Need to analyze this Magnet

[chivisor]

Hi friends, Im working on this(attached image) particular magnet right now. It is AlNiCo5. I want to analyze the magnetic circuit formed here and calculate the flux in the air gap. I want to design similar type of magnetic circuit with different shapes and sizes but I really cant understand how to use a B-H curve to design a magnetic circuit. I really need some help on this.

Thanks in advance....

 

[MagMike]

Knowing and understanding the B-H curve is fundamental to designing a magnetic circuit.

If your budget and travel schedule allows, try signing up for the Magnetics Boot Camp workshop organized by Stan Trout, as part of the Magnetics 2009 conference in Chicago next month. Stan knows his stuff and better yet, can explain it in a way to keep things understandable.

 

[MJR2]

A second vote for the Boot Camp. I'll miss this years conference. Leaving for a vacation in Israel at the same time.

What are the wires coming out for?

This circuit might lend itself well to 2D FEA solutions.

You still would need some understanding of the B-H curves.

Why don't you just measure the field you have now as a start.

Mike

 

[chivisor]

Well I'm in India so traveling upto Chicago will be quite expensive..

1) The wires are connected to a temperature sensor. There is no particular logic to that because we are trying to measure the temperature of the magnet. I have just been assigned the project and there is no documentation whatsoever...

2) I have understood the concept of B-H curves quite well (read from resources found on the net). Now I want to understand how to design using B-H curve.

3) I measured the flux density using a Gauss meter in the air gap which comes out to be 2890G. I really don't know what to conclude from this value.

4) We use impulse magnetizer. We get the AlNiCo magnets in 40mmdix24mmheight cylinders which are then magnetized
There are no calculations as to how much the magnetizng voltage should be. The magnets are saturated first and then demagnetized 5%(no calculations for this value either).

5) What I would like to know is how to calculate the impulse voltage/ or energy from the designed load line on B-H curve?


Really sorry for a long post but I really want to understand this completely before I get into designing anything.

Thanks a lot....

 

[electricpete]

1 - Solve the flux distribution. As stated, if this thing is axisymmetric (symmetric about it's centerline) you could solve it as a 2-D axisymmetric problem using the free software FEMM. Otherwise for rough order of magnitude use magnetic circuit concepts and interative approach that alters mu depending on flux density according to the B H curve.

2 - Use flux disribution to find force. For example could calculate total energy W from flux distribution and then F = -dW/dx. Could also use maxwell strensor type method. FEMM has these methods built in.

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[MJR2]

If you are charging these magnets outside of the assembly then they are demaging as a result of their rather poor permeance coefficient. Alnico should be or is best charged within it's final circuit.

Mike

 

[EdStainless]

With the low H of Alnico 5 you want to magnetize in the assembly. The saturate and knock back is a poor practice for this alloy. You would be better off saturating in assembly and then if you wanted to demag slightly to hit a specific field to it then.
You can determine saturation field needed by trial and error. Use a fresh magnet each time and just slowly turn the current up until the strength stops increasing.
There are a bunch of old graphical design methods, but trust me you are better off learning to use modern FE methods.
Ina design like this you need to check to make sure that none of your structure is saturated and that there are minimal leakage fields.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[chivisor]

Thanks guys for your replies....

1) The magnet is being magnetized with its complete assembly so i guess that part is resolved.

@electricpete :
1) It is axisymmetric.
2) Are you talking about the magnetizing force? I am new to this and would like to understand the theory behind it. Can you suggest some reference where I can read about this.

Have downloaded FEMM and will be working on it. will keep posting the updates.

Thanks again......

 

[MJR2]

An axisymemetric problem is one that can be reduced to a 2D problem and rotated on an axis. On in other words you could take a slice through the device and it looks the same everywhere.

2D problems can be solved very quickly with high accuracy.

Infolytica has a free 2D version of their software Magnet.

http://www.infolytica.com/en/products/trial/index.html

I have been a user of Magnet for more than 20 years and use it daily to solve 2D and 3D electromagnetic and permanent magnet problems.

Mike

 

[chivisor]

Hi guys,

have finally analyzed the magnet i was working on. I used FEMM and the results i got were pretty good matching closely with the gaussmeter readings.
here's the snapshot of the screen.
FEMM proved real useful in understanding the magnet design.

Thanks a lot...