does larger wire dia generate more voltage?

[ProblemSolver]

I am a newby at coil winding. Can someone help me with this general question.

I am making a wind generator/alternator that works well on the bench. Up until now I have been using 0.71mm (21AWG) to get a feel for how many windings I need to generate 12-20Vac at very low speed, so I have been using 5 coils with 900 turns each and 8 (50x30x10mm N52) magnets. Geez these magnets are extremely powerful. I'm hitting the desired voltage between 30-40RPM. However, I need to increase the output current from around 0.5 amps to around 15 amps to be useful.

My question is "by using 3.25mm diameter wire instead of the 0.71mm wire, is the larger wire more efficient at generating voltage than the smaller wire", if it is then I can get away with less turns. I have the same issue that other people have, and need to reduce the physical size of my coils, so I'm hoping to have less turns to achieve this.

[Bruce S]

The much thicker wire will have a lower voltage but will have the possibility of higher amps.
As the wise old saying goes "There's no free lunch" to get one you have to give on the other.
The 3.25mm is 8AWG! that's pretty thick! are you selecting this because you already have it?
Also, less turns can mean lower voltages even with the same sized wire.
Are you doing the 1 coil testing?
Also a bit more info of your setup would be helpful

Bruce S

[mab]

The open circuit voltage (i.e. at zero amps), should be independent on wire size - e.g. 100 turns at 40rpm will give you the same voltage with any wire size, so you would determine the required number of turns to give the volts/rpm you want (cut in voltage/rpm), then make your coils using the biggest wire size you can* to allow max amps, and still get that number of turns in the available space.

* sometimes people use 2, 3 or 4 in hand of a smaller wire as winding big wire into a small space gets very difficult. Also there may be an issue with eddy currents within the wire diammeter when using very large diammeter wire, but i don't know if that's actually an issue with axial flux generators running low rpm.

[joestue]

300 watts (20*15) at 40 rpm is 7.5 watts per rpm. this is on the order of 52 foot pounds of torque.
to give you an idea of how much that is, at 3600 rpm that would be a 20kilowatt generator.

the problem with smaller coils and magnets is that there is a lot more copper losses to get the same flux density. force on the magnet by the coil is proportional to flux density squared but so are the copper losses.

however the larger the magnets, the smaller the radius of the motor and so the forces increase, requiring more magnet and copper volume.

It may take me a while if I ever find the paper again but a few years ago I did find a collage level project where they simulated conditions that aren't usually tested, questioning what is what is the optimal diameter to get the most torque out of a given volume or mass of the magnet.

Turns out, an infinite diameter of an infinitely thin magnet ring resists an infinite amount of torque! so larger diameter is better.


The challenge is, a very high pole count, large diameter disk has four main problems:

The smaller the magnet, the higher the cost per mass.
The mass of copper increases significantly, eventually exceeding the cost of the magnets if it hasn't already at average size machines.
The coils get rather small and hard to position accurately.
The very high frequency produced eventually hits the frequency limit which is where the self inductance of the coil becomes an impedance limiting problem. Not likely to be a problem for air gap, 2 foot diameter, 100 pole count machines on slow moving wind turbines. 
The small air gap required of a larger pole count small magnet machine means machining and thermal expansion tolerances can get expensive.

[joestue]

I am a newby at coil winding. Can someone help me with this general question.

I am making a wind generator/alternator that works well on the bench. Up until now I have been using 0.71mm (21AWG) to get a feel for how many windings I need to generate 12-20Vac at very low speed, so I have been using 5 coils with 900 turns each and 8 (50x30x10mm N52) magnets. Geez these magnets are extremely powerful. I'm hitting the desired voltage between 30-40RPM. However, I need to increase the output current from around 0.5 amps to around 15 amps to be useful.

how are the magnets configured?

I would try again with a flat steel plate facing and rotating with an 8 magnet faced disk. I see no hope of fitting enough copper into a coil where you have two disks of 4 magnets in a 4 pole configuration, the radius is just too small and the 10mm magnets really need a solid 20mm thick coil at a minimum.

for the coils, wind a traditional 3/4 ratio test coil , just one for single phase.

[ProblemSolver]

The attached images show the magnet and air coil configuration. From day one I have used a 3mm thick steel backing plate with the eight 50x30x10mm N52 Neodymium magnets touching the rotor plate, I don't know where you got the 4 magnets in a 4-coil configuration from. The N52 magnets are so powerful that they attract nuts, bolts and tools that are 150mm (6inches) away. Perhaps the magnets I am using are too strong, because the configuration does not produce any increase in voltage above 20.5 Vdc.
The prime mover is a domestic whirlybird that is directly connected 1:1 to the alternator, it is not unattractive or out of place on a house roof and catches breezes from all directions. The final version of the alternator will have an eddy current brake for controlling the maximum speed and therefore the output voltage. 
My intention at this stage is to use the alternator to only recharge 12v storage batteries 24/7/365 per year. Where we live in South Australia, it is breezy (5km/h or higher wind's) for perhaps 95% of the day, 365 days per year.
I own two huge 3D FDM (430x430x500mm) printers and two medium sized 3D printers (300x300x400mm) and use these to print all the alternator parts, it also gives me the freedom to experiment with different designs at a moment's notice when required. 

