Electrical Engineering/Inductor core loss


No Gap core and Gapped core inductors
No Gap core and Gapped  
QUESTION: Hello Cleggsan,

I hope this message find you well. I have question regarding inductors Iíd like to ask you about - I have got myself to a point where I am now unsure of how to proceed.
I am trying to figure out how much an induced current will decrease when there is a gap in the inductorís core.
I have done some simulations using FEMM, comparing a gapped core inductor to one with no gap in the core, and I am just wondering if you could advise me on how to correctly interpret the results.
As you can see in the attached image, there is a coil around the left hand vertical section of a soft iron core. I havenít shown the coil in which the current will be induced, but it would go around the right hand vertical section. For the moment, I am just looking at the magnetic fields of each core.
As you can see, each inductor shows a variation in magnetic field strength at different points in their respective cores. My question is - which field strength measurement(s) should be looking at in order to accurately estimate the loss caused by the gap in the core?
I originally thought that I should be comparing the field strength in the right hand vertical sections of each, as that is where the coil will be which will have the current induced in it, but now I am just not sure. What would you suggest?

Thank you and best regards,

ANSWER: Long time since hearing from you.  

The color intensity of the two coil forms shows the answer to your question.  The red color is the strongest field strength are within the coil according to your FEMM calculations.  You can see that the opening in the core causes a big reduction in overall magnetic strength throughout the coil form.

Increasing the size of the open in the bottom core will decrease the magnetic field strength don't you think?

How far are you getting along with your project?

Good to hear from you.

Domo Domo

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QUESTION: Hi Cleggsan,

Thanks for the message, and your comments. My project grinds on. I appreciate your advice, as always.
In terms of accurately quantifying the difference between the magnetic fields in the No Gap core and the Gap Core, I was wondering if you could tell me whether the following method/reasoning seems valid.
I compared the field strength given by FEMM in the right hand vertical section (where the coil is) in each inductor. I also compared the left hand sections (where the coil I want to induce a current in will be placed)
The results were -
No Gap Inductor
Right section 1.0540 Left section 0.7215
Gap Inductor
Right section 0.4950 Left section 0.3046
On the right hand side, I have a difference of 0.5590 Tesla, and on the left, a difference of 0.4169 Tesla. Can I just average these two numbers to get the difference between the two magnetic fields? Does this seem like a reasonable way to arrive at the numerical value of the difference in field strength between the two cores?

Thanks again.

I think you're on the right track.  In magnetic circuits its always an approximation Only in well defined geometries and wide open spaces do we get calculations that are precise.  In practical circuits the variation in atmospheric stray fields, imperfections in the material and nearby distortions cause the calculations to wonder.  So, approximations are always in order hoping to give good enough results to guide the experimenter to the next iteration.

I have forgotten your original project targets and, sorry to say, I don't recall the need for the gap in the second coil form.  If you want maximum field strength and you don't pull enough currents to saturate the iron core material your best induction will be with the gapless core.  If that helps you in your end results.


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