercoated magnet rotors.  They're water jet cut from 3/8 inch steel, they are  15 inches in diameter.



Pictured above are two different hubs that I ordered for this project.  The one of the left is made in China, I get them from Southwest Wheel company.  The one on the right is a Dexter hub which I can now get from etrailer.com.  Until recently, etrailer did not offer such large hubs.  This is a hub for a 6000 pound axle which fits a  #42 spindle.  Normally I  use the one from SW wheel, but last time I got one (for Hughes workshop on Guemes Island) I noticed they stopped machining the back side of the hub.  In the past, I relied on that surface to be machined so that we could fit a rotor on the back side, which I like to do in order to keep the alternator 'compact' and reduce the length of the hardware that supports the stator.  (not a big deal really)  Lately the back side is a raw casting.  So,  I turned it on the lathe to true it up and we used it.  The Dexter hub from Etrailer would also work, but the back side is also not machined and the casting is much thicker.



Another pic of the two hubs.   Basically they are the same, but if one chooses to fit a rotor to the back side, the one on the left - from Southwest wheel, is still more practical, but a bit of lathe work is probably required to be sure the back rotor runs true.



Pictured above is the back magnet rotor, powder coated, with it's magnets on, stainless steel band and blue vinyl ester resin.  One note about powdercoat and vinyl ester resin...  if you ever accidently get a bit of resin on the front side of the rotor, it becomes clear that vinyl ester resin really sticks very well to the powder coat... which is good!



The  stator is finished in the picture above... again, I added a bit of blue pigment to the resin for fun!  The coils came in at 12.25 pounds, so the weight of a single phase (8 coils)  is about 8.13 pounds.  Going off a wire gauge charge, I figure  the length of wire in one phase then to be about 411 feet, which should make the resistance of 1 phase about  .66 ohm. 



Pictured above the machine is coming together....



The stator is mounted to the stator bracket with 5/8 inch hardware. 
 


We tested the machine on the back of my car.  Cutin speed (50 volts DC after the rectifier) is  right at 125 rpm.  The airgap is about exactly 15/16 inch.  After running the machine between 1 and 1.5kW for about 1 hour the hottest spots I could find on the stator were up around 180 deg F, which is within reason I think.. and I expect it would be quite a lot cooler if it  was up in the wind under such conditions.



There is the power curve we measured while testing it on the volvo rear end.  I also made a short video of the test on youtube which you can see here:
http://www.youtube.com/watch?v=1_DlgoTSEU8

[Fused]

Just curious, whats the temp on the stator running at 300 rpm?
Understanding that 300 is about max rpm for a 12 footer.

Fused

[DanB]

Hi Fused - figured I^2 R losses and what I see happening at about 1500 Watts (which maybe it could handle 2000 but I would prefer to furl well before that), 3000 Watts would be bound to burn up.  It's still reasonably efficient at 1500 though - seems with these machines, we can count on burning up once we get much below 65% efficient or so.

As it is now, it should stall 12' blades in higher winds, but add a bit of line loss (perhaps about half an ohm) and I think it should match the 12' blades pretty well and likely hold up to 1500 Watts sustained output.  Beyond that though - it will get hot.  (it did start getting pretty hot, pretty fast, at 3kW output)

[SparWeb]

That's a play on the old saw: with those coils you measure twice, "wind" once.

If I remember correctly epoxy is well past its "heat-deflection temperature" at 180F / 82C, but the vinyl-ester resin you use goes a bit higher than that.  Sounds like you've tested it right up to the thermal limit, held it there, and backed off with no damage.

[DanB]

That's a play on the old saw: with those coils you measure twice, "wind" once.

If I remember correctly epoxy is well past its "heat-deflection temperature" at 180F / 82C, but the vinyl-ester resin you use goes a bit higher than that.  Sounds like you've tested it right up to the thermal limit, held it there, and backed off with no damage.

Hi Sparweb ~
It ran at 180 for quite some time, before that we had it much warmer for a while (because we were running between 2 - 3kW) and still I didn't notice any damage or smell resin yet (usually the smell of resin is some sort of indicator of something!)

And again, it should run cooler in the wind ~ so I expect it's definitely good for 1.5kW sustained and maybe a bit more, although I believe it will furl before that.

