Coils wound in pairs using 2-in-hand 1.6mm diameter wire. Each coil has 37 turns in the one we did for the workshop.

Coils in each pair are roughly ‘in phase’ if one is flipped over as shown. (Actually there is still 30 degrees of electrical phase difference between them, so they are each 15 degrees off the total combined phase angle, which means about 3.5% loss of voltage.)

Pairs that are opposite to each other are ‘in phase’ if connected backwards as shown above. Then the phases are connected in star by linking all of the starts to a neutral (black wires).

This alternator uses 10 poles made from ferrite magnets. When magnets are fitted tightly together like this it makes sense to me to use smaller coils with smaller holes and benefit from the shorter turns in each coil. It’s fun to try something different anyway.

The same winding could work with 14 magnets. But I see no merit in doing this. Maybe somebody can? The inner turns would get more induction from smaller poles, but there would be more leakage flux.

Good Day Hugh,

what is the calculation behind 10magnets, 12 poles? how many coils if it is 6 magnets?

Vw

The calculation is a bit long winded but there is some discussion of the numbers here

There is no simple answer to “how many coils for six magnets” as this depends on the magnet shape in relation to the alternator as a whole but you could for example have 5 coils arranged in a 5-phase stator. doing a 3-phase output is harder.

thanks hugh, the magnets are ferrite and its 6″ x 4″ x 1″ in 17.2″ OD plate, outer dia gap will be 7″

Yeah i am following this thread, after this only, again thought of making use of those magnets.

copper wire thickness, is 14awg.

vw

Hi VW here is a picture of 9 coils on your 6 magnets. Connections are simple – just use 1,4 and 7 for one phase and so forth. No need to reverse any connections.

I’d suggest you get bigger disks (19 inch diameter) for this project.

Hi,

What will happen if i wind it this way but use a 12 pole as well (12 pole, 12 coil). Would it work even phasing is the same?

If you use 12 poles and 12 coils then this will be a single phase alternator. You will need to reverse the wires on every second coil. Finish of coil 1 is connected to finish of coil 2, start of coil 2 to start of coil 3 etc. It will work well but you will get some vibration/noise in the machine and there are other advantages to 3-phase.

Actual coils and poles were designed as a single phase, 1st coil connected to the 2nd, 3rd up to the 12th coil winded alternatively. Since pole modification is of my limitation right now, would winding the coils like of a 3 phase (preferably delta connection) produce more power output compared to the output of the original winding connected in series up to the 12th coil?

please send connection diagram of 12 magnets and 9 coils connected in 3 phase connection

hi

You can find a diagram at the end of this one

Hugh

http://www.6pie.com/images/flatcoil.jpg

Hi, are you having any problems when one magnet passes over both sides of same coil?

hi Lauri

That’s a good question, and in the past to be honest I would have thought that this would be a problem. When there is one magnet on both sides of the coil, it’s induction is indeed cancelled out. However this only happens during a certain part of the waveform when the voltage is low anyway. I would not say it happens when the voltage is anywhere near its peak, which is when the coil is conducting current.

That’s my explanation but whatever the reason I seem to get good results with these smaller coils.

The main advantages of smaller holes in the coils are that I can fit more coils with wider legs into the same space so more coil turns of wire, and at the same time the turns are shorter so the resistance is less. It’s a new way of thinking for me since I would have always said you should go for the maximum voltage by using a large hole in the coil but I am finding out that this way works well for alternators with magnets that are closely packed together, and the ferrite magnets are cheap enough to do that.

Hugh

respected sir

i am making axial flux generator of 16 pole AS i am refering ieee paper they have mentioned three phase stator winding

double layered full pitched ..

no of coil 48

turns per coil 7

thicknesss of the winding is 5mm

can u please help me .. i m getting confused as 16 pole and 48 coils so one pole would cover 3 coils

could u please make understand with drawing of three phase stator with pole and winding connection

sorry i had put some data misssing tht is..

outer diameter of rotor 200mm’

innner diameter of rotor 110mm

thickness of magnet is around 6mm

please help me out …

hi Mallikarjun,

the winding has overlapping coils, I would say and they are large. Full pitch coils means they span from the centre of one magnet to the centre of the next.

