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If I were to construct an air core transformer with multiple secondaries. Would the magnetic coupling be better if the primary was wound around the secondaries or the secondaries positioned around the inner primary. I'm thinking it wouldn't make much difference.

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  • \$\begingroup\$ Make a draw. I can't imagine how the windings will be hold, certainly they won't be suspended in the air. \$\endgroup\$ Oct 16, 2017 at 11:01
  • \$\begingroup\$ In the first instance the secondaries would be wound on pvc formers and taped together and the primary wound around the cluster of secondaries. In the second instance the primary would be wound on a pvc former and the secondaries positioned around the primary and the whole thing taped together. \$\endgroup\$ Oct 16, 2017 at 11:51

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The magnetic coupling of such coils is best when primary and secondaries are wound alongside, each wire tight to the other. The outer form is near to irrelevant. This is called a bifilar winding scheme or bifilar coil.

Three or more cylindrical or planar coils have the disadvantage there will be additional space between the windings.

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  • \$\begingroup\$ What about the case where different windings have wildly different numbers of coils? Can't really do multifilar windings then. \$\endgroup\$
    – ikrase
    Feb 28, 2018 at 11:49
  • \$\begingroup\$ If your winding ratio is e.g. 1:10, you do 10 windings of one coil per winding of the other one. Different wire cross sections help. \$\endgroup\$
    – Janka
    Feb 28, 2018 at 13:00
  • \$\begingroup\$ I have a bit of a hard time visualizing what this looks like. Just interleaving them? \$\endgroup\$
    – ikrase
    Mar 1, 2018 at 9:27
  • \$\begingroup\$ 10 windings of thin wire around one winding of thick wire. Use the thick wire as a "core". \$\endgroup\$
    – Janka
    Mar 1, 2018 at 9:55

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