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Forum Index : Windmills : permanent magnet alternator
| Author | Message | ||||
morganjones Newbie  Joined: 24/08/2010 Location: United StatesPosts: 3 |
can anybody tell me how big the coils for my PMA should be, the magnets (12 on each disk 24 total)(disk are 12 inches) 2x1x1/2 bar the wire is 14 gauge there are 9 coils thank you morgan |
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arpolis Newbie Joined: 04/08/2010 Location: United StatesPosts: 26 |
As big as you can get them! Don't just take my word for it but start with an inner diameter about the size of the magnet and wind as much copper as you can as long as all 9 coils still fit. However I think you shouldn't make the legs much thicker than your magnets are wide. Probably best idea is to go large on one coil, test it & see if that voltage is going to work out for ya. Will it work? Well lick your fingers and touch the two leeds. PZZZZZZZT |
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
morganjones Woah! First off, welcome to the 4m. Now, let's start you off systematically. It appears you've already started building a PMA, which is fine. Your next step is to provide us with size details and if you click on the picture of the tree with the blue arrow pointing up (in the "Post Reply" box), you can include a picture. Specifically, we need to know your individual magnet thickness, so we can determine the proper air gap before you start winding coils that perhaps won't fit. If "2 x 1 x 1/2 bar" is the magnet size, please verify that the thickness is 1/2" so we're all on the sam page. Also, what is the thickness of your magnet flux-return backing plate? Will this alternator be driven by a wind turbine? Have you decided on a blade and a cut-in speed? Do you have details about the TSR? You kind of have the cart before the horse. I know, because I started out the same way and it'll be a lot less painful if you back up a bit. Baby steps at this stage! After providing some details, so we can better direct your efforts. For now, you should think about what you want out of your alternator as far as voltage and current go and then we'll narrow in on the specific "how-to" items. If your magnet wheels are already built and this is an axial-flux rig, the first thing to do will be build a test coil and there are several folks here to help you do that correctly, but first things first: Details, perhaps a picture or two and goals please. 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| morganjones Newbie Joined: 24/08/2010 Location: United StatesPosts: 3 |
the prop is a 4 blade wooden blades each 4 ft long, the space between disk well idk what would you recommend and as for cut in speed the previous model started at 5mph and the magnets are 1/2 in thick i am trying to relicate this concept http://www.instructables.com/id/DIY-1000-watt-wind-turbine/ morgan |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
morganjones Do you have a lathe or something you can spin your magnet wheels with to produce an accurate a cut-in speed of 300 to 400 rpm? "Cut-in" will be the point at which the alternator starts pumping voltage to your energy capture system, like a battery. For a 12-volt battery, the cut-in should be about 13 volts or slightly higher. Depending on what you're after, namely low-speed or high-speed wind energy production, we can wind your coils accordingly. If your magnets are 1/2" thick, your air gap should be 2 x 1/2" x 75% = 3/4". That means your coils will have to be slightly smaller so as to allow a tiny air gap 1/32" to 1/16" each side so they clear the magnets as they whir by. Using these guidelines, wind a test coil with any gauge enameled magnet wire you have on hand. Shoot for 100 to 200 turns and fit it between the wheels, then turn them at a known rpm. Attach your volt meter to the two ends of the coil's wire and set the meter to read "volts a.c." then spin the magnets. Note the rpm and associated voltage. From your results, we will be able to determine the "turns per volt" number and then better know how to build the remaining coils. Do that much and we'll proceed further. Edit: Oops. Almost forgot; got any pictures? Also, what are your energy goals and as for the 4-bladed prop, it may yaw (turn about the tower axis with changing wind direction) a little bit hard. As it yaws, if one set of blades is in a horizontal position (very likely), it will "fight" the turning and cause things to wobble and throb. Three blades would be a better method, but four will work for now. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| morganjones Newbie Joined: 24/08/2010 Location: United StatesPosts: 3 |
unfortunatly i do not have any pictures however i do have it on youtube.com http://www.youtube.com/watch?v=SwoZhS7nGr4 and http://www.youtube.com/watch?v=AVKwW-A_HEQ i hope this helps also check out the instructable thank you morgan |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
morganjones Thanks; I'll check out the stuff on YouTube. By the way, see the little blue "Forum Codes" link at the bottom of the "Post Reply" box? Click that link, then copy and paste the code that has the ]My Link[ in it and exchange your information for the URL and link name and it will create a "User Friendly" link on the page. Doing this makes it easier for readers to follow along with what you're saying, having only to click the link, then hit their "back" button to return to the 4m board. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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ChrisOlson Regular Member  Joined: 19/01/2010 Location: United StatesPosts: 60 |