[cdog]

Any opinions on running a machine like this with a set of powermax 13'  blades and a midnite solar classic?

[cdog]

I should also ask what would the open voltage be @300 rpm? Would a 150 volt unit be enough?

[jarrod9155]

Any opinions on running a machine like this with a set of powermax 13'  blades and a midnite solar classic?
[/quote
Power max blades don't furl the same . I pushed a recipe book 14 footer that was retro fitted with some powermax blades and she pushed out 3510 watts in furl . The same generator with 18 foot royal wind blades furl at 2500 watts and slow down .

[cdog]

So you are saying the only real way to know for sure is try? I currently have a 24volt 10' machine and am going to purchase a classic, I have the powermax blades, but I also have aspirations of a 48 volt 13' powemax blade machine, and I want a classic that will handle that as well

[DanB]

I should also ask what would the open voltage be @300 rpm? Would a 150 volt unit be enough?

Voltage is pretty much related directly to rpm, so at 300 rpm I would expect about 120VDC open.  It's easy to change volts/rpm with different wire gauge and numbers of windings in the coils though.

[cdog]

Yes, I understand, do you think the 13' blades would be close enough for this setup with a bit of fuling and airgap tweaking? Does anyone have a classic on a hombrew machine yet?

[DanB]

I know that a couple of folks have classics on homebrew turbines like these at this point.  I do know one fellow who is actually using the classic with a very similar turbine and using 13' diameter 'power max' blades with reasonable results - I do not know the details of his alternator but it's similar.  He's on this board but doesn't post often and I forget his user ID.  I think 'halfcrazy' is using classics on both 10 and 17' diameter machines with good results.

How would this work, with a classic and the fiberglass blades, I am not sure.  I expect it should do OK though if you set the power curve properly and maybe add a bit of length to the tail or make a larger tail vane than I normally would for the 12' turbine.

[ChrisOlson]

Any opinions on running a machine like this with a set of powermax 13'  blades and a midnite solar classic?

It'll just burn up.  I'm flying two machines with those blades on them and they're a whole different animal than the homebrew flat-faced blades most people use here.  PowerMax blades, turned out of the wind with furling system used in most homebrew turbines, refuse to stall.  I've seen my machines push close to 3 kW in high winds with the turbine fully furled.

In short, the PowerMax blades require a completely different generator setup than the one illustrated here and they have to be turned at much slower speeds to get them stall when the machine furls.  The PowerMax blades use a S809 airfoil, which was developed by the NREL specifically for wind turbines.  The flat-faced profiles used in most homebrew blades are a variation of various NACA airfoils, where were originally developed for aircraft propellers.

To put it in a different way, PowerMax blades are like a diesel - the harder you load them, the harder they'll pull.  The flat-faced blades are like high-revving sports car engines - spin like crazy, but they got no torque.  You put that diesel blade on a generator designed for the high-revving sports car engine and it won't make any power in the normal wind range because it's not spinning fast enough, then when the wind really picks up and the high-revving sports car blades are all done and go into stall, the torque of the diesel PowerMax blades kicks in and spins that generator to rpm's that turn it into smoke.
--
Chris

[coldspot]

 I'm sorry but I got confused with this-
"a single phase (8 coils)"
 I counted 12 on the stator??

again so sorry!

$0.02

[cdog]

Chris, I have a 10' with the powermax blades, it previously had the dan~spec blades, it doesnt appear to behave that much differently than before? Would you think the dan blades a better match for the classic?

[cdog]

I also had the assumption the classic would let the stator actually run cooler, volts instead of amps

[halfcrazy]

That is exactly the case we are running 2000 watts out of the 800 watt 10 footer and have seen 10kw out of the 17 footer still dialing on that one we had to stack 2 classics and really need a third it is wanting to keep making more power. We wound the 17 footer for 65vdc at cut in specifically so the classic has some room to play with it and it loves to run up to 200 volts in 50mph winds I suspect the Classic will stop the majority of stator cooking simply because the turbine will not be stalled and the voltage clamped down. Let the voltage run up 2-3 times and the the stator will be happier.