Distribute them evenly, and you will find that you have 3 phase groups that match the pattern of magnets at different angles. Connect the first coil to the fourth and the seventh etc. That is one phase. 2nd to 5th and 8th is the next.

You will need to reverse every other coil, so swap the wires around on coils 2,4,6,8, etc. Then connect all the coils in each phase in series and connect the phases in star or delta as you wish. I prefer star.

I hope this helps? Hugh

sir

i taught that in double layer the winding would be laid side by side first phase R and R’ would be connected 6 and 7 of R and R’

and other phase would be connected to Y and Y’ would be connected to 8 and 9 of Y and Y’

AS it is axial ..

then

6×48/48 =6

so R – 1+6=7

R’-2+6=8

so on for other phase ..

please help me if i am wrong sir

and the above i stated will be for 8 pole and

magnet would be of NdFeB magnets in trapezoidal shapes with curvatures

magnet dimension would be of

outer diameter-60mm

inner diameter -47.5mm

height – 39.5mm

thickness -5mm

so the

rotor diameter would be 220mm

rotor inner diameter would be of 140mm

the stator coil would be connected as i stated above … does it work …sir

Sorry Mallikarjun but I can’t follow all this. Please email me with a full description document of some sort.

hi this mallikarjun i m making a generator ,”axial flux permanent magnet generator ” of 230 watts using Ne-Feb magnet of 42 grade ,

i have designed a rotor of outer diameter 236mm and inner diameter 116 mm

magnets shape is trapezoidal of 60mm in height and 47.5mm x 39.5mm top and bottom in length ..

i m using 8 pole rotor single sided not dual rotor so..

i need design the stat-or using toroidal coil winding three phase star connected single layer ..

i dont how to calculate the number of coils need and and number of turns per coil and thickness of wire to be used

for toroidal coil … pls do help me out ..

hi Maddy,

I’d suggest you use 24 coils on a toroidal core. Watch out for high thrust loads on the bearings. Before I can suggest a number of turns I’d need to know 3 things:

Type of magnet (NdFeB grade what or ferrite?)

Operating voltage

operating speed (rpm)

YOu can use trial and error instead and just wind some test coils to collect data and work from that. It’s the safest way in the end. But I can do some calcs if you give me all of the necessary information.

Hugh

thank for ur reply .. we are using neodymium magnet or rare earth magnets of grade 42 … not ferrite

magnet to withstand maximum temperature is represented as “grade” in my case 42 grade withdstand upto 180 degree Celsius..

Operating voltage.. 100v

operating speed (rpm) ..400rpm

please let me know any more information need …

There is a section at the end of my recipe book that explains how to design alternators. The toroidal one is a bit different because the coil presents only one leg to your single magnet rotor, but the equations will work in an adapted format.

total flux = magnet area A sq.m x flux density B (Tesla)

turns n = turns per coils x coils in series/phase

revolutions per second = rpm/60

Average voltage (which is 100/2.72 for star connected AC)

= total flux x number of turns x revolutions per second

= A x B x n x rpm/60

n=60 x V /(A x B x rpm) = 6000/(2.72 x 0.02 x 0.7 x 400) = 400 turns total

If this has 8 coils/phase I would say 400/8 which is 50 turns per coil.

There’s a bit of guesswork in there because I don’t really know the flux density.

sir dont we use average E=4.44* total flux x number of turns x revolutions per second

please let me know if i m wrong

sir

for star connected we use 100/1.732 but not 100/2.732..

i think we made missed typed

total flux = magnet area A sq.m x flux density B

=2160 x 10^-6 x1.29=2.8mwb..

Average voltage (which is 100/ 1.732for star connected AC)

= 4.44 x total flux x number of turns x revolutions per second

= (4.44 x 2.8 x 10^-3x number of turns x 400)/60

= 696.6090 turns total

8 coils/phase =696.6090/8 which is 87 turns per coil.

so i can take 88 turn per coil …

so can i use this one sir..

please let know sir if i have made any mistake ..

hi this Maddy,……. can u please the coil winding connection for the stator …as it 24 coil .. 3 phase 8 pole machine .. that is 8 coil per phase .. as the inner and outer diameter are 236 and 116.. please can u shown the diagram how it can be connected ….

sir let we know the above calculation i have made that are correct or not .. as i’m student there is no noe to guide me .. please assist me..sir

Maddy

hi Maddy,

I quote from the bottom of page 55 as follows:

“(Average voltage is a little lower than the RMS value that we commonly use to measure AC voltages.)

