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Mechanical free energy devices => mechanic => Topic started by: PolaczekCebulaczek on August 11, 2017, 10:11:26 AM

Title: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on August 11, 2017, 10:11:26 AM
I'm interested with this kind of magnet geometry (for my generator project but not OU) and have some questions:

1.Is such magnet even possible to make at home? how to magnetize a ring like this?
2.Would such magnet loose it strength overtime?
3.How field lines would look like?
4.Compass inside the ring, would compass point in any fixed direction?
5.What if compass is not positioned in exact center of the ring, would it make any difference?
5.Can I induce current in coil when ring rotates? (coils inside/outside, near edge of ring)

Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 11, 2017, 10:06:12 PM
Hi,

Some answers:

1) Of course I cannot know your technical knowledge and means, no offense but I do not think that an average experimenter could make such magnets at home.  I mean in general, for any magnet shape.
2) The direction of magnetization is not known to define long term strength stability for permanent magnets that are manufactured correctly.
4) Yes, but the length of a compass needle would be important to consider, say the length of the needle is less than the thickness of the ring: I may be wrong but it would stay put in axial direction when put in the exact center (axle) line of the ring
5) Then it would turn towards the direction of the stronger pole at an angle which would come from the difference between the attract-repel forces ruling between the needle_ends and the inside pole of the magnet wall.
6) Well, not much at all because inside and outside the flux does not change much when such ring magnet would be rotated

Imagine your ring is placed flat onto the surface of the table as if it would be a cake and you cut it up to some pieces radially as cakes are normally cut.  You may wish to consider assembling such ring from some pieces of arc or trapezoid magnet shapes that has the correct and same direction of magnetization. Of course you need to create a strong hardware, a hoop, to keep the repel pole magnets next to each other in a safe position. 

I mention this because arc shaped or trapesoid magnets are not rare nowadays, after some search I found these:

http://www.greatmagtech.com/product_cat_list/Arc-Neodymium-Magnets-c21616/0/45.html (http://www.greatmagtech.com/product_cat_list/Arc-Neodymium-Magnets-c21616/0/45.html) and this shape for example:
http://www.greatmagtech.com/products_info/Arc-magnet-with-countersunk-hole-generator-magnet--335493.html (http://www.greatmagtech.com/products_info/Arc-magnet-with-countersunk-hole-generator-magnet--335493.html) 

Or   https://www.magcraft.com/arc-magnets (https://www.magcraft.com/arc-magnets) 

Of course you can also search with such keywords like 'arc' or 'trapezoid' or 'special' shaped magnets.
I have no any affiliation with any of the manufacturers...  ;D

There would be another option for you. I know that most manufacturers gladly make such magnets for you but the cost can go skyhigh for the so called custom orders they force the buyers into by saying to pay for special tools etc.  At least  this has been so for years but maybe you can have some luck by seeing these free sample offers (probably for relatively small sizes) and the shipping should only be paid for.  See this link where even a single quantity, 1 piece radially magnetized ring magnets are offered:
https://www.alibaba.com/showroom/radial-magnetization-ring-magnet.html (https://www.alibaba.com/showroom/radial-magnetization-ring-magnet.html) 

They call such magnetization direction for rings as radially magnetized or even uni-pole magnets.

Perhaps it would be worth for you to choose a few offers and write them with your needed magnet sizes, perhaps they would be willing to make it for you a single piece for free or at a minimal price and you pay only for the shipping what you can select as 'by Sea' too. 

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on August 12, 2017, 04:37:46 PM
Hi,

Some answers:

1) Of course I cannot know your technical knowledge and means, no offense but I do not think that an average experimenter could make such magnets at home.  I mean in general, for any magnet shape.
2) The direction of magnetization is not known to define long term strength stability for permanent magnets that are manufactured correctly.
4) Yes, but the length of a compass needle would be important to consider, say the length of the needle is less than the thickness of the ring: I may be wrong but it would stay put in axial direction when put in the exact center (axle) line of the ring
5) Then it would turn towards the direction of the stronger pole at an angle which would come from the difference between the attract-repel forces ruling between the needle_ends and the inside pole of the magnet wall.
6) Well, not much at all because inside and outside the flux does not change much when such ring magnet would be rotated

Imagine your ring is placed flat onto the surface of the table as if it would be a cake and you cut it up to some pieces radially as cakes are normally cut.  You may wish to consider assembling such ring from some pieces of arc or trapezoid magnet shapes that has the correct and same direction of magnetization. Of course you need to create a strong hardware, a hoop, to keep the repel pole magnets next to each other in a safe position. 

I mention this because arc shaped or trapesoid magnets are not rare nowadays, after some search I found these:

http://www.greatmagtech.com/product_cat_list/Arc-Neodymium-Magnets-c21616/0/45.html (http://www.greatmagtech.com/product_cat_list/Arc-Neodymium-Magnets-c21616/0/45.html) and this shape for example:
http://www.greatmagtech.com/products_info/Arc-magnet-with-countersunk-hole-generator-magnet--335493.html (http://www.greatmagtech.com/products_info/Arc-magnet-with-countersunk-hole-generator-magnet--335493.html) 

Or   https://www.magcraft.com/arc-magnets (https://www.magcraft.com/arc-magnets) 

Of course you can also search with such keywords like 'arc' or 'trapezoid' or 'special' shaped magnets.
I have no any affiliation with any of the manufacturers...  ;D

There would be another option for you. I know that most manufacturers gladly make such magnets for you but the cost can go skyhigh for the so called custom orders they force the buyers into by saying to pay for special tools etc.  At least  this has been so for years but maybe you can have some luck by seeing these free sample offers (probably for relatively small sizes) and the shipping should only be paid for.  See this link where even a single quantity, 1 piece radially magnetized ring magnets are offered:
https://www.alibaba.com/showroom/radial-magnetization-ring-magnet.html (https://www.alibaba.com/showroom/radial-magnetization-ring-magnet.html) 

They call such magnetization direction for rings as radially magnetized or even uni-pole magnets.

