Wiring up a 12-volt stator

In order to reduce the size and stiffness and number of wires that are needed to wind each coil, I prefer to connect the coils of a 12-volt stator in parallel rather than in series.  This means each coil has more turns of thinner wire to achieve the correct voltage at the desired speed.

We could simply connect all of the coils in each phase together in parallel, but the reality is that they will produce a slightly different output signal (in voltage and in phase/timing) which would lead to some parasitic currents between the coils.

For this reason I prefer to rectify each coil separately.  The rectifier diodes block any mutual currents.  Connect in parallel the outputs of all the rectifiers, using DC buses, positive and negative, which conduct the current to the battery.

I start by connecting all of the ‘starts’ of each of the coils together using a ring of wire.  This ring can also be made tight enough to hold the coils in position against the island in the stator mould.

Next I connect a tail of flexible wire to the finish of each coil and lead it out to the rectifier box.  The rectifiers are usually single phase because they are cheaper to buy.  But it does not matter at all which wire goes to which rectifier unit.  Each coil finish just has to be connected to the AC terminal of one of the rectifiers.

About hugh

I live off-grid in NW Scotland and have spent my life playing with wind turbines. I also love small hydros. Hands on renewable energy is my thing and I like to learn and to share my experiences.
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50 Responses to Wiring up a 12-volt stator


    Hi everyone, i have 9 coils of 14AWG with 80 turns to connect together. i need a wiring diagram on how to connect them. What should i expect as output voltage?

  2. Mitchell Paul says:

    Hello sir, Hugh I have made a couple of 3 phase 9 coil stators, this one wired in parallel looks interesting, what kind of DC volts and Amps would I be looking at with a 10 coil stator. Also how do you orient the magnets on the magnet stator, and how many would I use for 10 wire coils?

    Thank you for any help you can give.

    • hugh says:

      Hi Paul,
      Yes this ten-coil design arose when I was building a machine with 12 magnets on each rotor and 9 coils in the stator to give 3-phase output. I found that I had made the coils rather small and there was room for a tenth one. Since they are connected individually to the rectifier it is not necessary for them to be in phase with each other. So I put in another coil. Technically this is 5-phase and it can run a bit smoother than 3-phase. This was the basis for my book “How to Build a Wind turbine” in 2005. A lot of these machines have been built.
      The only downsides that I have come across are first that if one diode fails it can burn out a single coil. A local rectifier failure is not enough to stop the machine dead in a high wind but it can overload a single coil. That’s the first downside. And the fact that the rectifier has to be at the top. With 3-phase you can bring 3 wires to ground level and it is easier to fix a blown rectifier. So make sure the rectifier is a good one if you do it as in this diagram.
      have fun

      • Mitchell Paul says:

        Thank you Hugh, I plan to put it together soon, I’ll send some pics of the finished stator with some volt and amp numbers when its done and tested.

      • Mitchell Paul says:

        Hello again Hugh, I was looking at the diagrams again, while I understand that when wiring the stator in the star configuration you have to have 3 magnets for each 3 coil phase, but if you had 10 coils in parallel wouldn’t you need to have just 10 magnets? I’ve watched a lot of your YouTube videos and your very well spoken I’ve learned a lot thank you.

        • hugh says:


          Each coil acts independently when you wire them like this, so it does not matter how many magnets you are using. The coils can be out of phase with each other and it makes no difference. It’s actually better not to have the same number of magnets and coils as this is single phase which is very rough in operation.

          You get the maximum output voltage when the coil pitch equals the magnet pitch. That is when one side of the coil lies on one magnet when the other side lies on the next. But there are many other factors to consider.

          If we use 3 coils for every four magnets (which is my normal rule) then we get a nice 3-phase output and we can connect coils in groups. This is what I normally recommend doing but it is not the only way to go.


          • Mitchell Paul says:

            Thanks Hugh I’ve made the stator 12 coils, 2 magnet plates 16 magnets each all made from parts taken from old microwaves which I can get for free. I’ll send you a video of the working model the bench test was productive at bout 500 rpm it was putting out 28 volts DC. I’ve been trying to figure out what to do with the other extra parts and wondered would it be worth stacking 2, 3 or 4 coils on top of each other to make a smaller diameter stator and cut down on weight? Thanks for all the info you put out there Sir.

