RE: Top Capacitance Dominant?
Subject: RE: Top Capacitance Dominant?
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Mon, 01 May 2000 00:16:49 -0600
At 05:03 PM 04/30/2000 -0700, you wrote:
>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?
>From: Tesla List [mailto:tesla-at-pupman-dot-com]
>Sent: Saturday, April 29, 2000 7:44 PM
>Subject: Top Capacitance Dominant?
>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> 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... ;-))