# material to coat secondary

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From:  Alfred A. Skrocki [SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent:  Monday, April 20, 1998 6:39 AM
To:  Tesla List
Subject:  Re: material to coat secondary

On  Saturday, April 18, 1998 7:52 PM Kevin Wahila
[SMTP:kevinw-at-stny.lrun-dot-com] wrote;

> how would a coating lower the resonant frequency?

The insulation painted on the coil has a higher dielectric constant than
air so it increases the distibuted capacitance of the coil.

> anyway, I always thought that a lower resonant frequency was better.

In a sense your right, a lower operating frequency tends to give more
lightening like discharges while a higher frequency coil's discharges
start to look like flames or a brush, BUT it isn't the operating frequency
that one has to consider here but the ratio of transformation, this is
approximated by either of the two following equations;

(1)    Es = Ep * SQRT ( Ls / Lp )

or since at resonance XL = XC

(2)    Es = Ep * SQRT ( Cp/ Cs )

Es = Secondary output voltage
Ep = Primary input voltage
Ls = Secondary inductance
Lp = Primary inductance
Cs = Secondary capacitance
Cp = Primary capacitance

>From these two equations it is easy to see that for maximum secondary
voltage output we must strive for four conditions;

(1) The secondary inductance should be as high as possible.
(2) The secondary capacitance should be as small as possible.
(3) The primary inductance should be as small as possible.
(4) The primary capacitance should be as high as possible.

It should not be to difficult to see that anything that might increase the
secondary's capacitance will also tend to lower the voltage at the
secondary output, BUT if we take this too far there will be little or no
insulation between turns and consequentially the coronal losses will
increase and this will subtract from the coils output. So as it always ends
up we are left with an engineering compromise, we use as little insulating
material on the secondary as we can with out inviting coronal losses. BTW
you run into similar design compromises in the primary circuit, ie. ideally
the primary should have as low an inductance as possible, BUT if it gets
too low, like around one or two turns or less, there isn't enough magnetic
flux to properly transfer energy efficiently from the primary circuit to
the secondary. Likewise smaller primary inductance requires larger primary
capacitance, which on first glance would look good for increasing the
output. But again there is a compromise, namely the larger amount of energy
being stored in the primary capacitor;

E = 1/2 * C * V * V

This increases coronal losses and increases the breakdown of the spark gap
electrodes and makes quenching more difficult.

Sincerely

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Alfred A. Skrocki
Alfred.Skrocki.Sr-at-JUNO-dot-com
alfred.skrocki-at-cybernetworking-dot-com
Visit my Do-It-Yourself Aquarium WEB page at;
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