coil formula
By jaskiainen, Section Newbies Posted on Wed Jan 23, 2008 at 07:22:57 PM MST
Hi all

Hi all Ive been googling and searching all around for hours before asking. Im trying to calculate proper coil lenght to start with and found the formula that i need. Only thing what is fuzzy to me is how to calculate the total area of magnet face in square inches? In the formula i did find it went like this: You plan to use 12 magnets that are each 1" diameter. Total area of magnet faces is 12 x 3.14 / 4 = 9.4 sq inches I think that number 12 comes from 12 magnets? 3.14 is also not so hard to figure out but where comes that 4? And what does it presents? I also think that if theres something "missing" in that formula? What does that formula looks like if im gonna use 2" diameter magnets?

coil formula | 20 comments (20 topical)

Re: coil formula (3.00 / 0) (#1) by TomW on Wed Jan 23, 2008 at 12:44:28 PM MST

jaskiainen; I can not say for sure but usually pi [3.14] is multiplied by the radius of circles to find other values of the circle. This leads me to believe the 12 is not magnets. Like I said, not really sure but the 12 probably represents the radius of a circle 2 feet across? Maybe I missed something but I cannot understand why you would factor number of magnets with pi? Good luck figuring it out. Cheers. TomW The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

Re: coil formula (3.00 / 0) (#2) by Bigwheel on Wed Jan 23, 2008 at 12:52:10 PM MST

Hi, Is there a particular voltage your looking to achieve?  Also, do you have any space constraints?  That is some of the recent problems I have come across.  Are you planning on a Vawt or Hawt.  Just looking for a little more info.  Chad

Re: coil formula (3.00 / 0) (#3) by jaskiainen on Wed Jan 23, 2008 at 01:06:38 PM MST

Hi Charging 12 volt battery is my goal. I understand everything else in that formula but the "total area of magnet face in square inches"? Im not sure yet what im going to built? windturbine? Waterturbine? If i go with the wind it would be a HAWT. Sorry i dont understand your "space constraints"? (dont have dictionary here with me) Best regards jaskiainen [ Parent ]

Re: coil formula (3.00 / 0) (#4) by Flux on Wed Jan 23, 2008 at 01:14:13 PM MST

12 is number of magnets. Area of a circle is pi.r^2 or if you use diameter it is pi.d^2/4. In the example d was 1".If the magnets were 2" diameter the area of a magnet will be pi.2^2/4 Flux [ Parent ]

Re: coil formula (3.00 / 0) (#5) by jaskiainen on Wed Jan 23, 2008 at 01:24:09 PM MST

Ofcourse! Why i didnt see it myself... Thanks again. Oh, by the way. Im gonna use quite small wire gauge for my coils and was just wondering that should i calculate some more coil windings because of voltage loss? (long, thin copper wire and lots of resistance) Best regards jaskiainen [ Parent ]

Re: coil formula (3.00 / 0) (#6) by TheCasualTraveler on Wed Jan 23, 2008 at 04:41:33 PM MST

pssssst... over here, tell them the wire gauge, not that it's quite small.. Andy [ Parent ]

Re: coil formula (3.00 / 0) (#20) by Bigwheel on Sat Jan 26, 2008 at 12:57:56 PM MST

Hi again, About the Space Constraints.  i'd like to elaborate a little more.  I recently constructed a VAWT designed by Ed Lenz.  He recommended to me to keep the coils as thin as possible to get the magnets closer together.  Inorder to get a 1/4" stator my coils ended up thin and the widths would overlap the next coil.  All of which needed to fit on a 8 inch dia. disk.  Take a look at the wounderful pictures posted below and try to immagine trying to stuff oversize coils in the constraints of the mold.  I was forced to go with thicker coils roughly a 1/2" stator plate to get around this problem.  I was using disks that I already had made up.  A larger magnet disk and mold would take care of my problem.  I wound my stator with 160 turns of 18 awg to get my open voltage of 24 volts non rectified at 100 rpm.  Hope this helps you out.  Chad [ Parent ]

Re: coil formula (3.00 / 0) (#7) by veewee77 on Wed Jan 23, 2008 at 09:27:23 PM MST

isn't the formula for area pi x R squared? So total area for all magnets would be pi x r squared x number of magents. Doug

Re: coil formula (3.00 / 0) (#8) by jeffbirkle on Thu Jan 24, 2008 at 06:48:57 AM MST

2 ways to calc area of a circle. 1st is R x R x pi(3.1416). The 2nd is dia x dia x .7854 Jeff [ Parent ]

Re: coil formula (3.00 / 0) (#9) by GeeMac on Thu Jan 24, 2008 at 07:12:03 AM MST

And so . . how does this determine the coil length? Jesus is coming. Try to look busy. GeeMac

