Another new 12 foot diameter turbine

[jarrod9155]

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-

3 kw in high winds  furled , I would have thought there was a  problem with the furling also , The only change to my machine was the blades . I went from 13 foot power max blades to 18 foot  royal wind blades and have since  had no problems with furling . The power max blades would allways furl at diffrent power outputs never consit ant  the 222 blades are more compatible with the home brew / recipe book alternator mostly built here . My alternator was built around the recipe book 14 foot plans and the powermax blades didn't mix well.

[SparWeb]

Now you got me on a little rant.

Okay I'm not that mad, but I've been reading silly stuff here.

222 blades are more compatible

concave front profile of the blade 

stalls at low angle of attack

Woah guys, you can't pretend to know as much as you say you do when it comes to airfoil shapes.  I sat through a lot of aerodynamics classes and I still don't know either.  There's some kind of group-think going on here and you're all together agreeing with yourselves.

This is not an art that accepts a piece of this and a piece of that.  "Flat bottoms" and "concave surfaces" are totally irrelevant to the big picture of a wind turbine.  I have tried working through the math with actual airfoil data, using all the right corrections and factors and so and any time there is the slightest glimmer of a possibility that one airfoil can do better than another, I can look at the big picture, add one inch to the radius, and all of the supposed advantage vanishes!

Who can tell me the difference between these airfoil coefficient curves?





Okay you thought that was so simple?  Which one is BETTER?  Ha you may still think that's easy to answer but have you calculated the CL / CD ratios?  You'd be very very surprised if you did!

Who can pick the right shape that corresponds with the data above?



No I can't either!  (well I wouldn't know if I hadn't made the graphics myself)

Who can tell me which will do better on such-and-such a turbine?

I don't know either!
Stop convincing yourselves that there is some particular part of the shape that does any thing for you.  That is not how it works. 

You want some math to help convince you?  Draw out to scale a NACA4412 airfoil and beside it draw a Clark Y.  What is the maximum different in the profile shapes?  On a 6-inch chord, the differences are less than 1/16 of an inch.  I defy you to carve or lay-up fiberglass by hand at that level of accuracy.

What about smoothness?
Tip Shape?
Root edge blend?
Trailing edge sharpness?

Your workmanship will have a 10x bigger effect on blade performance over airfoil selection.  The only way you can screw up airfoil selection is to ignore the point of zero-lift and adjust the basic incidence accordingly when aiming for a specific TSR.  Other than that you can sand down a fence board for all it matters at this scale.

[ChrisOlson]

(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?

Then you don't understand how furling really works.  Have you ever seen a turbine run in 70 mph sustained wind?  The timid shut their machines down.  I leave mine run to see if they can take it.  I got video of it.  I'll leave the math to you, but it don't take very much swept area to get 3 kW at 70 mph.
--
Chris

[ChrisOlson]

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''!

Well, I got five of them and I've been known to put one together and get it flying in a single weekend.  Takes a lot of beer though.

To me the Classic is an electronic gizmo.  Time will tell how reliable it is.  Everybody's results will be different when they use one.  When you depend on your turbines for your primary source of power it makes you hesitate a bit before bolting on an electronic gizmo that costs $700.  What's the payback time on that $700 investment in the extra kWh it will make?

I see too many people too interested in what sort of peak watts their turbine put out once in a howling gale.  What interests me is how many kWh or amp-hours I get out of it, day in and day out.  It's the kWh that gets the work done in my house, not the 2,000 watts, or whatever, that my turbine puts when a thunderstorm blows thru.

I need to see some evidence that the device will put more amp-hours into my battery bank to make the investment worthwhile.
--
Chris

[cdog]

I cant blame you for not wanting to part with your money on a whim, perhaps I am naive, but it looks like the real deal to me.
I am soon going to get the internet at my hunting camp, I have an old computer to take out and I hope to be able to have it plugged into the classic and have a web page so that anyone can see how it is behaving.
I ''guess'' that is doable?