???????????????? 300-400 rpm cut-in? For an 8 foot turbine? 100-200 turns? Is this a 208 volt machine, or did I miss something here? From what I read or gather, this is an 8 foot 12 volt. With a four blade rotor I'd expect a loaded TSR of about 5 and a cut-in TSR of 7 @ 7 mph wind speed, which is 170 rpm. Depending on the actual performance of the airfoil, it may be less than that, but with a four blade rotor it won't be more. At any rate, with N50 bars in a 12 pole you need a test coil with 36 turns. If in doubt on the performance of that rotor, wind it with 40 turns and open up the air gap if it tends to run in stall. -- Chris off-grid in Northern Wisconsin, USA |
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| ChrisOlson Regular Member Joined: 19/01/2010 Location: United StatesPosts: 60 |
Morgan Jones, I'll tell you right up front that you're not going to get 1,000 watts out of an 8 foot 12 volt turbine. A good 8 foot rotor running at a Cp of .36 only makes 1,043.7 watts at the shaft @ 28 mph wind speed. The best power efficiency you're going to get out of a stator wound with dual 14 AWG is 44% @ 870 watts, meaning you need almost 2 kW of shaft input power to get 870 watts out of it. And it'll overheat at that output (60 amps @ 14.5 volts) if you push it for very long. In reality, by the time you take into account power dissipation in the stator, rectifiers and wire run, what you're building is a 500 watt turbine. Bolt 10 foot blades on it and you might get 750 watts in a gale. But it'll burn up unless you furl it at 500 watts. -- Chris off-grid in Northern Wisconsin, USA |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=ChrisOlson]Is this a 208 volt machine, or did I miss something here? I think maybe we both missed something here. I looked at the video and this turbine is no bigger than the ones I build (maybe even smaller). I am basing my cut-in and turns on 1/4"-thick magnets doubled-up on two magnet plates with an air gap of 3/4" and the magnets placed approximately 2" from center. Unless this thing twists like a Texas tornado, it's not going to make any electricity. If the size were to be increased even a little bit, so the magnets spin farther from center, like 5 or 6 inches, it'll make a world of difference. Also, I'd cut it down to a two-blade prop as 4 blades will likely give slower results and not be any easier to yaw. Three blades or maybe even one blade with a counter-weight would be the ideal situation here. I used 200 turns for my test coil and found with my setup, I could produce 1.8 volts a.c with 161 turns @ 347 rpm so I was basing my advise here on those results. Unless I missed something, the turbine being built by morganJones is not that different from the ones I build-- size-wise. I am not an engineer and don't mean to lead anyone astray, but I think due to the small size here, the only reasonable thing for morganjones to do is to build a test coil and see for himself what works and what doesn't. Here's a link called Alton's Blade Calculator. Just enter your specific information and it will predict your production outcome in a variety of winds. It's at least a guideline, so you can have a reasonable expectation of your own results. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| ChrisOlson Regular Member Joined: 19/01/2010 Location: United StatesPosts: 60 |
"the magnets (12 on each disk 24 total)(disk are 12 inches) 2x1x1/2 bar the wire is 14 gauge there are 9 coils" "the prop is a 4 blade wooden blades each 4 ft long" Who's got the tape measure here? -- Chris off-grid in Northern Wisconsin, USA |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=ChrisOlson]Who's got the tape measure here? Did you watch the video? The turbine shown is nowhere near the stated measurements. This seems to be turning into a pissing contest. I never have liked competition, so I'm bowing out. From here in, I'm referring all requests for help and information to you, since you seem to be so well informed. I will no longer hand out information, since I seem to be so uninformed. I'll post progress on my own builds, but that's all. This is a DIY forum and that's exactly how I'll treat it from here in. I'll do it myself for myself. See you around the patch! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| ChrisOlson Regular Member Joined: 19/01/2010 Location: United StatesPosts: 60 |
I did indeed. And I see what looks like about an 8 foot rotor with some sort of small generator in it hooked up to what looks like garden tractor batteries. And if you read what Morgan Jones actually says here, he's evidently building a new turbine using this same rotor. He said in his presentation that it's a 12 pole, 9 coil three phase and he plans on winding it with dual 14 AWG. I'm no newbie to building turbines with axial generators. I could probably teach the class. And I'll tell you upfront that a ~8 foot turbine with a 12 pole nine coil 12 volt generator does not cut in at 300-400 rpm with N50 bars in it, nor does it require 100-200 turns of wire. He said in his presentation that he's using 35 turns, which may work with that rotor, I don't know. That's why I said that if there's any doubt as the loaded TSR of that rotor I'd put in 40 and adjust the air gap accordingly if it stalls. The other option is to underwind it and end up with a machine that won't cut in at all until you have a 10-15 mph wind - which I'm afraid will happen flying it on that tower made of 2x4's. I don't post here too often because I don't build turbines made from washing machine motors and I don't fly anything smaller than 10.6 feet in diameter. So this is no "contest". It's correcting inaccurate information for a newbie who doesn't need incorrect information, by someone who has the experience to know better. -- Chris off-grid in Northern Wisconsin, USA |
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