Extra coil inductance.
Two closely linked coils will double the inductance ; What will the addition of a third do? The third coil gets left out: The rule is ; Only two coils can couple and the two combined will out power any third coil. Now four coils can't beat the mutual inductance feature of two if you're halving the wire length. That would just be treading water. Any extra wire can just add to the two existing coils.
@Gotoluc,
Your choice of the highest perm toroid core rated in the Mhz range that you're operating in the a 55 Khz range, is not maximizing the full magnetic strength calculated by the permeability to inductance ratio formula. The core figure's out to have much more inductance strength on paper then it can deliver in magnetic field strength with the wrong frequency input!
"Magnetic permeability is not a constant figure, it changes with the frequency of the field".
Originally posted by rave154
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@Gotoluc,
Your choice of the highest perm toroid core rated in the Mhz range that you're operating in the a 55 Khz range, is not maximizing the full magnetic strength calculated by the permeability to inductance ratio formula. The core figure's out to have much more inductance strength on paper then it can deliver in magnetic field strength with the wrong frequency input!
"Magnetic permeability is not a constant figure, it changes with the frequency of the field".
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