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Coil turns for a 20/15 Big alternator?
By CmeBREW, Section Wind Posted on Sun May 13th, 2007 at 02:46:48 PM MST
Coil turns for a 20/15 Big alternator?

Greetings Re-enthusiests,
I am helping a friend (new to RE-) to make a fairly large 12 foot blade rotor 20 pole(40mags)15 coil dual rotor 3-phase alternator mainly for suplemental 120v heating.(air and/or water/primarily in Winter) Was hoping for about around 1200watts max. and controlling (furling out past 0 degrees) the blades somewhere around 25mph winds. I want to keep it SAFE and not push the envolope. The mags I'm thinking of getting are the standard 1"x2"x1/2"thick N42. I think 48volt would be best in case he wants to add battery bank later. He has the heavy duty hub and I am thinking 16" diam.x 3/8" thick rotors.(may need to be alittle bigger diam.) I haven't made the layout board yet but will soon. He works at a metal shop and is very mechanical like myself. However, this is somewhat over my head concerning the coils. My inexperienced, wild guess is something like: 5/8" thick stator. 15 coils, 2 in hand #14 ga. as many turns as will fit into the space??? Star connection. I haven't bought the wire yet, but I would rather not do more than 2 in hand winding. (I'm not among the best winders--and more than 2 in hand looks scarey to me.)
We are both working together on Variable pitch control hub designs for this (and my 8 foot) 12 foot alternator. It will have a mechanical emmergency brake on it also. We're both just private experimenters. He is not off-grid yet, but plans to be in a couple years. He has a great site in country and the alternator will have a VERY strong tower.(only 25 feet high for now--in a big open yard. Easier for testing)
... Or do you think we should switch to the 2" round diam mags or the 2" square mags? I quess the 2" square mags would make a similar powered alternator with a 16 pole 12 coil set-up. I guess it's about the same.
Can anyone help me to get to this 48 volt cut-in? (What GA. and turns)
Any help would be greatly appreciated!! -Thanks

Coil turns for a 20/15 Big alternator? | 19 comments (19 topical, 0 editorial)

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#1)
by Nando (nando37-at-tx-dot-rr-dot-com Correct theanti-spam) on Sun May 13th, 2007 at 09:04:45 AM MST
(User Info)

If the wind mill is going to be used for heating, 48 volts is NOT a good decision.

You need to determine the average wind and design for it for high voltage generator, like 230 volts at the peak average power.

Also, for good harvesting the you will need a controller with MPPT capabilities and if you are planning a pitch controlled hub then you will know the peak power behavior of the mill itself.

If you are interested, I can suggest benefits for a pitch controlled hub if you supply the information about it, which you can do privately if you need to keep the hub design protected. (correct my address for anti-spam errors).

Nando

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#2)
by Flux on Sun May 13th, 2007 at 09:34:11 AM MST
(User Info)

You seem to be trying to use your variable pitch hub to work in pitch to stall mode.

I don't like this method, it leaves you with a large thrust loading that will have to be supported by the tower and you will have blades being forced back towards the tower, most machines that have succeeded with this method are down wind machines.

You will do far better to pitch towards feather ( take your blades to large positive angle rather than beyond zero) but you will need to work through a far greater blade angle.

You will have to settle the details of the alternator before anyone can help you much.

You will need to settle the minimum power you consider worth extracting ( cut in speed) and the voltage at full operating speed. The same design will not be a good compromise for direct heating and battery charging ( if you want to combine both there are ways but you need to decide which has priority).

Nando is right that you will need some form of controller if you want to extract the most heat from the system. If you can make the pitch control work you will not have many of the limitations that others have and you can still keep it safe with a single resistor load but power extraction will be poor unless you forgo the low wind speed performance ( not much heat anyway)

You will not get a lot of heat from a 12ft machine except in very high winds, probably not worth the effort below 16 mph.

