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How to calculate a Tesla coil semi spherical top load capacitance? Answered

I want to know if you can calculate the capacitance a Tesla coil semi spherical top load by calculating what it would be then halving it?
Also if that is possible could you third it or quarter it because I am going to buy metal bowls for it and most aren't quite a semi sphere (a lot only go about 120 degrees)? 

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steveastrouk

Best Answer 7 years ago

It doesn't scale like that unfortunately, because of the way the electric field sets up around an object. On a sphere, that field is entirely uniform and forms concentric shells about the sphere. In anything not spherical, all bets are off.
Steve

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steveastroukThe MadScientist

Answer 7 years ago

It CAN be done, but it takes some extremely expensive software unfortunately. May as well just make it, then measure it.

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The MadScientiststeveastrouk

Answer 7 years ago

How can I measure it multimeter's don't quite go low enough for measuring that kind of capacitance?

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steveastroukThe MadScientist

Answer 7 years ago

A classic method is to make it resonate with an air-cored coil, and measure the resulting resonance.

Steve

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The MadScientiststeveastrouk

Answer 7 years ago

Unfortunately for me that can't be done because I am in the process of making a Tesla coil and I need to know a rough estimate of my secondary coil before I make the primary. I am going to make and measure the capacitance of my tank capacitor in the next few days.

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The MadScientiststeveastrouk

Answer 7 years ago

I think I will make an excessively large inductance for the primary so I can move around the tap to tune it.

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icengThe MadScientist

Answer 7 years ago

I'm curious, what will you do when you have a value for the capacitance calculation ?
Maybe test measure it ?

Here's the formula for the capacitance of an isolated charged conducting sphere,
                C = 4(pi)e0R

C   = capacitance in Farads
pi  = 3.14159 ratio of circumference to diameter of a circle
e0 = 8.854×10-12 permittivity of space
R  = radius of sphere in Meters

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The MadScientisticeng

Answer 7 years ago

I will calculate the resonant frequency of my Tesla coils secondary.

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icengThe MadScientist

Answer 7 years ago

You could calculate CLarge with the Largest Radius of your semi sphere
and also calculate Csmall with the smallest radius,
Then average the capacitance Cavg = ( CLarge + Csmall ) / 2

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