EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: mercurial on April 26, 2023, 03:47:02 pm
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Say I have a ferrite core with rating of 0.25T max flux density @ 1000 At/m
and the core has a effective length of 0.1 m
Now if I wind 10 turns of primary wire on it and give 10A into it.
that would make it 10 * 10 * 0.1 = 10 At/m correct?
Now if I wrap 100 turns of secondary on it and load the secondary to 1A.
Will this field strength of 10At/m increase or decrease due to the loaded secondary.
Does the field strength calculation for both primary and secondary coils need to be added up to get the effective field strength acting on the core/
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Transformer is more than a single component.
It's more like a black box where one side is in and one side is out.
So if that is the case then both sides can't have equal signs.
Field density is energy through area.
Around the core there is only one area through what the energy goes.
In electrical sense primary and secondary are also not connected, the other side is like a black box.
So if field density is added both sides must give energy and neither can take it.
One example is winding direction check.
There you put AC voltage to one winding and connect one end of the other winding to one end of the first winding.
The you measure the voltage from not connected ends.
If voltage increases from what is put in the winding directions are the same.
If voltage decreases the winding directions are the opposite.
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I subscribe to the thread
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Use dimensional analysis. You put 10 turns * 10A * 0.1m = 10 Atm.
But you need At/m. Something is wrong.
Divide by 0.1m --> 1000 At/m. Which will evidently give close to 0.25T, whatever that figure relates to.
As mentioned, if you're using this as a transformer, you must sum primary and secondary amp-turns. The core ONLY sees the total ampere-turns!
And that difference will in general be very small for a transformer. And is not defined by winding currents, but by applied voltage and frequency -- flux. So you don't need to know winding currents at all, but use the applied waveform instead. This makes calculating flux density of a transformer much easier in most applications.
Tim
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Normally the magnetic flux density produced by the primary winding cancels out with the density produced by the secondary winding.
But this is not the way to calculate a transformer.
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Some formulas you may find useful.
https://www.eevblog.com/forum/beginners/magnetic-circuit-formulas/ (https://www.eevblog.com/forum/beginners/magnetic-circuit-formulas/)
You must first calculate the reluctance of your core and then, from there, you can go on to calculate transformer or coil parameters.