# RE: Top Capacitance Dominant?

• To: tesla-at-pupman-dot-com
• Subject: RE: Top Capacitance Dominant?
• From: Terry Fritz <twftesla-at-uswest-dot-net>
• Date: Mon, 01 May 2000 00:16:49 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme
• References: <4.1.20000429202827.00a5dbe0-at-pop.dnvr.uswest-dot-net>

```Hi John,

At 05:03 PM 04/30/2000 -0700, you wrote:
>
>Terry -
>
>Another possibility is that the toroid loses capacity when it is mounted on
>the secondary coil. This would mean the coil self capacity is more than 3
>pf. In an earlier post I said the toroid looses 15 to 20 % of its free space
>capacity when placed on the secondary.

I am not quite sure how to interprete the program's numbers.  Of course,
the self C of the coil and the terminal C are place into each other's
fields so the total is less than the two in free space.  But the resonant
voltages at the terminal are very high so there is a vast amount of energy
storage there which is accounting for the high capacitance calculation.  I
wonder if it is correct but I don't have any reason to doubt it.

>
>A few years ago I read somewhere that a typical single wound TC coil would
>lose most of its self capacitance if the windings were spaced more than 31
>mils apart. Could this be one of the reasons why Tesla built the CS coil
>with about 3 inch spacing? The Medhurst equation does not even use windings!

I would not think that space winding is a factor.  My big TC has 20.1 mil
wire wound with 10 mil spacing and medhurst is still very precise.  Since
self C is a function of a coil's height and diameter, space winding should
not make that much difference as long as it was not far into the extreme.
Perhaps someone has a very space wound coil they could check?

Cheers,

Terry

>
>John Couture
>
>---------------------
>
>
>-----Original Message-----
>From: Tesla List [mailto:tesla-at-pupman-dot-com]
>Sent: Saturday, April 29, 2000 7:44 PM
>To: tesla-at-pupman-dot-com
>Subject: Top Capacitance Dominant?
>
>
>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>Hi All,
>
>	I ran the E-Tesla5 I modified for Bob on my coil.  Of the 18.13pF of
>secondary capacitance, the program says 15.16pF of that is in the top
>terminal!!  Perhaps this is why TC's with terminals and lumped models like
>each other so much.  If the vast majority of the capacitance is a big
>"lump" at the top of the coil, the transmission line fun a long the
>secondary may not be very significant.  This only leaves 3pF for the
>secondary putting the "line frequency" at 618kHz and the 1/4wave time at
>400nS when my coil should have a 1000nS delay (250kHz) which really does
>seem to match the real case.   Hmmmmm...  Not sure what it all means but it
>means something...  May be fun to do that square wave test with a terminal
>on the coil...
>
>Pounded the rocks just about into dust now... ;-))
>
>Cheers,
>
>	Terry
>

```