[ChrisOlson]

Chris, I have a 10' with the powermax blades, it previously had the dan~spec blades, it doesnt appear to behave that much differently than before? Would you think the dan blades a better match for the classic?

I don't know what you got for a generator on that machine, but PowerMax blades tend to self-stall at 8.5 TSR driving any sort of load, and pull like crazy around 6 TSR.  They'll run unloaded at 9.5-10 TSR, but DanB's blades like to cut in at the TSR the the PowerMax blades self-stall at.  So perhaps your generator is overwound for DanB's blades, then it will probably work with the PowerMax blades.  A generator, properly matched to the PowerMax blades, will cut in at around 7.5 TSR and reach 6 TSR by 12 mph wind speed or so, and they'll hold 6 TSR thru 18-20 mph wind speed, then start to drop slowly.  They have a very fat power curve over the entire medium range of wind speeds from about 12 mph up to 20 mph.

If you put PowerMax blades on a generator that cuts in at 8.5 TSR you'll get very poor performance from them at low and midrange wind speeds because they're trying to run too fast.  Then when the wind picks up above 20 mph, where they should be starting to drop below 6 TSR in order to control them, they'll just be getting into the "fat" part of their power curve and turn your generator into smoke.  I've probably flown more PowerMax blades, in different sizes, than anybody else here, and I can tell you from experience that if you swapped out blades and didn't notice any difference, then you're running them too fast.  When PowerMax blades run too fast they're very noisy (like whipping three pieces of cable thru the air), you're not taking advantage of what they can do in the midrange, and they're very dangerous in high winds because they can't be controlled easily.  If you're running a turbine in high winds and you throw the shorting switch, you can stop a set of DanB's blades.  PowerMax blades that are running too fast (above 6-6.5 TSR) will continue to pull hard all the way below 4 TSR when you throw that switch, and burn things up.

I don't know anything about the Classic other than the fact that it's expensive.  From a practical standpoint, I doubt the cost of that controller can be recovered in any reasonable time thru any extra power you might get from the turbine.  I can build a whole new 10 foot turbine for what that controller costs.  And that's what I'd do before I would buy one because I'll guarantee you I could get more power from two turbines than from one with a Classic on it.  So you'll have to ask somebody else who knows more about it, as I know nothing about it.
--
Chris

[DanB]

It'll just burn up.  I'm flying two machines with those blades on them and they're a whole different animal than the homebrew flat-faced blades most people use here.  PowerMax blades, turned out of the wind with furling system used in most homebrew turbines, refuse to stall.  I've seen my machines push close to 3 kW in high winds with the turbine fully furled.

Just for the record, you might be right but I'm not convinced what you so confidently claim is true here.  Plus - it's been a while since we had a nice argument/discussion here!  I've never tested those blades so I can't say much.  I have tested blades before on our 10' machines that had so much torque we couldn't stop them - although that was a 12 volt system with a long line and very wide torquey blades from royal fabrications.  No matter what sort of blade it is though, power you get is related to swept area and if the machine is fully furled then the power should be limited by that - furling is not to 'stall' the blades, it is to reduce swept area.  At the end of the day I suppose both things are happening.  But if a small 10 or 12' turbine is fully furled and still producing 3kW then I think the furling system is not correct. 

In short, the PowerMax blades require a completely different generator setup than the one illustrated here and they have to be turned at much slower speeds to get them stall when the machine furls.  The PowerMax blades use a S809 airfoil, which was developed by the NREL specifically for wind turbines.  The flat-faced profiles used in most homebrew blades are a variation of various NACA airfoils, where were originally developed for aircraft propellers.

What we use is close to various NACA airfoils and close to a Clark Y ~ which I had thought was designed for airplane wings.

To put it in a different way, PowerMax blades are like a diesel - the harder you load them, the harder they'll pull.  The flat-faced blades are like high-revving sports car engines - spin like crazy, but they got no torque.  You put that diesel blade on a generator designed for the high-revving sports car engine and it won't make any power in the normal wind range because it's not spinning fast enough, then when the wind really picks up and the high-revving sports car blades are all done and go into stall, the torque of the diesel PowerMax blades kicks in and spins that generator to rpm's that turn it into smoke.

