Make Air Core

[altec9440]

helloi

I need to make air core for a quad 405 amplifier. Online calculator can help to find turns number if you know core diameter and wire size.

But how to compute enamelled-wire size ? Do your knowledge help you to choose something between xxx diameter or have you approximative formula enough for audio spectrum?

 

[Osvaldo de Banfield]

The best air core inductors are those who have a wire diameter between turns and the diameter of the whole inductor is the same as its longitude, say, a cubic inductor.

Search in the web or in books, the "Wheeler formula" to design single layer inductors.

 

[Mark Tillotson]

Around 1 mm^2 will be fine for 100W into 8 ohms. That's about 17 milliohms per metre of wire, the coil will likely be less than a metre so only a fraction of a watt at full power even allowing for skin effect and proximity effect.

 

[altec9440]

Around 1 mm^2 will be fine for 100W into 8 ohms..

how do you get this value ?

 

[Mark Tillotson]

Resistivity of copper is about 1.68x10^-8 ohm-metre, so 1 mm^2 is 1.68x10^-2 ohm/metre, or about 17 milliohms/metre.


100W at 8 ohms is nominally about 3.5Arms max, I-squared-R for 1 metre of wire thus about 0.2W.


Also 1mm^2 wire is rated for 10A continuous, so a generous safety margin.