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Re: Spice simulation pictures


What formulas do you use for the skin and proximity
affect on your spreadsheet.  Bessel functions?
I am working on a spread sheet in Excel but
haven't figured out how to do summations
in spreadsheeteese for calculating the
bessel function expansions for solving for
Rac/Rdc from the formula I got in Reddick's
book.
Barry

 ----------
|From: "tesla-at-poodle.pupman-dot-com"-at-PMDF-at-PAXMB1
|To: Benson Barry; "Tesla-list-subscribers-at-poodle.pupman-dot-com"-at-PMDF-at-PAXMB1
|Subject: Re: Spice simulation pictures
|Date: Monday, October 21, 1996 1:21AM
|
|<<File Attachment: 00000000.TXT>>
|> Subject: Re: Spice simulation pictures
|
|From bert.hickman-at-aquila-dot-comSun Oct 20 22:12:01 1996
|Date: Sun, 20 Oct 1996 16:07:10 -0700
|From: Bert Hickman <bert.hickman-at-aquila-dot-com>
|To: tesla-at-pupman-dot-com
|Subject: Re: Spice simulation pictures
|
|Tesla List wrote:
|>
|> >From rwstephens-at-ptbo.igs-dot-netSat Oct 19 22:22:57 1996
|> Date: Sat, 19 Oct 1996 19:45:18 -0500
|> From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
|> To: tesla-at-pupman-dot-com
|> Subject: Re: Spice simulation pictures
|>
|> 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
|
|Robert,
|
|Well, I figured you knew the answer all along, and were just wanting to
|give the rest of us a test! :^)
|
|Unfortunately, when I did my original post in reply, I tried
|"faking-out" my spreadsheet model using some of your coil parameters,
|and managed to mess up on the calculations big time, since other
|parameters were still from my coil! Right concept - _wrong_ numbers -
|never blindly trust what a spreadsheet says!
|
|Straight #14 AWG wire at DC has about 2.53 Ohms/1000 feet. At 150 kHz,
|simple skin effect increases this to about 6.5 Ohms/1000 feet. Proximity
|effect from coiling the wire further increases this to about 11
|Ohms/1000 feet. Thus Rac/Rdc = 11/2.5 or about 4.4X the DC resistance
|(current flowing through only about 23% of the copper). The 8 Amps of RF
|current is like passing about 35 Amps DC. The #14 AWG at 150kHZ is
|conducting about as well as 20-21 AWG does at DC.
|
|Now that I'm sitting on the coil - turn the power on, please!
|
|-- Bert --
|