Re: New secondary

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Jolyon,

On 14 May 2002, at 16:49, Tesla list wrote:

> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> 
> 
> I have a new secondary 3" in diameter, 10 7/8" high, and wound with 440 turns
> of 24 SWG enamelled copper wire.
> 
> Calculations (Wheeler s and Medhurst s) suggest self-resonance at circa
> 600-700kHz.
> 
> The max inductance of my present primary (flat spiral) has been calculated at
> 21.321368 uH which will require circa 3.017 nF to 2.217 nF to resonate
between
> 600 kHz and 700 kHz but this will require more charging current from the HV
> transformer (an ignition coil)or less frequent firing of the spark gap.
> Alternatively a higher inductance primary will have to be used to match the
> secondary using the existing capacitor (530pF) but is this wise considering
> that inductors are usually more lossy than capacitors?
> 
> What is best -bigger cap or bigger primary? Or a compromise?

Good question. I'd go for the compromise. The ignition coil can only 
store so much energy and the trick is to get a capacitance such that 
its impedance matches what is effectively the internal impedance of 
the coil. Experimentation is definitely called for as specifics vary 
from setup to setup. Ensure you have sufficient primary turns to 
allow for the minimum-sized primary cap that you are likely to use.

Malcolm