21 Foot Turbine

[ChrisOlson]

I've been kicking around some different generator designs and have pretty much settled on a 24" diameter, 20 pole 15 coil wound with around 45 turns of AWG 14 three-in-hand.  I'll have to wind a test coil, but I'm pretty sure I got room in a 24 incher for that wire size.

Rather than attempt building blades for it I'm going to buy a set of cheap WindMax blades and drive it with those.

What types of magnets have others been using in larger turbines?  I've thought about using 2 x 1 x .75 bar magnets arranged in a "tee", or using 3 x 1.5 x .75 bars.  Using the single bars gives me more magnet surface area but there may be some advantages to using the "tee" layout due to the shape and concentration of the flux lines.

What have others had success with?

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Chris

[DanB]

I have a feeling you'll do better with the larger 3" x 1.5" blocks.  On such a big machine, you'll want a fairly large air gap I think, and the surface area plus the added thickness will help.

[ChrisOlson]

Yes, I know you've used those big blocks in your 17 and 20 and they seemed to work out pretty good.  I don't know about the performance of those WindMax blades either.  I know people who have bought the smaller ones and they say they seem to run OK - about a 6 TSR in moderate wind.  They claim they should reach 200 rpm in the sales propaganda.  I figured I'll set the airgap between the magnet surfaces at around an inch initially, and if the blades won't drive it I'll open it up a bit.  If the blades tend to want to overspeed I'll close it down.

I guess that was one of my worries about using the smaller bars in a "tee" - if I have to run the air gap really tight with the smaller magnets things might get too close for comfort.

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Chris

[DanB]

I would doubt the sale propaganda on those blades.  cP of .49 is surely pulled out of the air.  I've had a lot of reports of problems.  Of course... folks have problems with hand carved blades as well but at least you know who's to blame if you carve your own.  20' blades from windmax weigh a good bit more than what we've carved.  On smaller versions Ive heard of them delaminating... water getting into them and screwing up the balance and other issues.  I should say give it a shot and let us know how it goes.  I'm not optimistic though.

[fabricator]

What about that outfit that carves wood blades to order, any length and several types of wood, I just can't remember the name any more, I do remember they make some nice looking blades and relatively reasonably priced.

[TomW]

Royal Fabrication makes wooden blades.

Dave B from this forum knows the guy who does it.

Sorry, I do not have contact info on them.

Tom

[Dave B]

Fabricator,

  Here is the current link to the custom wooden blades. http://www.royalfabrication.com/custom.htm  I can attest to the quality and performance of these machine carved blades. I have run 18' and currently 16' sets and I am very impressed. They do create a lot of torque and this particular profile (Gottingen 222) has been flying on Wincharger and similar machines since the 30's I believe. Bergey has been flying a similar profile for many years as well.

 Contact Dave Moller @ 716-483-6123. Between 12:00 and 1:00 pm Eastern time is a good time to call otherwise leave him a message. There is also a link on his site for e-mail. I know he would be glad to talk with you.  Dave B.

 

[Dave B]

Whoops,

  I guess this blade link  http://www.royalfabrication.com/custom.htm  should have been directed to Chris. Thank you Fabricator from Dave M. for refferencing his blades.  Dave B.

[Dave B]

Thanks Tom from Dave M. also.  Dave B

[ChrisOlson]

Thanks for that!  Those blades look WAY more inviting than the WindMax blades.  It says he makes them 4' to 9' but perhaps he'd consider making me a set of 10.5's.

For my smaller turbines I milled out aluminum molds and made my own carbon fiber composite blades.  This is a photo of a 2/3's finished set of 43's:

http://picasaweb.google.com/christopher.w.olson/76FtWindTurbine#5430081442335594802

But when it comes to 10.5' blades it was like, balls, an aluminum billet to make the mold would cost more than the whole turbine.

If it's made from steel, aluminum or any other type of metal I can do anything.  When it comes to woodworking I can't even cut the end of a 2 x 6 square with a SkilSaw.

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Chris

[ChrisOlson]

I found an old ring gear off a Cummins ISX flywheel in the scrap bin today and suddenly got an idea.  I've been toying with the idea of using a servo motor yaw drive on this turbine.  I'll use a tail to steer it, but the tail would be short and only operate a microswitch to activate the servo motor.  That ring gear looks like it might work pretty good with the appropriate pinion gear to drive it and make the turbine rotate on its yaw axis.

I'm going to set up the tail so the wind has to change direction by 15° either way before the tail will activate the servo motor so the motor doesn't run all the time if the tail buffets back and forth a little.