Re: coil formula (3.00 / 0) (#10) by electrondady1 on Thu Jan 24, 2008 at 07:36:19 AM MST

with out the mag thickness or spacing how can one possibly determine what the lengh of copper wire contained in the coil. [ Parent ]

Re: coil formula (3.00 / 0) (#11) by GeeMac on Thu Jan 24, 2008 at 02:55:13 PM MST

I have no idea how it's done. Some instruction would be nice. Jesus is coming. Try to look busy. GeeMac [ Parent ]

Re: coil formula (3.00 / 0) (#12) by ghurd on Thu Jan 24, 2008 at 02:58:11 PM MST

How long is it if I run a rope around my property? Ghurd.info [ Parent ]

Re: coil formula (3.00 / 0) (#13) by picmacmillan on Thu Jan 24, 2008 at 11:21:02 PM MST

jask? you are missing some valuable information for us to help you..you say you want to use thin wire??? what gauge?? how many strands per coil?? how many coils do you intend to use..with these starting points we can help you to determine the right amount of turns per coil...do not do like i did when i first started...i thought the more turns i had the stonger my turbine would be...i ended up with too much resistance in my coils to make usefull power(at 12 volts)..my stator was more suitable for 48 volts(which is another issue) what are your plans?? 12 volt 24? or 48?? please give us as much information as possible and we can help ?? good luck with your project ...pickster good luck with your project...pickster http://www.frecklefarmloghomes.com

Re: coil formula (3.00 / 0) (#14) by jaskiainen on Fri Jan 25, 2008 at 10:01:55 AM MST

Hi Im gonna use AWG28-29 wire for my coils. My magnets are quite small also (12mm*3mm), so i need quite a lot turns per coil. Im gonna use 3 phase star connected stator. 9 coils/12 magnets. Ive already calculated a few different coils wich i can start. About 150-270 rounds/coil. depending on cut in speed and wire thickness. So 1 phase would be made of between 60-150 feet long wire. That wire size and lenght gives me quite a lot voltage loss wich i need to compensate with a few more turns per coil. (at least thats what i think?) I know that making a generator this size is NOT quite wise and the efficiency is really poor, but this is just a testing and studying phase for me right now. Later i will come up with more bigger one. Best regards jaskiainen [ Parent ]

Re: coil formula (3.00 / 0) (#15) by ghurd on Fri Jan 25, 2008 at 11:21:26 AM MST

You KNOW it won't work quite right, but built it anyway? Just to learn something? I don't know where you are, somewhere metric by the looks of your decimal point, but I'm tempted to get a ticket to there, to give you a big pat on the back! Yes.  The resistance will kill the output. But it will work, at least a little.  :-) G- Ghurd.info [ Parent ]

Re: coil formula (3.00 / 0) (#16) by jaskiainen on Fri Jan 25, 2008 at 01:10:36 PM MST

Thanks The power im gonna get out of it will be around 1 amp. maybe a little less. If you would like to come and visit me, ill wellcome you =) Im located here in finland. Best regards jaskiainen [ Parent ]

Re: coil formula (3.00 / 0) (#17) by ghurd on Fri Jan 25, 2008 at 02:05:09 PM MST

Finland? Is Finland about 25'C now?  Somewhere around 25'C is where I want to go.  Minus 12'C is where I am. I do not like -12'C. "I dont wanna buy any ready made parts from others, because I do this for a fun"? Around 1A, maybe a little less?   I understand. Losses and battery is 14V. Volts at the stated RPM - 14V = Y volts. Y volts divided by total resistance = A A multiplied by 0.85 = B.  (A x 0,85 = B) B is the amps into the 12V battery. It will not be correct.  But it will be close.  Sometimes. Sometimes anything is better than nothing? G- Ghurd.info [ Parent ]

Re: coil formula (3.00 / 0) (#18) by Bruce S on Fri Jan 25, 2008 at 04:52:33 PM MST

G- You stole my thunder:-) This post should be saved and pointed to each time there's one of "those" about building 17 footers right off the bat IMHO. The the original poster; My Apologies for not staying on track :-0 I would too like to say that you have the right idea of starting small, getting the ins/outs and math down before going on, with this you'll go on to being one of the go to people when someone else needs help. The greatest of luck and keep us posted ( PICS we love) Cheers Bruce S PS where in Finland? I think G- will not want to make that trip just yet:-) [ Parent ]

Re: coil formula (3.00 / 0) (#19) by jaskiainen on Sat Jan 26, 2008 at 09:45:26 AM MST

Hi I live near Tampere. The weather is not so bad right now. Between +2 - -5C. I think the global warming is doing the trick in here. (normally -10 - -30C in january) Its good to hear that someone thinks im not totally insane for this size generator ;) Best regards jaskiainen [ Parent ]

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