Author Topic: GrassHopper Need Help from The Masters  (Read 6386 times)

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zapmk

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GrassHopper Need Help from The Masters
« on: January 07, 2006, 02:40:43 AM »
Hi All,


This is my first time posting in this forum, But I have been reading it for a long time.


Need some advice on a VAWT gen I have been working on.   I have built the frame and a five section rotor, with each section staggered so that it forms kind of a twist from bottom to top, the sections are 48" X 54" so I believe I have 90sq feet of rotor area.


Here are the Questions: How Big of a Dual rotor Alt would you build for it?  

Coils, what wire size and number of turns? how many coils and magnets ? would like it to be 3 phase.

this will be for a 24 volt system

I am not very good at math.


 Any Advice or comments would be greatly appreciated.


 Mike  

« Last Edit: January 07, 2006, 02:40:43 AM by (unknown) »

RP

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Re: GrassHopper Need Help from The Masters
« Reply #1 on: January 06, 2006, 07:53:57 PM »
A few questions for you:


Is this a savonious (S) style rotor?


Which dimension (48" X 54") is the diameter?


What kind of wind speed are you expecting?

« Last Edit: January 06, 2006, 07:53:57 PM by RP »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #2 on: January 06, 2006, 08:07:41 PM »
Thanks for the reply,


Yes right now it is the S style savonious, I have made it so that I could play with a different styles later if need be. the sections are take a part with a keyed coupler.


It is 48" in diameter, as far as wind speed I don't know. are you asking about the rotor or how windy it is around here ?


 Mike

« Last Edit: January 06, 2006, 08:07:41 PM by zapmk »

RP

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Re: GrassHopper Need Help from The Masters
« Reply #3 on: January 06, 2006, 08:39:22 PM »
Sorry I wasn't clear.  How windy is it there.


Savonious rotors typically produce maximum power with a TSR around 0.3 so the outside edge of  the diameter would be moving at around 1/3 of wind speed.


If your typical wind speed is 12mph for example then:



  1. mph = 63360 ft/hour or 1056 ft/min
  2. ft = 12672inches


Now we know the circumference of your mill will be traveling at 12672 inches / minute.  The circumference of the mill is the diameter *pi so...


(12672 in/min) / (48in diameter X pi) = 84 rpm


Your target rpm for an alternator is going to be about 84rpm for maximum coupling to a 10mph wind.


For a mill this big you'll have lots of torque so you could probably use a mechanical speed increaser like a belt or chain to get your alternator rpms up to around 250 (X3) and use many of the designs that are popuar on this website for HAWT types.


Hope this helps

« Last Edit: January 06, 2006, 08:39:22 PM by RP »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #4 on: January 06, 2006, 09:21:56 PM »
Its windy here all the time, 10 to 15 mph is much the norm. but there is a lot of 20mph + windy days two. I live in Kansas and the wind hardly ever stops blowing here.


I was hopeing to stay away from the belt or chain option. And build a direct drive Alt. I was hopein to build a big dual rotor Alt for the slower speed of the rotor, maybe thats not possable ? or is it.


 Thanks for the math help. how I know what the rotor should turn at that wind speed.


 Thanks again


 Mike

« Last Edit: January 06, 2006, 09:21:56 PM by zapmk »

Waterfront

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Re: GrassHopper Need Help from The Masters
« Reply #5 on: January 06, 2006, 09:43:54 PM »
Hi!


If you really don't want a gearing system, you could build a quite powerful alternator, (even one that would probably choke your savonius) and then add some resistance in the line, which would decrease the current induced in the coils, decrease the power output, and would therefore lower the power input requirements.


You add more resistance till your savonius is able to handle the load from the alternator. You could even have a circuit with a switch, with a low/medium/high resistance, to adapt your savonius to the wind conditions (high winds wouldn't need as much resistance, as the Savonius would be better able to handle the load...)

 

« Last Edit: January 06, 2006, 09:43:54 PM by Waterfront »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #6 on: January 06, 2006, 10:22:25 PM »
Hi Waterfront,


That a cool idea, That would be easily doable for me to set some thing up like this.

I already use one of my computers for monitoring the battery bank and inverter and my weather station which gaves me the wind speed I could set some thing up to monitor the rpm of the savonius then use the output to control a resistance switch.


How all it comes down to is the design of the ALT for the slow rotor speed.

How big of disk, number of  mangets, gauge of wire, number of turns for the coils.


 Thanks for the Idea's


 Mike

« Last Edit: January 06, 2006, 10:22:25 PM by zapmk »

alcul8r

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Re: GrassHopper Need Help from The Masters
« Reply #7 on: January 07, 2006, 05:13:59 AM »
Mike,

Where are you located?