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#3)
by CmeBREW (smke833f@hotmail.com) on Sun May 13th, 2007 at 12:46:00 PM MST
(User Info)

Thanks,
Sorry,Yes, both of these machines are down-wind type. I know I Can't have the best of both worlds, so I think It must be a 48 volt machine more for batt bank charging than heating. You are both way over my knowledge, so I apologize for that. Computer control is a complex matter for me at this time. I use to do computers, programmable controlers, etc. when I was a kid, but I am a bit rusty and just now getting back into such things after a couple of decades. Later this year I will know more. I am going to do various experimental controller switching circuits for heating purposes later with my own 8 footer. Solid state relays and simple logic gate circuits,etc. (and the smaller the amps to control, the better,of course)
My friend has access to all the best equipment, computer lathes, cnc, etc,etc. He works at a place that makes big automation equiptment systems for factories. VERY impressive stuff. I've seen this guy's work and he is extremely mechanical and is very interested now in windmills and helping me experiment with making a very good pitch control hub.
Flux, the following is what I'm thinking about trying first. Is the second example what you basically mean by "pitch toward feather"?

So you are saying that the load on the tower will be very great when the blades go to the vertical zero degree point in the higher winds. So when it gets to this point, would it be very advantagous to have the mechanism furl the blades back further to say -15 degrees?. Or would that cause a severe shock and be too much for the tower and the alternator? I know that total shut down is wise for storms and very high winds. We are also going to try and have the blades automatically furl with centrifagal force in case of a free spin.(no load)
The other question then is the Ga. wire and # of turns. If you don't wish to answer on the pitch control , since its such a complex matter, can you please help with the wire ga. question. Will two in hand #14 ,STAR, get me close to the 48 vdc (after recifiers) cut-in at about 150 rpm? (the 12 foot rotor)
So to sum up: this is for 48vdc batt.charging with some extra suplemental dump water heating during the winter months.

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#5)
by wdyasq on Sun May 13th, 2007 at 08:48:12 PM MST
(User Info)

Perhaps the best pitch control mechanism has been the Jacobs style. It feathers forward as described. One would be well advised to look at the mechanism Marcellus Jacobs designed, built and was abandoned by Robert Byrd at the South Pole. It was still working properly many years later when the next party came along.

It will be difficult to guess what you need for wire unless rpm, air-gap and magnet size and type are defined. I see you have guessed at what you may end up with. Use quantities from 'Otherpower's' builds and you will be as close as can be guessed.

Good luck on the VP design. I shall be following.

Ron
Adventure is just bad planning." -- Roald Amundsen
[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#4)
by CmeBREW (smke833f@hotmail.com) on Sun May 13th, 2007 at 04:51:36 PM MST
(User Info)

Thanks Nando,
I think I see what you're saying now. Higher voltage is more efficient for heating. Sorta like driving down the freeway in 5th gear(over-drive) instead of just 3rd gear. It sure would be nice to 'change gears' from third to over-drive in order to have the best of both worlds. So I guess it would be best to have two different windmills. One for batt charging and one (or more) for heating at high voltage. Like to ask you a couple of questions in a month or so. -Thanks

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#6)
by RP (russp located-at fidnet (dot) com) on Mon May 14th, 2007 at 12:12:03 AM MST
(User Info)

SInce you're planning for 15 coils (5 in series per phase), one option would be to run all the coil ends out of the stator for external wiring.

You could then wind each coil for 48volts and run them in series for heating (5 coils at 48v = 240volts) and then later when you want to charge batteries, wire them in parallel for 48 volts at 5 times the current. To eliminate circulating currents betweent he parallel coils you'd need individual rectifiers but each coil will only have 1/5 the line current for each phase so other than a lot of tedious rectifier hookup it should be fine.

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#7)
by Flux on Mon May 14th, 2007 at 12:33:34 AM MST
(User Info)

If you use the 20 pole 2 x 1 x 1/2 magnet set up then it looks as though you will need about 50 turns. I think you will be hard pushed to get 2 in hand #14 in there but you may manage it with a stator 15mm thick.

With luck it will stall so you can add a series resistor in the battery dc lead ( pos) to keep it out of stall and match the prop better in the higher winds. This resistor can be part of your heating circuit but will be an awkwardly low value.

The rest of the heating can come from a dump load when the batteries are fully charged.

Your pitch control hub will take care of speed so you can use a higher value of series resistor than would normally be safe so you should be able to extract more heat. Just set your speed limit to what you think the blades can stand ( or to the maximum speed you can stand the noise).

