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I measured the AC resistance of my customized inductor with a network analyzer of core E70. I got 23 mΩ AC resistance and 2.3 mΩ DCR for a 14 μH inductor with 8 turns using Litz wire (1400) with a 4.3 mm diameter.

I also got 30 mΩ AC resistance and 11 mΩ DCR for a 54 μH inductor with 16 turns using different Litz wire (1050) with a 2.8 mm diameter. Both were measured at the same frequency.

I am confused now; which factor affects the AC resistance? I thought I should have gotten more AC resistance using the 54 μH inductor. Does it depend on the type of Litz wire we use? Or the number of the small wire? How can I reduce the AC resistance?

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  • \$\begingroup\$ The resistance will depend upon the length of the wire and its diameter (and also it's composition, but I assume both wires were electrical grade copper). If you want to decrease the resistance of an inductor without changing the inductance or changing the core (if it has one) then you need thicker wire or multiple wires connected in parallel. \$\endgroup\$ Commented Feb 11, 2021 at 13:28
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    \$\begingroup\$ Both measured at same frequency. - here's the problem - I'm struggling to see what you mean here because DC resistance has to be measured at DC or it will contain AC resistance artefacts. \$\endgroup\$
    – Andy aka
    Commented Feb 11, 2021 at 13:29
  • \$\begingroup\$ Also, try measuring both with the core removed. \$\endgroup\$
    – Andy aka
    Commented Feb 11, 2021 at 13:37
  • \$\begingroup\$ @Andyaka I measured both AC and DC in different equipments, here thats not an issue. What I mean is I was supposed to get more AC resistance for 54uH inductor right? because the wire dia is less compared to other. I still could not understand on what parameters does AC resistance depend on? \$\endgroup\$ Commented Feb 11, 2021 at 13:48
  • \$\begingroup\$ The AC resistance measurement has to include the DC resistance measurement because it cannot tell the difference. So now you are comparing 20.7 mohms (L1) with 19 mohms (L2). I.e. both are about the same for "true AC resistance". But, you are not measuring "true AC resistances" of the wire but also core losses because the core is in place. If you removed the cores and measured again you'd get virtually true value for AC copper resistance losses. \$\endgroup\$
    – Andy aka
    Commented Feb 11, 2021 at 14:01

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The AC resistance of your inductor is determined by the litz wire used. See the New England Wire website for detailed information on litz wire selection. https://www.newenglandwire.com/traditional-litz-wire-theory/

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