Alternator Inductor Coil Output Equation (?)

[Elektrostatik]

Hello!I'm working on an experimental alternating current generator project
and need specific equations to calculate voltage and current output
from a permanent magnet driven inductor, so I will have an idea what to expect
before I commit real money to expensive materials.

the only variables in the equations should be those which I can directly control and measure :

using the symbols below :

S - wire cross section area ( mm² )
t - total number of turns
L - number of winding layers
W - turns per winding layer
R - coil DC resistance (Ω)
C - coil diametre ( mm )
H - coil height ( mm )
c - core diametre ( mm )
h - core height ( mm )
T - magnetic flux density ( T )
M - magnet diametre ( mm )
m - magnet height ( mm )
a - polar reversals per second ( 1600 / s )
g - gap between rotor magnet and stator coil inductor ( mm )
A - output current ( A )
V - output voltage ( V )
K - ambient temperature ( 293.15 K )
P - core permeability ( mH )design component values :

alternating polarity permanent magnets mounted parallel to the rotation axis
near the rim of the rotor.

rotor magnets : 30 mm Ø x 30 mm sintered N52 grade Neodymium
magnet flux density : 1.5 T

inductor core : 12 mm Ø x 12 mm soft iron
core permeability : 80? mH
inductor coil : 12100 turns of 0.106 mm Ø polysol insulated copper magnet wire 110 windings x 110 layers
coil resistance : 2 Ω / m x 912 m = 1824 Ω DCR
thanks in advance!

 

[NascentOxygen]

Welcome to the physics forums, Elektrostatik! I hope you find the experience both illuminating and electrifying. :tongue2:

As for your specific questions, it's a pity that such design equations weren't available from the same source as you found all those electromagnetic terms and units. Your request does seem a tall order, but I shouldn't underestimate the capabilities of some of the people here.

Good luck with your project!

 

[Elektrostatik]

Welcome to the physics forums, Elektrostatik! I hope you find the experience both illuminating and electrifying.

Thanks!

As for your specific questions, it's a pity that such design equations weren't available from the same source as you found all those electromagnetic terms and units

the terms and units are all from my head, from years of hands-on experience making guitar pickus, so I don't need the internet for terms and units, I need equations to put the terms and units I already know to practical use, since I've never built a generator before,
and even though I have formulas for calculating inductance.. knowing the inductance of an air core coil is useless
without including the permeance of the soft iron core in the formula to calculate the total inductance of the electromagnet,
and then all the other variables to calculate the final output voltage and current.

the coil induction formula I use is :

Ø - coil diametre
H - coil height
T - coil turns
µH - induction (microHenrys)

µH = ز x T² / (Ø x 18) + (H x 40)

which tells me absolutely nothing about generator output

 

[jim hardy]

From Magnetics inc Bulletin FC-S8:

Background
Faraday’s Law continues to have the final word in magnetic design.
Faraday’s Law: V = 4.44 N A_e f B 10 -8
Where: V is the applied potential (volts rms)
4.44 is the form factor for a sine wave
N is the number of turns
A is the core cross-sectional area (cm²)
f is the frequency (hertz)
B is the peak flux density (gauss)
Since no practical materials have been discovered which allow extremely high current
density without loss, or extremely high flux density without saturation, the only variable
in Faraday’s equation that can be adjusted to significantly shrink the size of a magnetic is frequency.

for SI drop the 10^8, use meters and Teslas

4.44 is 2pi/√2

 

[Elektrostatik]

Perfect!

Thank you Jim for the link and for the equation
I appreciate that very much.

This is just about exactly what I needed,
although the induction gap is not included in the formula, which is an extremely important variable,
and also current is not included in the output - but this is a very good start.

So..

2∏ / √2 = 4.44288 for 3 extra digits of precision

in cgs units :

V = 4.44288 x 12100 t x 1.13097 cm² x 1600 Hz x 15000 G x 10^-8

= 14591 V

or strictly in mks SI units

V = 4.44288 x 12100 t x 0.000113097 m² x 1600 Hz x 1.5 T

= 14591 VSince Current is a product of Voltage and Resistance (Ohm's law) I = V/R
is it possible to extract the output current from the voltage potential and coil DC resistance?

if so.. then given the DC resistance of the coil (1824 Ω) 14591 V / 1824 Ω = 8 A ...Surely that can't be right (?)