So the output voltage from the thee-phase winding will peak at 2.72 times higher than the average voltage for one phase. (2.72 = 1.73 x 1.57). ”

We are looking at the peak voltage and not the average so that is where the 2.72 comes from.

I hope this helps.

Hugh

thank you sir.. for your kind reply

can i have some sort of pdf or copy of your book .. for reference purpose.. that would be very much helpful for us ..

thank you

maddy

My recipe book is available for only $5 on Kindle.

http://www.amazon.com/Wind-Turbine-Recipe-Book-ebook/dp/B003XVZADA/ref=sr_1_9?s=books&ie=UTF8&qid=1280727133&sr=1-9

Anybody can download it and if you don’t have a kindle you can also download a kindle reader for your computer from amazon too.

sir i do hav this edition

Hugh Piggott A Wind Turbine Recipe Book The Axial Flux Windmill Plans Jan 2009 Metric edition

i want to know more about 8 pole 6 coil diagram and

calculation part .. i want make this one

please help ..

sir

when u would be online .. that would more help full for us to chat with you and clear your doubts..

hi Maddy,

I am online most of the time I guess. I try to answer your questions. You can also email me. I don’t know what your doubts are this time. I am busy, so please ask simple, clear questions. If you tell me ‘I want to know more’ then I will not take time to answer. You have to tell me exactly what you do not understand.

Hugh

Hello !

How important is the weight of the Tail Vane and the angle of 20 deg at the hinge?

Regards,

Bipin

The weight and the angle of the tail will both be important in determining how the turbine furls. if they are too small and light then the output may be a relatively low, especially as the wind gets stronger. On the other hand if you increases them beyond a certain point you will burn the stator or cause some other problem.

Hi Hugh, great website. Is there an optimum size of coil winding compared the the dimensions of a neo magnet? For example if I have a magnet that is 30mm in diameter and 10mm thick. I understand that the coil will be wound to have an inside diameter to match the outside diameter of the magnet. So in theory the magnet could just fit inside the coil. What I dont understand is should I make coils that are tall and thin or coils that are short in height but thicker in diameter. For example, say I need 100 turns ,should I make the coil 10 turns high and 10 turns/rows wide or only 5 turns high and 20 turns/rows wide, or 20 turns high and 5 turns/rows wide? Does it make any difference?

Should the coil be the same height as the magnet?

hi Marc,

to be honest there is no simple answer and no ‘right’ way but some will work better than others. The spacing of the magnets will be just as important as their shape in determining the optimum coils shape.

Often a coil thickness similar to magnet thickness gives optimal results. Total gap between magnet faces similar to total thickness of the two magnets is a good rough idea for optimising the use of magnets.

I like to space the neos widely since they are expensive but if you want to maximise the power from a given disk you should cram them together, and this is what I do with ferrites. Then the hole in the coil can be smaller and this works well.

I hope this helps

Hugh

ok sir thank you… for your kind reply

reply for question 3

Normal we used for star connected

stator coil space = (3.14Dm/no of coils )

Dm mean =(inner diameter of rotor + outer diameter of rotor )/2

And stator coil space multipied by factor .85 we will get space for each coil ..each coil are placed at angle of 15 degree ..

and magnet were placed at angle 45 degree in the rotor

average voltage)=4.4 ( Phimax) x f xTph where f is frequency and Tph is the total number of turns per phasex.936

( 100/1.73)=4.4 ( Phimax) x f xTph where f is frequency and Tph is the total number of turns per phasex.936

(Tph)total number of turns per phase=103.908

Tph=ZxS/3

103.098×3/24=Z

Z=12 turns

instead of 12 we made 18 turns

we made this with 18 turns for each coil but we could get the voltage as the air gap between the stator and rotor was more than 5mm as stator mould was a bit more out of shape ..may be the no of turns were less

so couldnt complete the project so we trying with different stator coil design

.

