Author Topic: Multiple rotor and stator  (Read 1080 times)

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chevdodger

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Multiple rotor and stator
« on: June 07, 2009, 01:09:12 AM »
Hi this is my first time posting. I hope it works.


I did search the board for information but did not find the information I am looking for.


I wanted to build a wind turbine with 3 rotors and two stators. The middle rotor would have magnets on both sides. The stators between the first and middle rotor and the last and middle rotor. My idea is to control the blades rpm by loading the blades with one stator and when there is more wind to connect the second stator.( or more rotors and stators if need be) Instead of using a folding tail or other means of furling. Has anybody tried this? I live in a very high wind area and thought that I could get a lot more power this way. If nobody has tried this I may do this and will post the results.


I have built the otherpower 10 footer and made my 48V coils with 15 Gauge wire 105 turns 12 1"x2"x0.5" magnets per rotor it overheated so I rewound it with 2 in hand 15 gauge 105 turns. I have had to do the same with my 7 footer as well. All because of the high winds.


Also my 10 foot blades have a distant helicopter sound when they are running at about 150 rpm or faster. Also wondering if anybody knows what could cause this.


Any info or advice would be appreciated!


I have searched for and read a lot of info here on this board and has helped me a lot!


Thanks to everybody for contributing their time effort and info!


Bill

« Last Edit: June 07, 2009, 01:09:12 AM by (unknown) »

willib

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Re: Multiple rotor and stator
« Reply #1 on: June 06, 2009, 08:55:21 PM »
as for the helicopter sound , is your trailing edge paper thin?

if not this may be the cause.
« Last Edit: June 06, 2009, 08:55:21 PM by willib »
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hiker

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Re: Multiple rotor and stator
« Reply #2 on: June 06, 2009, 08:58:36 PM »
goggle search the board............. :}

 http://www.fieldlines.com/story/2006/8/18/221937/870
« Last Edit: June 06, 2009, 08:58:36 PM by hiker »
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Flux

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Re: Multiple rotor and stator
« Reply #3 on: June 07, 2009, 01:15:24 AM »
There is a lot of discussion here somewhere about loading with two machines but like you I wouldn't be able to find it. The idea will work up to a point. If you wind one section to load normally up to a certain wind speed you can bring the second stage in and hold things down to higher wind speeds. You would need to make the second alternator stage very powerful to be able to hold it to much higher wind speeds and you would never be able to make anything much bigger than 8ft work in this mode without furling.


The second stage has to be very powerful and efficient to effectively clamp the blades to constant speed so you are working in blade stall. Choosing the correct blade profile for stall operation like the early grid machines with induction generators did would help.


The whole thing is wasteful of copper and magnet and in the end it is better to use one winding with the extra magnets and copper arranged in a different way but you then have to have some control scheme that keeps you from stalling in the normal working wind speeds. To do what you propose you would have to use about 1/3 of your alternator for normal working and the other 2/3 just for stall operation in high winds. Not an efficient use of materials at any wind speed but certainly you would be able to raise furling speed to perhaps 40 mph if you got it right.


Second point, any 10 ft prop making helicopter noises at 150 rpm has serious problems. I suspect you are way off with your speed predictions. If you managed to rewind your stator with 2 in hand wire when the original specified single I can't believe you have kept the same number of turns. If you have got the winding in the same space then I suspect you have halved the number of turns. One turn will be a complete loop of 2 wires and you can't have got twice as much wire in there. If you have got this extra wire in with turns as you describe you will have to have increased stator thickness to near double and the increased magnet spacing will have lowered the flux and what I mention below about cut in speed will still apply.


If this is the case you will have doubled the cut in speed. The thing will perform very much better in high winds but the prop will run faster and be noisy. You will need to take more care with trailing edges and blade tips if you want to keep noise reasonable at higher speeds. I would expect a 10ft prop to start reaching helicopter type noises somewhere above 500rpm depending on the actual blade construction.


If you really have these noises above 150 rpm I suspect you have got your drop figures confused and the pitch angle is way too high.Or your trailing edges are over 1/8" thick.


Flux

« Last Edit: June 07, 2009, 01:15:24 AM by Flux »

chevdodger

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Re: Multiple rotor and stator
« Reply #4 on: June 07, 2009, 10:35:59 AM »
Thanks flux and everyone else for your advice and comments


The links were very helpful. I could not find them myself.


As for the 2 in hand 15 gauge wire coils, yes I made it the stator about an inch larger in diameter and also a bit thicker. I did the same with the seven footer with ed's from windstuff wedge magnets. It worked out very well.


As for the 10 foot blades the trailing edges are very thin. I could be of with the 150 rpm. If the angle at the tips of the blades is to steep will that cause the helicopter sound? It also shakes a bit when it does that. I want to check the balance again also just to make sure that it does not have an effect on this.


I had a loud whistling sound before. The trailing edges were not thin enough and also the tips were either flat or one blade was angled towards the leading edge. I think this happened because of leaving them unpainted for a long time after carving them. The wood twisted. After repairing this the whistling sound is gone. The only thing I can think of that the angle at the tips is too great or the blade assembly is still out of balance to cause the helicopter sound. It is only a distant helicopter sound not a loud one. Any help or comments would be appreciated.


Bill

« Last Edit: June 07, 2009, 10:35:59 AM by chevdodger »

Flux

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Re: Multiple rotor and stator
« Reply #5 on: June 07, 2009, 02:41:56 PM »
Things do get noisy when the pitch is too coarse for the operating speed. Your change of winding has no doubt increased the operating speed so you certainly won't want any coarser pitch than normal. You give no real indication of your blade construction, but if it is based on Dan's usual arrangement you should have no more than 3 deg at the tip.


If you have balanced things well then vibration is almost certainly due to tracking of the tips not being good enough or from differing pitch angles on the blades. If the timber has warped it may affect the tracking or it may have twisted one and increased its pitch.


I think your sped is probably way over 150 rpm, that is just about cut in with a conventional 10ft machine. With your changed winding it probably won't even be cut in at 150.


Flux

« Last Edit: June 07, 2009, 02:41:56 PM by Flux »