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##### Other (Public) / Re: Magnets

« Last post by**Vigorsaga**on

*September 12, 2017, 10:37:26 AM*»

Back to describe the details so easy to access in more clearly anymore.

Did you miss your activation email? October 21, 2017, 07:24:28 PM

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Back to describe the details so easy to access in more clearly anymore.

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Feel the resolution in saying that it is we want to stay fit.

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This is extremely helpful, thanks Silvio.

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Yes, given formula is for steel laminated cores at frequency of 50-60Hz.

If you change frequency or core material, that formula no longer apply.

The best solution is to find detailed specification of core material from manufacturer.

You can also test core to see how it behaves, but that is far more expensive.

If you change frequency or core material, that formula no longer apply.

The best solution is to find detailed specification of core material from manufacturer.

You can also test core to see how it behaves, but that is far more expensive.

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Hi Silvio

You did it again. I think congratulations are in order. Than you for the power formula and the zip file. Now the calculator work fine. Is it correct to think that the power formula CSA squared is for normal steel laminations. If it is so what happens when one uses an Amcc core. I am experimentind with an Acc core 320 CSA is 22mm x 50mm (11cm square)

Thank for everything and nice to chat with you.

Best regards

You did it again. I think congratulations are in order. Than you for the power formula and the zip file. Now the calculator work fine. Is it correct to think that the power formula CSA squared is for normal steel laminations. If it is so what happens when one uses an Amcc core. I am experimentind with an Acc core 320 CSA is 22mm x 50mm (11cm square)

Thank for everything and nice to chat with you.

Best regards

6

Formula for power of core is cross-sectional area squared: P=S^{2}

Where P is power in watts for 50/60 Hz, S is cross-sectional area in cm^{2}

Because many have problem with installation of my calculator on 64bit, here is archived installed version: transformer01.zip

Download it and unpack to C:\Program Files

You may run it on compatibility mode for Win XP.

Hope it helps.

Where P is power in watts for 50/60 Hz, S is cross-sectional area in cm

Because many have problem with installation of my calculator on 64bit, here is archived installed version: transformer01.zip

Download it and unpack to C:\Program Files

You may run it on compatibility mode for Win XP.

Hope it helps.

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Hi Silvio

Nice work on your website.

You did a lot of work.

I tried to download the program but unfortunately it does not work on my lap top due it is 64 bit

It is possible to give me at least the workings to calculate at least the power from core cross-sectional area.

I thank you for your time and for sharing

best regards

Charles

mbe 200

Nice work on your website.

You did a lot of work.

I tried to download the program but unfortunately it does not work on my lap top due it is 64 bit

It is possible to give me at least the workings to calculate at least the power from core cross-sectional area.

I thank you for your time and for sharing

best regards

Charles

mbe 200

8

I have a lot of unknown ferrite cores mostly salvaged from radio/TV and other devices.

Main problem with this is to how to know their permeability for calculating number of turns I need to make choke or transformer.

So I needed some simple method to test cores and get theirs permeability.

Simplest way to me is to measure inductivity of choke with unknown core when you know how many turns of wire you have on it.

Then calculate from this inductance factor*A*_{L} and effective permeability *μ*_{e} of core.

**Formulas**

Usually you can find formulas for calculating in manufacturer Data Handbook or production guide.

The A_{L} factor is the inductance per turn squared (in nH) for a given core.

Inductance formula is: L = N^{2}*A_{L} *(nH)*

When transformed, you can calculate A_{L} with next formula: A_{L}=L/N^{2}

Once you have core data, value of A_{L} is calculated from the core factor *Σ(l ⁄A)* and the effective permeability: A_{L}= (μ_{0}*μ_{e}*10^{6})/ Σ(l ⁄A) *(nH)*

To get effective permeability, formula is transformed into this: μ_{e} = (A_{L}*Σ(l ⁄A))/(μ_{0}*10^{6})

A_{L} is calculated from measured inductance and number of turns.

Σ(l ⁄A) is calculated by measuring and dividing core physical dimensions of effective length*l*_{e} (mm) and effective area *A*_{e} (mm^{2}): Σ(l ⁄A) = l_{e}/A_{e} *(mm*^{-1})

μ_{0} is permeability of vacuum - μ_{0} = 4*π*10^{-7} *(Hm*^{-1})

This formulae works for most core types except for rods and tubes, for them you need this formula: L = (μ_{0}*μ_{rod}*N^{2}*A)/l *(in H)*

After transforming we get: μ_{rod} = (L*l)/(μ_{0}*N^{2}*A)

where:

L is measured inductance

N is number of turns

A is cross sectional area of rod*(mm*^{2})

l is length of coil.*(mm)*

**Testing**

With this solved only thing to do is to determine optimal number of turns for measurement.

By using large number of turns there is problem with rise of loses by wire resistance, coil geometry and core loses.

Therefore best is to use fewer as possible.

With minimal number of turns, wire length is reduced, thus wire resistance is low.

Beside that with few turns we don't have overlapping wire and loses in coil construction.

However when using single or few turns there is problem with covering entire space on coil former to get fully distributed winding to use entire length of core.

