Estimate magnetic permeability and inductance factor A_L of an unknown ferrite toroid core:

Often radio-enthusiast can found in his spare box some unknown ferrite toroid core. However, he doesn't know anything about its characteristics, he doesn't know the A_L – the inductance factor or µ_r – relative permeability of the core. So far as the magnetic flux is closed in the core and don't have an air gap, we can quite easy to estimate these values. We have to wind some turns on the core and to measure obtained inductance by using an LCR meter. The following calculator helps to determine characteristics of the toroid core. Here you can see the formulas that the calculator uses. You can download the cross-platform app Coil64 to find the magnetic permeability of the toroid core offline.

ENTER THE INPUT DATA:

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Select units:

mm/cmmil/inch

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N	=	– Number of turns
L	= mHμHnH	– Required inductance
OD	=	– Outer diameter of ring
ID	=	– Inner diameter of ring
h	=	– Height of ring
C	=	– Chamfer

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Calculate

RESULT:

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µr	=	– Relative magnetic permeability
AL	=	– Inductance factor of the ring [nH/N2]

If you found the magnetic permeability of the toroid core, you can calculate the number of turns for required inductance with this core.