Let us now consider the design of 6 coil and 8 magnet

magnet dimension =43.5X60

thickness=5mm

Average voltage= 2xtotal flux x number of turns x revolutions per second

magnet area A sq.m=.002610

no of magnets=8 so..

Total magnet area A =.00261×8=.02088

flux density=N42=(Br) rem-anent flux density =.65

flux=.02088x,065=0.01357

Average voltage= 2xtotal flux x number of turns x revolutions per second

(60/2.72)=2x.01357 x Nx 400/60

N=121.91 approximate 122

for two coil per phase N will be 61

but in your calculation sir \

Question

B you have taken as .3 as flux density=N40=(Br) rem-anent flux density =.63 do we need to take it as .3 itself any reason for that

since i m using the single sided rotor not a dual rotor ..so the magnetic flux cutting the coil would be less so do we need increases the number of turn ?? if so mean.. by much ??

what is the air gap that we have to maintain between rotor and stator would

waiting for your timely reply

Thanking you

Mallikarjun(maddy)

hi Maddy,

I do not understand much of the above since it is mostly numbers and no clear explanation of where they come from nor where you are going with them. But I can expalin why the example in my book uses B = 0.3. This is because the example is the 1200 turbine which has only one magnets rotor (single sided). In my experience this has B=0.3 T.

And yes if you have taken B=0.6T then you will not have enough turns and you may have to double the number of turns to get the right speed. This will make the resistance four times higher.

Hugh

i want to know 6 pole single phase generators connection plz tell me about it with dia gram also

if you want single phase then the simplest scheme is to use 6 coils for the 6 poles. However the coils are not actually all in the same phase if you simply connect them in series. You will have to reverse every second coil. So the connections are:

Start of first to output wiring

finish of first to finish of second

start of second to start of third

finish of third to finish of fourth

…

finish of fifth to finish of sixth

start of sixth to output.

I am planning to design one alternator with 100mm X 12.5mm X 12.5mm

with 10 pole on a stator with rpm 900. What should be no. of coil, wire for coil, size of coil

for output of 50hz 230volt 4-5kva.

my magnets were N35.

Please let me know.

hi Rajeev

This type of alternator is unsuitable for producing 230V 50Hz. Also the 10 pole will produce 75 Hz at 900 rpm. I also doubt that you can get as much as 4 kW from this size alternator at this rpm. It’s much too small. sorry

Hugh

1 KW @ 220 Volts & 750 RPM with 10 N35 Magnets , Pls suggest what will be the best possible values of Number of Turns & coil dimensions.

you could try 400 turns and connect all four coils in series for each phase. It’s a rather stupid shape of magnet to start with though. YOu might get 1kW at 750 rpm 62 Hz or it might burn out. YOu’d need a large rotor to make room for thick enough wires.

I am trying with 600 rpm to get 50Hz, but I want to know the dia of winding wire for 400 turn as advised by you

Hi Rajeev,

You need to look at the rotor diameter and figure out the coil spacings and hence the cross-sectional area available for wire and hence the wire size from there. It’s all documented clearly in my Recipe book so I suggest you have a read of that and then get back to me with any questions when you have done some reading.

Any one can help me with a single phase output AC when i use a 8 poles and 8 coils?

All result i’ve got is 2.++ V(AC) and current around 0.5 to 1A(AC). How can i increase the voltage and current up to 6V and 1A by using:

•Copper wire SWG 23

•200 turns per coils

•parmenent magnet type N48 (square shape)

•size: stator 6.5″. Gap between each magnet 1.3″..

Please anyone reply my question as soon as posible.

Thank you guys!!!

hi Safwan,

YOu get more voltage and current by turning the altenator faster. Check that you have the coils correctly wired. If you are using single phase then you connect the coils in series for more voltage. But you have to reverse the connections on every second coil as it produces the opposite voltage. So connect finish of 1 to finish of 2, start of 2 to start of 3 etc…

Hugh

you mean for first coil in clockwise and second coil in anti-clockwise and the connection finish of 1 to finish of 2 and start of 2 to start of 3(clockwise)?

