Author Topic: coil winding size compaired to magnet?  (Read 1794 times)

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Paul69

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coil winding size compaired to magnet?
« on: August 14, 2004, 08:02:23 AM »


Hi,

was just wondering what size coil winding should be compaired to the size of the magnet?

Im planning on building an axial flux type windmill. Probally a 3phase disc brake rotor type as my first project.


i.e should the magnet be aligned so it passes the sides but not the top and bottom of the coils, or should the windings be sized so the magnet cover the whole coil top/bottom/sides as it passes by.


I was thinking I would make the coils with iron core fillings in an apoxy resin inside of the  coil windings or is that less effective than air type core.


Im hoping to produce average 800watts @ 12 volts per hr with the use of two windmills.

although I havent been watching wind speed for long, the wind averages around 16kph think thats about 10mph . I live in South Australia urban area (no double story buildings and near the beach) so Im hoping for some advice on rotor size and tower hight.


well thats a big first post so I will stop myself here.

looking forward to your answers

Paul

« Last Edit: August 14, 2004, 08:02:23 AM by (unknown) »

edy252

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Re: coil winding size compaired to magnet?
« Reply #1 on: August 14, 2004, 08:39:10 AM »
hi....


concerning coils size vs. magnet size: the coils must have the shape of your magnets AND the inside "opening" in the coils should be equal or slightly larger in size of your magnets...for example: if u have a round magnets of 1" diameter, the gap of the coil should be 1" +....


about adding iron core (laminates is the name i guess)....that will give u more flux and inductance but will make it hard for ur machine to start at low windspeeds and will cause vibrations.


at 16 kph, u can't expect too much power from a small sized wind genny....for example...using my blade calculator (not my own calculations) a 3 m (10') diameter wind turbine will give 145 watts

« Last Edit: August 14, 2004, 08:39:10 AM by edy252 »

Electric Ed

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Re: coil winding size compaired to magnet?
« Reply #2 on: August 14, 2004, 08:46:19 AM »
Quote
"should the magnet be aligned so it passes the sides but not the top and bottom of the coils,"


Yes, the portion of the coil conductors that is parallel to the direction of motion (top and bottom) has no voltage induced into it.


Electric Ed


« Last Edit: August 14, 2004, 08:46:19 AM by Electric Ed »

Ungrounded Lightning Rod

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Re: coil winding size compaired to magnet?
« Reply #3 on: August 15, 2004, 12:46:08 AM »
Ed's description of the primary goal in design (have the leading edge of one pole reach one side of the coil just as the leading edge of the other reaches the other side) is dead on.


A secondary goal is to have the width of each side of the coils slightly narrower than the gap between the magnet poles.  This is because the field spreads out somewhat, so if the coils' side is wide enough the trailing edge of the magnet that just left it is still cutting the coil with field, canceling some of the generation from the next pole's leading edge.


You want some gap between the poles, so only a little of the field detours sideways and misses cutting the coils.  But you don't want a LOT of gap - because that would mean a longer period when little field is cutting the coil and thus the coil is generating negligible power.

« Last Edit: August 15, 2004, 12:46:08 AM by Ungrounded Lightning Rod »

nack

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Re: coil winding size compaired to magnet?
« Reply #4 on: August 15, 2004, 03:47:22 AM »
I know I should answer this one by building and testing a model, but it's been bugging me for a while now, and I still haven't found time to build it, so here goes...


The potential voltage induced is calculated as (this is cut from picoturbine notes)

Vmax = NARPB/2

Where:

· N is the number of loops of wire.

· A is the area enclosed by a loop of wire, in square meters.

· R is the rotational velocity of the magnets, in cycles per second.

· P is the number of magnet poles per cycle.

· B is the strength of the magnetic field of each pole, in Tesla.


