Tabletop Tesla Coil

Step 6 The Capacitors

Two things matter most in choosing capacitors for a Tesla coil--capacitance and voltage rating. I'm not going into the theoretical requirements here because there are many authoritative texts who do that much better than I ever could. Suffice it say you need at least double the DC voltage rating of a capacitor for it to survive life in a Tesla circuit, and more is even better. With a 7.5 kV power source, I would want at least a 15kV rating, and more is better.

To figure capacitance required by the coil, a design program like TeslaMap is invaluable. For various practical reasons I ended up with two 4nF, 20kV ham radio capacitors I got off eBay. I linked them in series, doubling the voltage rating to 40kV. I measured the capacitance of the two caps in series and got 2.75 nF. I tried using one of the caps alone and it burned out. Perhaps it was defective, or perhaps the voltage rating of 20kV just wasn't enough.

(Since starting I have burned out two more of the ham radio polystyrene capacitors. They apparently don't stand up to the severe stress of Tesla circuits very long. I don't recommend them.)

I next tried my homemade Leyden jar array.

Update 6/16/09: I reworked my soda can Leyden jar battery (12 jars linked in parallel) by joining them with strips of HVAC tape and binding the whole array tightly together to insure contact between the individual jars. This upped the capacitance to 5.76 nF, which works very well with the bipolar coil as built. The Leyden battery takes the power from the spark gap and NST with no signs of over-voltage, heating, etc. Homemade proves better than factory made, in this case!

Update 9/14/09: New photos added of my homemade Leyden jar array. This battery has 18 jars, for a total capacitance of 8.05 nF. It works very well with all of my tabletop coils, upright and bipolar.

Update 10/7/09: I have added a complete Instructable on how to make the Leyden jar battery for a small Tesla coil.

Comments

[rodsy]

 im sry i dont relly get science dat well so im askin , why do u need a capacitor?

[xio]

and i would like to say this in the nicest way possible, but i think that you should'nt start things on this big of a scale if you don't fully understand what a Tesla coil is.

[xio]

it generates power for the tesla coil. (giant battery)

[wii552]

no not at all. A capacitor stores energy, not makes it. All that the caps do is make the pulses of electricity for the coil.

[jimmydean123]

it's like a baterey but it dosnt generaste power it stores it until thgat charge is big enough for it to discharge it