Inductor Coil Design

If size is not a problem.

Use a 1" diameter plastic pipe.

Use #25 AWG (american wire gauge) film insulated wire.

Calculate wire skin depth. If skin depth is less than twice wire diameter, go from one wire to multiple wires.

Use a single layer and close wind wire 2 inches long.

Calculate the wire's DC resistance.

Calculate inductance using formula for one layer solenoid.

Calculate watts/inch squared for inductor. Use DC resistance of wire.

Calculate wire temperature rise using outside diamiater and length of solenoid.

If watts/inch squared is too high or too low or inductance is incorrect, change wire size, or tube diameter or winding length/# of turns. Repeat calculations and changes until you have smallest size and correct inductance.

If you want a multiple layer inductor, there may be capacitance problems. This gets complicated.

If you want a ferrite core then it gets more complicated still.

Good Luck

Carl

The tube diameter, wire size and winding length were selected at random so actual sizes may be very different from starting point.

check here coil design

Clicked "coil design" in previous post.

Looked like easy way to calculate inductance, so decided to try it out for 1.02 inch diameter winding 97 turns wound 2 inches long.

The answer came out 97.6 henry. This answer was obvisouly incorrect.

Calculated inductance using formula and it came out 99.5 microhenry.

DOUBLE CHECK ANY ANSWER YOU GET USING www.ajdesigner.com/phpinductor_equation.php.
Used inches and permeability of 1 and this may have confused the program.

The formula for current carrying capacity in amperes for copper magnet wire wound into a coil is: d² x 4869.48 (d = diameter in inches).

Assuming (dangerous thing to do) that your formula is correct, then

d² x 4869.48 =20, so d² = 20/4869.48 = 0.0041; d=√0.0041=0.064"

That would be AWG 14 wire.

Source for your formula?

DK -

The last time I got involved in the design & manufacturing of Transformers was in the late '60s to early 70's. As far as I can recall I satisfactorily used the (1000 CM/A) criteria as a very conservative constant in determining the size of the conductor in the design. Depending on the available core window or opening, this wire sizing criteria can only go down as low as (800 CM/A), (permissible derating factor), for a maximum allowable temperature rise at full rated capacity of the transformer.

Using the above sizing criteria, I can safely assume that magnet wire size #12 AWG, has the closest equivalent cross sectional area in circular mills that can safely carry the 25 ampere as requested by the OP..

have u considered 20KHz frequency that leads to increase in AC resistance