I'm in Wichita but hope to move a little further north.

Rex
« Last Edit: January 07, 2006, 05:13:59 AM by alcul8r »

Norm

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Re: GrassHopper Need Help from The Masters
« Reply #8 on: January 07, 2006, 05:22:38 AM »
  As it's already been calculated ..what the

rpm is...It might be to your advantage... also

interesting to use a calculator to find how fast

it really is going....also

make a simple Prony brake....to see how much torque

it has....You probably know how to make

a Prony brake....if you don't...do a Google search

   Armed with concrete data such as this ...

a few of our number crunchers should be able to

give you the amount of coils, the number of turns,

the size wire, etc.

      At any rate your project looks like fun.

                (  :>) Norm.

« Last Edit: January 07, 2006, 05:22:38 AM by Norm »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #9 on: January 07, 2006, 06:12:27 AM »
Rex,


about 20 min. north west of you.

« Last Edit: January 07, 2006, 06:12:27 AM by zapmk »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #10 on: January 07, 2006, 06:23:15 AM »
Norm,


 The prony brake looks easy enough to make, just have to get some scales, so I can gather some data.


 Thanks for the info.


 Mike

« Last Edit: January 07, 2006, 06:23:15 AM by zapmk »

tecker

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Re: GrassHopper Need Help from The Masters
« Reply #11 on: January 07, 2006, 06:30:10 AM »
I assume your using 55 gal . I'll share a mod on my test rig that seems to overcome the

the spot where ther's no powercycle . I included a snapshot of that point where the drums will actually turn backward from a dead stop you see I added  couple of wings

to vector the wind around and thru the dead zone . Sofar so good it starts at any point in rotation and really smooths out at around 100 rpm . almost no noise at 600 rpm.

tring out a magnetic bearing instead of a thrust bearing two neo doughnuts.  




« Last Edit: January 07, 2006, 06:30:10 AM by tecker »

tecker

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Re: GrassHopper Need Help from The Masters
« Reply #12 on: January 07, 2006, 06:39:41 AM »
 Sorry I try again with the right format




« Last Edit: January 07, 2006, 06:39:41 AM by tecker »

Waterfront

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Re: GrassHopper Need Help from The Masters
« Reply #13 on: January 07, 2006, 07:13:56 AM »
Hi Mike.


VAWT's are bit harder to plan for, because less people build them, and you've got less reference examples.


However, looking over the Hugh Piggot design for a 16 magnets/12 coils HAWT, I see the alternator has a cut-in speed of 120rpm, for 12V. It uses 25 turns of #13 AWG wire, 2 in hand. So, to make it a 24V, we'd simply use 50 turns of #13 AWG wire, 1 in hand. (Same thing exept instead of winding the copper two in hand, you wind it one in hand).


Now, based on the calculations of RP (previous poster), your gonna get around 84rpm in a 10mph wind. So, 120rpm cut-in is looking a bit high. I'd double the number of turns again so that you'd have reached cut-in and would be producing some amps at 10mph. So, the coils would become 100 turns of #16 wire. Now, if we look at the resistance of that, 2.4 ohms, that's quite a lot, and the plan is to put the resistance out of the stator, so you can play around with it. So, I'd keep 100 turns, to keep the approximate cut-in, but I'd go with thicker wire. Probably #14. It will give you bigger coils, but it will drop the resistance way down, and you'll be able to add some more outside of the stator. (which you can then use the heat for other things, fryed egg anyone? hehe).


I'd look at this table http://www.amasci.com/tesla/wire1.txt as it gives quite nice comparative values for different wire thickness. The thicker the better, since the plan is to have a stator with a low resistance, and add some more outside to keep the current down.


Option #2 would be to use the bigger 3"x1.5"x0.75" magnets. I saw a post about somebody having bought some, and he said that although they have 3.375 times the magnetic material, they weren't close to 3X the cost, so, you might be able to get yourself a quite powerful alternator with those. They're larger, so you could have quite bigger coils with quite thicker wire, and have more flux pass through them. Since you don't have the expense of a tall tower, that's probably the way I'd go, to invest my money. You might have to do a bit more trial and error, but If your looking for a cut-in speed for say 70rpm, you could look at the 16/12 17' HAWT DanB built, and probably estimate a starting point from there.


Anyways, hope it helps,

« Last Edit: January 07, 2006, 07:13:56 AM by Waterfront »

Waterfront

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Re: GrassHopper Need Help from The Masters
« Reply #14 on: January 07, 2006, 07:17:16 AM »
Nice pic.


