Author Topic: Characterizing magnetic cores  (Read 4940 times)

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Offline NiHaoMikeTopic starter

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Characterizing magnetic cores
« on: March 16, 2011, 03:49:46 am »
I have a few ferrite cores from old monitor deflection coils and I'm looking to reuse them as inductor cores for power supply circuits.

How would I go about characterizing them? One thing I did was to wind 7 or so turns on one of the cores, connect it in parallel with a capacitor, and use a pulse to excite it, at which point the resonant frequency (and thus the inductance) can be measured. It measured about 29uH. But that only tells a part of the story. Is there an easy way to figure out how many A*N (amp*turns) the core can withstand without saturating?
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Online Psi

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Re: Characterizing magnetic cores
« Reply #1 on: March 16, 2011, 03:58:28 am »
I have the exact same problem, lots of cores and no idea what frequency they are good for.

At one point i planned to build a testing rig to scan frequency for a few different turn numbers and attempt to work out the core parameters.
So far i've not had time to build one though, i figured it was probably more cost effetive to just buy the core type i needed than try to build something to reuse old cores.
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Offline jahonen

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Re: Characterizing magnetic cores
« Reply #2 on: March 16, 2011, 06:37:29 am »
You could build a suitable setup for driving a pulse into an inductor and simultaneously measuring the current, that gives you saturation characteristic. I built something like that a while ago. Losses are more difficult, though.


Offline tecman

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Re: Characterizing magnetic cores
« Reply #3 on: March 16, 2011, 05:00:39 pm »
Simple tests can be made by winding some turns, and using a signal generator and a scope or AC voltmeter that will measure the frequency, and a couple of resistors, you can approximate the inductance by measuring Xl of the coil.  You can also predict the saturation by increasing the drive level until you see saturation.  A larger number of turns would be better to see saturation.  Some calculation is required to determine the saturation level.


Offline scrat

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Re: Characterizing magnetic cores
« Reply #4 on: March 16, 2011, 05:27:07 pm »
I agree with Janne.
If you're building a switching converter, you can just use one of its switches and an MCU to generate the pulse and change its duration live (if you have a debugger). Starting from a low duration makes the test safe.
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Offline AdShea

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Re: Characterizing magnetic cores
« Reply #5 on: March 18, 2011, 05:28:18 pm »
If you have a scope, and a function generator (only needs to make sine waves (square waves can work too if you are doing SMPS)) you can get nice curve traces for B-H curves using a bifilar winding and a circuit as described at  You run it at your target frequency.  You can get the saturation just by reading off where the B-H curve closes over.  Losses per cycle are just the area inside the B-H curve.

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