.

 

[Elektrostatik]

I found this inductor core loss calculator on TDK's site

http://www.tdk.com/core-loss.php

unfortunately I won't have all the values to use it until I have equations for calculating
inductance with a soft iron core, as well as impedance and current in the coil.

from what I've found so far, soft iron is quite lossy at AC frequencies
due to eddy currents, so maybe I would need to use a laminated core instead.

 

[jim hardy]

Well you DO have a lot of turns there...

0.1mm wire is mighty small stuff, suitable for signal but not power. Isn't it around #30?

Take apart a discarded electric motor and measure the armature wire's diameter.
probably you need fewer turns of larger wire.And yes, at 1600 hz you probably want a laminated core
here's a starter:
www.micrometals.com/appnotes/.../corelossupdate.pdf

 

[Elektrostatik]

0.1mm wire is mighty small stuff, suitable for signal but not power. Isn't it around #30?

Take apart a discarded electric motor and measure the armature wire's diameter.
probably you need fewer turns of larger wire.

I normally work only with signal wire in voice coils, so armature wire is quite massive by comparison.

Here in Europe - all wire gauges are the same as wire diametre in mm, not including insulation,
but I believe 0.106 mm gauge is somewhere around 37 AWG.

With power inductor wire, it seems that bigger is better, and with fewer turns.
Around 0.5 - 0.6 mm gauge is what I'm finding in motors, so I will design a new coil
with wire in this range.

I'm not sure if I can find a round laminated core,
and I'm not so excited about using a square core.

Thanks for the link!

 

[Elektrostatik]

so now I've made some extreme design changes to the inductor

new values :

10 mm x 10 mm soft iron laminated square core (chamfered or slightly radiused edges)

36 turns of 1.5 mm Ø polysol insulated copper magnet wire, wound directly to core
resistance : 0.01 Ω / m x 2.88 m = 0.0288 Ω DCR

V = 4.44288 x 36 t x 0.0001 m² x 1200 Hz x 1.5 T

= 28.7 V

if this voltage is correct, then after rectification, it's well within the limits of the LT1083 voltage regulator
I plan to use for 12 V regulated output

I would still need to calculate the current before going any further

 

[jim hardy]

I would still need to calculate the current before going any further

your V/Ω would be upper bound.

Be aware you'll get somewhat less because the current in your armature tends to oppose the flux from your magnet.

I don't know how to calculate that. But this link suggests that these rare Earth magnets' equivalent amp-turns per meter is quite substantial, well in the tens of thousands... with just 36 turns and modest current my intuition says you'll be okay.. but it is a guess.

http://www.kjmagnetics.com/specs.aspin fact it's an interesting site, nice glossary and tables...

http://www.kjmagnetics.com/

you know to keep air gap as small as possible and have a complete magnetic circuit.

 

[Elektrostatik]

your V/Ω would be upper bound.

I wonder if using a bifilar coil would be a solution

it depends on whether or not the strands of a bifilar winding are counted separately per turn

 

[jim hardy]

i stumbled across a transformer tutorial you might enjoy.
It's aimed at 60 hz but shows thought processes...

http://mysite.du.edu/~jcalvert/tech/transfor.htm

 

[Elektrostatik]

Thanks Jim

The transformer tutorial has quite a lot of useful equations and information that apply to any type of inductor.

Some of which has actually helped solve some core eddy current and loss issues

there is also a current capacity issue

the current capacity of copper wire is 3 A / mm² , so 1.5 mm gauge wire can only handle 5.3 A

Be aware you'll get somewhat less because the current in your armature tends to oppose the flux from your magnet.