Yes I don't know, perhaps the powermax blades are very forgiving of running over a wide range of TSR - I've not tested them because I tend to think they're very heavy and I wasn't impressed with the fiberglass work...
The only experience I have with them is feedback from other folks who have used them ~ some very good, some very bad.  You definitely give the best report I've heard and I really should get around to testing some myself some day.  I have been in contact with a fellow lately who is involved with 5 turbines, which were built basically to Hughs older plans for a 12' diameter turbine - but they were fit with the 13' powermax blades.  Those plans for that turbine called for a 48 Volt machine to be wound with coils that were made with over 100 turns of AWG 16 wire if I'm not mistaken.  All 3 battery charging machines have burned out.  Two of those machines are grid tied with windy boy inverters, those ones have help up fine, except for blade failures (blades coming off at the root)... so, in response to whoever asked what might happen with those blades, on this alternator with a 'classic' controller... there is a good chance it would work out fine.  The alternator I built here (this story) has less than half the resistance of Hughs original plans and more area to dissipate heat, so my guess is it may be up to the job.

I know another fellow who is manufacturing something very similar to what I made here (he's using less surface area in his magnets but quite thick magnets and I expect his stator is similar) - he's also flying powermax blades and he's built several of these.  So far as I know, two of his machines are through classic controllers and working fine for a couple years now - others are grid tied without batteries, also working fine.

So hard to say...
With wind power I'm not sure I can ever be 'sure' of anything.

[Flux]

You should be able to programme the classic to suit any blade profile.

Once you can do that you will get much the same results. When you are stuck with a fixed alternator characteristic you see much more difference with various blade profiles.  

With conventional loading much more depends on the way the blades match the load than on actual blade performance. Until you take the step to mppt loading you are mainly fiddling with matching . Decent aerofoils certainly work better than planks but most half decent blades work surprisingly well as long as you can get a match.

The big change comes with the alternator, once you can let the voltage rise with wind speed you can get much more power than when they are clamped to a fixed voltage. If you can go up to 3 times the voltage you can get 3 times the power from a stator for the same heat within it. This rise in alternator efficiency on load and the added power from the prop being on the peak of its power curve makes more difference than any fiddling with aerofoils. You would need to make the prop exceed Betz by a lot to get a similar performance from direct connection.

I am pleased to see that halfcrazy is getting these sort of results from the classic and I strongly suspect the improvement is also significant in lower winds where we tend to assume conventional machines are fairly good. I was quite surprised to find this, the matching in the lower winds is far more tricky than I expected where the prop curve is fairly flat.

This may be the point where the Powermax blades do out perform others with direct loading if they can avoid the rapid approach to stall in the region above cut in. With the classic this is no longer an issue but the programme would have to be chosen to best suit the blades.

Flux

[cdog]

Well I will say the powermax blades are a tad bit louder, the machine is 72 turns 14ga, 2X1X1/2 mags, 24 volt.
Besides the possibility of different windings for higher voltage, if the classic will let the machine run faster, should I be looking for a blade profile with a tsr to compliment the expected rpm??

[ChrisOlson]

Yes I don't know, perhaps the powermax blades are very forgiving of running over a wide range of TSR - I've not tested them because I tend to think they're very heavy and I wasn't impressed with the fiberglass work...

Dan, I think you're confusing the WindMax blades, which are cheap, poorly finished junk, with the PowerMax blades.  If you weren't impressed with the fiberglass work then you've never even seen a set of PowerMax blades, much less tested them.  They do not like to run over a wide TSR range.  They're designed for maximum midrange power in wind speeds of 12-20 mph and run at a Cp of .44 (tested and verified by me) in that wind speed range at 6 TSR.