  3. alobest onyekwere says:

    how do I over come the force that opposes or reduces the speed of rotation of my rotor when ac load is connected ,why is that happening ,and the voltage drops to only 3v ac

    • hugh says:

      The alternator converts energy. To get energy out you have to put energy in. You will need some force to turn it when it is producing current.

      Also when it is producing current, the wires inside the alternator will warm up due to their resistance, and this also takes some energy that is lost. This is the reason why you lose some voltage when you are generating power. If the voltage drops too much then you need to use a larger alternator with more magnets and thicker wires.

      I hope this helps.

  4. hugh says:

    hi Stuart,

    Yes 2 x 1mm is equivalent to 1.4mm so you can do 76 turns. Your magnets are plenty strong so you could even use fewer turns or have a bigger gap to avoid being too slow when the battery is low.

    I can’t say if the controller is a good one but you can try it of course and it seems compatible.


  5. Stuart Morrison says:

    Hi Hugh, sorry to be a bother. Hope your can help. I am in the process of building a 1200 12 vault wind turbine. I have bought two reals of 1mm winding wire and am going to use two in the hand. My questions are: do I still use 76 turns – as it states in your book, or will that have to be changed. My magnets are 25mm x 50mm – N52. The next question is: I am thinking about using a 500w DC 12v-24v wind turbine generator battery charge control unit with three phase input and DC output. Would this be suitable?
    Hope you can help.
    Many thanks
    Stuart Morrison

  6. Vimal says:

    Dear Hugh,

    I am trying to rewind my motorcycle lighting coil for a better brightness. Currently its a 12v setup which charges a 2.5 amp 12v battery, a 35W halogen bulb and some other small bulbs which total will be around 20W. I am able to read a 13.5v at battery charging wire when the bike is running. I would like to run a 100w halogen on this bike along with the current other bulbs and a big battery of 12v 5 amp or 7.5 amp or 9 amp. What should be the guage wire to use and how many turns to achieve the above setup? and what will be the reading

    On the coil there are around 152 turns and the rotor will runs from 1500 rpm to 8000 rpm. and there are 4 pieces of magnet with a size of .25 inch thick, 1.5 inch width and 2 inch length.

    • hugh says:

      hi Vimal,

      I do not have any experience with motorbikes but I will say that you can use a smaller number of turns of thicker wire to get higher current output at high rpm. If you use a smaller number of turns you will find that it does not work at low rpm, but it will give more output at high speed without being damaged. Of course this depends on the rectifier and the regulator too.

      I cannot specify the wire gauge because that will depend on the space where the wire fits. As a rule I would find out the total cross sectional area, divide this by the number of turns and then choose a copper wire with area about half of this answer. So if you have 100 sqmm of area and 50 turns you can use a wire that is 1 sqmm copper. This is the area and not the diameter of the wire.

      I hope this helps.

      • Vimal says:

        Thank you for the reply. Really appreciate the same. We tried by winding 4 layers of 19 guage copper wire of total 152 turns. And the voltage output is nearly 14v. But couldnt measure the current. So If I want to get more current with the same voltage so that I can put more load(lights) what should be the solution. I mean whether I should increase the guage of wire or increase the no of turns?

        • hugh says:


          sorry for the delay. More turns will give more voltage (although higher speed also gives more voltage so you may not need this). Fewer turns means you can use thicker wire which will delivery higher current without overheating. So I suggest you use fewer turns, higher speed and thicker wire. I think that is what I told you before.


        • hugh says:


          Use a smaller number of turns of thicker wire at higher speed and you will get the voltage and the current.


  7. habib says:

    hi Hugh

    please, I have some other questions:

    The diameter of the coil has no effect on the voltage and power? because U=2*total flux*number of turns* revolutions per seconds.
    Can I use the above diagram to make 24V alternator : I will minimise the “coil winder shap” (for example 8*8 mm in the place of 30*40mm) and I multiplay the number of turns by 2

    • admin says:

      hi Habib,

      No, sorry, the diameter of the coil is important and if you make the core of the coil very small then this will reduce the voltage produced.