There is actually no armature in the design

Sixty N55 Neodymium magnets with a mass of 159 g each will be mounted in force fit holes around the perimeter of a polycarbonate flywheel, parallel to the rotation axis, the 28 kg flywheel has 35% of it's mass at the perimeter
and stores kinetic energy with a moment of inertia of around 16 kg/m², an angular velocity of 125.6 rad/s ( 20 rev/s),
so an angular momentum of 2009 N·m·s

at this rotation speed, the 60 magnets produce an alternating frequency of 1200 Hz

120 inductors are to be fixed on 2 stationary ring mounts, 60 on each side of the flywheel
aligned with the 60 flywheel magnets, so that the magnet poles pass directly over the inductor coils coaxially (orientated face to face)
the inductors on the opposite side are mounted 90° out of phase for full DC rectification,
with each inductor having it's own bridge rectifier and each fed into it's own voltage regulator.

So this is not like any existing generator

 

[jim hardy]

make sure your magnetic circuit is a closed loop - only air part should be the airgap you need for mechanical clearance.

Kirchoff's Law for Magnetic Flux, if you will allow me that misuse , says the flux must get back to opposite end of your magnet. You want it to get there through iron not air.I suppose that's what your ring mounts do?
Sorry for the endless questions, just it's so hard to paint or imagine a mental picture from words only...
"Science is language well arranged" - Lavoisierold jim

 

[Elektrostatik]

make sure your magnetic circuit is a closed loop - only air part should be the airgap you need for mechanical clearance.

Kirchoff's Law for Magnetic Flux, if you will allow me that misuse , says the flux must get back to opposite end of your magnet. You want it to get there through iron not air.

If you mean the air gap between the poles of the flywheel driver magnets and the tops of the inductor cores,
the mechanical clearance gap would be no more than 1 mm.

you can get a good mental picture of the design if you visualise an 810 mm Ø x 30 mm disk flywheel
rotating on an x axis, with sixty 30 mm holes drilled around the perimeter, parallel to the rotation axis,
10 mm from the outer edge, with a 40 mm centre-centre spacing, forming a ring of 60 magnets,

Each neodymium magnet is 30 mm Ø x 30 mm and force fit into the 60 holes around the outer perimeter of the flywheel,
with both poles sitting flush with the left and right side surfaces of the flywheel,
the polarity of each adjacent magnet is reversed : N - S - N - S..
inducing an alternating current in the inductors as the flywheel rotates at 20 revolutions per second,
with 60 alternating poles per revolution, producing a 1200 Hz alternating current.

The flywheel magnets hover past the stationary inductors in a parallel plane,
the inductors form 2 inductor arrays, one on each side of the flywheel, one array shifted 90° out of phase
relative to the other, and each mounted on two 810 mm Ø support rings on either side of the flywheel.

Both the flywheel and inductor support rings are non-conductive polycarbonate
and have no influence on the magnetic field.

I may be having second thoughts on the iron cores.. which seem to cause more problems than they solve,
not least of which is the magnetic drag effect of 120 iron cores on the angular momentum of a magnetic flywheel.
such a drag effect could effectively act as a brake (!)

Perhaps I've been underestimating the extreme flux density of the N55 Neodymiums to induce enough current in an air coil.

N55 magnets this size actually have so much magnetic force, they're considered a 'safety hazard'..

 

[SirAskalot]

First off all i can say that (if I have understod the design correct) you wouldn't get 1.5 T through your armature coil. Look at the B(H) curve of your magnet. This because your flux path has a very high reluctance ( mostly material with permeability of 1). Thus the leakage flux in the machine would be large.

As mentioned before, like a transformer core, the complete flux path should be closed ( except the air gap between rotor and stator) by a material with high permeability. Related to your design, the inductor support rings should be made of soft iron.

Or have I miss understood the design? A simple drawing (from the top) would be helpful.

 

[Elektrostatik]

First off all i can say that (if I have understod the design correct) you wouldn't get 1.5 T through your armature coil.

Hello,

I'm afraid you have indeed misunderstood the design, as there is no armature and no stator.

A standard generator is simply a motor operating in reverse, so rather than 'drawing' current to drive an armature..
standard generators 'produce' current when their armature is externally rotated by some mechanical means.

