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Can cardboard be used as core of the transformer? I read that

core of transformer do not conduct current, induction produces current in secondary coil.

So can cardboard be the core. How do it affect the functioning and effectiveness of transformer?

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    \$\begingroup\$ The iron core of a transformer helps concentrate the magnetic field - so what do you think the change to cardboard will do? \$\endgroup\$ – Solar Mike Dec 10 '17 at 16:16
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    \$\begingroup\$ The core of the transformer is usually a material high in iron, such as iron, steel, or ferrite. The magnetic properties of the iron core are extremely important for the transformer. For 50 Hz or 60 Hz power transformers, it is not really practical to consider making an air core (or cardboard core) transformer. For RF frequencies it may be practical in some cases to use either air or some other lightweight material as a core. One drawback to cardboard specifically is that it might catch on fire during a fault. \$\endgroup\$ – mkeith Dec 10 '17 at 16:17
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    \$\begingroup\$ Magnetic cardboard. \$\endgroup\$ – StainlessSteelRat Dec 10 '17 at 23:47
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Cardboard's magnetic properties are much the same as air, or vacuum.

If you try to make a mains transformer (50/60 Hz) on a cardboard core, you'll find the magnetising current to be so high as to be unusable. The iron in a conventional transformer core allows a much lower H field (primary ampere turns) to develop a decent B field, the variation of which induces the voltage in all the windings.

Once you get up to 100s of kHz and above, air/cardboard cored transformers become more practical.

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How do it affect the functioning and effectiveness of transformer?

То get comparable characteristics of transformer without core we'll need much more turns (approximately 100 times) in all windings. At low frequencies such transformer will be much heavier, expensive, large and less efficient. Though it will work worse, because it will not concentrate magnetic field in the core, but spread it to surrounding space, making undesirable interactions.

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