For furling control, and I got this idea in my head right now but not on paper yet, I'm thinking I'm going to use a side vane on an arm working against spring pressure to "sense" wind speed.  When the wind pressure gets strong enough on the side vane to close the furling switch it will bypass tail control, steer it out of the wind, and simultaneously apply the brake to stop it.  At that point I'm not interested in how much power it will make in high winds - I just want to save my stator and blades.

I'm going to use a simple mechanical disc brake on this turbine with a linear electric actuator.  I've been toying with my eddy brake on my 7.6 footer and it just doesn't work well enough for anything bigger.  And I'm not sure at this point if it will even stall the 7.6 in a 30 mph wind.

This control system is nothing really exotic - if you look at combines, round balers and big square balers they've been using these types of switches and controls for years with almost 100° reliability in dust, dirt, grease and vibration.  Those microswitches and servo motors that operate things like the twine arm on a John Deere round baler never fail - if they quit working it's usually a broken wire someplace, or a chain derailed and tore the wires off.

And that's what I'm going to use for the brake actuator - a twine arm motor and gearbox off a John Deere round baler.  It has a worm gear and screw drive in it so it has a shaft that extends and retracts like a hydraulic cylinder.  And it is VERY powerful - put a 2 x 6 on the end of the shaft and brace it, turn the motor on and it will slowly punch that shaft right thru the 2 x 6 and it doesn't hardly make the motor grunt.

The motor I'm going to drive the yaw pinion with is a concave adjusting motor from a CaseIH 2388 combine.  They turn very slowly, have enough torque to bend a 3/4" wrench (with your hand underneath it - don't ask me how I know), weighs less than a pound, and I've run them in temperatures from -20 to heat so intense it'll melt plastic and they "just work".  I've never seen one fail.

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Chris

[Dave B]

Chris,

  I know Dave Moller with Royal Fabrication has just carved a 20' 3 blade set of Ash blades for his latest turbine and they are beautiful.

  I am not ceratin of his current length limits for carving but I know he would be more than willing to discuss details with you.

  To be honest with you my previous 18' 3 blade set of these blades over powered my axial alternator. Dave wanted to set up his machine to carve for counter clockwise rotation also so we decided my current set would be 16' and turn counter clockwise. The swept area now is a great match to the alternator and it is a very strong performer currently being used as a 24 vdc battery charging system.

  Give Dave a call or E-mail, he would like to help you I am sure.  Dave B.  

   

[ChrisOlson]

Thank you very much for the info, Dave.

I called Dave Moller a few minutes ago and left a message on his machine.  When he calls me back we'll discuss specifics - perhaps my 21 footer might turn into a 20.  The only reason I picked 21' is because that's what the WindMax blades are.  But when I get a chance to discuss this with Dave (Moller) we'll figure out the specifics of the generator, cut-in, top end, etc. and I'll go from there.

I've decided I'm definitely going to use Dave Moller's blades because they're proven.  On a machine this size I don't want to take the chance of a cheap Chinese blade delaminating and tearing the tower down if (when) it fails.

Thanks again,

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Chris

[Wags]

This forum is Fantastic, what a group of knowledgable people so willing to help! I have been reading most all the wind stuff for about 6 months, and hope to turn what I have learned here into a turbine sometime soon. This is my first time posting anything, so I hope I don't mess anything up.

Chris,  Good luck with this project, it sounds like a lot of fun, and a considerable challenge. My plan is for a similar sized machine, but a grid tied induction generator, and I have a few questions about your yaw and brake concepts if you don't mind. First, how much torque would be required to yaw a turbine this size? I guess that would depend on the yaw rate, and it sounds like you plane to yaw out of high winds, so what kind of yaw rate would be required? In high winds do you plan to yaw first and  brake only if required, or just brake and yaw together and shut it down? Will your mechanical brake be fail safe, if so could you suggest how you plan to design this? My concern is a failed actuator or broken wire could disable both your yaw and brake devices.

Thank you for your time and good luck with your project.

Jeff

[ChrisOlson]

First, how much torque would be required to yaw a turbine this size?

I don't know that yet, Jeff. I have to talk to Dave Moller first and find out how many rpm his blades run (safely) at the top end, and how much they weigh.  Once I know that I can figure the amount of force generate by precession of the blade circle to figure the turning torque.  This turbine's thrust will be inline with the yaw shaft, i.e. it will not use an offset mainshaft.  As is usual in most designs, I'll add 50% to the calculated minimum torque value and design my yaw drive to have at least that amount of torque.

so what kind of yaw rate would be required?

That I do have figured out, using the motor and pinion/ring gear I plan to use.  It will yaw the turbine at 710°/minute.  So it will take it 7.6 seconds to yaw it 90°

In high winds do you plan to yaw first and  brake only if required, or just brake and yaw together and shut it down

For simplicity (at least at first until I get a chance to do some testing) I'm going to have the furling switch bypass the tail switch to turn it 90° and simultaneously activate the brake motor to apply the brake and stop it.

