Impulse magnetizer design

Thread Starter

1bibo

Joined Nov 18, 2017
1
Hello,

I am considering a home project of designing and building a capacitive-discharge magnetizer. My aim is to build
a device that could axially magnetize ferrite rods into a magnetic dipole configuration.
I have read several papers on impulse magnetizer design to understand the main approach, but I have not been able to
find a resource which explicitly states the necessary design/fabrication steps in sufficient detail. Specifically, I have
found a lot of material relating to the simulation/analysis of complicated fixture structures, but not so much on choice
and design of power-supply, according to the magnetization requirements. Therefore I have some questions relating to the
approach and feasibility of such a project. I will first state my current understanding.

The fixed parameters are the dimensions and material of the object to be magnetized - in this case, that would be
barium ferrite rods with a diameter of 1cm and a length of 14cm. This determines the required magnetic field necessary
to magnetize the material to saturation, and sets approximate limits on size of the fixture. If I understand correctly, saturation in Ba-ferrite
occurs at fields strength of roughly 20 kOe [1]. The fixture would in this case be a solenoid, with a length approximately
1.5x the magnet length in order to create a homogenous field distribution, and a thickness dependent on the number of windings.
Then, what needs to be done is to design and simulate the fixture, and to analyze the magnetic field strength at the location of
the material to be magnetized. If I'm not wrong, this would require a transient analysis, plus varying the excitation parameters
to determine the power-supply requirements that correspond to the required magnetic field. Additionally, thermal analysis of the
conductors should be done and the forces acting on them during magnetization should be computed. I have some experience with
Ansys Maxwell software, which I think could perform all these tasks.

What I don't understand is:

1) How to design the capacitor bank according to the computed excitation parameters? The excitation voltage is chosen during simulation,
so that is known, but how to relate the impulse discharge current through the fixture to the required capacitance? I know there are
capacitor discharge calculators available online that will calculate the peak discharge current [2]. Then, by varying the capacitance
until the required peak current is obtained (corresponding to the excitation current from the simulation) one can determine the capacitor
bank parameters. Would this be a correct way of doing it? And if not, what would?

2) How to choose the number of windings of the fixture and the required wire gauge? With regards to turn number, can this somehow be
estimated a priori, so that the parameters (inductance, series resistance) can be fixed and entered in the simulation? And how to determine
the current-carrying capability for an impulse discharge for copper wire of a particular gauge - are there tables for that?

3) Is this feasible as a home project? I am completing my BSc.EE. and have some experience with power electronics, but have not attempted
a project of this difficulty before. Even though this concerns magnetization of ferrites, and not of rare-earth magnets, I recognize I might
be out of my depth here, so if somebody with more experience in high-power electronics would care to answer my questions or give advice
I'd be glad to listen. In case I am discouraged from pursuing this project in a practical way, I would still appreciate to know the correct
design/simulation approach.

Thank you.


References
1. https://warwick.ac.uk/fac/sci/wmg/a...al_properties_of_mtype_barium_hexaferrite.pdf
2. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html
 
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