Yes your second diagram is pitch to feather and is the one that I would use. With a battery charging scheme with an air gap alternator there is no start up problem and no need to start in coarse pitch. Start and work at low winds in normal pitch ( 3 to 5 deg) when you reach speed limit the mechanism will need to be able to go up to about 45deg to hold the speed under all conditions.

This was the method used by Jacobs, Elektro, Dunlite etc .

If you must use the stall method then your working range would be from normal pitch to probably about -5 deg. The stall region is very unstable and probably noisy.

If you needed the coarse pitch for starting then this method may have some attraction but even then it would need a tricky mechanism to start in coarse pitch, move to and stay in normal pitch for low winds and then move to stall in high winds. More suited to active control with a servo motor ( but even then I would go towards feather).

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#8)
by rpcancun (hobbyshopmx@hotmail.com) on Mon May 14th, 2007 at 03:41:58 AM MST
(User Info)

"Yes your second diagram is pitch to feather and is the one that I would use. With a battery charging scheme with an air gap alternator there is no start up problem and no need to start in coarse pitch. Start and work at low winds in normal pitch ( 3 to 5 deg) when you reach speed limit the mechanism will need to be able to go up to about 45deg to hold the speed under all conditions."

Flux, I'm kinda confused on this one,....wouldn't be better to start at like 20, 30 degrees + then go towards feather as it speeds up?

Thx

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#9)
by Flux on Mon May 14th, 2007 at 04:29:25 AM MST
(User Info)

If you start at 20 to 30 deg then your pitch is too coarse for normal running. It would take a very clever mechanism to start at say 30 deg, come down to 5 deg for normal running and then go back into coarse pitch to limit speed with a final setting of over 45 deg.

Are you confusing feather with the propeller case of zero pitch?

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#10)
by rpcancun (hobbyshopmx@hotmail.com) on Mon May 14th, 2007 at 01:10:11 PM MST
(User Info)

"If you start at 20 to 30 deg then your pitch is too coarse for normal running. It would take a very clever mechanism to start at say 30 deg, come down to 5 deg for normal running and then go back into coarse pitch to limit speed with a final setting of over 45 deg.

Are you confusing feather with the propeller case of zero pitch?

Flux"

maybe I am,....lets say 0 degrees is leading edge facing directly into wind,
if you go negative from there,..you may turn machine backwards, at 0 no wind is pushing on bottom of wing therefore i beleive it wont have much speed or power, as the leading edge rises (and trailing edge lowers) more power and speed,...what i would like to try is start at the 20, 30+ degree for most torque for start up, then as it goes faster the leading edge would start to dip down towards 0 degrees until the desired speed.

Thx

Rob

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#11)
by Flux on Mon May 14th, 2007 at 03:28:30 PM MST
(User Info)

I think we are assuming different things for 0 deg. If you assume 0 deg to be leading edge facing the wind, then that would be what I considered to be 90 deg. I assumed 0 deg was no pitch and that would be with the leading edge pointing into the plane of rotation. Full feather would be 90 deg ( your 0 deg) but a speed based mechanism could never achieve that. ( would need a servo controlled mechanism.)

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#12)
by Flux on Mon May 14th, 2007 at 03:43:20 PM MST
(User Info)

I think the confusion comes from the difference between pitch angle and angle of attack.
The aerofoil characteristics depend on angle of attack. The angle of attack is the angle between the pitch angle and the apparent wind.

Apparent wind is a vector related to the wind speed and blade tip speed. The faster the blades rotate the nearer the apparent wind comes towards the leading edge.

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#14)
by Nando (nando37-at-tx-dot-rr-dot-com Correct theanti-spam) on Mon May 14th, 2007 at 09:22:44 PM MST
(User Info)

You can do that, which can be done with high voltage wind mills.

The controller should have MPPT for heating and in addition an ELC circuit for ultimate protection.

In parallel, one can have a high voltage converter to bring the voltage down to desired range, also with MPPT capabilities.

It is not difficult is just to add the proper piece of equipment.

