# COMMUNITY : FORUMS : GREEN

## Axial Flux Wind Turbine

24 pole, 3 phase alternator. 18 coils of #20 wire 80 turns each, 6 coils in each phase connected in series, then wired 3 phases in star config. Put out lethal voltages at a very low rpm. Using N45 2" x 1" x 1/2" Neo Mags, two discs of 24 each attracting each other through coils. I need to know what the number of turns would be for #13 wire, same configuration for charging batteries.

glasswool11 months ago

Hello all, I have put together a 24 pole dual rotor axial flux alternator with a distributed winding, the middle phase is always producing less voltage can some one suggest why?

ISU-Joe5 years ago
I realize a lot of people already know all of this, but this is what I've learned so far while researching the subject.
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Umm the power output of the generator is governed by Faraday's Law of Induction.  The current it each of the loops of wire is induced to counteract the change in the magnetic field change when the magnets are moving over it going from North to South.  The magnetic field strength drops off in strength with the cube of the distance so it's important to get the coils close to the magnets.  I'm still trying to figure out how the amperage works.  My best guess is that as long as you keep the generator turning at the same speed you can pass any amount of amperage through the thing.  So the more amps you pull the harder it is for the generator to turn at that RPM.  Of course increased amperage will result in your coils heating up, as the copper wire has a resistance that is correlated to the diameter and length.

V=-N*A*(2*pi*RPM/60)*B
where V=voltage, N=turns per loop, A=area (magnet or wire loop?), B=magnetic field strength in tesla

B=u/4*pi*2*U/d^3
where B=magnetic strength, u=permeability constant, d = distance from center of dipole (center of magnet), U=magnetic moment

Also it's important how you wire your coils.  Of course with the 3 phase setup you are able to put the 3 phases which are 30 degrees out of phase of each other through a rectifier and produce a steady DC current; as the summation of the three waves results in a line.  So assuming you have 9 coils you can have 3 sets either in parallel or in a series.  If you put them in a series you can produce hire voltage at lower RPMS.  Although apparently putting them parallel has benefits at higher RPMS.

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I'm thinking of trying to make my generator with 2 stators and 3 rotors.  Thus allowing the average distance each of the coils to be closer to the magnets.  I still have not run the calculations to see what benefit this would product.  I'm hoping to lower the number of coils needed.  I'm trying for 24 volts at 300 RPM, well actaully I would want what 28 volts so I could then charge two 12 volt batteries in series.   Apparently due to lenz's law you need 14 volts to charge a 12 volt battery.  I haven't had the chance to look into this.

Oh I had another thought.  If all the magnets had their poles facing the same direction rather than alternating (alternating current) the generator would produce direct current rather than alternating.  However, this would surely reduce the power output.

3 years ago
I hope it's not too late to comment.
I ran an excel to calculate what can be expected from a 3phase PMA.
Since I cannot attach a file here is the sheet.

The basic formula I used is: V=#phase*n*A*B/t
I will be happy to hear comments, and also send the excel if someone wants to review it

number of poles 24
magnet placement angle (degrees) 15
#Phase PHASE 3
n coils per phase 6
n per coil 21
N per phase 126
A cm^2 11
A A m^2 0.0011
B (Gauss) 13200
B B (Tesla) 1.32
RPM (for 2*pi rotation) 120
time to rotate 15 degrees (sec) 0.020833333
"since the coil enters the N pole and S pole simultaneously
we probably need to consider the time it takes to rotate 7.5 degrees"
t time to rotate 7.5 degrees (sec) 0.010416667
V V per phase 17.563392
V star 52.690176
V delta 17.563392

resistivity Ohm-cm 0.00000167
wire cross section cm^2 0.01227
single loop length cm 14.4
single coil resistance Ohm 0.041157946
jetboy4 years ago
how many turns to produce 12+ v with 14 gauge wire (9 coils) thanks
charlie_ruizpr4 years ago
How many turns would I need with a #22 gauge wire for 12volt application?
Rahdzhillaxxx4 years ago
Great 'ible :)