This design cannot operate as a motor under any conditions, there is no armature and no stator.
The flywheel is brought up to operating velocity by mechanical means, and continues to spin by angular momentum.

My previous post gives a detailed description of mechanical, electrical and magnetic design and construction.

the only conductive parts of the generator assembly are the inductor coils - which are stationary,
and the magnets - which are mounted on a rotating flywheel.

The inductor coils operate in isolation, absolutely independent of one another,
and there is no electrical or magnetic communication between them.
Each coil is individually rectified by it's own bridge rectifier, and each drives it's own independent voltage regulator.

As an analogy - you can think of the support rings as two 81 cm Ø plastic hula hoops,
which only function to hold the inductors in position as the rotating flywheel spins passed them.

.

 

[jim hardy]

Magnetics is not well taught.

There's a magnetic circuit analogous to an electric one.
Magnetomotive force (MMF) is what makes magnetic flux flow(pardon the expression) around a magnetic loop,
just as electromotive force (EMF) moves charge around a Kirchoff's Law closed loop.
Reluctance is opposition to magnetic flux, analogous to ohms.

Flux is MMF/reluctance

Air is a only decent insulator for magnetic flux, but an EXCELLENT one for electric current.
So it's not intuitive to us just how much magnetic flux gets reduced by an air gap. We can feel magnets acting through air, so we forget to notice how much stronger they pull when close(not much air).
Put one of your magnets in a C-clamp so there's a closed iron loop and experiment with air gap .

The MMF around a magnetic circuit is the sum of the rises and drops, just as in an electric circuit, and it adds to zero.
Your magnet is a strong MMF source (rise). See that magnet manufacturer link, he gave MMF in oersteds and a conversion to amp-turns/meter.

Your flux will be MMF / Ʃ(reluctances)
The airgaps are large reluctances
Iron is a smaller reluctance by its relative permeability ratio.
So you want as much of the magnetic path as possible to be in high $\mu$ material.

Take apart a car alternator and observe - they spin a multipole electromagnet rotor,
and the magnetic path comes out rotor point, through laminated iron core, back into adjacent rotor point.

A motorcycle alternator is similar but the rotor is a permanent magnet with many alternating poles like yours, just it'a all one piece not discrete magnets. Their coils are also on an iron core.

So - build yours with "hula hoops" of whatever you planned, but leave yourself ability to substitute iron and see whether voltage increases. old jim

 

[Elektrostatik]

Magnetics is not well taught.

That's actually more than true, given that most of the population are quite familiar with basic electric units :
Volt, Ampere, Watt, Ohm.. even those with no interest in electronics, but relatively few people have ever
heard of SI magnetic units : Weber, Tesla, henry.. even within the magnet 'industry' the old cgs units :
Gauss, Oersted and Maxwell are still in standard use, but most likely due to the size of the cgs units being more managable.
Amazingly the photomagnetic effect has been unknown until only a year ago,
and would likely have remained unknown - if all electromagnetic science and engineering research
were based strictly on standard equations.

So - build yours with "hula hoops" of whatever you planned, but leave yourself ability to substitute iron and see whether voltage increases.

The hula hoop analogy is intended only to build a mental picture of the rings, not to be taken literally of course.
The actual inductor support mounts are flat, 20 mm thick polycarbonate rings, the same diameter as the flywheel.

The inductor coils were originally designed with soft iron cores, due to the high permeability of iron.
Undoubtedly iron cores would produce a much higher output than an air core, my only concerns are eddy currents
and frying the insulation with excessive current.

The air gap between the magnets and inductor cores will be kept to a minimum,
mechanically limited by clearance requirements that account for deviation and distortion
of the flywheel during operation at maximum angular velocity on high precision bearings.

I've calculated a tensile stress of 18 MPa on the flywheel at 20 rev/s,
which allows a 4-fold tollerance below the 75 MPa tensile limit of Polycarbonate.

The only real variables in the design now are the inductor core material and wire gauge.

With the information you've given me, I've been able to do most of the calculations needed to make predictions,
mind you, all the values that count will come from real-world testing.