[Dave B]

Sparweb,

 All neat stuff, the math and calculations etc. Bumble Bees can't fly either but maybe by now someone has massaged the numbers enough to figure maybe they can fly after all. I'll stick with my real world observations and tweak from trial and error from there. It's a system of components that work together, those of us who get it near enough right win the prize. Any design can be better, congrats to all those who tweak the variables of their own system and machines are running.  Dave B.

[ChrisOlson]

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

The GO222 and S809 are very similar in their operating characteristics.  Both profiles are designed for torque, not speed.

In my experience it's easier to build generators for torque blades than for racing speeders.  The racing speeders cut in nice because they reach very high rpm early, but as soon as load is applied a decay in Tip Speed Ratio starts and progresses rapidly to full stall.

The thing I like about the S809 is that it does not reach high TSR at low wind speeds for cut-in.  Instead of cutting in a 10 foot rotor at 140-150 rpm, a PowerMax 10 foot's ideal cut-in rpm is 127.  At 12 mph wind speed the TSR should be 6 and it will hold that 6 TSR from 12 to 18 mph wind speed.  As the wind speed increases from 12 to 15 to 18, the rpm increases in proportion to the increase in wind speed, and so does generator output.  This is the "fat" part of the power curve for the S809 blade.

I fiddled with all sorts of flat-face profiles and the S809 makes, on average, between 20-30% more power in the 12-18 mph wind speed range than any flat-faced blade I ever ran.  And it's due to pure torque and the airfoil's ability to maintain that flat TSR in that wind speed range.  The huge majority of the power generated by most wind turbines is in that 12-18 mph wind speed range because that's the normal average speeds the wind blows at on most sites that are suitable for wind power installations.  Up to 12 mph, there's little power available, the percentage of the time that the wind blows faster than 18 is very small for most people.

As the wind speed picks up beyond 18, the TSR starts to decay with the S809, and it pulls happily down to 3.5 TSR and still does not stall even at 36 mph wind speed.

When you look at the GO222 vs the S809, they're kind of the same.  The S809, due to the "cusp" on the trailing edge of the wind-facing side of the blade, also has somewhat of a concave face.  The S809 profile was developed by the NREL specifically for wind turbines to extract more power from the average wind speeds available on the majority of sites, and it definitely works.  The other nice thing about it is that that turbine won't spin itself to destruction if you lose the generator.  The S809 stalls at high Tip Speed Ratios above 8.5 and goes into hard stall, unloaded, at 10 TSR.

I see a lot of people here relating their experiences with flat-faced blades and thinking that what they know about running those applies to them all.  It doesn't.
--
Chris

[scoraigwind]

Well this has been an interesting read.

A lot of attention still seems to centre on the peak power output.   For me that is misplaced because battery systems are more vulnerable in low winds, whereas in high winds they are often dumping power already, so high power is not that useful.  Good efficiency in everyday winds will pay better dividends for battery-based systems in my view.  That means you put your resources into large blades and small alternators so as to catch what is going day by day.  If you go grid tied or heating and you can really profit in high winds, then it is easy enough to do MPPT maneouvres with grid tie inverters or series heaters and get optimum blade performance, and run hard, and score high kW points.

For me as a battery user the issue is survival and reliability, and having a good furling system will mean that you do not have to structure your tower and electricals for a sustained high kW output that thrashes the turbine for a short time without any real energy supply benefit.

In my 2005 plans 'How to build a wind turbine' I published 12 footer plans that I regret because they did have an undersized stator for a 1kW output (which people rightly expect as a minimum there) and that has caused some grief in places where high power was seen.  That 2005 design used a 14 inch rotor as I recall and N35 magnets, and I would not recommend it (too small stator) and I no longer print those plans.  For the last few years I have used 16 inch rotors and N40 magnets on the 12 footers, and am very happy with my Recipe.  However you can also get even higher peak power using bigger magnets if you want to spend on them  (or an even larger rotor/stator if you want to do it on the cheap).