Given that A is significant, would it make sense to stretch the coils out some?  Say for example if the above diagram had only one coil occupying the span of both the coils in the diagram it seems that you'd get almost 3x the voltage for less wire than it would cost to make 3 smaller coils in series.  The thing is I am not sure how much current you'd lose to the increased inductive Z, but I strongly suspect that a net power gain is possible.


Has anyone played around with this notion, or can anyone tell me if I am missing something?

« Last Edit: August 15, 2004, 03:47:22 AM by nack »

Flux

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Re: coil winding size compaired to magnet?
« Reply #5 on: August 15, 2004, 12:16:29 PM »
Nack

The area must only enclose the field from one magnet.

As Ed has drawn it, that is the maximum area, if you increase the span any more you will enclose some field from a magnet of oposite polarity and this will subtract from the emf.

If you make the coil span twice as wide, you will get complete cancelation, i.e no output.

I hope I haven't misunderstood what you are asking.

Flux
« Last Edit: August 15, 2004, 12:16:29 PM by Flux »

nack

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Re: coil winding size compaired to magnet?
« Reply #6 on: August 15, 2004, 01:16:50 PM »
Flux,

Thanks, but I am not sure (due to the twice as wide coil example you cite) that I asked my question well enough.


It seems that I have seen somewhere - can't say for sure exactly where - that it is OK to have more mags inside the loop, as long as one N cuts one leg while one S cuts the other, thus my example of the loop enclosing 3 poles.  I know that enclosing two poles - or any even number - will get you complete cancelation, I just was not sure what effect the additional poles inside the loop would have WRT flux cancellation.  Some people have opined that the extra poles inside the loop are not relevant until they actually cross a coil leg, and if the other leg is seeing an opposite pole at that moment all would be well.  What I am not entirely clear on, and have heard both ways (thus my perceived need for an experimental model) is if the entire area of the coil is considered as active, or if the active part is just the legs that are swept by the magnets.  I suspect that the truth might lay in the middle ground somewhere, but I just don't know in the case where each end of the coil is seeing an opposite pole, but there happens to be some extra poles inside the coil area - are the extra poles "idling" until they hit a coil leg, or are they active members of the circuit any time they are inside the enclosed area?

« Last Edit: August 15, 2004, 01:16:50 PM by nack »

Victor

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Re: coil winding size compaired to magnet?
« Reply #7 on: August 15, 2004, 05:22:02 PM »
Yeah but, Having the multiple pole inside your loop will cancel any addvantage of the bigger area and you will have more resistance with the bigger coil.

Victor
« Last Edit: August 15, 2004, 05:22:02 PM by Victor »

Paul69

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Re: coil winding size compaired to magnet?
« Reply #8 on: August 20, 2004, 09:23:39 PM »
thanx for all the answers.

So this probally leads to the next question.


So what is the best size/shape of magnet and coils?


And while we're at it, what produces better voltage/amp's (or is that watts) many windings of thin wire or fewer windings of heavy wire. Im thinking heavy wire less windings would produce higher voltage/less amps , and thiner wire more windings would produce lower voltage / higher amps.

« Last Edit: August 20, 2004, 09:23:39 PM by Paul69 »

Paul69

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Re: coil winding size compaired to magnet?
« Reply #9 on: August 20, 2004, 09:55:00 PM »
I should add one more question to make my newbie status complete 8)


If I build my alternater as 3phase, example 9coils/3coils to a phase should all 3 coils of the same phase hit south(or north) poles of the magnets at the same time or doesnt that matter? from what I can tell by reading this forum it should make a big diffrence.

« Last Edit: August 20, 2004, 09:55:00 PM by Paul69 »

commanda

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Re: coil winding size compaired to magnet?
« Reply #10 on: August 21, 2004, 12:26:49 AM »
It's the other way round. Voltage is proportional to number of turns. More turns,more volts, (and less current).


Heavier gauge wire for more current. But you can't fit as many turns into a given space, so less volts.


Amanda

« Last Edit: August 21, 2004, 12:26:49 AM by commanda »