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Author Topic: Electro magnet design software advice?  (Read 12790 times)

Honk

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Electro magnet design software advice?
« on: July 24, 2007, 03:44:24 PM »
Hi.

As most of you readers know I've been helping Jack to build a controller for his very promising Magnet Motor.
http://jackh.pbwiki.com/
http://www.overunity.com/index.php?topic=2386.0

I have come pretty far in my own design of a Hilden Brand style motor but now I would like to simulate the flux fields
of the electro magnets within the motor. I could of course make test windings but this takes a lot of time.
I wonder if you guys can recommend a good program that can calculate the flux in electro magnets with a silicon steel core?
Once I have the motor and magnets calculations completed I will release my my stuff here at OU forum.

Paul-R

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Re: Electro magnet design software advice?
« Reply #1 on: July 24, 2007, 03:57:37 PM »
You will know of FEMM:
http://femm.foster-miller.net/wiki/HomePage
and I presume that it cannot do it. Why not ask
the boss if he will write up an implementation of
exactly what you need?
http://femm.foster-miller.net/wiki/DavidMeeker
No harm in asking.
Paul.

Honk

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Re: Electro magnet design software advice?
« Reply #2 on: July 24, 2007, 06:26:45 PM »
I have installed the FEMM software but I find it very difficult to use. Perhaps I'm stupid
but the interface is not very self tutorial. Just to form the desired shape is hard to do.
Isn't there just a simple spreadsheet where I can input the numbers and get the result.

If the input numbers would look somewhat like this it would be nice.

1 ) Square Area of Silicon Steel Core.
2 ) Length of Silicon Steel Core.
3 ) Outer radius of Silicon Steel Core = Inner radius of coil
4 ) Diameter of used wire.
5 ) Number of wire turns.
6 ) Number of wire layers.
7 ) Total wire resistance.
8 ) Output gauss of the electro magnet with steel core.

acp

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Re: Electro magnet design software advice?
« Reply #3 on: July 24, 2007, 08:18:19 PM »
Hi Honk,

I had the very same experience when I first tried to use FEMM, until I downloaded the tutorial and worked through it, and then everything seemed fairly straight forward. Now I find it very quick to develope new models. Also invaluable is the Lua script facility, which allows to automate incrementing the rotor of a model a few degrees as desired and torque measurements or gif pics saved for every increment, all at lightening quick speed. I would recommend making the effort to learn the Lua scripting.

Regards

Albert

Honk

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Re: Electro magnet design software advice?
« Reply #4 on: July 24, 2007, 08:23:19 PM »
Thanks, where can I download the Lua scripting?

acp

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Re: Electro magnet design software advice?
« Reply #5 on: July 24, 2007, 09:00:48 PM »
It's part of it, the lua scripts are just text files with a ".lua" ending. I'll send you a model with a script if you like. check your private mail in 1/2 an hour or so.

acp

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Re: Electro magnet design software advice?
« Reply #6 on: July 24, 2007, 09:19:23 PM »
Hi Honk I found your email adress, let me know if you got the files and if you were able to run it. If you have questions I will try to help.

Regards

Albert

dingbat

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Re: Electro magnet design software advice?
« Reply #7 on: July 25, 2007, 05:12:15 AM »
Honk,

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcon.html#c1

this is a pretty good site on magnetism in general.  It explains a lot about the relationship between turns, current, core materials, etc.

The formula for flux is basically amps times turns time the permeability of the material. (until you saturate the core)  Units are gauss, I think. (1/10000 tesla)

The length of the coil does come in to play somewhat, but not like the permeability and ampere turns.  The coil weakens as it gets longer.

I think the area of the core will mainly affect the saturation point.  You need enough core area to carry the flux.

For example:
1000 turns
0.05 amps
2000 permeability

flux = 1000 x 0.05 x 2000 = 100,000 gauss, or 10 Tesla

Your core must have a large enough area to carry 10T without saturating.

Honk

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Re: Electro magnet design software advice?
« Reply #8 on: July 25, 2007, 09:02:02 AM »
For example:
1000 turns
0.05 amps
2000 permeability

flux = 1000 x 0.05 x 2000 = 100,000 gauss, or 10 Tesla

Your core must have a large enough area to carry 10T without saturating.

This is how I understand it. The magnetic flux in the core will behave much like pressure (like water in a hose).
In a large diameter hose the pressure is low. When the hose is getting more and more narrow the pressure will
increase until the point that it cracks the hose. The cracking point = The saturation point of the core.

Using a big core with 1000 turns the flux will be lower than using a smaller core with 1000 turns.
But the smaller core will saturate at the same number of turns and current.
This why the coil and the core have to be calculated to never go past 2 tesla.
Trying to get 10 tesla is just waste of energy that will heat the core until damaged.

Your formula above is great but I'd like the area of the core to be included in the equation if possible

Thanks /Honk

dingbat

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Re: Electro magnet design software advice?
« Reply #9 on: July 25, 2007, 01:15:58 PM »
Quote
This is how I understand it. The magnetic flux in the core will behave much like pressure (like water in a hose).
In a large diameter hose the pressure is low. When the hose is getting more and more narrow the pressure will
increase until the point that it cracks the hose. The cracking point = The saturation point of the core.

Using a big core with 1000 turns the flux will be lower than using a smaller core with 1000 turns.
But the smaller core will saturate at the same number of turns and current.
This why the coil and the core have to be calculated to never go past 2 tesla.
Trying to get 10 tesla is just waste of energy that will heat the core until damaged.

You are right about the area - I forgot Tesla is flux density, which implies flux lines per square meter.  The ampere turns times the permeability will give flux lines, but not density.

I think your analogy to a hose applies, but don't confuse flux with pressure in the magnetic sense, because the term "magnetomotive force" is given to ampere-turns.  It is defined as the "force" that causes flux.  It is described as being analogous the voltage in electricity.  Voltage is the driving force that cause current where there is a path for the current.  The amper-turns is the driving force that causes flux in a permeable path.  Similar to electricity, the more "conductive" (permeable) the path, the higher the flow of current (flux).

The area of the core is somewhat like the cross sectional area of the wire.  Bigger wire = higher current capacity.  bigger core = more flux capacity (not more flux density, which is flux per area)

mostly just thinking out loud to help myself try to get a better understanding of all this.

db

Honk

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Re: Electro magnet design software advice?
« Reply #10 on: July 25, 2007, 03:27:23 PM »
Good input.

I will try to get hold of an old laminated transformer that I can mill into the desired shape.
Then I will compaire calculations to trial and error windings.....
That should help me getting a good and practical result.

Honk

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Re: Electro magnet design software advice?
« Reply #11 on: July 26, 2007, 10:02:36 AM »
Have any of you guys tried Visimag?
Is it any good or easy to work with?
www.vizimag.com

dingbat

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Re: Electro magnet design software advice?
« Reply #12 on: July 26, 2007, 01:49:50 PM »
Never heard of it.  looks interesting, and it isn't expensive.

Honk

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Re: Electro magnet design software advice?
« Reply #13 on: July 26, 2007, 09:53:47 PM »
I will perhaps evaluate the free 30 days trial download.
If it's any good I will recomend it.
But I don't have any spare time right now. I'll have to wait.

acp

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Re: Electro magnet design software advice?
« Reply #14 on: July 27, 2007, 08:50:59 AM »
Visimag has a very nice transformer design module which I used recently to build an audio transformer. It's a nice programm but I think Femm has the edge tho.

By the way, In Femm if you want to type in coordinates for each point placed on the screen while building your structure, just press the TAB button on your keyboard and a small dialogue appears allowing you to type in the coordinates exactly.

Regards

Albert