If you use Powermax blades then you obviously do need to be careful because from what I am reading here they do not furl at all easily, and you may have to use a smaller angle on the tail hinge, or do what you need to do to make sure they steer clear of the burnup experiences so vividly evoked by Chris.  Making the tail smaller as such is not a great idea because you need a large rotor and you need a good offset to the side for reliable furling.  But you can cut down the moment of weight by making the tail light and by reducing the tail hinge angle off-vertical.  Just be sure that the tower is exactly vertical when you do that. 

Umm and I am still a bit confused about the use of the word stall.  For me it happens when the blades are running too slowly (high angle of attack like a plane) but for some it seems to also happen at the high tip speed ratios.  Anyway, I like blades that like high tip speed ratios which charge my battery in very low winds.

I'd just like to return to the lovely job that Dan did of the new 12 foot design and say "thanks for sharing that" :-)

Cheers,

Hugh

the Classic is a great idea and has been showing a lot of promise but for now it's quite pricey in terms of what it has to offer.  I would personally try to make a machine that is best matched (blades to alternator) in low winds and that runs a bit less well ( but very quietly as it moves toward stall) in stronger winds and then furls and continues to produce adequate output in the very strong winds.  Maybe I got lazy but all of those high winds disasters got old a few years back.  So yes you can run your rpm up and improve the efficiency of both the blades and the alternator if you actually need all that power in strong winds, or you could also just put a heater in series with the battery and warm your house with that.  But in the end I wonder if it's actually adding to the useful energy you actually need, which is battery charge in low winds in my circumstances.

[97fishmt]

Hi Spar,

I think that's what your getting from a few of these posters with different ideas,
just gut feelings and seat of the pants trial and error experimenting.

The subject of straying from the worked out plans that Hugh, Dan and the crew,
have perfected into complete working machines, is being challenged or altered
to see where it can go.

I know I have put quite a few different rotors on the servo motors I fool around
with.  By changing one to another I can see what works better.  I settled on carving
a set with  more width at the root than normal.  Because after years of listening
to the wind slip by the blades at little wind times.  I was determined to try and do
better.  

After playing with a turbine enough, you do come up with an educated guess of what
could work better based on it's performance and your many years of tinkering experience.

Although I play around with a few different motors and the windings are all different.
So over the years I have carved many props in different ways and they all worked
on one machine or another,  But the fun in it for me is the carving of the props.

That's what keeps me hooked on this hobby.  (i have stared at the math and the
                                                                     other stuff that is supposed to get
                                                                     you in the ball park and i guess i
                                                                     just keep going by the seat of my
                                                                     pants feelings now.  I haven't had
                                                                     a prop failure in over 10 years now.

                                                                       In the beginning I broke em quicker
                                                                       than I could make em because of the
                                                                       lack of a nice tower and all the fun of
                                                                       raising and lowering.  It sure is cool to
                                                                       get her flying in 10 to 15 minutes now
                                                                       with no worries.)


                                                                       All the best

                                                                                  Mike

[97fishmt]

sorry i was very slow to respond
to steven

[ChrisOlson]

If you use Powermax blades then you obviously do need to be careful because from what I am reading here they do not furl at all easily

Hi Hugh - --

What happens is the S809 airfoil pulls so well at low Tip Speed Ratios that turning the rotor out of the wind has little effect on power output.  For the most part they run as well at about 45 degrees to the wind as they do head-on into the wind.  Reducing the swept area exposed to the full wind blast causes them to reduce power output like any rotor, but my experience with them is related by running them in fairly high winds over 50 mph and seeing the turbine develop full rated power, or more, with the tail folded right up against the stop.

