High Voltage Forum
Tesla coils => Spark Gap Tesla Coils (SGTC) => Topic started by: fpicoral on April 21, 2019, 08:41:25 PM

Hello there!
I'm building a small Tesla coil (a little bit taller than 1 foot) and I was wondering how many Farads should my capacitor bank have to I get bigger arcs. My power supply is around 15kV (flyback from CRT tv) and I will build the capacitors (saltwater capacitors) from 16oz bottles. I was thinking about something around 10.5nF, is this enough?

That's not a simple yes or no question. It all depends on something. First you should match the primary frequency to the secondary frequency. Howmany bottles that may take. Then you have to experiment yourself if more bottles and less turns is better or the opposite.

the question is how much capacitance is in 1 bottle what is the inductance in your primary and what is the resonant frequency in your secondary with topload toride. how many bottles will it take with your primary inductance to make your primary equal to your secondary frequency. caps in parallel add so you will have to make some mesurements and your flyback may have enough energy to make 23" sparks if you want more you will need more power.
https://www.daycounter.com/Calculators/LCResonanceCalculator.phtml

You should use some of the good old tools available on classictesla.com
Bottle capacitor calculator: http://classictesla.com/home/5702/
Use the MMC calculator: http://classictesla.com/home/javammc/ and pay attention to the LTR values
Static Gap LTR Value (uF):
SRSG LTR Value (uF):
Last but certainly not least, use JavaTC to design the rest of your coil: http://classictesla.com/home/javatc/
Some good information and links on SGTC design: https://www.teslacoildesign.com/design.html also loneoceans writes some good explanations: https://www.loneoceans.com/labs/teslacoil1/

A SGTC design usually starts with two things. The first is what HV power supply do you have (voltage and current)? The second is what type of HV pulserated capacitor can you make or buy? In your case I think the driver here is how much capacitance you can make with a reasonable number of beer bottles. The capacitors have to be reasonably compact so that short heavy wire can be used, which is probably one bucket's worth.
After you have determined the number of beer bottles that you can squeeze into one bucket, compute the capacitance using the tool mentioned in a previous reply. Once you know the capacitance, you can now start using JAVATC to design the rest of your TC.