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I found this online (
):
[image: image.png]
As with air wound inductors, the inductance for fixed ?r, the inductance
varies as the square of the number of turns. The ? in the above equations
should be the ?r of the toroid material times ?o (of free space).

So the scaling between 33 turns and 21 turns would be [21 / 33]^2 or
0.401. If you measured 36 ?H with 33 turns, you should have 33 ?H x 0.401
= 13.4 ?H with 21 turns. Of course, the 33 turns is with 0.1 mm and the 21
?H is with 0.2 mm. But with a larger core, I would expect greater
inductance than the original 0.1 mm core.

Bear in mind that the tolerance in ?r from unit-to-unit may be as much as
20%. This is quite normal even with toroids from the same batch from the
manufacturer.

Dave - W?LEV

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Dave - W?LEV