My concern is a failed actuator or broken wire could disable both your yaw and brake devices.

That could always happen.  It's unlikely that the yaw motor and brake motor would simultaneously fail.  So I figure that the brake will be powerful enough to stop it even faced into the wind if the yaw motor failed.  If the brake motor failed but it still turned 90° it will stall it anyway without the brake with the stator shorted.  If the furling switch fails I'll have provisions to control it from the ground in my control box that bypasses both the steer and furling switches on the turbine head.

If the control wires get tore off somehow, the stator is gone so that can't be used to brake it, and nothing works, retreat to a safe distance and just hope the blades and magnet rotors hold.  At that point you're at the same place where you'd have a conventional furling tail that failed to work, you got no brake, the stator dropped a coil and the wind is still howling at 50+.  All you can do is retreat and watch from a safe distance, and if you see it starting to come apart, take cover.

When I sat down this morning and started drawing out an electric yaw drive on paper, it's not really all that complicated.  It's just a matter of building it.  Nor am I going to waste time building a brake - I found an old disc brake from a transmission from an International 1640 combine laying in my shed.  The nice thing about the brake is that it uses linear actuation - just pull a 1/2" rod that's sticking out of the brake housing and it applies it.  Push the rod in and it turns 100% free with no drag.  That brake will stop both drive tires on a 45,000 lb combine going 12 mph and make them skid on blacktop.  It'll easily stop a 21' turbine.  It weighs about 35 lbs though.

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Chris

[fabricator]

This sounds like a dream machine to me Chris, my dream machine would be no tail at all, just like the big utility size boys, is your plan something like they handle yaw?

[ChrisOlson]

The design I got in my head is sort of like the utility-scale machines except that they use a little vane on the back of the nacelle to sense wind direction.  I've thought about that, and maybe it will change when I start the build this weekend, but I'm thinking that a short 3 foot or so tail would be better because it would more accurately sense the wind direction and not start and stop the yaw motor all the time just because the tail buffets a little.  Those big machines have a bunch of electronic controls in them to prevent that sort of thing, where mine is going to be all mechanical control.

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Chris

[ChrisOlson]

For Dave B:

I talked to Dave M on the phone a bit ago and he said you may be able to give me some insight as to what's required to furl a set of his blades.  He indicated that even steered out of the wind they'll continue to turn and make power, but just with the tips running at wind speed and not operating at design TSR.  On a 20 or 21 foot machine that can be quite a bit of power in a 25-30 mph wind.

He thought you may perhaps have some experience you could share on what's required to actually bring it to a stop when I want to shut it down in high wind (over 22 mph sustained).

Thanks,

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Chris

[Dave B]

Chris,

  It might be easier to e-mail me here at :  bruggelog at netsync dot net  so we can discuss the details further.  Thank you,  Dave B.

[RogerS]

I've looked at a number of brakes and I have a question. How may rpm is the disc turning when then combine is running at 12MPM?  A lot of older tractors used a pretty small area of brake pad, but the brake drum or disc was geared to a lot higher rpm than the wheel they were to stop, giving them lots of power.  I would think a 20ft machine running at peak output may put out 500 to 600 ft/lbs of torque on the main shaft (just an estimate from looking at induction grid tied machines.  I may be way off, but someone may be able to correct me).

I like you yaw idea a lot.  I can see that there are more simple ways to do it than I have considered.  Love the ideas batted round on this forum.    

RogerS

[ChrisOlson]

It runs on the bull pinion shaft of the transmission and the reduction gear is 9.6:1.  I'm estimating it should be good for 2,000+ lb-ft of torque.  I know you can stall a DT466 with one of these brakes, and the DT466 pulled down to 1,800 rpm makes about 760 lb-ft at the flywheel before it goes thru any reduction gears.

30.5 x 32's are turning at 60 rpm at 12 mph, so with 9.6:1 reduction between the bull pinion and the final drive, the brake is spinning at 576 rpm at that speed, which means there's a 3.8:1 reduction between the engine flywheel and the bull pinion.

The amount of horsepower you have at the bull pinion is lower than at the flywheel because of losses in the gear train, but the torque is much higher.  At 2,200 rpm the DT466 is making 260 hp, or 620 lb-ft of torque.  Assuming 92% efficiency in the gear train to the bull pinion, you got somewhere around 240 hp @ 576 rpm at the bull pinion, or roughly 2,190 lb-ft of torque where that brake is mounted.  Stand on the pedal and it'll lock up both drive tires and stall the engine at the speed we're talking about.

It's a powerful brake.  But it's not very light (about 35 lbs).

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Chris