Skin effect

[zachtheterrible]

Let's say that I have a #22 copper wire inductor and a #30 copper wire inductor (because i do :lol: ).

Just how much better will the #22 wire perform than the #30 wire at 100MHZ? Minimal? Or should I use #22?

 

[Nigel Goodwin]

Let's say that I have a #22 copper wire inductor and a #30 copper wire inductor (because i do :lol: ).

Just how much better will the #22 wire perform than the #30 wire at 100MHZ? Minimal? Or should I use #22?

It doesn't make any difference - don't worry about things like 'skin effect', it's very rarely a problem.

 

[pike]

accordingly to this textbook i have, it says that the RF signal has a tendency to travel on the surface of the conductor. This causes unexpected resistances in the conductor.

From memory Audio-G (Audio Guru, but comon Audio-G sounds cool) said that the bigger the wire the more surface area for the FR signal to travel on. And this provided better performance???

I'm not to sure, but this is all from memory .

 

[Pommie]

Skin effect is caused by the electrons repelling each other. This has an effect in straight conductors but tends to cancel out when they are wound into coils as the repulsion is the same at all point due to neighboring wires.

Mike.

 

[Circuit Seeker]

At high frequencies the current travels only along the outer of the conductor the depth the current travels into the conductor is the skin depth which is determined by the frequency.

So at high frequecies it is better to use several thinner wires twisted together, that way the curent will travel in all of the conductor (no wasted copper).

 

[Styx]

onlt really an issue IF you are passing current - sounds like you are after signal (ie low-level current) so dont worry abt it

 

[zachtheterrible]

30 guage wire is awful darn small for a VHF inductor. I have never heard of using an iron core for such a high frequency.

I used 9 turns of 1mm enamelled wire tightly wound on a 3mm former. The end wires have exactly 0.4" spacing and I spaced these air-core inductors about 2mm above the board. Even though I used Veroboard, my layout was tight without any extra track lengths so my wiring was extremely short, like a pcb.

This is a quote of "audio-G". 30 gauge enamelled wire is exactly what I'm using. I think just for the heck of it, im gonna try 22 gauge.

 

[Nigel Goodwin]

If you want to worry about skin effect?, try searching for 'litz wire'.

But! - have you EVER seen a VHF coil wound using Litz wire? - including coils in high power radio transmitters!. The only place I've ever seen Litz wire used is in old IF transformers, and old shortwave radio coils.

 

[Styx]

We have an SR generator getting wound atm with Litz wire (due to skin effect why we are using it) and:

1) very hard to get hold of
2) not very good to work with

We keep getting told it is getting delayed

 

[Nigel Goodwin]

We have an SR generator getting wound atm with Litz wire (due to skin effect why we are using it) and:

1) very hard to get hold of
2) not very good to work with

We keep getting told it is getting delayed

So what's an 'SR generator'?.

Is skin effect actually a practical problem for this application?, by the sound of it Litx wire doesn't sound like it's going too well either :wink:

 

[Styx]

SR generator is a:
Switch REluctance generator.

Litz wire was chosen not for its skin effect propoties (not to much of a concern - switching freq only 12kHz with abt 600A per phase).

But it was chosen to fill the stator slots + environmental conditions

 

[audioguru]

I used 1mm enamelled wire for the coils in my FM transmitter and they work fine. I used such a heavy wire not only for its high surface area which helps "the skin effect", but also because it allows the coils to be tightly wound. The coils are so strong that they don't change if I bump them or even if I stand on them. :lol:

 

[zachtheterrible]

oh, i see. thanx for the tips everyone :lol:

 

[mstechca]

To me, it really makes no difference either.

But take note of this. Wires and resistors are the same thing with two exceptions:

1. A wire looks different (obviously :lol
2. The resistance of wires are very small.

I dont know the exact resistance of wire, but I do know that different types of wires and different gauges of wires have different resistances.

If you use the parallel resistance equation, you will be able to figure out that the 30 gauge wire has more resistance than the 22 gauge wire.

If you want the exact figures, I dont know them, but I can tell you that the resistances are way less than 100 ohms per centimeter.

 

[audioguru]

Hi MS,
Oh yeah? If the power cord to your toaster had 100 ohms per cm then at 1m in length and at 120VAC it would pass a max RMS current of only 6mA! The wire would heat with 0.72W and the toaster would heat with only 0.4mW.
The toaster is probably only 12 ohms to dissipate about 1KW, and the cord is two wires each with a resistance of probably only about 0.05 ohms to dissipate about 10W. Therefore the resistance of the wires in the cord are about half a milli-ohm per cm.
But you are correct, the wire is way less than 100 ohms per cm, about 200,000 times less! :lol:

 

[drrogla]

...................(specific resistance [ohm m] )*(lenght of wire[m])
resistance=-------------------------------------------------------------
......................pi*(diameter^2)/4 [m^2]

Now all you got to know is the specific resistance constant for the material:

copper: 0,018 ohm-meters *10^-6
aluminium; 0,028 ohm-meters *10^-6
gold: 0,022 ohm-meters *10^-6
sliver(!): 0,016 ohm-meters *10^-6

that means that a meter long copper wire with the area of 1mm^2 has the resistance of 0,018 ohms!!!