Perhaps it would be worth for you to choose a few offers and write them with your needed magnet sizes, perhaps they would be willing to make it for you a single piece for free or at a minimal price and you pay only for the shipping what you can select as 'by Sea' too. 

Gyula

Thank you such much!

well, it's quite tricky to magnetize a ring magnet like that using coil or another magnet(I don't know how...yet)
Is this a correct picture of field lines?
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 13, 2017, 11:36:00 AM
....
Is this a correct picture of field lines?

Hi,

Yes, for a six-pole radially magnetizatized ring it is correct.
The N and S poles alternate within the inside area (or space) as seen in the drawings here
for instance: http://www.aomagnet.com/radial-ring-magnets-c-19/ (http://www.aomagnet.com/radial-ring-magnets-c-19/)  while for a unipole ring there is a single pole
(say South) in the total inside diameter area or space of the ring and the opposite single pole (the North)
on the total outside surface and nearby space of the ring.

Here in this link you can see some more field line distributions that includes the fields of unipole
ring magnets too (unfortunately their picture is rather small and blurry):
http://www.jjmagnet.com/f_products1.htm (http://www.jjmagnet.com/f_products1.htm)

In this pdf file you can see a clear picture on the fields of a unipole ring magnet as compared to a multipole ring:
http://www.aicengineering.com/files/2014328143328.pdf (http://www.aicengineering.com/files/2014328143328.pdf) I copied this picture from the pdf file, see attached.   

Finally here is a large sized hence rather expensive (OD=70 mm) unipole radially magnetized ring magnet
with its nearly homogeneous South field inside and all North field outside:
http://www.materialhandlingzone.biz/product/aomag-uni-pole-radial-oriented-magnetization-neodymium-large-ring-magnets-diametrically-magnetized-od-70-x-id-62-x-20mm/ (http://www.materialhandlingzone.biz/product/aomag-uni-pole-radial-oriented-magnetization-neodymium-large-ring-magnets-diametrically-magnetized-od-70-x-id-62-x-20mm/)   
 
Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: phoneboy on August 13, 2017, 04:02:14 PM
@ PolaczekCebulaczek, this was just an untried method I had come up with to try for a design I had.  I had read about people making weak magnets by heating iron and allowing it to cool oriented in the earths magnetic field, so I wondered if I could do something similar with a ferrite ring.  The idea was to make a two part mold as if i were going to cast a part.  You would need some wood, sand, sodium silicate, a co2 source, a ferrite ring magnet, and copper wire for the flat coils.  Once the form was made for the ring and the coils,  the magnet would be placed in an oven and the temp raised to past its curie point.  The ring would then be placed back in the form and the coils energized while the ring slowly cooled, hopefully reorienting the domains and creating a reasonably strong radial magnet.  See old vizimag pic for ref.
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on August 14, 2017, 12:33:31 AM
Gyula thanks for pdf file, so in radially magnetized ring/unipole magnet there are almost no field lines extending , fascinating...

phoneboy your idea sounds interesting but I'm not sure if I understand the picture correctly, you meant something like this:

so two opposing poles-coils should produce N N outside and S S in the middle of the ring?

here is a method to make magnet using pancake coil but I cant see why this should work.

http://overunity.com/6856/how-to-simply-make-a-radially-magnetized-magnet-a-2d-magnetic-monopole/ (http://overunity.com/6856/how-to-simply-make-a-radially-magnetized-magnet-a-2d-magnetic-monopole/)



Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: phoneboy on August 14, 2017, 02:26:32 AM
This might help more, whipped up an image of the top half of the mold with the coil placed and the ring.
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 14, 2017, 12:36:30 PM

Gyula
thanks for pdf file, so in radially magnetized ring/unipole magnet there are almost
no field lines extending , fascinating...
.....


Your statement is misunderstandable how you mean so let me tell: field lines do extend
from an unipole ring magnet but the green viewing foil shown in pictures are somehow
mask them, not good quality pictures for unipole example, unfortunately. 
Magnetic lines of flux surely come out from the body of such ring magnets, especially
at the edges where the perpendicular sides meet but of course at the in-between surfaces too. 

You can imagine this when you consider a long rectangular bar magnet, magnetized length wise,
the lines of flux extend from mainly at the ends in quasi every direction from that 'uni pole' 
a long enough bar magnet has at its ends. 
In case of such radially magnetized ring magnets the smallest number of flux lines that extend
or come out from them can be found in the virtual center circle of their thickness.  (for a long bar
magnet this area can be found in the center or the middle of the full length as you surely know)

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on August 15, 2017, 07:26:50 AM
phoneboy thank for 3d picture now I understand, NN poles would meet inside the ring and SS outside the ring.

gyulasun soo in very center of the ring there should be no magnetism ? (due to repulsion?) if I put a compass in exact center of the ring and if needle is not reaching field lines then the compass should point only to magnetic field of the earth, right??



Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 15, 2017, 07:07:11 PM
...
gyulasun soo in very center of the ring there should be no magnetism ? (due to repulsion?)
 if I put a compass in exact center of the ring and if needle is not reaching field lines
 then the compass should point only to magnetic field of the earth, right??

No offense but I did not write, did not mean or did not imply that there is no magnetism in the
very center of a radially magnetized ring magnet.
Read my posts again, perhaps there is some language barrier?

Consider the following setup: you have say 4 identical bar magnets, each 5cm long, with 5x5mm
cross section, magnetized length wise. Say you fix these magnets onto a CD disk at 12, 3, 6 and 9 o'clock
positions so that their North pole ends point radially towards the disk center and each magnet North end is say
2 cm away from the very center point of the disk. Now try to increase in theory the number of bar
magnets you would also place radially to fill up all the space and get a radially magnetized ring
magnet that would have an OD of 7+7cm and an ID of 2+2cm, ok?