If you make the connections that I suggest then the effect is to reverse the direction of the turns. If you reverse the turns (turn coil over for example) then you do not need to connect finish to finish etc. Just connect finish to start of next one if you are turning every second coil over.

Hi Sir, you know what? I’m very thanks to you about this discussion. with all clockwise direction I can produce more than 6V, now my output voltage arround 10-13V.

I use connection all in clockwise, finish of coil 1 to start of coil 2. finish of coil 2 to start of coil 3 and so on until at last coil of 8. Finish of coil 8, it was my output(-).

But sir, what is the different between both connection? All my research I do, every connection must be in clockwise and anti-clockwise (forward and reverse). And Sir, I use formula, I=V/R to get the current value, it is the right method to get the current?

Can you explain to me about this situation?

I really appreciate your help. very very very appreciate.

when making a single phase stator (which I don’t really recommend) with the same number of magnets as coils, you will have half of the coils under north poles while half are under south poles. So they will produce the opposite voltage and you have to reverse the sense of the coil, or its connections.

do you mean all in same direction of coil is wrong?

If all the coils are wound in the same direction, and you have equal magnets and coils like this, then you need to reverse the connections to every second coil, or the voltages will cancel out and a well made machine will produce little or no output.

thanks you sir for your time.. may have a nice day.. hehe

Dear Sir(Admin)

I am a student and interested in Low RPM PMG. Through Google I had been searching for some designs for 5kw PMG for river current and I got a link which led me to this discussion board and now I know what to do. Thanx for all.

But what is your idea to get constant frequency suppose at 50Hz when RPM of the turbine varies in a wide range from 50 to 200 RPM??

I will be glad to being answered by you.

Thank you sir.

Use an inverter if you need constant frequency. Rectify the output to DC and inverter again. You will also need a battery or a grid connection to stabilise the situation.

Dear Sir,

I appreciate that you are among rare people who works on axial flux generator.

I am going to design 500W generator for vertical axis wind turbine.

I have used 23 gauge wire.

12 coils (wedge shape) having 130 turns each, application battery charging 12v/3amp.

We are using N48 grade neo. magnets

I request you please suggest below things.

Shape of the magnets:

Starting Torque required for the generator:

Let me know if we need to change upper selection done yet:

Although we have given order to our library department to purchase your recipe book for reference, but we also need your expert advise.

Thanks

Hi Shahid,

This is backwards. it’s better to start with the 12V 3A specification (and you also need to know RPM), then choose magnets and finish with the design of coils, wire size and number of turns.

Personally I think you are wasting your time with vertical axis but the funny thing is that almost everyone does this, so I am not surprised.

Let me know the rpm (for cut-in, and also for full power at 40 watts electrical) and also the size of the coils if you have already wound them.

Starting torque will depend on the seals in the bearings. There is no torque in the magnets and coils until you start to produce a current.

I hope this helps.

Hugh

Dear Hugh,

Thanks for the suggestion but we are in a project and need to design vertical axis, and torque issue is cleared from your ans.

Coils are not an issue I can make it again easily,

Cut in speed is 3m/s and rpm is around 70rpm.

coils are WeDGED shaped type, 130turns, having wire dia. 0.574mm, wounded on 30mm top length and 10mm bottom length.

I want to know the design procedure for it.

Is your book is helpful for such design.

If not please suggest,

My recipe book describes the design process completely from page 54 onwards. you may need to use some trial and error to find the best size and number of magnets. But it will help if you use the 46 x 30 x 10 ones in the recipes, which are also widely available.

70rpm is very slow, but the power is also very low so the rotors should not be too large. Get back to me with any questions.

Have fun

Hugh

I will get back to you when completed.