 

[SirAskalot]

In my mind your coils are, by definition, armature coils. Also your coils are stationary hence they compromise the stator! Different name, same sh**! Your flywheel with PMs ("field winding") are rotating hence the name rotor.

But what the heck, that's just the industry standard, let's use some other weird name for it!

Unless you can come up with a drawing who says different, I do believe I have the correct design and operation of your machine. It is widely used in some applications, but with 'some' modifications i order for customers to want to buy it.

Take advice from professionals like Jim. It can save you from much frustration.

 

[jim hardy]

Well, HERE's a neat demo of field surrounding a magnet !

http://www.kjmagnetics.com/magneticfield.asp

 

[Elektrostatik]

In my mind your coils are, by definition, armature coils. Also your coils are stationary hence they compromise the stator! Different name, same sh**! Your flywheel with PMs ("field winding") are rotating hence the name rotor.

There is no armature and no stator in the design.

Here is an image of an armature :

http://www.gearseds.com/curriculum/images/figures/web_met_armature_and_brushes.jpg

the magnetic field induced in the armature coils creates an electromagnet
which repells the permanent magenets in the stator, causing the armature to rotate.

the rotating armature is the part of the motor that does mechanical work.In my design the permanent magnets are mounted on a rotating flywheel,
there are no coils on the flywheel, the flywheel is neither a stator nor an armature.

no part of the design does mechanical work, the flywheel is free spinning on it's axis
and only continues to spin by angular momentum. the coils have no effect on this rotation.

for clarity - we can forget that there is more than 1 coil
the device operates whether there is 1 coil or 1000000 coils

this single coil is stationary and sits like a magnetic sensor 1 mm from the side of the flywheel,
so as the flywheel rotates, the magnets in the flywheel pass over the stationary sensor coil and induce a current.

this coil cannot be called a an armature, it has no motion and no contact with anything that has motion.
it is absolulety not a stator, it is only a single coil of insulated wire epoxied to a flat sheet of polycarbonate,
it's only function is that of a transducer.

Here is an image of a permanent magnet stator

http://lh6.ggpht.com/_X6JnoL0U4BY/S20Oc-R1-rI/AAAAAAAAPbA/YEnxv2EKZ1k/s1600-h/tmp28C57_thumb3.jpg

 

[jim hardy]

Actually, "Armature" means the coils wherein the magnetic field and current interact.

4. That part of a dynamo or electric generator or of an electric motor in which a current is induced by a relatively moving magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.

http://dictionary.webster.us/armature



You are correct that an open circuited coil is a flux 'transducer', voltage induced is per Faraday's law.

i say go ahead and build it, and see how well it works.
Open circuit voltage will tell a lot about your magnets and their field strength. You could connect your coils to an electronic integrator and o'scope to observe flux.
If you DO connect your coils to an external circuit,, plot torque versus current at some constant speed..

 

[Carl Pugh]

Actually I may have what you describe in my car.
It's a magnet rotating around that induces a voltage in a coil when the spark plug is to fire. At least that how they did it 20 or 30 years ago when they got rid of points.

 

[Elektrostatik]

Well, HERE's a neat demo of field surrounding a magnet !

http://www.kjmagnetics.com/magneticfield.asp

nice demo*

In the north of Sweden you can see the Earth's magnetic field in living colour (green)
otherwise known as the 'northern lights'.

Actually, "Armature" means the coils wherein the magnetic field and current interact.

Aha, okay.. I've always interpreted the term 'armature' as the rotating electromagnet and drive axis of a motor.

Actually I may have what you describe in my car.

Hm.. what model car do you have?

Most cars since the mid 80's have microprocessor controlled electronic ignition, which have no moving parts.

Unless you can come up with a drawing who says different, I do believe I have the correct design and operation of your machine.

Here is a diagramme of the machine :

1. EDGE VIEW
2. SIDE VIEW
a. axis - high precision bearing
b. polycarbonate flywheel
c. neodymium N55 permanent magnet 30 mm Ø x 30 mm
d. electromagnetic transducer coil
e. bridge rectifier

 

[Elektrostatik]

This is a simplified example of the design - showing only 1 transducer coil

in the actual working model - there are 120 transducer coils operating independently
60 on either side of the flywheel, Group A and Group B - 90° out of phase with Group A.