[ProblemSolver]

Let me address some of these replies.
In answer to Bruce S response, I purchased a 28Kg roll of 0.71mm magnet wire a couple of months ago, so to achieve the required 15amps then I need to wind a coil with 5 strands of wire or purchase a thicker wire to achieve the higher amperage.

Perhaps because of my newby ignorance in this subject, I thought that the age old saying of "the more copper the better" was referring to the fact that we get a higher voltage if we use more copper or thicker copper? Obviously, I was a wrong.

I will wind a single coil later this week with more strands if I get the chance, and compare the results with one of the coils I have been using.

The magnets that I am using are big and strong, not small 20x10x5mm magnets as mentioned. I have recently ordered 20pcs 60x15x10mm N52 Neodynium magnets that should arrive in the next two weeks, these will cover more of the coils and being narrower they will hopefully not flood the area with flux. Does this sound possible ?

I guess I'll just have to suck it and see what works and what doesn't? I'll let you know how I get on.

[Bruce S]

Depending how much of the wire you have left, you could follow both Mab and Joestue's posts. THEY ARE tons better at this that I am.
The multi-strand in the hand has been quite successful for a bunch of people on here.
Also; it might be the angle of the pics, but, try getting the wire lengths to match the length of the magnets,

Ahhh, the magnet attractions  , yup !! I've had more than 1 tool come marching towards the brake rotor!!

Apologies if this goes off post, but I'm curious about your 3D printers and the filament you've decided to use.
Using those printers should also allow you the ability to lengthen the center wire posts


Cheers
Bruce S

[JW]

when there talking about "wire in hand" there using a situation that reduces eddy currents in the coil, that's why its done.

 Years back Danb said hay lets put in some rectangular type copper wire. (it actually caused smoke off the stator)

What was learned is that a thick conductor has eddy currents.

 When you do wire in hand, using several small thinness of wires they are wired in parallel for each coil winding.

JW     

[joestue]

do you have a plate behind the magnets or is the magnetic flux having to flow through air behind the coils?

[ProblemSolver]

What do you mean by centre wire posts?

I've been 3D printing since 2018, and have printed an estimated 6000 items, and worn out the original printer. So for this project I am currently using up old rolls of ABS and PETG filament, I have been using these filaments as they have higher tolerances for outside all weather applications.
At this stage I am not using ASA which is an filament specially for all seasons outside use, because that filament is very expensive.
My alternator at the moment is only designed to last about 6 months as it is a prototype, the final design will be all metal, because it has to last for 20-30+ years and must be maintenance free.

[ProblemSolver]

Joestue, yes, the 8 magnets are sitting on a 3mm thick steel plate. Earlier crude experiments show that the magnetic fields appear to be much stronger when sitting on steel.

Bruce S, The 60x10x10mm magnets (I said earlier they were 60x15x10mm, that was incorrect on my part) that hopefully will arrive next week sometime, are 10mm longer and will cover the more of the parallel sides of the coil.

I see no need to have magnets that are the same size as the overall size of the coils, because the magnetic fields at the top and bottom of the coils run parallel to the magnets and are therefore not being influenced by the magnets.

[mab]

Joestue, yes, the 8 magnets are sitting on a 3mm thick steel plate. Earlier crude experiments show that the magnetic fields appear to be much stronger when sitting on steel.

If i could ask what i think Joestue was asking:- Do you have a second steel rotor on the other side of the coils to the magnet rotor? This would help link the flux through the coils.

Bruce S, The 60x10x10mm magnets (I said earlier they were 60x15x10mm, that was incorrect on my part) that hopefully will arrive next week sometime, are 10mm longer and will cover the more of the parallel sides of the coil.

I see no need to have magnets that are the same size as the overall size of the coils, because the magnetic fields at the top and bottom of the coils run parallel to the magnets and are therefore not being influenced by the magnets.

It's hard to tell from the pictures as the coils and magnet rotor are not in the same picture, but it does look to me too like the coils are similar in height to the magnets, and that the centre hole in the coil looks much smaller than the pictured magnets. Do you have a picture of the coils and magnets to show their relative size (or dimensions of the coils?)?

Generally the hole in the centre of the coil would be a similar height to the magnet as that way most of the flux will pass through the side into the centre of the coil then pass out again through the other side, rather than through the top and bottom, which as you say, doesn't do anything useful.

[JW]

If i could ask what i think Joestue was asking:- Do you have a second steel rotor on the other side of the coils to the magnet rotor? This would help link the flux through the coils.

With these alternators can be single rotor or duel rotor(one stator in the middle). what were asking relates to complete the magnetic circuit and duel rotor machines are more efficient.   

[ProblemSolver]

Joestue: No, I don't have a steel plate behind the coils, I have been thinking of doing this for quite a while, thanks for the reminder, I will do it. I do need to increase the efficiency, because this will allow me to also reduce the bottom charging point. I need to get more rotors laser cut, so I'll add a few steel plates to go behind the coils.