I have bought 11 sets of those blades for my own turbines and machines I have built for other people, and I have yet to ever have to sand one or even add a single gram of balance weight to balance the rotor.  This is the hub that comes with the PowerMax 10.58 foot rotor - it fits a 30mm shaft with a 1:10 taper, 30mm x 24mm x 60mm:



The blades come with the hub, the rotor comes as a balanced unit, and it the nose cone is included with it.  The blades are marked with a tag as to which location (A, B or C) they are to be bolted on to the hub:


And below is a fully assembled 3.2 meter PowerMax rotor ready to be mounted to a turbine:


And this is a set of PowerMax 085C's, just as they came out of the box:


One final note about PowerMax rotors is that they are not that easy to assemble.  Nothing on the root mounting to the hub is a "loose fit".  The bolts don't come with them and you have to use 12mm Grade 9.8 hard bolts.  If you don't observe the proper torque sequence and spec (72 lb-ft) you'll have problems with tip tracking.  If you end up with a rotor with one blade a mm or two off, you have to use a special puller to remove the rotor from the tapered shaft, loosen the entire assembly up and redo it, this time taking care to observe the proper torque sequence.

And drilling the blade roots for a loose fit is also hard to do because the blades have spring steel inserts in the root section.  Whatever spring steel they use in there is harder than hell and it'll melt the tip off a regular drill bit.  I did manage to drill one once using a cobalt drill so I could use SAE 1/2" bolts in it.  But after that experience I just use the 12mm bolts they're designed for.
--
Chris

[cdog]

halfcrazy... how much faster would you estimate the rpm's with the classic, compared to the direct connect method?

[SparWeb]

Chris, I have a 10' with the powermax blades, it previously had the dan~spec blades, it doesnt appear to behave that much differently than before? Would you think the dan blades a better match for the classic?

I don't know what you got for a generator on that machine, but PowerMax blades tend to self-stall at 8.5 TSR driving any sort of load, and pull like crazy around 6 TSR.  They'll run unloaded at 9.5-10 TSR, but DanB's blades like to cut in at the TSR the the PowerMax blades self-stall at.  So perhaps your generator is overwound for DanB's blades, then it will probably work with the PowerMax blades.  A generator, properly matched to the PowerMax blades, will cut in at around 7.5 TSR and reach 6 TSR by 12 mph wind speed or so, and they'll hold 6 TSR thru 18-20 mph wind speed, then start to drop slowly.  They have a very fat power curve over the entire medium range of wind speeds from about 12 mph up to 20 mph.

If you put PowerMax blades on a generator that cuts in at 8.5 TSR you'll get very poor performance from them at low and midrange wind speeds because they're trying to run too fast.  Then when the wind picks up above 20 mph, where they should be starting to drop below 6 TSR in order to control them, they'll just be getting into the "fat" part of their power curve and turn your generator into smoke.  I've probably flown more PowerMax blades, in different sizes, than anybody else here, and I can tell you from experience that if you swapped out blades and didn't notice any difference, then you're running them too fast.  When PowerMax blades run too fast they're very noisy (like whipping three pieces of cable thru the air), you're not taking advantage of what they can do in the midrange, and they're very dangerous in high winds because they can't be controlled easily.  If you're running a turbine in high winds and you throw the shorting switch, you can stop a set of DanB's blades.  PowerMax blades that are running too fast (above 6-6.5 TSR) will continue to pull hard all the way below 4 TSR when you throw that switch, and burn things up.
--
Chris

Tip Speed Ratio is the opposite of angle of attack.  High TSR means low AoA.  If you consider 8.5 a high TSR for the Powermax blade, then that is a low angle of attack, meaning the blade is not stalled at all.  It's low on the lift curve, and probably low on the drag curve, too, which isn't a bad thing.  TSR is a moving target all the time.

Either you accept that fixed-pitch blades will have to perform through a range of TSR, or you go to the trouble of mounting them to a pitch control mechanism that compensates and tune it to a specific TSR.  Even well matched, fixed blades will start and cut-in at a rather high TSR and progress down in TSR until medium wind speeds, where it should meet its ideal.  This is (partly) what "matching" means and it doesn't really matter what type of blade you have for this principle to work.  It can happen to be that a Powermax may be better suited to generator A, but there will be no proof unless the power curve of the generator and the blades are tested separately and then compared.  Way too much science there for we mere mortals.  We settle for trial and error - and some copying what's worked in the past.

When badly matched, what you say about your blades goes for any blade - if it's turning too fast even at cut-in, and the generator is always overwhelmed, then this is a poor match in any case.