Umm and I am still a bit confused about the use of the word stall.  For me it happens when the blades are running too slowly (high angle of attack like a plane) but for some it seems to also happen at the high tip speed ratios

Yes, what causes that is that symmetrical airfoils do not create any lift at zero angle of attack, where NACA-series airfoils do.  Stall happens any time the airfoil stops making lift.  Running a symmetrical airfoil like the S809 at high tip speed ratios brings the angle of attack close to zero, where it stalls.
--
Chris

[cdog]

Hugh, this makes a lot of sense to me.
When I built my 10' I had the idea in my head that a long large tail would ''steer'' my mill better. It has 8'' of offset because of this, and this could be why I dont find the powermax blades to furl much differently than the recipie blades?

[DanB]

I know different blades furl differently.
I have both of the 'powermax' and the 'windmax' blades here, but I must admit I've not got 'round to testing either because I love the idea of making blades at home, with wood.

Could be the powermax blades have gotten better - I have some, they seem heavy - I like the look more than the 'windmax' blades.

One used to claim a cP of .48 and the other claimed a cP of .49. Both claims seem unrealistic to me.  And looking at the websites one says:

'Consumer Beware: We found that some of our competitors have tried to copy our blade design ! these poorly made blade copies from our competitors have lower quality, more defects, lower performance and shorter service life. These defective blade copies are made of poor quality fiber glass material that last much less time than our blades. '

and the other says:

'Note: Keep away from those fraudulent copies from our competitor, which have the thicker poorly made seam lines, that severely change the aerodynamic characteristics and make lots of noise.'

one is 'magnet4less.com' and the other is 'magnet4sale.com'

I'm sure both blades work fine.  Honestly I do like the look of the 'powermax' blades better (they come from magnet4sale.com) but it all has my head spinning a bit.

I prefer just to start with some lumber.

[cdog]

Dan, what changes would you make to your blade design if you planned on running them with a classic?
I found building my own blades very rewarding as well.

[ChrisOlson]

one is 'magnet4less.com' and the other is 'magnet4sale.com'

I've talked to Jeff at CMS Magnetics and the guys that have the WindMax blades used to be partners and they split off due to some sort of disagreement between them.  The fact is, neither blade is a copy of the other.  They come from totally different places.

If you have not bought any PowerMax blades for awhile you have the old ones, which are really WindMax.  When the WindMax guys split off and started up their own outfit they both handled WindMax.  Jeff said those blades came in a big crate and when somebody ordered a set they had to search thru the crate and find three blades that were good.  I don't remember how many blades he said came in a crate but I know he said that usually almost half of them were no good and had to be thrown away.  So they went to a different manufacturer.

The current line of PowerMax blades that have the spring steel inserts in the root (check it with a magnet to see if it's in there) have only been out for a little over a year.  They are somewhat heavy but that's not really a problem.  I would guess a 10 foot rotor weighs about 40-50 lbs fully assembled.

The WindMax blades are absolutely horrible.  I had one set that I only flew for about six months and one day the turbine started vibrating something horrible.  I lowered it to take a look and the leading edge had opened up and water had gotten in it.  I can't say that I'd recommend those WindMax blades to anybody because I think they're downright dangerous.
--
Chris

[Dave B]

Right on the mark Chris, there is no recipe and all bets are off when you add a different motor (blades) to the system. Like you, I would rather be logging flying time than crunching numbers and saying shoulda, coulda, woulda. Get'er done, kudos to you  !!!   Dave B.

If you use Powermax blades then you obviously do need to be careful because from what I am reading here they do not furl at all easily

Hi Hugh - --

What happens is the S809 airfoil pulls so well at low Tip Speed Ratios that turning the rotor out of the wind has little effect on power output.  For the most part they run as well at about 45 degrees to the wind as they do head-on into the wind.  Reducing the swept area exposed to the full wind blast causes them to reduce power output like any rotor, but my experience with them is related by running them in fairly high winds over 50 mph and seeing the turbine develop full rated power, or more, with the tail folded right up against the stop.

