Re: Spice simulation pictures

To: tesla-at-pupman-dot-com
Subject: Re: Spice simulation pictures
From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
Date: Sat, 19 Oct 1996 19:45:18 -0500

All,

Yesterday I (rwstephens) wrote:

>I was able to swing the 100 pF load to about 85 kilovolts RMS (120 kV 
>peak).  The secondary winding got so hot in just 120 seconds of operation that
>I shut the system down for fear of melting the PVC tube on which it was 
>wound!  My circulating current was 8 amps RMS according to the 
>measured output voltage across a capacitive reactance of some 10.6 K 
>ohms, but the heat produced in the wire felt more the equivalent of 
>maybe 30 amps RMS.  Can anyone explain where my figuring leads to 
>such an error?  The interconnect between the top of the secondary and 
>the drum capacitor was #14 PVC covered solid wire.  It got bloody hot 
>too.  If I had had one then, that's where I would have liked to place an RF 
>thermocouple ammeter.

The answer to my own question occured to me last nite.  And of course 
I feel foolish for not thinking of it.  My math is fine.  I had 
forgotten about skin effect!  I just calculated how much of the 
actual cross section of that #14 AWG wire is carrying my 8 amps of RMS
current.  Assuming a skin depth of 0.1 MM at 150 kHz then only 24.3% of the
copper is carrying the RF current.  If we scale up the 8 amps proportionately 
times 4 , (4 times 24.3 % is 100%) that is the equivalent current of 32 amperes
RMS in the whole of the #14 guage wire and I had guessed the equivalent of 30 
amps at 60 Hz from experience based on the heat felt in the wire by 
my hand.  I'd say my guess was pretty good after all.

Ahhhh, a mystery solved.  : )

rwstephens
half asleep