nolte9195 years ago
Hey what's that middle picture of? The tall cylinder looking thing?
dna11207 (author)  nolte9195 years ago
That is the slip ring assembly that I am building. It allows the wind turbine to rotate into the wind without twisting up the wires. The flange part bolts to the turbine and the pipe on the bottom attaches it to a pipe or some sort of mast. There is a large sealed bearing in the middle to allow it to move freely.
4 years ago
instea of making the wires turn make the magnets turn
5 years ago
Why are there 9 conductors on the slip ring? Don't you only need 3 or maybe 4?
The 3 larger ones at the bottom are for the 3 phase output, the others are for remote monitoring(amps, volts, rpms) and for relay control to switch from star to delta.
rustyallen5 years ago
One more thing to say about your alternator being hard to turn. Double check that you did not accidently place one of your coils so that the wrapping direction is opposite of the others. Three phase should be all in the same direction.
rustyallen5 years ago
You said you were having trouble producing amps from your alternator. A possibility here is that you have your magnets to close together so that one side of a coil was passing a north pole and south pole at the same time. That will kill your amps quick. Its like trying to get the coil to produce an electric flow in both directions at the same time. This would mostly happen at the bottom inner circle of the magnets. It makes your alternator harder to turn with less amps being the result.
frolick5 years ago
Hi, I'm thinking about building an axial flux alternator for an underwater application. Right now I'm trying to wrap my head around how you estimate how much power you'll get out of one of these as a function of the magnets and coils. From what I've seen people have been just building part of the system, experiment with it, and then change variables without doing any calculations. Do you know what a good starting point is for those calculations?
dustyplans5 years ago
On a generator we are making. I am using 24 mags on 2 disks.. 12 on each. 12 guage wire 35 turns. 9 coils. Hoping for 1000 Watts. with a 10 foot swing on the blades. I got this Idea from an instructable 1000 Watt Wind generator. What we found out is that ONLY one set of Coils can be charged at a time. Otherwise there is a decrease in output. does that help?
Wind Friend5 years ago
hi dna11207 just one of my three 180 Ah batteries looks like .009 ohms at a 4 Amp load.(measure the open circuit voltage of your battery, now connect a known load and measure the voltage again, subtract the voltages, now divide by the current and you will have the internal resistance of the battery) open circuit voltage of your alternator doesn't mean much because it will never rise above the voltage of your connected battery. the faster your alternator turns the more current passes through your battery- remember we are trying to move the electrons from the positive plates back to the negative plates. transformers are designed to operate at a given frequency( the higher the frequency the less iron is required within the core) any transformer would be most unhappy being on the end of a wind turbine(its called wild AC). i'll have to poke around the interweb and become familiar with gauge wire size(more familiar with millimetre squared sizes in Australia). by the way great site
dna11207 (author)  Wind Friend5 years ago
This is how I plan on doing my next tests, the first stator I made produced a lot higher voltages than the second one. I went back to the first stator and tried rectifing and running directly to batteries, but the high voltages produced saw the battery as a short, locked up the rotor. I than connected a 60hz 20:1 transformer using 240v input and getting 24 out. This design produces 60hz at 300rpms. I know at lower speeds the effiecency will go down but I think the loss would be acceptable given the power out. Spinning the rotor at 300rpms I was able to produce almost 20 amps to the battery with a lot less effort to turn then the other stator. I am going to wind another stator to produce even higher voltages at less rpms because this transformer is capable of 480v input. 1 amp on the high side would give me 20 amps on the low side. Much easier to produce 1 amp at a higher voltage than it is to produce high amperage at low voltage. Just my opinion we will see what happens. This alternator consists of two rotors with 24 magnets each facing each other attracting through 18 coils. This configuration is correct.