So to solve that problem I did some testing. For my test I chose RM6S/I ferrite core.

I was using three different core materials 3H3, 3C90 and 3E5 and I make coils with different number of turns, form 1 to 31.

For measuring inductance I was using Agilent U1731C LCR meter (resolution 1-100nH, accuracy 1%) with 100 Hz and 1 kHz setup.

Wire thickness is another important part, if it is too thick you can get losses from skin effect.

On another hand if you use too thin wire you can get losses in wire resistance.

For my setup maximal measuring frequency is 1 kHz and on that frequency skin depth is 2.088 mm, thus wire must not be larger than AWG 6.

I choose to use SWG 25 (diameter 0.5 mm) with max frequency of about 80 kHz. Using this wire I can fit 9 turns on former in single row.

**Measuring**

One set of measuring was done from 1 to 31 turns with all cores exchanged on that turn. I repeat that set three times.

At end after several hundreds core swapping I compare readings from beginning and end.

Difference in data is from -4.62% to 43.37% which is primary result of loosening mounting clip after so many reassembling.

Most difference (higher than 10%) I got after 22^{nd} turn which just confirms that less turns are far better for precision even in loose clip mounting.

Comparing 100 Hz vs. 1 kHz measurement data gave me difference from -7.51% to 0.98% which is not that bad.

Data from 1 kHz are much more close to datasheet values so it confirms that higher frequencies are better for measuring lower inductivity.

**Data**

All processed data are from measurement at 1 kHz setup. Those values are used to calculate A_{L} and compared with value from datasheet.

Here on this graph you can see difference for each core material.

For 3H3 material stable results is between 5^{th} and 20^{th} turn, for 3C90 is from 3^{rd} and 31^{st} turn and for 3E5 it looks there aren't stable results however after 21^{st} turn difference are gone totally wild.

So it is safe to say that measuring from 5 to 20 turns gives best results.

**Conclusion**

To get and calculate permeability the best method is:

Main problem with this is to how to know their permeability for calculating number of turns I need to make choke or transformer.

So I needed some simple method to test cores and get theirs permeability.

Simplest way to me is to measure inductivity of choke with unknown core when you know how many turns of wire you have on it.

Then calculate from this inductance factor

Usually you can find formulas for calculating in manufacturer Data Handbook or production guide.

The A

Inductance formula is: L = N

When transformed, you can calculate A

Once you have core data, value of A

To get effective permeability, formula is transformed into this: μ

A

Σ(l ⁄A) is calculated by measuring and dividing core physical dimensions of effective length

μ

This formulae works for most core types except for rods and tubes, for them you need this formula: L = (μ

After transforming we get: μ

where:

L is measured inductance

N is number of turns

A is cross sectional area of rod

l is length of coil.

With this solved only thing to do is to determine optimal number of turns for measurement.

By using large number of turns there is problem with rise of loses by wire resistance, coil geometry and core loses.

Therefore best is to use fewer as possible.

With minimal number of turns, wire length is reduced, thus wire resistance is low.

Beside that with few turns we don't have overlapping wire and loses in coil construction.

However when using single or few turns there is problem with covering entire space on coil former to get fully distributed winding to use entire length of core.

So to solve that problem I did some testing. For my test I chose RM6S/I ferrite core.

I was using three different core materials 3H3, 3C90 and 3E5 and I make coils with different number of turns, form 1 to 31.

For measuring inductance I was using Agilent U1731C LCR meter (resolution 1-100nH, accuracy 1%) with 100 Hz and 1 kHz setup.

Wire thickness is another important part, if it is too thick you can get losses from skin effect.

On another hand if you use too thin wire you can get losses in wire resistance.

For my setup maximal measuring frequency is 1 kHz and on that frequency skin depth is 2.088 mm, thus wire must not be larger than AWG 6.

I choose to use SWG 25 (diameter 0.5 mm) with max frequency of about 80 kHz. Using this wire I can fit 9 turns on former in single row.

One set of measuring was done from 1 to 31 turns with all cores exchanged on that turn. I repeat that set three times.

At end after several hundreds core swapping I compare readings from beginning and end.

Difference in data is from -4.62% to 43.37% which is primary result of loosening mounting clip after so many reassembling.

Most difference (higher than 10%) I got after 22

Comparing 100 Hz vs. 1 kHz measurement data gave me difference from -7.51% to 0.98% which is not that bad.

Data from 1 kHz are much more close to datasheet values so it confirms that higher frequencies are better for measuring lower inductivity.

All processed data are from measurement at 1 kHz setup. Those values are used to calculate A

Here on this graph you can see difference for each core material.

For 3H3 material stable results is between 5

So it is safe to say that measuring from 5 to 20 turns gives best results.

To get and calculate permeability the best method is:

- if possible, use high measuring frequency but close to working frequency of core
- use 5 to 20 turns (closer to 5 turns for high amplification cores)
- use thickest wire possible depend on measuring frequency and space on former
- fill up equally entire length of former in single row

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It's difficult to find good information about magnets and how they behave.

So here I will put some info about them which I found over the years.