Thanks……………………

Hi Hugh,

Your wind power “Bug” has bitten me. I have 24 neo magnets 46 x 30 x 10 mm and 6kg of 1.6mm magnetic wire. I have made up two magnet plates of 6mm x 305mm, and fitted 12 magnets on each plate N..S..N..S placing. This info I got from ” Other Power” website. I then turned 9 x coils of 140 laps of 1.3mm magnetic wire, and did the castings. My problem is that I see good voltage, but very little amps. The machine is meant to give 48 volts. The blades are 3 x 1.5m alluminium. If disconnected from the batteries, I get up to 130 volts output. The coils are connected in3 x series/star configuration. As the wind speed increases, the battery (4 x 12volt 105 a/h) increses in voltage up to 62 volts and even higher, but very little amps. I have even replaced the amp meter. I first though the blades are stalling, but this does not seem to be the problem. I have a fairly good electrical back ground.

I would like to turn new coils for the machine with the 1.6mm wire on hand, that would give me as low as possible cut in speed, with good amps at higher speed.

Could you please assist me with this. What number of turns should I use per coil.

I will be ordering your metric book next week.

Regards

Hi

If you have volts but no amps this usually means a high resistance. Check each battery when on charge to see if they all go up to 15 volts? I suspect there is a resistance between the voltmeter and the batteries. Or the batteries are each and all high resistance themselves. Seek out where the voltage is going. That’s your high resistance.

turns per coil will depend on blade design. I make high speed blades but your aluminium ones may be rather slow. However this would be a voltage issue at first.

If you want to avoid frustration the best way is to read and follow my recipe book 140 turns should work for 48 volt output if you wired it up correctly.

Hugh

sir

For 750 rpm permanent magnet alternator 1 kilowatt (8 poles)

what should be the wire guage & connection & stator width length & slots

please send me details to my email address

mohdy246@gmail.com

yousuf India

hi Yousuf,

I’d need a bit more detail for this including the size of the magnets and the desired output voltage.

Hugh

very helpful

Hi sir .. Your blog is really helpful in constructing PMA.

i am trying to build up a permanent magnet alternator which can run in low rpm ..

I need your suggestions for 2 KW or more output setup for home use ..

I have 24 neodymium disk magnets N38 grade, having diameter of 30 mm and 5 mm thickness.

please suggest me the the setup of coils, wire guage, no of turns per coil, no of coils or any thing which may help ..

I have been thinking of dual flux permanent magnet alternator ..so that 12 magnets on each rotor disk and stator sandwhiched in between.

I have setup the basics now just stuck upp on the stator. confused relating the winding stuff ..

please suggest me proper solution ..

hi Syed,

To be honest it will be difficult to get 2kW from these magnets. You will need to run at quite high rpm. If you want 2kW at low rpm it would be better to use more, larger magnets. for example you could use the design for the 4200 mm diameter machine in my Recipe Book. It can produce 2kW at 300 rpm. But it needs to be well cooled by the wind to work like this.

If you need 220 volts for home use then you will need to use an inverter. The alternator will produce 3-phase power with variable frequency and normally you would charge a battery or connect to an existing grid using a grid-tie inverter.

Hugh

thanx for your reply sir.

is their any possibility .. like if I could use double magnets on each rotor .. i mean 24 magnets on each rotor (one magnet attached to another forming 12 pairs on each rotor) .. as neodymium magnets are magnetised through thickness .. so that if I attach two magnets together so their flux would increase ..

48 total magnets on two rotors ..

***from above

the desired output voltage is 220 volts for home use ..

Sir !! please guide me regarding the above query ..

hi Syed,

Even doubling the magnets will not reach the level you need. I’d say you need about 6 times that magnet volume to do what you describe. Also you need to study the question of supply voltage. You need to understand the need for storage in the system if you are not connecting this to the grid. So you will need to have a battery. Then you can produce 220 volts from that battery using an inverter.

I hope this helps. I’d need to know a bit more about what you are doing before I can help in any more detail. You want to run at low rpm but that is pretty vague and you do not say what is driving it.

Hugh

I’m looking to build a low RPM 12V DC generator. I would like to build one that has two revolving groups of magnets turning past a group of coils stationed between the two groups of magnets.

At moderate RPM’s I would like to see an amp or so. I would like to charge a battery bank and am not very interested in an AC generator because of the required step down rectifiers needed. I would rather create power that can be stored as is.

I can not seem to find clear answers on how many magnets, what size magnets, how many coils of which size wire, how many turns on each coil and how the coils should be wired together.