Now ask yourself: can the very center point or line of this setup free of magnetism?

My answer is no. There must be magnetism in the very center too. Very probably the strength of the
North pole fields in the very center is the smallest but not zero compared to any other point within
the virtual 2cm+2cm inner diameter area of this setup.

Generally speaking, maybe there are no lines of flux in some very narrow area between two
facing like poles (think of two block magnets in this example now) that are pushed together with a
strong force: the lines of flux are said to be pressed out from within the nearly or fully touching facing
surfaces of the two like poles BUT this is not an equivalent example to be compared to the very center of
a radial ring where there is always the 'distance' of just the inner ring diameter between any facing
like poled points, ok? And like poles cannot fully cancel within the inner diameter of a radial ring:
the squizing-out force of the like poled lines of force present in the ID area or space of the ring is not
enough to sweep them all out.

Now imagine that you have a radially magnetized ring magnet with an ID of say 5 cm, with an OD of say
7 cm and the thickness or height of such ring would be say 6 cm. If you could place a say 3 cm long
compass needle into the exact center line of this ring magnet, then I think the compass would stay in the
very center line.
A better example would be: instead of the compass you would use a say 3 cm long cylinder magnet
that would have an OD of say 2mm and would be magnetized length wise, then this cylinder magnet
would also stay in the very center line I think.

Hope this explains and puts an end for your dilemma... If still in doubt, please try to assemble such
radial ring magnet setup from cheap ceramic block magnets magnetized lenght wise and check it.

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 15, 2017, 07:19:17 PM
Ive looked for radially magnetized rings and only found these so far.

You would think they could magnetize a ring radially just by having one part of the magnetizing core in the inner radius and the other end of the magnetizing core on the outer radius. But so far i only see pies. magpies.

https://supermagnetman.com/collections/neodymium/products/rr0100n?variant=11410371011

https://supermagnetman.com/collections/neodymium/products/rr0090n?variant=11410370819

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 15, 2017, 07:29:00 PM
Hey Mags,

Manufacturing radially magnetized rings has come to reality it seems.
Check these links from my earlier posts above:
 
https://www.alibaba.com/showroom/radial-magnetization-ring-magnet.html

http://www.materialhandlingzone.biz/product/aomag-uni-pole-radial-oriented-magnetization-neodymium-large-ring-magnets-diametrically-magnetized-od-70-x-id-62-x-20mm/

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on August 15, 2017, 10:32:07 PM
gyulasun ok I understand now, thank you for better explanation, you are right about repulsion however if the ring is wide enough there should be no magnetism in the center because filed lines wont reach that far?

and my last stupid question, how such magnet can be used as generator? I have one (from speaker) and only when I move coil (coil is inside the ring in vertical position) or magnet up and down then current is generated, is there any other method ?
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 16, 2017, 12:47:55 AM
gyulasun ok I understand now, thank you for better explanation, you are right about repulsion however
if the ring is wide enough there should be no magnetism in the center because filed lines wont reach that far?
 

What do you mean on wide?
IF you mean that the inner diameter of a radially magnetized ring magnet is high enough, then yes
the magnetic field strength should be at a very low level in the very center axis line of the ring.
IF you mean something else on wide then I do not understand your question, try to put it otherwise.

Quote
and my last stupid question, how such magnet can be used as generator? I have one (from speaker)
and only when I move coil (coil is inside the ring in vertical position) or magnet up and down
then current is generated, is there any other method ?

Sorry to ask but are you sure your speaker magnet is magnetized radially? 
Because most speaker magnets are magnetized through their thickness i.e. axially:
one of their flat surfaces is say North and the other flat surface is the South pole.

This would explain your current induction in a coil moved axially through the center line of the your magnet.
If your ring magnet would be indeed radially magnetized, the induction would be at a minimum level
when you move a coil in it as you described. I am not saying there would be no induction in it but it would be
rather small compared to a similar sized and strong ring magnet magnetized axially like most speaker magnets.

Is your speaker magnet made of ferrite i.e. ceramic? By the way, you can check very easily how the poles
are made for your speaker magnet by a compass. Did you check it?  Is your speaker magnet magnetized
radially indeed like your drawing shows for a radial ring in your first post above.
In attachment below I included an axially and a radially magnetized ring magnet drawing.

Of course I am not saying your speaker magnet cannot be a radially magnetized ring magnet, in this case
you have to find the best coil-ring magnets arrangement to utilize it in a generator.
I think however that with multipole radial ring magnets you could get higher output
versus an unipole one of same size and strength.

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on August 16, 2017, 03:54:40 PM
Quote
Sorry to ask but are you sure your speaker magnet is magnetized radially?
Because most speaker magnets are magnetized through their thickness i.e. axially:
one of their flat surfaces is say North and the other flat surface is the South pole.

You are right, I just did some better tests and I found that my magnet is magnetized axially :(

Quote
What do you mean on wide?


yes by wide I meant inner diameter, big hole.

Quote
IF you mean that the inner diameter of a radially magnetized ring magnet is high enough, then yes
the magnetic field strength should be at a very low level in the very center axis line of the ring.

yet compass needle(that can't reach magnet field lines would still point to earth pole?

I will buy some magnets online meanwhile can you tell me which of (7) induction methods would generate current when coil or magnet rotate.(I know that some of the configurations have 0 difference between then when we consider induction law but I just want to be 100% sure)
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 16, 2017, 06:28:25 PM
...
yes by wide I meant inner diameter, big hole.

yet compass needle(that can't reach magnet field lines would still point to earth pole?