The best start is to look K&J Magnetics FAQ. On their site you have also other useful stuff like magnetic calculators etc.

Here are my expanded data from theirs FAQ which I have done thru measurements and experiments:

Further tests which are currently in progress, result will be posted upon completion:

So here I will put some info about them which I found over the years.

The best start is to look K&J Magnetics FAQ. On their site you have also other useful stuff like magnetic calculators etc.

Here are my expanded data from theirs FAQ which I have done thru measurements and experiments:

- Both poles of magnet are equally strong, but only when measuring in magnetic neutral environment. If you don't measure in magnetic neutral environment results will differ from pole to pole.

For example if you measure poles of magnets in nature on earth northern hemisphere where is south magnetic pole, you will get data with stronger south pole than north. - Stacking magnets will get you slightly higher magnetic field, but there is limit how much magnets you can stack.

Magnetic conductivity of used material is not that good; therefore there will be resistance to magnetic field.

You can look values of permeability for different materials:

So as you can see neodymium magnet has slightly higher permeability than air, but only small fraction than regular steel/iron.Material Relative permeability Air 1.00000037 Neodymium magnet 1.05 Steel 100

Here are some measurements which I was performed on cylindrical neodymium magnets stacked together on top of each other (in series).

Diameter of magnet 5 mm, length 5 mm, grade N35, maximum strength 3900 gauss.

Measured only on magnet south pole with gauss meter HGM0200 (resolution 10 G, accuracy +/-2%):

Stacking magnets together does not give you too much more power and stacking more than 9 magnets is a total waste.Number of magnets Field strength (gauss) Strength increase Length (mm) Max strength Max strength increase 1 3590 0,00% 5 3900 0,00% 2 3770 4,77% 10 3 3880 7,47% 15 4300 9,30% 4 3980 9,80% 20 5 4000 10,25% 25 6 4010 10,47% 30 4400 11,36% 7 4020 10,70% 35 8 4020 10,70% 40 9 4030 10,92% 45 10 4030 10,92% 50 11 4030 10,92% 55 12 4030 10,92% 60

So no, you can not get more than 25% of initial (single magnet) field strength in any combination. Therefore combining magnets to get stronger field have no sense. - The bigger the better? Not really, but it depends for what you need them.

If you are interested in building magnetic motor, holding weight or something where magnetic force is important, then this doesn't apply.

Bigger magnets have much less force per volume/surface than bunch of small ones.

Here is calculation for square magnets grade N35. Each is 10mm thick, with magnetization thru thickness.

Price and all data are from company that sells them in my country, so price can be variable to other places, but point here is to show difference in strength.

Pull force is calculated using The Original K&J Magnet Calculator.

This data can be easily tested and some of my tests confirms that this is close to real thing.height (mm) width (mm) max strength (gauss) price pull force (lb) surface (mm ^{2})pull force/surface pieces for 3600 mm ^{2}total force (lb) diff total force total price diff total price 10 5 4300 0,56 € 4,9 50 0,098 72 352,8 314,04% 40,55 € 8,30% 40 10 4000 4,34 € 27,67 400 0,069175 9 249,03 192,25% 39,03 € 4,25% 50 10 4300 5,33 € 31,9 500 0,0638 7,2 229,68 169,55% 38,40 € 2,55% 60 10 4200 6,36 € 35,79 600 0,05965 6 214,74 152,01% 38,13 € 1,85% 40 20 3800 8,43 € 42,1 800 0,052625 4,5 189,45 122,33% 37,92 € 1,29% 50 25 4000 12,64 € 52,61 1250 0,042088 2,88 151,5168 77,82% 36,41 € -2,76% 40 40 4000 15,34 € 59,54 1600 0,0372125 2,25 133,965 57,22% 34,50 € -7,84% 60 30 3900 18,51 € 63,27 1800 0,03515 2 126,54 48,50% 37,03 € -1,11% 100 20 3900 22,80 € 67,77 2000 0,033885 1,8 121,986 43,16% 41,03 € 9,59% 50 50 3600 24,39 € 73,96 2500 0,029584 1,44 106,5024 24,99% 35,12 € -6,21% 60 60 3600 37,44 € 85,21 3600 0,0236694444 1 85,21 0,00% 37,44 € 0,00%

So what it shows is that single big magnet is several times weaker than bunch small ones for same volume and surface.

Also you can see that price of single big magnet vs. smaller ones for same amount volume/surface is very close (10% difference).

However if you compare forces, then you need 3 times less smaller magnets to replace big one, thus total price, volume and surface is 3 times smaller for same amount of force.

Conclusion:**smaller is better!**

Further tests which are currently in progress, result will be posted upon completion:

- Magnetic force between two magnets at different angels passing by each other on rails.
- Suppression of magnetic field on one side by redirecting it using different materials aka "magnetic shield".
- Forces between magnets in linear motor with "shielded" magnets.

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Original program is 32bit and there is no 64bit version.

New program will work on any operating system.

New program will work on any operating system.

silvio, where can you buy the lamination iron to make the cores for a transformer?Usually you can buy from transformer manufacturer or you can dismantle some old/burnout transformer and use core from it.