The target output for each transducer coil is 18 - 30 V with a peak current of 10 A

You are correct that an open circuited coil is a flux 'transducer', voltage induced is per Faraday's law.

i say go ahead and build it, and see how well it works.
Open circuit voltage will tell a lot about your magnets and their field strength. You could connect your coils to an electronic integrator and o'scope to observe flux.
If you DO connect your coils to an external circuit,, plot torque versus current at some constant speed..

Thanks Jim, I will follow your advice, and let you know the results.

 

[Elektrostatik]

Jim, do you think a 10 mm spacing between magnets will produce an unbroken sine wave?

I will not be able to test the output with an oscilloscope until both the flywheel and 1 transducer coil are completed,
and once I build the flywheel I've already invested quite a bit of time and money in materials,
so I need to get it right the first time.

 

[jim hardy]

do you think a 10 mm spacing between magnets will produce an unbroken sine wave?

Knowing how much trouble manufacturers take to produce a sine wave flux i will be surprised if you get a precise one with just magnets.

Here's a calculator that figures flux a point in space near a magnet of given shape
http://www.kjmagnetics.com/fieldcalculator.asp

i used it to figure a couple points 15mm above a 30mm X 30 mm N42 cylinder; it didnt offer me N55.

Y component on center 1597 gauss
halfway between center and edge 1417
at edge 879
5mm beyond edge 550
10mm past edge 290
40mm past edge it's 6.3, essentially zero
so the flux is highest in center like a cosine function
and if we take 40cm as distance from peak to zero
879/1597 is arccos of 56.6° but 15/40 of 90° is 33.6°
similarly 550/1597 is arccos of 69.8 but 20/40 of 90° is 45°
so flux from a single magnet only resembles a sinusoid at that distance, it's too peaky.. as one would expect.

What will the adjacent magnet do to field?
I assume your magnets will alternate N-S ?
My intuition says that'll pull the flux down away from coil and sideways over into adjacent magnet. So a short fat coil with its turns near the magnet would be better than a tall skinny one. It'll also move zero crossing of flux Y-component nearer to magnet, probably reducing that 'peakiness'.
Use that button on calculator labelled "See magnetic field", to lower right . It makes clear that you need coil close to magnet. And something to encourage flux to stay inside the coil would be a nice touch.

Forty years ago i might have tackled that flux calculation myself but not anymore. In air it's a field problem, in iron it'd be just algebra.

Keep studying this. It's interesting.

But to answer your question, i think you will get a function that rises and falls and is curvy amd symmetric and is continuous like a sine wave but will be a poor mathematical fit to one.

For making DC a flat-topped wave is better anyhow, because the valleys between peaks are narrower easing job of filter capacitor.

Objective is to learn, eh?
Have fun.

old jim

 

[Elektrostatik]

Y component on center 1597 gauss
halfway between center and edge 1417
at edge 879
5mm beyond edge 550
10mm past edge 290
40mm past edge it's 6.3, essentially zero
so the flux is highest in center like a cosine function
and if we take 40cm as distance from peak to zero
879/1597 is arccos of 56.6° but 15/40 of 90° is 33.6°
similarly 550/1597 is arccos of 69.8 but 20/40 of 90° is 45°
so flux from a single magnet only resembles a sinusoid at that distance, it's too peaky.. as one would expect.

What will the adjacent magnet do to field?
I assume your magnets will alternate N-S ?

Aha, so for N42 the centre to centre spacing between magnets would need to be 110 mm for a zero to peak sinusoid,
and for N55 an even wider spacing.

For making DC a flat-topped wave is better anyhow, because the valleys between peaks are narrower easing job of filter capacitor.

of course, a square wave would be ideal, since a square wave would rectify to flat DC
without the need for a second wave 90° out of phase. I was planning a coil with a square cross section, which has a 3:1 aspect when the core is also square,
and this gives a low and fat inductor profile.