      I hope this helps. If you want 24 volts then you can connect the coils in series. You would need slightly fewer turns per coil and use thicker wire. It is all described in my Recipe book.

      Have fun

  8. habib says:

    Hello Hugh,

    many thanks for your tutorials.

    I apologize for my English mistakes.

    Please, I Have 3 questions about the Wiring in the above schema:
    1- because the conexion of coils is in parralele, my question is : “each 2 coils will give more than 12V ?”
    2- is the battery will accept more than 12 V, in the case of high RPM?
    3- rectifier in above diagram will not give us a pure DC courant (needs to a Capacitor), the batterey will accept That?

    • admin says:

      hi Habib,
      1. Connecting the coils in parallel gives more current but it does not give more voltage. Actually the output of each coil is AC and the combined output of the stator is maybe around 10 V rms AC but the peak will match the battery voltage DC.
      2. What you need to understand about the battery is that it controls the voltage. It has low impedance and very stable voltage. If you try to increase the battery voltage you have to deliver a lot of current. In reality the wind turbine voltage will be the same as the battery voltage (plus a small voltage lost in the cable). The battery wins the battle.
      3. AGain you do not need a capacitor becuause the battery is a steady DC voltage. The rectifier provides pulses of DC current into the battery as the AC voltage rises enough to bias the diodes forward and feed the battery.


  9. Nito Morelli says:

    Hi Hugh,

    This should be ever so simple based on the discussions above, my apologies in advance that it is a little off topic!

    I have a question regarding 3 phase AC Motorcycle Stators. In a forum debate, the Stator outputs 470w. There are three wires that run to the voltage Rectifier. Amperage say 470w/12V=39 amps. Is that amperage split more or less between the three wires so a 30 amp connector is sufficient, or, is each wire receiving 39 amps intermittently as the phases/pulses fire?

    I use a 46amp rated connector, some 30amp rated connectors have been burning out recently. What would be a sensible connector rating and wire gauge.

    Many thanks for any help.
    Kind regards

    • admin says:


      The rms current in an AC wire feeding a rectifier is about 0.8 times the DC output of the rectifier. So 30 amps is a bit light on that basis.


      • Nito says:

        Thank you for the prompt response Hugh. It’s a Shindengen FH800 Mosfet rectifier, protected by a 30A fuse but from what I can gather on the internet 40amp rating! From your earlier response, you state in ‘an’ AC wire, therefore that rating is per wire and not divided by three wires or spread between the wires. So a 40amp rectifier x 0.8 =32amp ish.


        • admin says:

          Hi I probably do not have the whole picture here, but I will say that a 40 amp rectifier does not mean you will automatically get 40 amps out of it. Normally I would use a rectifier that is rated for much higher current than I would actually use it for day to day. If the fuse is 30 amps then the working current is likely only about 20 amps and a 40 amp rectifier is a good choice for better reliability long term. Power ratings are often the maximum rating rather than the normal load you’d be wise to put on a product. The output of the rectifier will depend on a lot of factors, but its rating is not really one of them.

  10. Rolando says:

    Hello Hugh,

    many thanks for your tutorials.
    I want to ask, should I recalculate the number of turns on a coil if I am using magnets that are half in thickness as the ones you use? For a 12v machine how would you calculate it?

    • admin says:

      hi rolando,

      If the magnet is half the thickness then possibly the flux is half the strength. Or maybe it is not so big a change – maybe only 70% of the flux you would expect with full size magnets. Anyway I suggest you use 50% more turns at least to compensate. This will mean thinner wire so the maximum safe output will be lower.

      • Rolando says:

        Thank you Hugh,
        I made a 12v stator using these magnets with two pairs of 15 wire (50 turns)… after I test it, it didn´t gave me 12v (at about 180 rpm). So, I did another stator duplicating the turns with only one wire (15) and it came up to 24v! I guess the first stator had some failure on the position of the coils.
        I guess I could take advantage of this 24 v system

        Could you please tell me how to cast correctly the stator? After 4 times it still cristalice and it looks cracked on the inside.

        Many thanks again!