Mab: The 3D design of the magnet holders was superimposed over the centre of the coil fixing holes, and I am using M6x 25mm nylon countersunk screws to fix the coils to the stator. So yes, the magnets are over the middle of the coils.

I have a newly designed a 3 phase stator which I am about to use once it is printed, that will allow me to correctly and simply align phases A,B,C with the ability of adding additional pre-aligned stages as required.

JW: Your suggestion of dual rotors makes a lot of sense, it is also something that I have been contemplating doing for a while now, so thanks for raising this again, it is on my list to explore this further.

[JW]

No, I don't have a steel plate behind the coils,

the rotors with magnets should have a steel rotor. Have a look at this topic

https://www.fieldlines.com/index.php?topic=137926.0

[joestue]

Joestue: No, I don't have a steel plate behind the coils,

if that plate is solid, it has to rotate with the magnets.

you might have a chance using pallet banding strap as a laminated disk that doesn't rotate with the magnets, at low speed the eddy current shouldn't be too high. however the pull forces from the magnets will be quite high, so you'll need a tapered roller bearing at a minimum to handle the thrust. 

[ProblemSolver]

Hey guys, I've added the second rotor with magnets as suggested, WOW what a difference it has made. I am now able to generate 20Vdc (open circuit) at just 28rpm.

The next thing to work on is using the single coil testing method, to work out how many turns and coils I need to achieve the required 15 - 20 amp for the final configuration.

I am not only a retired Electrician, but also a R&D Electronics Technician, hence my alternator has an embedded built-in Hall Effect Sensor, which currently acts as both a rev counter and also a speed control sensor, an Arduino microcontroller will start pulsing a coil forcing the Eddy Current Brake to restrict the top speed of the main shaft. I am using the alternator to only charge storage batteries, so in hopefully in 6 - 12 months we will be off-grid permanently.

My intention is that the Alternator generates power in the slightest breeze (between 5 to 7kph), so it will normally be working in trickle charge state 24hrs/365days, maintenance free for up to 25-30years.

[JW]

I made a quick post earlier today, hoping one of the others on the forum to notice.

Arduino microcontroller will start pulsing a coil forcing the Eddy Current Brake

The eddy current -- Eddy Current Brake

I have never heard of this being done... whether it is possible I don't know. Because eddy current doesn't run at right angles its a surface emission. But it does make heat in the inductors/conductors.

Arduino microcontroller

Arduino is your friend 

JW

[ProblemSolver]

JW, Google 'Arduino', there are thousands of pages on the different uses of this brilliant little microcontroller, they are very cheap (usually less than $10 each). Their uses are only limited by your imagination.

I will be using the Arduino in PWM (Pulse Width Modulation) mode, by monitoring the speed of the main shaft, so how it works is that when the main shaft is spinning at say 23 rpm, then the eddy Current Brake coil will receive a very thin pulse (maybe just a few milliseconds long) that will start to keep the main shaft speed in check. When the revs are at say 24rpm then the pulse width will be applied for a little longer, and so on, when the speed is at say 28 - 30rpm then the pulse width will really be starting to grab the Eddy Current Brake. I am not sure at this stage whether I need to use AC or DC applied to the brake coils (I think there needs to be two coils opposing each other, but to be honest it is only an idea).

The Permanent Magnets provide multiple pulses dependent on how many magnets are on the rotor, this would be in the order of 6 or 8 pulses per revolution. If there is a strong gust of wind, then the Arduino will react accordingly within just a few microseconds, but the concept that I am after with this control method, will be designed to always allow the alternator to generate power. As the revs decrease, then the Eddy Current Brake receives narrower pulses until they completely turn off, and the alternator generates what it can based on what wind is available. Very simple really.

I hope this answers your question?

[JW]

Ya that helps, will enjoy watching your progress.

JW

[ProblemSolver]

Just dropping a line to let you guys know the progress that I have been making over the past few weeks.

My original working design used 5pcs x 900 turn of air coils (no iron used), then I went back and resurrected just one of the original 500 turn coils that I initially started out with, as part of my one coil experiment but with the twin magnetic rotors, and I am still able to generate 4Vdc at 20RPM using the single coil.

I need to wind new high current coils that will give me between 15 - 20amps.

My Alternator is a single phase 5coil 8magnet set up. The magnet to Coil distance is between 1-2mm.

The next stage that I need to embark on is to wind somewhere between 300 to 400 turn coils with 5x strands of 0.71mm enamelled wire on a 3D printed former with a footprint of 25mmL x 13mmW x 30mmH.

Where I come unstuck, is that at my age (I'm over 75), I am struggling with the maths. Can someone please do me a favour and work out the approximate physical overall size of the coil for single 300turn and 400turn coils and the wire lengths? I purchased a single 25Kg roll of the 0.71mm wire, so I will need to somehow remove 5 seperate lengths of wire and place them on separate drums so that I can carefully feed them onto the coils that I need to make.

[esposcar]

The diameter of a wire itself does not directly determine the voltage generated; however, it can affect other factors that influence the overall power transmission and the behavior of an electrical system, such as resistance and current carrying capacity.

[JW]

There is a factor that shows the comparison of the factors you are asking about. It called Ohms law. We all use this but it can be complicated.