Only in case the inner diameter of a radial ring is high (big) enough so that when
you approach this magnet with a compass alongside the ring's center line axis,
then the presence of the inner unipole field cannot influence the compass needle
any more. Likely sizes to experience this I speculate you would need an unipole ring
with inner diameter of say 20 cm and needle length say 2 cm.
Suppose the ring has an ID=12 cm only, then the same needle would surely be influenced
by the small center field of the unipole ring and the needle would not show
true Earth North pole any more due to the presence of a stronger than the Earth's field.

Quote
....
I will buy some magnets online meanwhile can you tell me which of (7) induction methods
would generate current when coil or magnet rotate.
...

No, I cannot, you need to explore that by doing tests.

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 16, 2017, 11:25:00 PM
I was looking into them for my resonant pendulum using the speaker coils as drivers and pickups. These magnets if pushed back and forth in the coil would have very dense field passing through the coil, with small tolerance. If we look at a speaker motor, the magnet is sandwiched between 2 plates, the top plate with a hole in the middle and the bottom plate with a post in the middle that is just smaller in dia than the top plate hole so the magnets poles have a path of shortest distance at that pole gap, saying that all the field of the mag is concentrated there. Well I say not all and the field is not as dense as it is directly out of the face of the magnet.

So possibly the best induction with one of these magnets is to pass the mag through a coil that is just bigger than the mag dia. And to increase the flux get another ring mag that the other can fit into the larger ones hole with a gap for the coil. So now you have magnets on the outside and inside the coil. very dense field and all of the winding is induced, not just portions of it like in motors.

Then you can get another pair of those rings, with opposite poles of the first 2 and put them on axis near the first set and have another coil in that to generate also. The point is now you can put a rod core in the holes of the inner mags, which would link them magnetically, and an outer tube core to magnetically connect the outer diameters of the mags to close the magnetic loop, making the flux in the gap that much stronger.

Like a rod magnet, when it is just in open air, the fields at the poles faces are not as strong and or dense as they would be say per sq mm as it would be if the field had a core to use as a more direct path back to the other pole. So there is a flowering out of the fields from the poles making them less dense at the time. Probably the best reason why is that like polls repel, once it is out of the magnetic medium.  When a polarized field is in say an iron nail, the iron seems to neutralize the effect of the field wanting to flower out and repel its near by field of like polarity. Like they are attracted to each other when in the iron and the iron just may not be attracting the field, it may just be a medium that the fields issues with its close neighbor are negated and they can live together there in the iron. But once out of the iron they spread like a colony of bats out of a cave hole

So when we examine magnets by themselves the N pole is not just coming out of the face of the pole, some comes from around the sides on that half of the magnet and similarly at the S pole. When the fields come out of the face of the mag, they immediately start doing this i hate my neighbor thing, thus the spread of the field and that is translated within the magnet where they are being pulled away due to what is going on outside the magnetic medium.  So adding the path core to shorten the loops from N to S, then at the faces the flux gathering in the iron core in close proximity helps to make the pole face field denser and feel stronger.

So by adding the cores to the double dual ring mag gen, the field at the gap should be incredibly dense and strong, all making for a very efficient gen or motor, like a speaker.

Since standard speaker motors use a gap in between 2 cores that carry each mag fields to the coil gap, there is leakage that Im afraid hurts the field at the gap. Like if you look at most standard speaker motors the plates that capture the fields are a lot less volume of mass than the surface of the mags have to give. So as you can see by bringing a speaker near a crt, that field is leakin jim.    But if the coil is directly in the gap of 2 magnets instead and just use the cores as outer an center field looping, Id say the field in the gap would be a way better use of the field than the standard speaker motor which are pretty eff already as is.



mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: triffid on August 17, 2017, 03:55:18 PM
test,just wanted a link back to this thread.triffid
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 19, 2017, 09:24:32 AM
I was asked to clarify some things in my last post..

Normal speakers have axially mag poles and they use the top plate and the bottom pole plate to bring the fields of the magnet to the coil gap.

Where in my post I would like to try these radially magnetized magnets, a large ring and a smaller ring that fits the hole of the larger ring with space enough for the coil to move within, both with same poles in and same poles out, N out S in for example. I believe that the field between the 2 rings( inner S pole of the large ring and outer N pole on the inner ring) would have a denser field in the gap, rather than just making cores(top plate and bottom pole plate to basically carry the fields of the magnet to the gap. I think there is a lot of flux wasted that way due to leakage, like I said when you bring a speaker near a crt, that flux didnt make it from the magnet through the cores to the gap. So I would like to reverse that and make the coil gap with the actual pole faces of the mags, where the inner ring is attracted to the outer ring, and then the inner rod core and the outer tube core to close the magnetic circuit. Even if there are loses in the circuit closing cores, the gap between the magnets will still be denser than having the core carry it to the gap.

mags

mags

Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 19, 2017, 10:42:32 AM
here are pics

First is a normal magnet motor using the top plate and the bottom pole plate to bring the magnets fields to the coil gap

Second is closer to what Im getting at, but they only have 1 ring magnet on the outer side of the coil and just core on the inner side, of which the core just does not completely contain the field. Did like 5 vids on this subject. So I think the field would be denser if the inner pole had a ring mag too.

Cant get deep into it right now, but I believe there is a difference between flux density and actual field strength, where I think that expanded fields outside of a magnetic medium are weaker and possibly further more attribute to a weaker pole at the face, not just because of density at the face. Will be testing that theory.  If we have 2 mags in attraction with some measuring device to detect the pull force, and then we add a core to give the outer poles a shorter path to the other, will the pull force between the mags increase?  In that, without the outer return core, is the flux density between the 2 attracted mags any more when we add the return core( if not why), or is the field stronger because the flux loops are shorter rather than open air loops that can expand basically infinitely?  When the 2 mags are spaced face to face very close, there is little if any flowering of the field at the poles and the percentage of it all being there in the short gap is very high.  So if we add the outer return cores, and the force between the 2 mags increases substantially, can we only attribute that to the smaller percentage of flux density possibly added by adding the cores to have even less flowering at the gap?   I think its more of the shortening of the loop that increases field strength, along with density, naturally.