[tecker]

You can see the blades are not that important . Getting to that  happy zone in the real world is a Crap shoot. The plastic stator is a Art form really . To make them last there's got to be some attention given to out put . Here we have real time data to look at
1.5 k is the happy zone in Star however there's a lot more power out there either at higher voltages or power out
 I think the Blades made on site are by far the best Choice for service and learning curve .
 A Wye Delta switch to get more power or a feed back coil to pulse the charger at higher rpm is an easy build that will protect the stator in the heat of summer or Cold in winter  Where one needs a lot of power and tends to run the stator hard . Bottom line is If you have good wind a Furling drive to keep it from coming apart and stator controls the design is good .
 I say this only to give myself some finality to the hawt progress for the year Looks like the same machine and is by far the best unit of it's kind for good solid wind   
I think if you enclose the Mech and work on routing air flow in that enclosure you have a 20 year machine . The target figure for Temp is 180 F  and below .

[halfcrazy]

Chris, I have a 10' with the powermax blades, it previously had the dan~spec blades, it doesnt appear to behave that much differently than before? Would you think the dan blades a better match for the classic?

I don't know what you got for a generator on that machine, but PowerMax blades tend to self-stall at 8.5 TSR driving any sort of load, and pull like crazy around 6 TSR.  They'll run unloaded at 9.5-10 TSR, but DanB's blades like to cut in at the TSR the the PowerMax blades self-stall at.  So perhaps your generator is overwound for DanB's blades, then it will probably work with the PowerMax blades.  A generator, properly matched to the PowerMax blades, will cut in at around 7.5 TSR and reach 6 TSR by 12 mph wind speed or so, and they'll hold 6 TSR thru 18-20 mph wind speed, then start to drop slowly.  They have a very fat power curve over the entire medium range of wind speeds from about 12 mph up to 20 mph.

If you put PowerMax blades on a generator that cuts in at 8.5 TSR you'll get very poor performance from them at low and midrange wind speeds because they're trying to run too fast.  Then when the wind picks up above 20 mph, where they should be starting to drop below 6 TSR in order to control them, they'll just be getting into the "fat" part of their power curve and turn your generator into smoke.  I've probably flown more PowerMax blades, in different sizes, than anybody else here, and I can tell you from experience that if you swapped out blades and didn't notice any difference, then you're running them too fast.  When PowerMax blades run too fast they're very noisy (like whipping three pieces of cable thru the air), you're not taking advantage of what they can do in the midrange, and they're very dangerous in high winds because they can't be controlled easily.  If you're running a turbine in high winds and you throw the shorting switch, you can stop a set of DanB's blades.  PowerMax blades that are running too fast (above 6-6.5 TSR) will continue to pull hard all the way below 4 TSR when you throw that switch, and burn things up.

I don't know anything about the Classic other than the fact that it's expensive.  From a practical standpoint, I doubt the cost of that controller can be recovered in any reasonable time thru any extra power you might get from the turbine.  I can build a whole new 10 foot turbine for what that controller costs.  And that's what I'd do before I would buy one because I'll guarantee you I could get more power from two turbines than from one with a Classic on it.  So you'll have to ask somebody else who knows more about it, as I know nothing about it.
--
Chris

That,s a pretty bold statement there so you can build a second 100 ft tower and a complete 10 ft machine cheaper than I can buy a Classic? I have more in copper on my machine than the cost of a Classic. I think there are a lot of people on here myself included that would buy a 10ft machine and tower hooked up for 750 bucks and I suspect they can be bought cheaper that is the first price I found. Even if you could you would not make more power than I would with one turbine and you have twice the headaches.

The true benefit of the Classic is that you can make the turbine do whatever you want I personnely do not have a problem with my 10ft machine spinning at say 3 times cut in speed thus making roughly 3 times the power. But if you did and only wanted say twice the speed than you can build your power curve accordingly. We see big gains right from the start basically because we can keep the blades in there most efficient spot in any wind speed as well as match any stator to any battery bank. Feel free to email me with any Classic related questions ryan at midnitesolar.com

[cdog]

Great conversation guys, I love this board! Perhaps santa will have a classic in his sleigh!
I have been watching the development of the classic, if it requires a blade change I will do it.
I would be really interested to see a classic on a pitch controlled machine!?

[Flux]

The classic will be fine on a pitched control machine. You make the pitch control operate from your full load point and it will maintain constant power in high winds.