Umm and I am still a bit confused about the use of the word stall.  For me it happens when the blades are running too slowly (high angle of attack like a plane) but for some it seems to also happen at the high tip speed ratios

Yes, what causes that is that symmetrical airfoils do not create any lift at zero angle of attack, where NACA-series airfoils do.  Stall happens any time the airfoil stops making lift.  Running a symmetrical airfoil like the S809 at high tip speed ratios brings the angle of attack close to zero, where it stalls.
--
Chris

[ChrisOlson]

Right on the mark Chris, there is no recipe and all bets are off when you add a different motor (blades) to the system. Like you, I would rather be logging flying time than crunching numbers and saying shoulda, coulda, woulda. Get'er done, kudos to you  !!!   Dave B.

That's right.  Getting them on the tower and putting hours on tells me more than 52 pages of calculations.

If you seen my latest conflagration I'm testing you'd shake your head in disgust and go have a beer.  It's a 10 foot machine with dual stators in it and a bunch of relays switching the two stators in and out from star to delta.  Flux knows some of the details of the thing and it's required quite a bit of tweaking since I put it on the tower.  But it works - sort of   
--
Chris

[SparWeb]

Hi Spar,

I think that's what your getting from a few of these posters with different ideas,
just gut feelings and seat of the pants trial and error experimenting.

The subject of straying from the worked out plans that Hugh, Dan and the crew,
have perfected into complete working machines, is being challenged or altered
to see where it can go.

I know I have put quite a few different rotors on the servo motors I fool around
with.  By changing one to another I can see what works better.  I settled on carving
a set with  more width at the root than normal.  Because after years of listening
to the wind slip by the blades at little wind times.  I was determined to try and do
better.  

After playing with a turbine enough, you do come up with an educated guess of what
could work better based on it's performance and your many years of tinkering experience.

Although I play around with a few different motors and the windings are all different.
So over the years I have carved many props in different ways and they all worked
on one machine or another,  But the fun in it for me is the carving of the props.

That's what keeps me hooked on this hobby.  (i have stared at the math and the
                                                                     other stuff that is supposed to get
                                                                     you in the ball park and i guess i
                                                                     just keep going by the seat of my
                                                                     pants feelings now.  I haven't had
                                                                     a prop failure in over 10 years now.

                                                                       In the beginning I broke em quicker
                                                                       than I could make em because of the
                                                                       lack of a nice tower and all the fun of
                                                                       raising and lowering.  It sure is cool to
                                                                       get her flying in 10 to 15 minutes now
                                                                       with no worries.)

                                                                       All the best

Mike

Hi Mike.  I can only agree with what you say.  Trying new stuff is fun and often worthwhile.  Why are any of us doing it but for the fun of tinkering?

I think I went overboard.  I don't pretend to know more about aerodynamics than I really do - it bugs me when others do.

[SparWeb]

Well this has been an interesting read.

Hi Hugh,

I may be contributing a bit too much to that effect.  Anyway, I've written some stuff on the topic of prop-generator matching.  Seems as good a time as any to put it out there: 
http://www.sparweb.ca/Forum/Prop_Curve_Match_Draft.pdf

Having graphs like these to look at, the question of stalling at high speed or stalling at low speed can be teased apart into separate questions, but you can still see how they're really the same thing.

[scoraigwind]

Yes, what causes that is that symmetrical airfoils do not create any lift at zero angle of attack, where NACA-series airfoils do.  Stall happens any time the airfoil stops making lift.  Running a symmetrical airfoil like the S809 at high tip speed ratios brings the angle of attack close to zero, where it stalls.
--
Chris

This condition where the angle of attack is too small is not usually called stall, but so long as we know that's what you call it then we'll understand you.  I would call it runaway.