DeanC9935 years ago
hi i am intrested in one of these but i have a question, instead of all those coils could you just have 1 big coil? Brgds, Dean
dna11207 (author)  DeanC9935 years ago
Well the way this works is I have 6 coils connected in series x3 to give 3 seperate ac generators if you will. The stator I started with had 80 turns per coil x6 connected in series x3. Thats 480 turns total for each phase. Now if you wanted to build a single phase unit and had one coil of 480 turns I guess it would produce the same results that I got, less the 2 other phases. I am looking at trying something else with one coil so when I do that I will let you know how it works out. Another thing is the number of magnets. The less magnets, the more pulsing you will have or voltage fluctuation at low speeds. Hope this helps, if you have any other questions just ask.
5 years ago
hi thanks i will try 480 turns but how do you connect all the coils together and what do mean by voltage fluctuation?
dna11207 (author)  DeanC9935 years ago
The space between magnets will produce no voltage. You only get voltage when a magnet passes over a coil.
dna11207 (author) 5 years ago
5 years ago
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dna11207 (author)  Yeasayer5 years ago
This is the reading taken right from the output of the stator. The stator puts out ac voltage. The frequency 60 hz is approx. at 300 rpm. The voltage reading on the scope I don't understand because the multimeter shows much less. The multimeter is accurate as I tested it on known sources. Maybe I have a setting wrong on the scope. I am still testing, also testing the previous stator with a transformer to reduce the voltage. As I get more results I will let you know.
5 years ago
I noticed the reading on the Scope was Peak to Peak 82.4 , The Multimeter will show approximately 58 volts for the same set up. Is this about Right?
The RMS voltage (Root Mean Square) is the average effective voltage of a sine
wave. An example of how this RMS value is applied.
Say you have a toaster oven, an oddball, the Mfr. rated input is 100 volts DC.
Your source of power is AC. An alternator The Oven is resistance circuit only.
If you dial up a hundred volts with readout from a scope P to Peak the Oven
will barely heat up. The answer is, multiply DC volts by 1.41 = 141 volts AC.
Your multimeter or any RMS AC meter will be reading 141 volts but will show
the effective DC equivalent of 100 volts.
Peak to peak voltage of 100 is equal to 100 * .707 =70.7 RMS.
The 240 volt service to your home is actually 338 volts. P-P.
A more involved explanation on the link below.
http://www.tonmeister.ca/main/textbook/node82.html
dna11207 (author) 5 years ago
Ok. I am having some problems. It seems to take a lot of effort to maintain a 10amp charge rate to the battery. It's very hard to keep the rotor turning while connected to the battery. The 10 amp draw is almost enough to stop the rotor. I switched the stator to delta and it made it a little bit easier but had to spin faster to prodce the same current. Still an excessive amount of effort is needed to turn the rotor. I switched back to the original stator ad used a transformer to step the voltage down and had much better results. I was able to maintain the 10 amp charge rate with alot less effort. Producng apprx. 200v to the transformer, I was getting aprox. 15 to 20 vdc. Seems like it is easier to produce higher voltage and then transform it down to usable power.
dna11207 (author) 5 years ago
Ok, here are the preliminary results. I hope to have a complete test done by the end of the week. It seems like it is working out to be 1 volt for every ten rpms.

