Electronics > Beginners
Low frequency coil arrangement
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Zero999:
Winding the coil in flat spirals, sandwiched together will most likely give a high capacitance, why not add an external capacitor? Relying on the parasitic capacitance means the inductance and therefore effective series resistance will also need to be higher, thus a lower Q, than using a separate inductor and capacitor.
LaserTazerPhaser:

--- Quote from: Zero999 on September 22, 2019, 10:08:44 am ---Winding the coil in flat spirals, sandwiched together will most likely give a high capacitance, why not add an external capacitor? Relying on the parasitic capacitance means the inductance and therefore effective series resistance will also need to be higher, thus a lower Q, than using a separate inductor and capacitor.

--- End quote ---
External capacitor is prone to damage from high voltage and obtaining just the right capacitance won't be the same over a duration however the a coils wire diameter does not vary its capacitance unlike an external capacitor.

Wire diameter does have specific capacity but weres the table depicting capacity per length of wire size?
MagicSmoker:

--- Quote from: LaserTazerPhaser on September 22, 2019, 09:34:13 pm ---...External capacitor is prone to damage from high voltage...
--- End quote ---

And wire insulation isn't just as prone to damage from high voltage?


--- Quote from: LaserTazerPhaser on September 22, 2019, 09:34:13 pm ---...and obtaining just the right capacitance won't be the same over a duration however the a coils wire diameter does not vary its capacitance unlike an external capacitor.
--- End quote ---

Whut? Are you saying that it would be harder to tune a resonant LC circuit using an external capacitor than relying on the stray capacitance of the inductor itself?


--- Quote from: LaserTazerPhaser on September 22, 2019, 09:34:13 pm ---Wire diameter does have specific capacity but weres the table depicting capacity per length of wire size?

--- End quote ---

That table - were it to even exist - would need a near infinite number of entries because capacitance depends on area *and* separation distance *and* permittivity.
LaserTazerPhaser:

--- Quote from: MagicSmoker on September 22, 2019, 09:53:16 pm ---And wire insulation isn't just as prone to damage from high voltage?
--- End quote ---

Tuning a coil without a cap is more reliable any coil insulation can handle =>400v and doesn't have issues with ripple current - a capacitor is prone to destruction from conducting large currents regardless of the type it is. Magnet wire is well over 1kv in insulation.


--- Quote from: MagicSmoker on September 22, 2019, 09:53:16 pm ---Whut? Are you saying that it would be harder to tune a resonant LC circuit using an external capacitor than relying on the stray capacitance of the inductor itself?
--- End quote ---
Its by far easier to simply wire the coil properly to attain the proper LC frequency and not use troublesome capacitors which would incur damage and degrade rapidly from transients, heat and conducting large currents.



--- Quote from: radiolistener on September 22, 2019, 08:08:53 am ---Use coil diameter equals to the coil length, it gives best coil parameters

--- End quote ---
What does keeping diameter and wire length acheive for increased capacitance?
magic:
https://quickfield.com/advanced/parallel_wires_capacitance.htm
This gives a formula for capacitance of two parallel wires, supposedly from some book on power electronics. Probably capacitance isn't affected much by the wires being bent, as long as they are parallel.

There is also a bunch of air core inductor calculators on the Internet, have fun.

You will probably find you need something like 3 tightly spaced turns and 10m diameter.
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