There has been a lot of talk about the different characteristics of different airfoil sections, but I suspect that the biggest difference is the actual blade angle.  If you have a coarse blade pitch angle (or you use asymmetrical section at the same blade angle as you would a cambered one) then you will get:

Lower angle of attack,
More torque at low tip speed ratio,
Lower maximum speed,
Noisy performance at high rpm

All you are doing is shifting the performance peak down to a lower tip speed ratio.  You should also increase the width of the blades at the same time.  I prefer the high tip speed ratio because it allows me to use lighter alternators.  I don't mind a bit of stalling (in the sense that I understand stalling which is when something is moving too slowly to work properly) in strong winds, because that is not when I am most concerned to charge my battery.  it's also quiet and reduces wear and tear.

I would say that anyone using Powermax blades would probably do well to wind their alternator for a lower cut in rpm and of course this means using thinner wire so that the efficiency is reduced.  But if you do not care about the low-wind performance then they will work OK on the standard recipes.  But evidently they produce more power during furl, which could mean modifying the tail arrangements.  Tail furling is always a bit of a black art.

[ChrisOlson]

I would say that anyone using Powermax blades would probably do well to wind their alternator for a lower cut in rpm and of course this means using thinner wire so that the efficiency is reduced.  But if you do not care about the low-wind performance then they will work OK on the standard recipes.  But evidently they produce more power during furl, which could mean modifying the tail arrangements.  Tail furling is always a bit of a black art.

I've been winding delta generators for 12 volt (not star/delta switched - pure delta) and they have worked very well for me with the PowerMax rotors.  I try to wind them so I get a 6 TSR at 12 mph wind speed (~5.5 m/sec for the metric folks).  Using that "rule of thumb" produces a cut-in speed of slightly over 6 mph and excellent low and midrange performance up to about 18 mph wind speed.  And it makes the rotor turn slow enough so that in high winds the TSR drops to 4 or below so it doesn't attempt to push large amounts of amps into my batteries.

Like you, I see the excessive power generated in high winds to be not that useful for battery charging systems.  The ideal, for my 12 volt system, seems to be in the range of at least 10 but no more than 30 amps from each turbine, which is only about 450 watts peak.  Any more than that can tend to drive the system voltage higher than it should be, even though the batteries aren't fully charged, and dump it.  Batteries charge better at long, slow, steady, low rates of charge, like around 2 amps per battery.

So that's what I have done, long term, too - go on a quest to make more kWh in the more normal wind speed range instead of making more peak watts in high winds.  I've made some really good progress with that compared to some of my older turbines that would push hellacious power when the wind blew hard, then five minutes later go up in smoke.
--
Chris

[DanB]

Hi Chris -
I guess I shall have to try some of the powermax blades again, it has been a few years.  The ones I got from Jeff were quite different than the ones I got from allen though... and I should say they look a lot better and completely different, and I prefer the quality of the finish, but they still fall well short of the quality of other fiberglass blades I've seen.  Like many things though,  I can imagine that they have improved over the years.  Mine definitely do not have steel inserts, which seems a good improvement.  On all of those blades I worry about the small area at the root where they are attached - it's probably plenty good enough but to me it seems small.

I'll have to order a set/see how they do - we have plenty of machines around that we could try them out on ~ it would be interesting.

[ChrisOlson]

I guess I shall have to try some of the powermax blades again, it has been a few years.

I'm building a new turbine that I hope to have done sometime before the end of the year and I'm going to try a set of the wooden GO222 blades on that machine, from Royal Wind & Solar.  Those blades are also a very torquey type of profile and should work well with the generator I'm building for it.

This is a couple photos of my latest 10 footer I built - the one with dual stators in it:

[DanB]

DaveB will suely getin here with a comment....
I am not sure if blades from Royal Fab come in different widths or not.  I got a 12' diameter set from them and, while I hated to do it, cut them down to a bit ove 10' to try out.  The ones I had though were quite wide for a 10 or a 12' machine ~ compared to what I normallly do, which.. lends itself to gobs of torque and lower rpm.  That said, they did work pretty well on the 10' machine, but as I mentioned before - the thing burned out when it was shorted out (Stopped).  I believe though, the machine only had 1 phase shorted at the time so perhaps it would have been fine if the stop switch was setup properly.