Do you have any output figures?

« Last Edit: January 07, 2006, 07:17:16 AM by Waterfront »

tecker

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Re: GrassHopper Need Help from The Masters
« Reply #15 on: January 07, 2006, 08:39:07 AM »
 I need some time but I 'm putting a laminated rotor together I'll post some pic's as it's kind of the direction your heading with your machine . I's getting heavy fast even with the laminated plates by the time I get the stator together I'm sure the weight will force the use of a drive mech spline belt coupled below . There's a movie clip in my uploads .she likes to turn even in a slight breeze . The mag bearing is going to hold a second tear with no problem.







« Last Edit: January 07, 2006, 08:39:07 AM by tecker »

alcul8r

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Re: GrassHopper Need Help from The Masters
« Reply #16 on: January 07, 2006, 09:43:04 AM »
I'd like to see it sometime if you wouldn't mind.  Always nice to see someone who's doing.

Rex
« Last Edit: January 07, 2006, 09:43:04 AM by alcul8r »

electrondady1

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Re: GrassHopper Need Help from The Masters
« Reply #17 on: January 07, 2006, 10:06:33 AM »
zapmk, congrats on you mill. i'm also into vawtes. my little unit is only 22" wide. it tops out at about 120 rpm. i'm designing the geni to produce at 60 rpm. it seems to spend a lot of time at that speed. i like direct drive as well.

its not easy to transfer the techniqes the hawt guys are coming up with to suit a machine that turns at perhaps 1/4 the speed.

i think ultimatly with a drag type design, the rotors could be the same width as your mill. with as many poles as possible.   the mags/coils could of a modest size but the number of them compensates.

it probably all comes down to how much you can spend on magnets.


   

« Last Edit: January 07, 2006, 10:06:33 AM by electrondady1 »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #18 on: January 07, 2006, 10:25:41 AM »
Waterfront,

Those wire charts will come in real handy. thanks for the link.


 Mike

« Last Edit: January 07, 2006, 10:25:41 AM by zapmk »

Waterfront

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Re: GrassHopper Need Help from The Masters
« Reply #19 on: January 07, 2006, 10:30:06 AM »
Look on the bright side, at least VAWTs don't need a furling system! hehe

« Last Edit: January 07, 2006, 10:30:06 AM by Waterfront »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #20 on: January 07, 2006, 10:59:43 AM »
Tecker,

Iam not useing 55gal drum. Right now the rotors are made like the picoturbine 250, The test rotors were made useing 3/4" electrical conduit for the frames, and 1/8"  lexan for the covering. The shafts are 1" 6061 T6 aluminum. it a very light weight assembly. I did design this so I could replace each section with a different style of rotor for testing .


 mike

« Last Edit: January 07, 2006, 10:59:43 AM by zapmk »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #21 on: January 07, 2006, 11:18:39 AM »
Electrondady1,


Man that would be a big set of rotors ! dang how many magnets could you get on a 48" rotor.


Right now I will be limited to 64-2'X 1" X 1/2 40 neo's that I have, and this what I will  base the rotor size on. Now I need to figuer out what the rotor plate size would need to be.


 Mike

« Last Edit: January 07, 2006, 11:18:39 AM by zapmk »

Waterfront

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Re: GrassHopper Need Help from The Masters
« Reply #22 on: January 07, 2006, 12:11:23 PM »
64 magnets, that's 32 per plate?


If your using a coil opening equal to magnet face, then you might want 1 inch between your magnet so that the coil is always seeing some flux change, and contineously making power.


So that would be 32 inches circ. for the magnets, 32 inches circ. for the spacing, so 64 inches total. Divide by pi = 20.38 inches for the inner diameter, so plus 2 inches twice for the magnets, gives just about 24 inches for an outter diameter.


I suggest you could use a 2 feet diameter plate, and that would give you just about 2.5 inches wide per coils...


Let us know what you decide!