25 = 2.3v ac
40 = 3.9v ac
63 = 6.2v ac
100 = 9.5 v ac
125 = 12.56 v ac
160 = 15.10 v ac
200 = 19.10 v ac
250 = 24.90 v ac
315 = 30.50 v ac
400 = 37.50 v ac
500 = 49.50 v ac
630 = 59.20 v ac
800 = 74.00 v ac

These measurements were taken across 2 leads of the 3 phase output and it was wired in a star configuration.
5 years ago
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dna11207 (author)  Yeasayer5 years ago
Where would the capacitors be connected? On the dc side or ac. Motor capacitors are ac. I planned on having the rctifiers hooked up today for getting dc measurements but my partner in this has the lathe tied up with some real work. Maybe tomorrow I can get this done. I would really like to see whatthis thing is capable of as far as current goes in the 12v range. I will try both star and delta configurations and record measurements on both. Also, I think I may be able to squeeze the extra turns of wire in there. The stator is filled with resin and ends up being approx. 1/2 inch thick. The coils are wound to be a 1/4 inch thick. Maybe I could wind the coils just a little bit wider to accomodate the extra turns and do the resin differently. I will try that this weekend. Anymore suggestions would be appreciated.
5 years ago
On The DC side. I;m unsure about the number of output wires but I made a quick Sketch to point out the place where the Capacitors should be connected.
dna11207 (author)  Yeasayer5 years ago
doesn't the battery do the same thing here without the capacitors?
5 years ago
A good way to find out is to try it.
I stumbled on to this bit of info, could be a good way to lower the cut in speed
also lots of good stuff here.
http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1138&PN=3
dna11207 (author) 5 years ago
Ok. I decided to go give this new stator a try. This one is made of #13 wire and each coil is 21 turns each. I am hoping this stator will produce a voltage range much closer to charging my battery bank than did the previous one. Just about a 60 turn difference in each coil and wire size change from #20 to #13. My guess is open voltage range of 10v to 50 volts and maybe 45 amps or so at full capacity and load. 80 to 100 rpm should produce enough to start charging the batteries. When I finish this stator and test it, I will post the results here. Anyone have a better idea what this stator might do? Good idea? Bad idea? Potential problems? Let me know. Thanks
darksparks5 years ago
Do you have any drawings of this?
dna11207 (author)  darksparks5 years ago
Flying by the seat of my pants on this one.
darksparks5 years ago
So when will you have this all together?
dna11207 (author)  darksparks5 years ago
Soon.
dna11207 (author) 6 years ago
Well, I screwed up so I only got it up to 600 rpms before the magnets flew off. I didn't securethe mags to the steel disc for testing. Stupid mistake, but any way it was putting out around 390 volts dc and when connected to a battery for a load, it was like shorting the stator. It started to slip in the chuck on my lathe. Over 400 rpm the lathe could not turn it anymore with a battery load on it. The lathe has a480 3 phase 5 hp motor. Higher voltage loads seemed to do and sound much better. I used a 100 watt 120v light bulb for a load on the ac side. Here is a picture of one of the magnet rotors that I made. The broken magnet on it was from slamming into aother one when installing them.
6 years ago
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dna11207 (author)  Yeasayer6 years ago
I am charging 4 12v batteries connected in parallel. I was thinking about 35 turns each, 3 coils connected in series and 2 sets of 3 connected in parallel in each phase. That should give me more amperage but the problem is the coil size is still too large. I am thinking the max turns I could use with #13 wire is about 16 to make them fit. So back to 6 coils connected in series.
6 years ago
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dna11207 (author)  Yeasayer6 years ago
Vehicle alternators are designed for very high rpm's so I don't think they could compare to what I am trying to accomplish here. Also, most axial designs that I have seen, have a small number of magnets ie: 16 or less. That means 1 magnet will cross each coil before the next one comes into play. My design allows the coil to see 2 mags (n on one side and s on the other side of the coil) therefor increasing the amount of flux each coil see's. Also the number of mags allows for slower rpm operation. More north south changing in 1 rpm than say a gen with only 16 mags combined with 2 mags hitting each coil at the same time = more power at lower rpm. I need to come up with a voltage controlled switch to operate a relay for switching between star and delta. I will have one extra coil in the alternator isolated from the rest for controlling the relay. Slow speed will be star, faster will switch to delta. Also need to find a brush supplier for a slip ring that I am building. Anyone know where I could purchase brushes and holders by size? Once I have this all completed and tested, I will post an instructale on everything that I have done. So far I am having good results, just need to get this coil thing worked out.
5 years ago
Taken from my reference book
"one volt of electrical pressure is created when 100, 000,000 magnetic lines of force are cut per second."
as an example, If your dual magnet system produces 150 thousand lines and your magnets pass
the coil in 1/100 second. This is 100 X 150000 =15 million lines per turn. you would need 6.6 turns per volt.to achieve the 100,000000 required when 2 more coils are series wired to this calculation the number of force lines cut per second is tripled, coil turns would have to be reduced accordingly. If you do not know the field strength of the magnets then perhaps the MFR. could supply it for you. again good luck