So that is why Im looking into this ring magnet idea also.  Like the 2 mags face to face to measure the pull, that outer core would have to be massive to contain the highest percentages of the return flux.  So in the sec pic example, Im betting on better flux density with an inner and outs mag ring around the coil will do better than core to core and even mag to core gaps. 

The mag pull test could be done with a short return core vs a longer larger return core to see if shorter loops create a stronger gap. dunno yet, gota git back to work work. As in making a living.

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 19, 2017, 10:54:17 AM
Another thing is the difference in coil vs gap.  The first pic shows an overhung coil where only a portion of it is in the densest flux in the gap, and the second, which I prefer, is an underhung coil which all of the windings are in the flux at all times.  In the overhung, parts of the coil that go out of the flux when moving are wasting input power, where the unerhung is not.

So these are things to consider if you are using these rings. Been thinking on it all for some time and Im giving what I know of it to you.  Pushing the levels and limits on these things leads to more output.  If we took a toy motor apart and replaced the magnets with weaker ones, we would have the same or more current flow into the armature and less speed and torque. Now we put in stronger mags, more speed and torque. Then stronger mags, more speed and torque.  So gen or motor, the stronger the mags the better the performance.

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 19, 2017, 11:08:56 AM
Found a good example of how the dual sets of rings would work

Here in the pic JBL is doing it with 3 stacked strontium mags and the top plat has a pole gap and the bottom plate has a pole gap.  So we get rid of the 3 mags, and replace the top and bottom plates with neo ring mags, and replace the inner pole with the 2 smaller ring mags and center them with an inner core rod, and make an outer core tube for the outer dia of the large rings. So the bottom large and small ring have S outer dia and the top rings have N outer dia poles Now the 2 coils, just reverse polarity one coil and connect in series or parallel with each other.

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 19, 2017, 11:11:04 AM
Except my rendition would have taller mags with underhung coils

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 19, 2017, 04:03:54 PM
...
   .... a large ring and a smaller ring that fits the hole of the larger ring with space enough for the coil
to move within, both with same poles in and same poles out, N out S in for example.
...
   .... where the inner ring is attracted to the outer ring, and then the inner rod core and the outer
tube core to close the magnetic circuit. Even if there are loses in the circuit closing cores, the gap
between the magnets will still be denser than having the core carry it to the gap.
...

Hi Mags,

Yes, it is very possible the magnetic flux density would be higher between two radially magnetized
ring magnets when one of them is embedded into the other. I have made a drawing as you described,
and although I did not include the inner rod and the outer tube cores for closing the magnetic circuit,
it is a must to utilize all the flux available in the two rings AND increase magnetic field in the gap manyfold. 
By the way, the magnetic circuit between your mentioned rod and tube could be closed by both a soft steel
ring or by just a third radially magnetized ring magnet, both with the correct ID and OD sizes to fit to the rod
and to the tube.  When you use a third radial magnet between the rod and tube to close the magnetic
circuit of the first two rings, the field in the gap can increase even higher than with a soft iron ring.

...
  If we have 2 mags in attraction with some measuring device to detect the pull force, and then we add
 a core to give the outer poles a shorter path to the other, will the pull force between the mags increase? 

Yes it will.  Just consider a magnetic door lock in which a simple ceramic block magnet is used with two
soft iron plates. The plates fully cover the side poles of the magnet (that is magnetized through its thickness)
and the magnetic circuit is closed between an outside third plate (to which the locking happens) and the two
iron plates that outreach the magnet.  The two soft iron plates 'collect' and focus most of the fields coming from
the sides of the magnet and make the attraction force to a third plate stronger, this is the same 'trick'
you can find in pot magnets and of course in speakers.

Quote
...
 So if we add the outer return cores, and the force between the 2 mags increases substantially, can we only
attribute that to the smaller percentage of flux density possibly added by adding the cores to have even less
flowering at the gap?   I think its more of the shortening of the loop that increases field strength,
along with density, naturally.

I think the first and stronger factor responsible for a stronger field is the less flowering i.e. less possibility
for stray fields and the second factor is the length of the loop. For this latter factor I think the cross section
area and the permeability of the soft iron material used for closing the magnetic circuit do matter.

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 19, 2017, 04:41:18 PM
Yeah thats the idea you drew there. The second set would be of opposite polarity. And yes the rod and outer tube could be magnets. Id rather they were magnets as I think there is too much leakage with iron core paths.   I said it before, I wonder if the core paths were made of neo but not magnetized, if they would work better than iron?

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 19, 2017, 09:28:03 PM
Quote
Id rather they were magnets as I think there is too much leakage with iron core paths. 

Well, it depends...  See this hard disk picture with its back plate behind it (I took the pictures
from this site: http://www.reuk.co.uk/wordpress/wind/hard-disk-drive-magnets-for-wind-turbines/ (http://www.reuk.co.uk/wordpress/wind/hard-disk-drive-magnets-for-wind-turbines/) )
You know such magnets are quadrapole ones, they act like two magnets stuck together side by side.
On one face there is a South pole on the left and a North pole on the right, on the other face there is
a North pole on the left and a South pole on the right. And the back plate connects the N and S poles
that are at the bottom face. Some time ago I checked with an office pin how magnetic the back side of
such a back plate + magnet assembly had been. The pin was not attracted to the back of the backing plate,
this means the plate surely had high permeability and was thick enough to avoid saturation so a negligible
amount of flux could exit (i.e. leak) from the back of the plate.

Quote
I said it before, I wonder if the core paths were made of neo but not magnetized, if they would work
 better than iron?

I have not had a chance to have such unmagnetized material so I do not know, I assume they should have
a high magnetic permeability before the magnetization.  Such materials should have the same rigid, hard
and next to impossible to form_to_shape properties like the Neo or any other permanent magnets have.
I think even if one had say metglas material, he would have a hard time to shape it.