Nando

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#13)
by CmeBREW (smke833f@hotmail.com) on Mon May 14th, 2007 at 09:00:34 PM MST
(User Info)

Thanks guys,
Flux has changed my mind to pitch forward (feather) instead of back. Thanks. I also was very concerned about the first method (back pitch) in high winds since it would be spinning VERY fast with the blades totally vertical (about 0 degrees), and a 60 or 70mph wind hits it--and it would be like the giant sail on a ship. It could bring the whole thing down. I did not know I could do start-ups at such an efficient angle as only 3 to 5 degrees. That was the only real reason I was looking at the other method was to easily proceed to an efficient angle. So that simplifies some things now. It seems the winds are getting more and more violent each year--so yes I will pitch toward feather. I can see now it is far more smooth, controlled and MUCH SAFER. I may switch to an upwind generator design, then, which is more responsive to turning into the low wind directions than a downwind design.
I think I'm going to try to get it to go alittle more than 45 degrees forward though --if it will. Perhaps 50 degrees. I like the idea of compressing the main spring more anyway. I can have bigger cams this way too. There is only one thing I am concerned about though. How to KEEP the blades in the efficient angle during moderate winds (15-25mph) without turning forward into an inefficient angle, which would degrees power potential. This was the only reason I disliked pitching forward. However, I'm sure we can design the mechanism to prevent this. I would like to HOLD (somehow) the blades at say 5 degrees until a higher wind hits it and only THEN it starts toward forward pitch. That would be nice to accomplish. Also the auto furl with centifugal force in case of no load freespin. So theres really two different things I'd like to accomplish here. This should keep us busy all summer. It is very interesting and challenging I must say!
As for the coils. Thanks for giving me some numbers on my limited info. I think, it might be alittle better then if I went with #15 GA. wire, 2 in hand, 50 turns or so --- So that I could get closer to 1/2" thick stator. I would like to have almost a 1/8" gap between mags and the stator surface - for a very good saftey margin. I will do a test coil and get back to you at that time and ask for more help.
I will search for a diagram of the Jacobs pitch hub.
-Thanks guys for helping me go in the right direction!! Have a great summer friends!

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#15)
by Flux on Tue May 15th, 2007 at 01:24:39 AM MST
(User Info)

Holding the blade angle at the normal operating point until you need speed regulation is inherent. The normal angle is determined by a stop and the control spring will be pre loaded against it. No movement will take place until the cf from your control weights overcomes the pre load. Beyond this point the blades will pitch forward to attempt to maintain constant speed.

Without this pre load you will have big trouble obtaining enough control force to overcome the various frictions in the blade pivots anyway. Just think of the thing as an engine speed governor, where the weights never move until you reach operating speed.

Regarding the alternator, If you must have 1/8" clearance each side of the stator then you will be reducing your maximum output capability a fair bit. I am not even sure you can get 2 in hand #15 into a 1/2" thick stator. Try a test coil and see what you can manage.

You were only hoping for a modest output so you should manage what you want from those magnets. By keeping the alternator efficiency high and adding series resistance to dissipate the heat outside the windings and with a precise control of top end output I was thinking that you may get well over 2kW in total heat and perhaps 1.5kW into the battery. If you can settle for less then you can use the larger clearances and work with thinner wire.

The very top end power will not happen very often with a 12ft rotor unless you are in a very windy area so you may loose very little on the average days.

I have not found large clearances necessary, but I don't follow the usual construction with the gyroscopic forces acting through a load of allthread. I mount my props directly on a flange of the bearing hub so it may be a lot more rigid.

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#16)
by CmeBREW (smke833f@hotmail.com) on Tue May 15th, 2007 at 04:25:44 PM MST
(User Info)

Thanks Flux,
I think I understand more now. The main 'control spring' in my head (brain)wasn't strong enough. (The Pre-load) So, nothing under 20mph will move the blades from their most efficient position anyway. (or wherever I set it) -I can see keeping the weight of this hub down will be difficult. I think everything has to be mega-strong (Beefy) to handle great forces like that. The hub may weigh more than the alternator! I got alot to go on now. -Thanks for advice.

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#17)
by Flux on Wed May 16th, 2007 at 01:09:15 AM MST
(User Info)

You are right that the hub will weigh more than the alternator, the concept is simple but it needs good engineering, which I think you can manage.