« Last Edit: January 07, 2006, 12:11:23 PM by Waterfront »

tecker

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Re: GrassHopper Need Help from The Masters
« Reply #23 on: January 07, 2006, 12:30:25 PM »


 Sounds like a tall unit .The vertical weight with the rotor inline the drive shaft is

gona be heavy . I've used a thrust bearing set in 90 weight that holds up fine . A wheel hub is ok but it takes a little torque to get it rolling with 20 or 30 lbs sitting on top and the upper bearing drys out . If you were to set the wheel hub in oil

you could leave the nut loose and eliminate a little start up torque.
« Last Edit: January 07, 2006, 12:30:25 PM by tecker »

electrondady1

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Re: GrassHopper Need Help from The Masters
« Reply #24 on: January 07, 2006, 12:46:21 PM »
zapmk, 64 mags is cool!(wish i had them) i think waterfront has it right. 24" hey , i 'm off to the hardware store for epoxy and sanding disks. i'll check back
« Last Edit: January 07, 2006, 12:46:21 PM by electrondady1 »

Waterfront

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Re: GrassHopper Need Help from The Masters
« Reply #25 on: January 07, 2006, 02:07:07 PM »
Did you put anything over your magnets? I'm thinking a piece of plywood is way cheaper then resin, and probably works as well... You could make a jig and just leave it on the metal plate! The only thing is then your magnets aren't covered in a protective layer of resin... I guess there's nothing stopping you from taking a brush and painting a thin layer of just the fiberglass resin... I would probably work as good...

« Last Edit: January 07, 2006, 02:07:07 PM by Waterfront »

RP

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Re: GrassHopper Need Help from The Masters
« Reply #26 on: January 07, 2006, 02:31:48 PM »
"Your target rpm for an alternator is going to be about 84rpm for maximum coupling to a 10mph wind."


Duhh, I meant 12 mph wind like I started with in the math!

« Last Edit: January 07, 2006, 02:31:48 PM by RP »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #27 on: January 07, 2006, 02:46:15 PM »
Tecker,


The total Height for this will be 24 feet tall, and Free standing, I built it in three sections,

that will stack on top of each other.


First section holds one 54" tall rotor and ALT. ( when I get it built )

Second section holds two 54" tall rotors

and the last section holds two 54" tall rotors


All the frame sections will unbolt from the other, as of right now just the frame to hold the rotors weighs in at 250 Lbs. ( ground mount only )


each 54" rotor section weighed 20 Lbs, so I will have 100 Lbs of shaft and rotors.

The way I have made the sections each 54" rotor has a top and bottom sealed bearing for each rotor. it turns quite easily


 Mike

« Last Edit: January 07, 2006, 02:46:15 PM by zapmk »

electrondady1

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Re: GrassHopper Need Help from The Masters
« Reply #28 on: January 07, 2006, 03:10:10 PM »
zapmk, if you get a chance, snap some pics of your rig. i am curious about how it looks and what your using for bearings and a base . if you post in the diary section and mention vawt it will give more time for everyone to jump in.

 use some hefty steel for the rotors 1/2" at least.

 danb has posted some really good assembly techniques in his monday posts.

 good luck, shawn

   
« Last Edit: January 07, 2006, 03:10:10 PM by electrondady1 »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #29 on: January 07, 2006, 03:15:09 PM »
Waterfront,


I me see if I got this right.



  1. " in diameter disk for 32 mags, 1" Spacing between mags inside diameter
  2. coils (?) with app 100 turns of 14 gage.


Question: how would I wire the coils up for three phase ?


 Mike

« Last Edit: January 07, 2006, 03:15:09 PM by zapmk »

electrondady1

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Re: GrassHopper Need Help from The Masters
« Reply #30 on: January 07, 2006, 03:20:31 PM »
you'll need 24 coils for three phase with 32 poles
« Last Edit: January 07, 2006, 03:20:31 PM by electrondady1 »

tecker

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Re: GrassHopper Need Help from The Masters
« Reply #31 on: January 07, 2006, 04:25:19 PM »
 Haven't finished the lamination I 've done some finishing on the plates and will set aluminum top and bottom center plates fiber glass over the mags and paint with 2 part epoxy  .The thing that was cool about the cutsaw blade is it's porous

and the urethane expanded into it and is very rigid.Time will tell though .I put 40 lbs

 of brake rotors on the outside edge and set it on a 2" pipe coupling to test let it sit all night remained true .  
« Last Edit: January 07, 2006, 04:25:19 PM by tecker »

zapmk

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Re: GrassHopper Need Help from The Masters
« Reply #32 on: January 07, 2006, 07:35:17 PM »
electrondady1,


I don't no were I came up with the 16 coils thing. doing to many thing it once I guess.


Going to be gone up to kansas city, kansas for about the next week or so to set up some more computer systems for one of the companys I do work for.


I have to leave in the monring, When I get back I'll post some pic's of my project, under my Diary.


 If this thing doesn't work  It will still going to be a good looking piece of yard ART


 Thanks Guys for all your Help!


 Mike

« Last Edit: January 07, 2006, 07:35:17 PM by zapmk »