One more notice: if you use magnets to complete a magnetic circuit, you need to stack several of them
to reduce their own leakage too.   Also, at most uncovered surfaces of a magnet the lines of flux can freely
come out because all the body of a magnet is in an almost complete saturation, while the same lines of flux
'have a hard time'  to come out from a highly permeable soft iron material like the backing plate of a HD magnet. 

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: lancaIV on August 20, 2017, 02:19:40 PM
Hello questions-bunch holder,here probably a "brainstorm"-questions/answer treasure :
https://worldwide.espacenet.com/publicationDetails/biblio?CC=DE&NR=19741256A1&KC=A1&FT=D#

I would prefer to increase "mon-ocle view" views by twi(ce)light and then tri-nity-lightning with 4d-thinking
                                                        and real material use experimenting.

Also testing 1 ball-cup generator (or motor) with supplement to 2-ball-cup-system .

Happy day
                 OCWL
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 20, 2017, 04:10:47 PM
Well, it depends...  See this hard disk picture with its back plate behind it (I took the pictures
from this site: http://www.reuk.co.uk/wordpress/wind/hard-disk-drive-magnets-for-wind-turbines/ (http://www.reuk.co.uk/wordpress/wind/hard-disk-drive-magnets-for-wind-turbines/) )
You know such magnets are quadrapole ones, they act like two magnets stuck together side by side.
On one face there is a South pole on the left and a North pole on the right, on the other face there is
a North pole on the left and a South pole on the right. And the back plate connects the N and S poles
that are at the bottom face. Some time ago I checked with an office pin how magnetic the back side of
such a back plate + magnet assembly had been. The pin was not attracted to the back of the backing plate,
this means the plate surely had high permeability and was thick enough to avoid saturation so a negligible
amount of flux could exit (i.e. leak) from the back of the plate.

I have not had a chance to have such unmagnetized material so I do not know, I assume they should have
a high magnetic permeability before the magnetization.  Such materials should have the same rigid, hard
and next to impossible to form_to_shape properties like the Neo or any other permanent magnets have.
I think even if one had say metglas material, he would have a hard time to shape it.

One more notice: if you use magnets to complete a magnetic circuit, you need to stack several of them
to reduce their own leakage too.   Also, at most uncovered surfaces of a magnet the lines of flux can freely
come out because all the body of a magnet is in an almost complete saturation, while the same lines of flux
'have a hard time'  to come out from a highly permeable soft iron material like the backing plate of a HD magnet. 

Gyula

This is why I believe that there will be more flux density between 2 magnet faces than from a magnet to a return core or even core to return core with remote magnet.

If we have a magnet facing another magnet, both already have very dense fields within. If it were magnet to return core, the gap end of the core is not going to hold or say carry all that flux from the other end of the magnet to the gap due to leakage of the core. And then in the case with the standard speaker motor with top plate and bottom pole plate, there will never be as much flux in the gap as there would be in the next better step, magnet to core gap. So having the magnet on both sides of the gap would be the densest field in the gap. Was reading on speaker design(not a lot out there like its forbidden knowledge. Only 2 software progs out there specific for speaker driver design exist as far as I know at this time and very pricey) and one of the ingredients to increasing the eff/sensitivity of the driver is to have a stronger mag field in the gap.  Im looking into creating my own subwoofers. Looked into a couple companies in china and they dont even know what Theil/Small parameters are, which are all the specs that are used to evaluate and calculate proper enclosures for each. These companies seem to just bang out what looks good, big triple stack magnets, large rubber surrounds, long heavy voice coils(most all overhung up to possibly only 1/8th of the coil in the gap. What a waste of power.) capable of taking on thousands of watts. Its a scam.

About 7 years ago Pioneer was beating everyone at SPL contests. They had subs that were longer than they were wide, 5000w to 8000w.  Now everyones in on it and raking in the cash.  After that pioneer dropped all the big equipment and went another route. They designed their speakers and subs to be more eff than most any out there, especially for the price, as the few others that have high sensitivity numbers charge big bucks.  Pioneers Champ Pro 12 is 96db @1w and can be had for under $100. They also have a pro 12 that is 105db @1w. Its more of a stage driver, not a bottom boom sub.  3db increase is a doubling of power. Many subs out there are under 90db @1w. So just in the case of the 2 pioneer 12s, the champ needs 4 times the power to just catch up to the pro 12. Im ordering one of those pro 12s 105db just to try it and compare to the champ.



So my buddy has 6 PSI 15in subs powered by 15kw in amps. His subs are 88.5db@1w.  My other friend, we are going to do 6 Pioneer champ pro 12s with only 5200w and they are 96db@1w ea.
My first bud needs to increase his amp setup to 30kw to beat the pioneer system that is only running 5200w. So now we are really seeing what efficiency can do for us.
My buddy with the PSI 15s is going to regret ignoring me on this subject and going with expensive monster equipment, spending over 10k vs 1k for equipment, let alone wires, etc.  Each of his amps take 2 + 0awg and 2 - 0awg.  Lots invested in that. His amps may not be super eff either. Thats another post.

So if you see the graphs of each setup in the WinIsd Beta speaker box program, it is ridiculous what people are spending because they dont know what the sensitivity spec is, and the ones that do have this idea that more is better.  Nuts

So Im going for a sub design that is aiming for efficiency. Hopefully more than whats available. The highest I have seen yet is 112db@1w, but it wasnt a sub woofer exactly. More of a stage driver.

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 20, 2017, 04:32:09 PM
Like simple pulse motors with say 1 coil and mags on a wheel. All of that is very inefficient. No return cores, open ended mags and coils. If just those things were installed, along with a full load of coils around the wheel, the same input will get you more output. The Pulse motor build off should be looking at these things. Actual measurements of the in and out and that should determine the winner. Not the coolest looking thing and all that jazz. But those numbers would be tough to prove without judge attendance, so it is what it is.

