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# Electronics/Ask for electromagnetic induction model

Question

Electromagnetic genera
QUESTION: Hello.
I'm doing a project of electromagnetic generator, I have a magnet bar with 10 cm length, 2.5 cm diameter (composes of 3 blocks of sub-magnet with 2.5 cm each along its length). The magnet is inside a tube with 30 cm length and wrapped with coil from the length of 10 cm to 20 cm. The tube is lifted at its tips to make the magnet moving to induce electric through the coil.

The following is information of the components.

1. Wrap coil 6 layers, 120 turns each. The total is 720 turns.
2. The outside magnetic flux density (B) along it length by Gauss meter measurement is about 1 Tesla. The magnet mass is 380 grams.
3. The measurement of the coil resistance (R) and inductance (L) is 5 ohm and 6.3 mH respectively.

I would like to do an electrical model of the generator system for circuit simulation. I attached its output waveform when no load connected and other physical structures for references.

Especially, I would like to know how to calculate the EMF voltage (the waveform shows that its amplitude and frequency increase by time, how to identify B(t)?)

Thank you.
Bundit

ANSWER: Current is induced by moving a coil of wires in a magnetic field. In your example I don't understand the movement of the magnetic field (or the coil if the magnetic field remains stationary).  Can you explain it?  Do you move the permanent magnets by hand?  Or by gravity?  And if so, what are the friction coefficients of the sliding parts?

Please clarify it to me.

PS:  Most textbook equations are based on the assumption of uniform rotation or movement which produce either  sine wave output or dc transient.  In your case I am not sure what the mechanical input energy is and how you are taking out the electrical energy.....

PPS: I rather expect that your mechanical model will very difficult to quantify due to its non-linear characteristics and variable field strengths along the magnetic bars.

---------- FOLLOW-UP ----------

QUESTION: Thank you for reply.

My project is to construct an electric generator by electromagnetic induction of a moving magnet through a fixed coil wire.

The magnet is in a cylindrical tube. The tube is lifted up at both ends alternatively to make the magnet moving inside the tube by gravitation force. The coil is wrapped outside the tube which is induced by the moving magnet. I apply some lubricant to the magnet surface and the inner tube which I think there is low friction when the magnet moves.

(I used a DC motor to drive the tube movement instead of human lifting force as you can see in the attached picture).

The waveform output (shown in the attached picture) is the signal when the magnet moves pass through the coil. It consists of 3 peaks sinusoidal(the magnet is also composed of 3 blocks small magnet)and varied in amplitude and frequency. The magnetic field strength (B(t))is quite complicated as you commented.

I would like to get the electrical model of this generator system (electrical source + source impedance) which can bring me to describe the system behavior when connecting to load (rectifier + storage capacitor).
What's about your idea to describe the modeling?

Thank you.
Bundit

ANSWER: OK.  I understand what you have and why the output looks the way it does.  The equivalent circuit is too complex for my quick analysis.  A mathematical model is possible, I suppose, but way too complicated for a quick reply  -  it is a very non-linear system with discontinuities that must be joined together and summed thus requiring large matrix equations that are not easy to manipulate.  To make a model that would produce the output as shown with the generator you have developed is very impractical it seems.

The task is too great for my mind just know.  I will think on it and see if I can send you something later on after developing some idea.  I am thinking of a CAD/CAM model - maybe.  I will work on it.  But believe me, an accurate modeling of your generator is not an easy task.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your kind attention.
I will looking forward to hearing from you.

May be if possible, a draft model with a draft calculation if you can advise me.

Thank you.
Bundit

For a starting point:

E = N x dB1/dT + N x dB2/dT + N x dB3/dT

Where E = voltage sum from each of three magnetic fields.
N = Number of turns in each coil  (N is same for each ?)
dB/dt = rate of change of magnetic field.

It is an integrational problem  E equals integrated total of each of the three magnets.

What is not included is the velocity of the magnet through the pipe.  It would involve gravity feed and friction that would slow it down.

???

Electronics

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#### ZZ

##### Expertise

Electronics questions about AC, DC and digital theory.

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Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

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BSEE University of North Dakota