Main question though for Dave - are these blades available in different widths to better accomodate different diameter machines?

[ChrisOlson]

I am not sure if blades from Royal Fab come in different widths or not.  I got a 12' diameter set from them and, while I hated to do it, cut them down to a bit ove 10' to try out.  The ones I had though were quite wide for a 10 or a 12' machine

Well, that's what I want - really wide blades for maximum torque at low rpm.  I'm building the generator specifically for that and mine is also going to be a 12 foot machine.  The PowerMax blades are pretty wide at the root - I think about 10" for the 10 foot rotor, but they taper down to only about 3" wide at the tips.  The Royal blades are wider at the tips, and I'm hoping will deliver even better torque in that 6 TSR area than what I get with the PowerMax ones.
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Chris

[scoraigwind]

Well, that's what I want - really wide blades for maximum torque at low rpm.  I'm building the generator specifically for that

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Chris

Mostly people prefer to build generators at higher rpm.  They are lighter, cheaper and more efficient at higher rpm.

[jarrod9155]

I have a set of 18 foot royal wind blades  I am very happy . Now mine are grid tied so hard to compare to what alot of people are doing with battery bank but compared to my powermax blades  big diffrent no comparison and the craftsmanship A plus . I clear coated mine with car paint and they almost look to good to leave out side .

[opo]

very interesting discusion. so, for us mortals, what would low rpm mean? What would high rpm mean?

I'm assuming you guys are talking about a fixed diameter blades, 12' in this case. I suppose a cut in of 80-100 rpm is not too high or not too low for a 12 footer.

Cheers,

octavio

[ChrisOlson]

I'm assuming you guys are talking about a fixed diameter blades, 12' in this case. I suppose a cut in of 80-100 rpm is not too high or not too low for a 12 footer.

With the blades I use it would be about 115 rpm and they'd start making power at about 6 mph wind speed.  I think the blades DanB uses would require higher rpm for cut-in.
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Chris

[ChrisOlson]

Mostly people prefer to build generators at higher rpm.  They are lighter, cheaper and more efficient at higher rpm.

Which is a good argument for a geared generator, which is what I'm experimenting with on my new 12 footer.

Back when I was a kid we had an old Aeromotor windmill on the farm, and the well head had long been pulled but the lift rod was still in the mill and it would clank back and forth in the steel loops inside the tower.  That was a 8 foot diameter windmill.  My brother and I used to climb inside the tower, grab on the lift rod, and both of us ride up and down on it.  It was great fun.

Another instance - there's a fellow not too far from here that has an old 8 foot Aeromotor windmill and he rigged up a bunch of roller chains and jackshafts and he drives a 200 amp Leece-Neville truck alternator with it.  I have seen that thing put out 100 amps continuous at 14.5 volts in a good stiff wind and it makes 60-70 amps without even breathing hard.  With just a 8 foot rotor on an old 40 foot windmill tower turning at not more than about 200 rpm.

Another illustration on torque vs speed - you can take a Freightliner powered by an N14 Cummins that makes 525 horsepower and 1,970 lb-ft of torque @ 1,200 rpm, and climb a hill with that truck with the rig grossing 80,000 lbs with no problem.  Now, pull the Cummins out and replace it with a 600 hp small block Chevy dirt track engine, change the gearing so the engine can run at 7,000 rpm, and try to climb that same hill with it.  The small block will run out of steam less than 1/4 of the way up the hill.

The SAE HP formula is HP = torque x rpm / 5252.  It's easy to get horsepower by increasing rpm.  But it's raw torque that gets the work done.  Whether it's an engine powering a truck, or a turbine rotor powering a generator, torque is what gets the work done, not speed.