Your help would be greatly appreciated.

Thank You, John

hi John,

When magnet move past coils, they produce AC voltage in the coils. If the coils themselves rotate past magnets then it is possible to switch this to DC using a commutator but by far the simplest way to get DC is to use a rectifier. So I suggest you generate 3-phase AC and rectify it to DC with a bridge rectifier. This will not reduce the voltage by much and is much simpler and more reliable than a commutator.

My Recipe book describes how to choose the magnets, wind and connect the coils and so forth. There is even a section on how to design the alternator near the end of the book, but you should not need it. If you have a specific cut-in rpm in mind for 12-volt battery charging them I can help you design a suitable alternator based on one of my standard designs or using magnets of your choice.

Have fun

Hugh

Hugh,

I have bookmarked your book page just in case. I certainly appreciate your incredibly quick and informative response. I honestly figured I’d be lucky to have an answer inside of one week.

I have built several where the coils spin within a field and commutators pick up the power. I have made a couple of cool machines and one pair of AWESOME commutators. These are small though and put out from .01 to .03 volts with RPMs so high that coils balloon out and commutators take a viscous beating.

I really like the design type that I mentioned previously where the coils are stationary between two magnet boards and the coils are hard-wired instead of using commutators.

Well I guess it’s time to build and rectify me some 3-phase!

Thanks again Sir,

John

p/s i need help,for 20kva alternator with 6 coil ,swg 17 1/2,7wires in hand, 0 to16 all round of 5 coil.how to connect is a little bit difficult?

hi

I need a bit more information. I think it will need to run at very high rpm to produce 20kVA!

But it’s important to know the size and number of magnets, the desired voltage, the number of phases, the RPM of operation, and whether it is on a wind turbine (well cooled by wind). You need to tell me all these things or at least most of them and I can begin to help you.

Best

Hugh

Hi Sir,

Am currently doing 3 phase brush less DC motors project,16 poles ,18 slots i want to know how to determine number of turns per slot the winding scheme is AaABbBCcCAaABbBCcC.

It might be a trivial question to ask but please help me out.

Thank you in advance

Regards,

Shruthi

hi

Sorry I can’t help as I have no experience of the type of machine you are designing.

Hugh

Hi Sir,

I found a formula after a lot of searching but i didnt understand how it is derived and is it a standard formula

here is it

Turns per phase = 17000 x (System voltage V +1.4) / ( Desired cut in speed RPM) / (Strength of flux in Tesla) / (total area of magnet face in square inches)

can anyone please explain it?

and total area of magnet face means the area of magnet it is facing the stator?

magnet dimensions:

2.5cm length,and 2.2cm height thickness 7mm

so area of magnet facing stator is 16(poles) X 2.5 X 2.2=88cm2=>13.6sqinches

is this right way?

hi Shruthi,

That formula is a guide for designing an alternator that will charge a battery (at “system voltage”) via a 3-phase rectifier. I am not sure how useful it can be for designing a motor. I have never designed a brushless motor so I cannot help you there.

Yes the total magnet area is the area of magnet surface facing the stator on one of the two rotors. So if you have 16 poles on one rotor then you are correct.

Hugh

Good Day Sir. I am now working to make a permanent magnet generator with a 8 inch diameter rotor and 9 inch diameter stator. The rotor will have 10 magnets with 1 inch diameter and 1/2 inch thick. While the stator will have six coils. Will this generator creates great output. I am worried because the gap between the magnets is 0.6 inch only. If the rotor with magnets rotates through the coils there will be two magnets in one coil. I saw a picture above that the output will be cancelled out if this happen. Is this true? Thank you.

hi angelo,

I don’t understand why you only want to have 6 coils. You are right that much of the magnetic flux will be wasted in cancellation and the length of the turns will be excessive and the number of coils only few. So I don’t think this is a great design, no.

Hugh

But will this design creates an output for a 50 watts per 12 hours?

Hello Hugh. Thanks for the response but if I will make the diameter big enough will that be great?

For example. 10 magnets with 6 coils and a diameter of 12 for rotor and 13 for the stator? Thanks i just need it very bad. Thanks a lot.

