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I have a SMPS transformer and a LCR meter. I can measure 3 different resistance on a winding:

  1. R on a certain frequency(10kHz): 0.065R
  2. Rs: 0.086(I don't know what is this)
  3. DCR: 0.06

Which one is the transformer winding resistance here? I didn't shorted the secondary like leakage measurements, should I?

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    \$\begingroup\$ DCR is DC Resistance, so I presume you want this one? \$\endgroup\$
    – Eugene Sh.
    May 11, 2021 at 19:30
  • \$\begingroup\$ BTW, What is L at 100kHz , 1MHz? L/R ratio? Rs includes Eddy current Re at some f. Which increases with f^2 \$\endgroup\$ May 11, 2021 at 19:39
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    \$\begingroup\$ ” I didn't shorted the secondary like leakage measurements, should I?” For resistance, it does not matter. For inductance, it it the difference between measuring magnitizing inductance and leakage inductance. \$\endgroup\$
    – winny
    May 11, 2021 at 19:45

1 Answer 1

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There's the primary DC resistance, and the secondary DC resistance.

In addition, there's an AC resistance for each which will be frequency dependent. This is not the impedance due to the magnetizing or leakage inductance, it's a true lossy resistance due to the skin effect, proximity effect and core losses. So it will add to the losses in the transformer. [There's also the concept of mutual resistance or the AC resistance of a winding changing due to the current distribution in an adjacent winding, but it's mostly ignored.]

If you just want the DCR, you measure at DC. If you want to measure the true AC resistance vs. frequency it's a difficult measurement and is sometimes even done via a calorimeter.

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  • \$\begingroup\$ Thank you for answer, actually I'm trying to simulate a smps on simulink environment and transformer block has a winding resistance parameter. But it doesn't mention that it's the dc or ac resistance. That's why I'm trying to find. \$\endgroup\$
    – Das D.
    May 11, 2021 at 20:07
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    \$\begingroup\$ @DasD. For simulation purposes you can use the DC resistance. It's possible but not easy to simulate the AC resistance as well, but you would have to characterize it first. \$\endgroup\$
    – John D
    May 11, 2021 at 20:12

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