There's an old adage in the power generation business - "HP is how fast you hit the wall.  Torque is how far you take the wall with you."
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Chris

[97fishmt]

Hi Chris,
        
          I agree with a lot of the things you present to us, (or not) from your experience and the real world application.
I have been approaching it as having a motor with a particular winding and carving a prop to its power
curve.  More torque is always put into the equation.  I have had success with more chord at the root and
tapering it down at the tip with twist to gain the best of both worlds.  

I can tell my current  set of blades is a big improvement over the previous set.  I haven't tried to get into
the motors to find the splice points to be able to bring out more wires yet, or if I will.  Some are wired "y"
and some are delta.  That would be fun to play with though.  I have tried resistance in the line and that doesn't
seem to do a lot for me.  Trying higher voltage seems like the way to go for more wattage for the cottage.

         Mike

[scoraigwind]

Mostly people prefer to build generators at higher rpm.  They are lighter, cheaper and more efficient at higher rpm.

Which is a good argument for a geared generator, which is what I'm experimenting with on my new 12 footer.

The SAE HP formula is HP = torque x rpm / 5252. It's easy to get horsepower by increasing rpm.  But it's raw torque that gets the work done. 

Actually it's quite clear from the formula that you have just given, that power is the product of both torque and speed.  The higher the speed, the lower the required torque.  This means a lighter and more efficient alternator.  You can achieve this with gearing but for all sorts of reasons this is not desirable, and you will now see direct drive alternators on even the larges wind turbines.

There is no evidence that high tip speed ratio blades will fail to get the job done or 'quit' any sooner than an old style wind pump, so long as you don't run the rpm up too high and wear them out.  It's common sense wind turbine design to use a high tip speed ratio and avoid gearing and improve the alternator efficiency.  For best energy production into batteries you want large diameter blades, and you don't need high peak power output you just need to maximise the rpm in low winds.  This can be done using a low friction axial flux alternator and blades that have a very small angle on them.

[ChrisOlson]

Actually it's quite clear from the formula that you have just given, that power is the product of both torque and speed.  The higher the speed, the lower the required torque.  This means a lighter and more efficient alternator.

Yes, it's torque that turns shafts.  With minimal torque and simply using speed to generate horsepower (kW) any changes in load cause or require a substantial change in speed.  When you go the other way and use an engine (blades) with substantial torque, changes in load don't require as much change in speed and it's easier to match the load to the available power.  Go back to my truck illustration and study what happens there.  You need to keep that engine (rotor) running always in its peak power band if you want maximum work done.  Where the small block has an rpm range from idle to 7,000 rpm, only a very narrow band of that range on the upper end near 7,000 rpm generates the most efficient power because it has no torque - anything below 6,000 rpm is unusable.  The Cummins N14 generates massive torque, only requires an operating rpm range from idle to 1,900 rpm, and the torque curve is almost flat from 1,200 to 1,900.  The same applies to wind turbine blades.

You can achieve this with gearing but for all sorts of reasons this is not desirable, and you will now see direct drive alternators on even the larges wind turbines.

You'd have to convince one of the must successful small wind turbine companies on earth - Jacobs - that a geared generator is not desirable.  Compare the power curve of a Jacobs 23-12.5 to a Bergey Excel, both with 23 foot rotors, both using variable pitch, with the Jake using a mechanical governor and the Bergey using PowerFlex blades, and you'll see that the Jacobs with a geared Winco generator is more efficient at all points in the power curve even though they both peak at about the same output.

The bottom line is that if the efficiency gains in using a geared high speed generator combined with a rotor that turns slower and generates more torque outweigh the losses in the gearing, you end up with an overall more efficient turbine.  I've been working on a gearbox for almost a year for a 12 foot turbine and am starting construction of the turbine in the next couple weeks.  It uses the basic concept used in the Jacobs except the generator rotates in a parallel plane with the rotor.  Like I said, it's an experiment simply because I like to experiment with things to make them better instead of accepting the status quo as being "the only way to do it".
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Chris