I also considered using a Tesla spiral coil http://www.theoldscientist.co.uk/Bifilar_Tesla_Coil.html which has the most extreme voltage drop
between turns, but maybe this is a bit over the top.Yes, the poles are alternated N - S

Thanks very much for this information, it's extremely helpful!

Integral equations give me a headache

 

[jim hardy]

Integral equations give me a headache

i'm okay with those. It's dels and curls that make me hide under the bed.

Try some graphical attacks on your magnets side by side geometry.
We solved fluid flow problems that way in early 60's before programmable calculators.

And don't worry about producing a sinewave flux yet.
Your challenge will be in making intense flux go up through your coils instead of straight across into adjacent magnet.

Output can be filtered if you need a sine wave. The coarse power inverters to which i am accustomed have only third and fifth harmonic filters. Okay for most electronic loads.

It is rewarding to see your thoughts progressing. That's how we learn, small steps.
When you start in with the hand tools , design in escape routes for those ' what if's '.

Good luck!

 

[Elektrostatik]

i'm okay with those. It's dels and curls that make me hide under the bed.

Dels and curls are what make Maxwell's equations the next best thing to a nervous breakdown.

Yepp, small steps in the right direction are way better than giant leaps towards catastrophe
I'm glad I decided to post these problems here, your input has been extremely helpful.

Hopefully after some days of milling, winding, soldering and blasphemy,
I should have something resembling a working generator.

Thanks Jim!

 

[Elektrostatik]

I've updated the design to account for adjacent magnetic field geometry at 110 mm centre to centre spacing.

To keep the flywheel size within 1 m Ø I've reduced the magnet count to 20
so at 20 rev/s the frequency is now down to the aviation standard of 400 Hz

This not only improves the sinusoidal output and transducer efficiency but also reduces the cost of N55s to 33%

 

[jim hardy]

Can you get some iron filings and place two magnets under a sheet of paper? That'd let you see what flux does.

Something is counterintuitive here. Dynamos squeeze flux together but you are spreading your magnets apart.

not saying it's wrong, just I'm perplexed by the logical conflict in my alleged brain.
Chewing on it.

Check this thread in General Physics

"" Increase magnetic field density near surface of magnet "
https://www.physicsforums.com/showthread.php?t=584655



Perhaps one of the fellows from that thread will have a suggestion.

old jim

 

[Elektrostatik]

Can you get some iron filings and place two magnets under a sheet of paper? That'd let you see what flux does.

I will pick up 2 sample N55s and put them under my green magnetic field viewer film

I based the design changes on your N42 zero to peak gauss curve - 110 mm centre to centre.
I just assumed it would be more efficient to allow a full zero to peak sinusoid by spacing 40 mm from the edge.

Y component on center 1597 gauss
halfway between center and edge 1417
at edge 879
5mm beyond edge 550
10mm past edge 290
40mm past edge it's 6.3, essentially zero
so the flux is highest in center like a cosine function
and if we take 40cm as distance from peak to zero
879/1597 is arccos of 56.6° but 15/40 of 90° is 33.6°
similarly 550/1597 is arccos of 69.8 but 20/40 of 90° is 45°
so flux from a single magnet only resembles a sinusoid at that distance, it's too peaky.. as one would expect.

But then.. what seems intuitive to me doesn't necessarily make it right.

Traditional dynamos are DC generators that operate on the reverse DC motor principle using a commutator,
so would these same density rules apply to an open alternating principle?

 

[jim hardy]

I just assumed it would be more efficient to allow a full zero to peak sinusoid by spacing 40 mm from the edge.

i was trying to demonstrate that the sine function results from design of the flux field
i don't see connection between its shape and "eficiency". Sine wave is aesthetic though.

best 'efficiency' will be achieved by maximixing the fraction of field flux from your magnets that links (goes through) your windings.

That's why your iron cores in middle of your coils were a good feature IMO.

You do understand that the magnetic path for each magnet is from N to S pole , and you want as much of that path as possible to be through the coil.
Iron core can encourage the majority of flux to take that route. An iron return path will help too.

EDIT :: and yes, a synchronous machine can motor or generate.