HI Angelo,

I don’t know what else I can tell you. 10 magnets is not a great idea. 8 magnets and 6 coils is a good combination, yes. It’s the classic ratio 4 to 3 which I almost always use. Go ahead and do it that way. I cannot promise you will get 50 watts without a whole load more information about what you are doing such as the type of magnet, the turns per coil, the system voltage, the rpm, and what you plan to use to drive it. Have fun.

Hugh

I just need a 50 output for that will that be enough? Or can i make it 8 magnets with 6 coils though?

Sir,

Please may I know the best type and shape of Magnet to use with a Triangular Coil or say Trapezoidal?

I am not building a Wind Turbine. No. My project is totally different. But I need an High Output Power to achieve my main aims.

I am having 2kg of 1.86mm thick Enameled Copper Wire.

Also, is the Trapezoidal shaped coils MOST effective or the Rule of Center Wideness of Coil to Size of Magnet the most important issue?

I mean if my coils are Circular in shape and are 70mm Outer Diameter and 50mm inner diameter, must I use just use 50mm diameter magnet?

Is Triangular or Trapezoidal coils the most efficient shape?

Can a Block magnet be used over a Trap. Coils?

Will the output efficiency be the same with if Trapezoidal Shaped magnets were used?

I am deeply curious sir.

hi Dare,

The best coil shape depends on many factors. If the magnets are widely spaced then I consider that it’s best to have a hole in the coil which is the same shape as the magnet face. But to be honest you can often get more copper into your coil by making the hole trapezoidal so it is smaller at the inner end. As the magnets get closer together it becomes attractive to use a triangular hole in the coil.

I like to study the way that the coil legs move through the magnetic flux. Of course the flux itself is not uniform nor does it have sharp changes in density. But if both legs of a coil are under (different) magnets at the same time then I consider that this will produce a good peak voltage.

A trapeziodal magnet is a good thing but only marginally so I don’t worry about that too much. You can get good results with rectangular and even with circular magnets. If you want to get the best out of your magnets then I would say use a large disk and space them widely. If you want to get the best out of your small disk then use many magnets and even trapezoidal ones and cram them in tightly. It depends on your goals.

Hugh

Thank you so much for your surprisingly timely reply.

“If you want to get the best out of your magnets then I would say use a large disk and space them widely. If you want to get the best out of your small disk then use many magnets and even trapezoidal ones and cram them in tightly. It depends on your goals”

By cramming, do you mean I should place my magnets on rotor as is was done here => http://xindaenergy.en.alibaba.com/product/1978948961-221458799/5kw_150rpm_axial_flux_permanent_magnetic_generator_PMG_for_vertical_wind_turbine.html ??

yes this is crammed in all right.

I do not like the stator inside the casing like this. It will not be well cooled. When it gets hot there is a danger it will detach from the shaft in the centre. It’s more reliable to support the stator at the outside and allow cooling air to flow over it.

Hugh

Alright. I do not intend to use that type of design. I plan to use Cardboard Sheet and Plywood for my Rotor and Stator respectively with Split Stator Method.

So this allows for pure ventilation and constant cooling.

Now may I know if I can use Block magnet over Trapezoidal or Wedge Coils?

If my Stator is 30cm wide, what type of coil shape is best to use over it?

Wish I can show you some pictures of what I have done so far before I contacted you.

How can I do that?

yikes I never heard of cardboard rotors before. But have fun!

Use the magnets you can get. Trapezoidal is too expensive for me, with very little gain. Block is fine for me.

Coil shape depends on how close the magnets are together. If they are quite close together then I use triangular shaped coil formers.

you can send me pictures by email of course.

hugh@scoraigwind.co.uk

Hugh

I today sent the pictures.

Do you mean it is best to use Block magnet over block coils?

Will it not be better to use Vortex connection instead on connecting the coils in phase?

Vortex connection means using Eleg eletrolytic Capacitors and Diodes to collect power from each Coils and later connecting the coils in Series or parallel Series or parallel using Diodes and caps again?

sorry I do not know about vortex connections but using capacitors and extra diodes is all going to increase your losses. I’d suggest you keep the circuit simple.

Hugh