You won't benefit from altering the pitch in the working part of the Classics load control region. Pitch control does give you an absolute limit on voltage if for some reason you loose the load and is an easier option for the controller than a furling mill.

Flux

[ChrisOlson]

Tip Speed Ratio is the opposite of angle of attack.  High TSR means low AoA.  If you consider 8.5 a high TSR for the Powermax blade, then that is a low angle of attack, meaning the blade is not stalled at all.  It's low on the lift curve, and probably low on the drag curve, too, which isn't a bad thing.  TSR is a moving target all the time.

Well, yes.  But the question was whether or not a 13.1 foot PowerMax rotor can be used with the generator illustrated in this thread.  It cannot.  The PowerMax blades will run too fast with this generator and reach their peak power producing TSR range in higher wind speeds.  DanB said this generator is good for 1.5 kW sustained.  A 13.1 PowerMax rotor running at 6 TSR at 25 mph wind speed puts roughly 3.1 kW to the shaft and is running at 320 rpm.  If the generator is below about 60% efficient at that point, meaning the generator should be putting out almost 1.9 kW, it will smoke it.  A generator that's only good for 1,500 watts sustained is not going to take it.  Period.

The S809 airfoil, being a symmetrical airfoil except for the "cusp" on the wind facing side, stalls at low angle of attack.  I think you're trying to compare it to flat face profiles that create lift at zero angle of attack and typically stall around 14 degrees.  The S809 is a different animal and goes into accelerated stall at low angle of attack, and hard stall at high angle of attack.  It will not put out any significant power running at TSR above 8.5 because it is starting to go into stall due to the airfoil running at too low of angle of attack.
--
Chris

[ChrisOlson]

That,s a pretty bold statement there so you can build a second 100 ft tower and a complete 10 ft machine cheaper than I can buy a Classic?

On a 54 foot free-standing steel lattice tower, not a 100 foot.  I can built both the tower and the turbine for less money in materials than a Classic controller costs.  For off-grid folks like me it's better to throw up more turbines than spend money on an electronic gizmo.  If one goes down I still got power.  When they're both working I got double the power I get with one.

It's not double the headache to fly two turbines instead of one - it's double the fun.
--
Chris

[ghurd]

Back to DanB's statement-
"power you get is related to swept area and if the machine is fully furled then the power should be limited by that - furling is not to 'stall' the blades, it is to reduce swept area."

(output of) "3 kW in high winds with the turbine fully furled" sounds like a furling issue to me.
3KW out, plus the many KWs of 12V inefficiencies, and there has to be very considerable swept area still left when fully furled!
Sounds like it could use less sq ft of tail?
G-

[cdog]

Chris, I think for many people getting one machine flying is a huge undertaking, not everyone can raise a new one in an afternoon!
I think the classic is much more than a ''gizmo''!
Has anyone ever embedded some sort of temperature sender in a stator to get some real world temp data?
Any suggestions on this?

[Dave B]

I just want to add my observations of the flat faced blades (I have carved my own previously) and the concave front surface Gottigen 222 profile blades. I believe there is no argument these are two very different performing blade profiles. In general as commonly carved in the "book" the flat faced are a faster running blade than the 222 blade. I do not want to assume anything but possibly the concave front surface (and maybe similar profiles) can offer more torque in the lower end RPM. Chris seems to have a lot of experience with and describes well his findings with different combinations of blade diameters, alternators and blade profiles.

  I will also add that all things the same the blade profile used can and probably will affect the furling no matter the type of load. For those who don't believe a machine can run a substantial output when fully furled you are probably most familiar with the flat faced profile blades. My machine can be held in the furled position for shut down etc. The concave front profile of the 222 blade can act as a scoop to the wind to anything but exactly parrallel. This often starts the blades moving and in turbulent winds the yaw lags enough to allow the blades to "fly". This is not the same as improper furling adjustment and seeing the tail ramp up during yaw. This is held in the furled position. I have often seen 500 watts from my 16' 24v machine in this condition.

  We have a pretty good grasp on the alternator design and limitations, not so yet with how the geometry and or loading needs to be altered to effectively run different blade profiles.  Dave B