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 20, 2017, 08:18:38 PM
Just found a couple more software for speakers and some interesting fem pics. I gota put it up later though

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: TinselKoala on August 22, 2017, 02:28:54 AM
Well, it depends...  See this hard disk picture with its back plate behind it (I took the pictures
from this site: http://www.reuk.co.uk/wordpress/wind/hard-disk-drive-magnets-for-wind-turbines/ (http://www.reuk.co.uk/wordpress/wind/hard-disk-drive-magnets-for-wind-turbines/) )
You know such magnets are quadrapole ones, they act like two magnets stuck together side by side.
On one face there is a South pole on the left and a North pole on the right, on the other face there is
a North pole on the left and a South pole on the right. And the back plate connects the N and S poles
that are at the bottom face. Some time ago I checked with an office pin how magnetic the back side of
such a back plate + magnet assembly had been. The pin was not attracted to the back of the backing plate,
this means the plate surely had high permeability and was thick enough to avoid saturation so a negligible
amount of flux could exit (i.e. leak) from the back of the plate.

I have not had a chance to have such unmagnetized material so I do not know, I assume they should have
a high magnetic permeability before the magnetization.  Such materials should have the same rigid, hard
and next to impossible to form_to_shape properties like the Neo or any other permanent magnets have.
I think even if one had say metglas material, he would have a hard time to shape it.

One more notice: if you use magnets to complete a magnetic circuit, you need to stack several of them
to reduce their own leakage too.   Also, at most uncovered surfaces of a magnet the lines of flux can freely
come out because all the body of a magnet is in an almost complete saturation, while the same lines of flux
'have a hard time'  to come out from a highly permeable soft iron material like the backing plate of a HD magnet. 

Gyula

The metal backing plate shown is made of "mu-metal" and indeed is very high permeability. This is how it acts as a "magnetic
shield", by "sucking up" the magnetic field into itself and making the connection between the opposite polarities with very very
little flux leakage. The "mu-ness" of the alloy is created by a special heat-treatment and annealing schedule, and any working
of the finished piece, such as the bending shown in the photo, or sawing or other cold-working, reduces or even destroys
the "mu-ness" of the material.

Here's an interesting motor design that bears some studying and thoughtful consideration.


Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: gyulasun on August 22, 2017, 03:16:35 PM
Hi TinselKoala,

Thanks for the additional comments on the backing plate. The guy showing how he removed the magnets from the backing plates by bending the plate coners with vice grips may have been interested to scavenge only the magnets for building wind generators and may not have needed the plates and / or was unaware of the ill effects of abusing the plates mechanically.

Indeed you show an interesting motor design. Surely the backing plates do their job and keep the stator magnet fields in a closed magnetic circuit for all the outside poles, and the radially arranged copper stripes (i.e the rotor "coils") are sandwiched between the inner facing poles, within a narrow air gap. This way the rotor can have a very low self inductance hence the brush sparking can also be at a minimum due the low counter emf. Due the total lack of any ferromagnetic material in the rotor, there can be no cogging at all, no rotor core loss and there can be very little  I2R heat loss in the copper stripes.

Gyula
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 23, 2017, 01:07:19 AM
I  have one of those motors, and we talked about them before. They are unique in that hey are coreless armatures and have advantages as such that core losses are reduced and they can change speed very quickly, in this case a car cooling fan that accelerates very quickly. I wanted to make a new holder and mount neos in place of the poles you see in the multi pole ceramic in the pic above. Neos are stronger than the ceramic shown and the return path casing may have difficulty containing the fields as well as it handles the ceramic. What I wanted to do was mount neos on both sides of the armature and only have outer core return like a large washer on each side which would link all the outer poles to opposing poles of each side.

Similar to speaker motors, the ceramics rely on large surface area and thickness to obtain the desired field  density at the gap. There are guys trying to copy some companies speaker motors where the ceramic is replaced with multiple neo disks between the top and bottom plates. They take the speaker apart and separate the plates from the ceramic mag and install the disks and put it back together.  I think the mistake is that the plates will have a harder time containing the field than the ceramics.

I hadnt tested the fan disk motor before I took it apart to see if there was any outside leakage. And it is a different monster compared to the speaker motors as the disk motor casing is a closed system but the speaker motor is not. Most speakers back when crts were popular had mag shield cups covering the speaker mags and they did well with leakage containment.

I have some pics of fem analysis of a couple speaker motors. Ill get those up when I have time in a day or so. Im swamped.  One shows a very thick core return and another shows 2 different core changes that maximized the fields in the gap compared to the other.  It is a little misleading when you see the cross section of the mag having like 10 lines in the mag and having most all taking the core path to the gap, with only a few strays out of the core. But as many of us have seen in the past, that leakage can be detrimental to a color crt at a distance. If the field lines were shown to be denser than 10 field lines, the leakage lines would be way more than the fem shows in those examples.

Ill get those up soon.

mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 23, 2017, 02:45:14 PM
Here are the fem pics.

Ill get back on later to talk about them

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Lakes on August 24, 2017, 10:02:28 AM
I've never head of speaker motors before now, are they some sort of actuator?

Do you have a link?
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Magluvin on August 25, 2017, 01:26:39 PM
I've never head of speaker motors before now, are they some sort of actuator?

Do you have a link?

Look at the pics of speakers above on previous page. The magnet, plates, center pole and coil mounted to the cone. Speaker motor. Piston action without the crank shaft.

Mags
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Low-Q on September 03, 2017, 10:11:26 PM
Making a radially magnetized magnet is quite simple. If you have a ferrite magnet for speakers, you simply place a coil on each flat surface. These coils must repel each other when current flows through them.
This way you destroy the axial field in the magnet, and create a radially magnetized field in it that will sustain after you remove the coils.