You need strength to support the bending moment from the blades without fatigue. You need free bearings for the blade spindle pivots to turn freely with the thrust on them and you need a large control force to move them easily against these forces and the torque that may turn the blades if your centre of pressure of the blade is not at the rotational centre. This means a strong spring and heavy control weights.

I think you will need ball or roller bearings for the blade spindles. Jacobs managed to use sleeve bearings on the blade controlled unit, but the combined sliding and twisting motion would help overcome stiction.

I made a small unit that worked for years, I started 2 other larger units but never finished them but I might one day. I don't have the ability that some have of raising several hundred pound lumps into the air. At that time I was using a wound field alternator with gearbox and that alone was way too heavy without a massive hub.

I think that with extreme care you could combine a pitch rotor with the front disc of an axial alternator but it would need careful construction to confine the forces to where it can be managed. That would reduce the weight very considerably.

Flux

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#18)
by CmeBREW (smke833f@hotmail.com) on Wed May 16th, 2007 at 06:25:01 PM MST
(User Info)

Thanks for that further good description. I can see now that I also was not taking this 'stiction' problem from the tremendous thrust pushing back on the blades, serious enough in my design. I must admit, I was thinking of trying the easier route and making my first design WITHOUT the control weights in the hub. I'm not sure what you do, but I was going to put the axis on the blade mounts very high up, even with the leading edge of the blade, hoping that would be plenty of blade surface and thus, leverage, to more easily turn in the blade pivots, and thus overcome the stiction problem. Of course, they are only 5.5' long blades.(+hub=12'total radius) I realize this would require an even stronger main control spring in the center. I just like the idea of keeping the weight down as much as possible on this thing! Of course, control weights, and their mechanism would DOUBLE the weight of the hub. However, I know almost nothing of the countless experiments and mechanisms done over the last 100 years by some great mechanics. Heck, I can barely find any partial diagrams of pitch controlled hubs, anywhere. So I'm sure I will do all (or,most of) the obvious common mistakes. So please bear with me and my lack of knowing.(The complex forces involved) My friend had also suggested we go with tapered roller bearings for blade pivots. Since you mentioned it too, sounds wise, so we will certainly go with that for the 12 footer. The easier they turn, the better,to reduce stiction as you said. He gets all the bearings he wants for free.(and everything else) He can easily do such things since he has access to all that equipment. He is currently making his own precision hub (his own design) with tapered bearings.
I am going to also make it so that I can mount and re-mount the blades on the blade mounts ANYWHERE up or down with the axis line, to find out where is best.
If this simple design fails (which it probably will) then I will try the control weights. I've been reading what you wrote several times. I noticed you mentioned, "...if the centre of pressure of the blade in not at the rotational centre." It just seems to me that the blade may not have to be in the rotational centre to accomplish easier rotation in the blade pivots. I'm probably wrong. We will see! -Thanks for the advanced info. Flux. -I'm just happy I'm going the right (better) direction this time!!

[ Parent ]

Re: Coil turns for a 20/15 Big alternator? (3.00 / 0) (#19)
by CmeBREW (smke833f@hotmail.com) on Thu May 17th, 2007 at 07:58:03 PM MST
(User Info)

OK. I think I see alittle more of the light now. It really HAS to have some centrifugal force help in the turns. I did find this simple design. I am going to incorporate a simple arm that sticks out from each blade with a weight on it. I like the simplicity. Taken from the design of the EOLTEC. http://www.eoltec.com/English/Main_en.htm

This shouldn't add too much extra weight to the hub. I could just use 1/4" plate for the arms, and even put adjustable holes in it for experimenting with the weights (big tractor washers) in different places. I could even make the arm itself adjustable. I don't see any reason this won't work after adjustment testing to the maximum electrical load. I will bring the blade mount axis down also. Probably not the middle of the blade though. I want SOME torque (force from wind)control from the blades also. I will try locating the blade turning axis 3/4 ths the way up on the blade. Of course, that will be adjustable too. I will still go with the 3 cams and a big control spring in the middle. I can't wait to try this. -Thanks guys for all the help!!

[ Parent ]

Coil turns for a 20/15 Big alternator? | 19 comments (19 topical, 0 editorial)

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