Amps
[Top] [All Lists]

[AMPS] Coil heating

To: <amps@contesting.com>
Subject: [AMPS] Coil heating
From: MM@plextek.co.uk (Mark Marsden)
Date: Mon, 26 Jun 2000 11:32:54 +0100
>> RF current flows on the outer surface of the 6mm tube but 
>>can't flow on the surfaces of the 1mm wires on the inside of the
>>twisted bundle.
>
>>In fact it's confined to 6 thin lines on the outside, at 50MHz my 
>>guess is the Q drops about a factor of 3-4
>
>Then how does bunched conductors, let alone Litz, work?
>

>From http://www.wiretron.com/litz.html

"Why Use Litz Wire?

 Litz construction is designed to minimize the power losses exhibited 
 in solid conductors due to "skin effect".
 Skin Effect is the tendency of radio frequency current to be
concentrated
 at the surface of the conductor. Litz constructions counteract this
effect
 by increasing the amount of surface area without significantly
increasing 
 the size of the conductor. Generally speaking, constructions composed
 of many strands of finer wires are best for the higher frequency
applications.
 Polyurethane-Nylon is the film most often used for insulating
individual strands
 because of its solderability. However, you may feel free to inquire
about 
 other higher temperature insulations as well.

                        Frequency vs. AWG Strand Size
                                  All Values in KHz
                                 1 To 10.0 - 30 AWG
                                10 To 50.0 - 33 AWG
                                50 To 100.0 - 36 AWG
                               100 To 200.0 - 38 AWG
                               200 To 400.0 - 40 AWG
                               400 To 800.0 - 42 AWG
                                800 To 1600 - 44 AWG
                               1600 To 3200 - 46 AWG
                               3200 To 5000 - 48 AWG "


Seems the trick is to use thinner wire at 50MHz so the RF current uses
more
of the available metal.

Skin depth in copper at 50MHz  is 2.5micrometers. I wonder if the
thickness
of the isulation is significant?

Mark G4AXX
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
            

--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com


<Prev in Thread] Current Thread [Next in Thread>