        • admin says:

          hi rolando,

          It could save you a lot of trouble and expense to buy and read my recipe book. You need to add powder to the resin so as to moderate the heat of the reaction. Talcum powder or alternatively Alumina trihydrate are good choices for this. If you simply pour in liquid resin then it will heat up and as it cools it cracks.

          I hope that helps.


  11. Eki Honkakoski says:

    Hello just for FYI, a publication that seems to present a mathematical model on the motor issue that should be applicable in dimensioning. Also interesting references. Here is the link.
    International Journal on “Technical and Physical Problems of Engineering” IJTPE Journal (IJTPE) http://www.iotpe.com
    Published by International Organization of IOTPE
    June 2013 ISSN 2077-3528
    Issue 15, Volume 5, Number 2, Pages 161-166
    H. Hatami, M.B.B. Sharifian, M.R. Feyzi, M. Sabahi
    Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran
    [email protected], [email protected], [email protected], [email protected]

    • jake says:

      i was just wondering if it would increase the magnetic flux of each coil id a man was to put metal shavings or fine steel wool in the center of each coil prior to sealing the stator? hope to hear from you soon

      • admin says:

        yeah it might improve the flux very slightly. At the expense of some slight cogging and some extra loss and choking of maximum current.

  12. Laurent says:

    Hi Hugh,

    In a stator with coils in series the 3 outgoing wires correspond to the 3 phases. As it is completely symetrical you can mesure the voltage between any two wires.

    In a 12v stator with coils in parallel if you choose randomly two wires they may belong to the same phase.
    The voltage measured will be 0v.

    In my case, voltage and current have to be measured before the rectifiers because it will be done with sensors that only work with AC.

    My guess is that if the voltage or current mesured between two wires is around zero then they belong to the same phase. If if gives a higher value then it is measured between two different phases.

    In order to calculate the power generated I can then multiply the current by the voltage by the number of coils with a factor of 3 square root.

    Is that correct ?



    • admin says:

      hi Laurent,

      The current will not be sinusoidal in this case so this is probably not the best way to measure power. I strongly recommend you measure the voltage and the current after the rectifier if you want to get an accurate result. If you use AC sensors then you will need to take a lot of measurements (one on each wire) becuase the current is unlikely to be perfectly balanced. And even so the result will be rough because the waveform is complex.

      Measure with a shunt or a hall effect CT.

      cheers, Hugh

      • Laurent says:

        Hi Hugh,

        The device to mesure current is based on the emon project.

        I already use it to measure the output power of a 24 V stator.
        It works fine.


        I wanted to use the same device with CT hall effect sensors to measure the power output of the 12V stator.
        From what I’ve read CT sensors only work with AC current.

        If current is measured after the rectifier it will look more like a DC than an AC one.

        In that case will the CT do a proper job ?



        • admin says:

          hi Laurent
          A current transformer will only work with AC. A hall effect current transducer can measure DC. There may be a temperature dependent offset but it’s workable. I recommend measuring DC as I think this will be more accurate.
          cheers, HUgh

  13. admin says:

    The current you get out depends on the torque you use to drive the alternator. Work harder and you will get more amps out. Higher speed makes higher voltage. Higher torque makes more amps. Power out depends on the power you put into it. this will depend on the size of the blades (area) and on the windspeed (cubed). I don’t know what a flap turbine is but unless it is large and placed on a tall tower to reach wind then you may be disappointed by the output amps.

  14. Harold says:

    Hello Hugh,
    You describe how wire thickness effects voltage, thank you.
    How does wire size effect AMPs?
    I built a stator with a unique coil and need advice on how to produce more amps. I am now putting out 2.5 V at 50 milliamps.
    It’s a hand crank now for testing purposes but will be put on my FLAP wind turbine.

  15. Darrow C says:


    I am building a wind turbine in a student organization. We want to connect our coils exactly like this, but we are concerned that if our wires aren’t insulated that there will be some issues with the coils touching each other, the neutral ring touching the outside edges of the coils, and the “finishes” of each coil crossing/touching the neutral wire. Do you know if we should be concerned this? Are the wires in your image insulated?