Vidar
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: lancaIV on September 04, 2017, 10:05:52 AM
         Has the FEMM-program the TMR-Effect included ?

              https://www.google.pt/search?q=TMR-Effect&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&dcr=0&ei=LQWtWfn_FMap8we1ooWwAg (https://www.google.pt/search?q=TMR-Effect&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&dcr=0&ei=LQWtWfn_FMap8we1ooWwAg)

     Attention: learn to use the wikipedia-lexikons correct !

     f.e. compare the content
     a. https://de.wikipedia.org/wiki/Magnetischer_Tunnelwiderstand (https://de.wikipedia.org/wiki/Magnetischer_Tunnelwiderstand)
     b. https://en.wikipedia.org/wiki/Tunnel_magnetoresistance (https://en.wikipedia.org/wiki/Tunnel_magnetoresistance)


    if become translated by the different automatic language tools
    do not expect to get an 1:1 translation,

    probably positive mind will get a "negative aura" : chaotic

You ever heared about him,  THE LAST german UNIVERSALGENIUS :
https://www.google.pt/search?q=carl+friedrich+august+von+weizsaecker&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&dcr=0&ei=fQqtWeLpL5DY8geP3r3QAg (https://www.google.pt/search?q=carl+friedrich+august+von+weizsaecker&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&dcr=0&ei=fQqtWeLpL5DY8geP3r3QAg)

http://www.spiegel.de/wissenschaft/natur/carl-friedrich-von-weizsaecker-tod-eines-mahners-und-vordenkers-a-480059.html (http://www.spiegel.de/wissenschaft/natur/carl-friedrich-von-weizsaecker-tod-eines-mahners-und-vordenkers-a-480059.html)

http://www.faz.net/aktuell/feuilleton/carl-friedrich-von-weizsaecker-synthesen-eines-jahrhundertmannes-1438060.html


                      learning by showing and doing
      https://pt.wikipedia.org/wiki/Pit%C3%A1goras (https://pt.wikipedia.org/wiki/Pit%C3%A1goras)
Segundo os pitagóricos, o cosmo (https://pt.wikipedia.org/wiki/Cosmo) é regido por relações matemáti
             
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on September 26, 2017, 08:10:20 PM
Interesting speaker stuff here... but before I start  making my magnet I want to ask another important question, that is: what would happened when radially magnetized ring is rotated while compass is inside the ring(1)? would a compass needle rotate with ring or not? (needle just stay at position where I put it) and what if compass is off the center, closer to one edge than another? (2). Please see diagrams below.
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Low-Q on September 26, 2017, 09:45:40 PM
These magnets or speaker magnets does not have a field gradient along the circumference. So there will be no interaction between the rotating magnet and the compass needle.
This statement is only true if the magnet is uniformly magnetized. Most magnets are not that precicely manufactured.
So in a practical experiment you will probably se some movement in the needle.


Vidar
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on September 27, 2017, 07:36:38 PM
These magnets or speaker magnets does not have a field gradient along the circumference. So there will be no interaction between the rotating magnet and the compass needle.
This statement is only true if the magnet is uniformly magnetized. Most magnets are not that precicely manufactured.
So in a practical experiment you will probably se some movement in the needle.

Vidar

very interesting... so lets assume that I have a perfectly uniformly magnetized ring (just like one on picture)  then I put compass in the center of the ring and set its needle to point east west earth direction and now needle will STAY STILL at this E-W position forever regardless of magnet rotation? is this correct?
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Low-Q on September 27, 2017, 08:53:46 PM
very interesting... so lets assume that I have a perfectly uniformly magnetized ring (just like one on picture)  then I put compass in the center of the ring and set its needle to point east west earth direction and now needle will STAY STILL at this E-W position forever regardless of magnet rotation? is this correct?
Yes. However, the earth magnetic field dominates the compass needle. So it will point north/south.
Remove the earth, and the needle stays E-W (except there is no E-W when the earth is gone :) ).



Vidar
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on September 27, 2017, 09:29:08 PM
Yes. However, the earth magnetic field dominates the compass needle. So it will point north/south.
Remove the earth, and the needle stays E-W (except there is no E-W when the earth is gone :) ).



Vidar

dominate you say? I think that depends from strength of ring magnet or its inner diameter... so earth will only slightly pull the needle or even not at all.(earth field vs. magnet pull)
by putting compass  inside the ring i was thinking about a way of determining if magnetic field rotate with ring or not, Faraday paradox stuff, yet even if field is rotating needle should not move since field is all around equal and uniform, only induction and open circuit approach can tell if any tiny current is present.
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Low-Q on September 27, 2017, 11:06:06 PM
The thing is:
At center, the magnet does not pull anything. The magnet could have a thousand gauss. It does not matter. Because at the center, all fields cancel each other out. The extent of the needle is equal in both directions. Any magnetic influence on one side is equal on the other.


So what magnetic field do we have left? The Earths magnetic field - which will be the only field left that directs the needle.


Vidar.
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: PolaczekCebulaczek on September 28, 2017, 02:47:02 PM
The thing is:
At center, the magnet does not pull anything. The magnet could have a thousand gauss. It does not matter. Because at the center, all fields cancel each other out. The extent of the needle is equal in both directions. Any magnetic influence on one side is equal on the other.


So what magnetic field do we have left? The Earths magnetic field - which will be the only field left that directs the needle.


Vidar.


yeah i think you are right, thats correct for case nr 1 and probably for case 2 as well because inner circle of the ring will be completely filled by mag field... so the second picture is wrong.
Title: Re: A bunch of questions regarding radially magetized ring magnet.
Post by: Low-Q on September 28, 2017, 04:58:02 PM
In case 2, the compass is closer to the magnet at one particular spot - off center. The magnet in case 2 will therefor dominate.


The magnetic field has no outer limit of how far it can reach.



Vidar.