    Thank you very much for any advice,

    • admin says:

      hi Darrow,

      The wires are insulated with a layer of enamel so that they can be wound in a coil, where all the wires touch. If you are working at grid-tie voltages then you should probably use sleeving over the wires that go between coils. At battery voltage it’s not necessary to insulate the enamelled copper wire, as its coating is sufficient.

      have fun

  16. Graham says:

    Hi Hugh
    Could you please tell what amp is needed for rectifiers?

    • admin says:

      hi Graham,

      You can get 35 amp ones pretty cheaply now so I tend to use them for most cases like this where I need a lot of rectifiers. You need a fair safety factor and in reality it’s not wise to use a 35 amp unit for more than ten amp currents in each rectifier. Try to find good quality PIDG style connectors that grip tightly as this is worth the money. Loose connections heat up and cause recitifiers to fail.


  17. admin says:

    hi Adrian,

    I need more info to be confident in my diagnosis of what is wrong. It would help if you told me what design you are using (from a book or not?) and what the coil connection scheme is and the rotor diameter, operating environment, and so forth. But the basic problem is likely to be the tail furling system if your stators are burning out. Make a lighter tail or reduce the angle of the tail hinge to reduce the peak power output. That’s the most likely cause of your problem.

    I have rarely seen a burned out stator. Once or twice it has occurred where there are a lot of wires to the rectifier (as in the above post) and part of the rectifier fails, overloading just one coil. Otherwise it has been a sign of pushing too much current and the simple answer has been to change the tail hinge.

    I hope this helps.


  18. Adrian Onsare says:


    We make some 48 v alternators,but in windy areas with speeds of between 6-8m/s,the stators keep burning up,with most of the burns being localized on a coil or two.

    could you kindly advise me on troubleshooting techniques and possible solutions?

  19. admin says:

    Hi Sanjeev,

    The number and size of wire for the 12-volt stators is clearly set out in the table on page 36 of the Recipe book. The purpose of the above post is to explain how and why to wire the coils in parallel to a rectifier like this.

    Every different turbine will need different numbers of turns and sizes of wire depending on the rpm, number of magnets etc. Where the coils are connected in series you will notice that the number of turns is proportional to the desired voltage. You need twice as many for 48-volts compared with 24-volts. But when we change to the parallel arrangement for 12-volts (marked with a *) then the number of turns is more than you would use for the series connection.

    Wire size is the largest wire size that fits in the space. You will see that the coils with more turns also have smaller wire sizes or fewer wires bundled together.

    • Waskly Wabbit says:

      Dr Hugh,

      I am wiring up a 12 coil, I have your book and have done some study.
      I am using 15 gauge (1.45mm) and have estimated doing my coils with 2 of the 1.45mm wires per coil @ 39 wraps to get a heavy amp capacity for a 12 volt charging system. Doing the math, it appears to be a 20-30 volt output in 3 phases AC and I would like to know your opinion.
      12 coils
      16 magnets
      3000mm 3 blade circ,

      Whats your suggestions.

      • admin says:

        hi Waskly,
        what size magnets are you using? If they are the standard ones in my recipes then why use 16 of them for a 3 metre diameter machine? what is the diameter of the magnet rotor? Seems to me that you ought to be able to fit more wire in than 39 turns of [email protected] diam wire. I need just a bit more completeness to be able to give an opinion here.

        • Waskly Wabbit says:

          Our Magnets are 1″ Wide, 2″ long, 1/4″ thick N-48
          the wire is 15 gauge, as I watched one person make his but they never shared the winding count. Seems no one really defines this very well. The rotors are 12″ and will have 16 magnets on each one, 32 total. The windings will be 12 total on a 14″ stator frame, from my best guess 39 wraps with 2 strands connected at start and finish, of 15 gauge in each winding acting as one wire, in a normal 3 phase connecting layout.
          Do you see a problem with this design??
          the blades are 3 @ a total o 9’foot 3″ diameter.
          The design is a

          • admin says:

            hi Wabbit
            I am not clear if you are conecting the coils in series/star of parallel star or some kind of delta. Series would be a bit slow and parallel a bit fast. Based on 12V battery and 9 foot blades.

  20. sanjeev says:

    You have discussed this in otherpower board, “more turns of thinner wire”, what will be the wire size you recommend? and how many turns.

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