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Tesla coil tank capacitor? Answered

Ignoring resonance what should the average capacitance of a Tesla coil tank capacitor be?
In what  appliances can you find large high voltage capacitors, preferably above 10nF?
And can you use microwave capacitors in series for a Tesla coil tank capacitor?



Best Answer 8 years ago

Your capacitance value will be determined by the properties of your secondary. The resonant frequency of the primary circuit should be close to that of the secondary. The inductance of your primary will depend on its construction, number of turns, size, etc., and so the capacitance value needed to make it produce a frequency that matches the secondary will depend on what the inductance of the primary ends up being.

I can't think of any common appliance that would have a capacitor of suitable rating for use with a tesla coil. Caps from a microwave would have a fairly high voltage rating, but I don't know what their capacitance is typically.

Most mid size coil builders use either a home made capacitor constructed from glass bottles wrapped in foil, or a parallel plate type made from sheets of foil separated by plastic or glass. There are lots of such designs documented on the web.

The ones that use commercially made caps often use "doorknob" type capacitors. These are usually not as large as an actual doorknob, but rather they are cylindrical and about 1" in diameter. I use this type in my coil. The ones I have are rated for 25kV, and are about 500pF each. I have an array of about 20 of them in parallel for my primary capacitor. The nice thing about using these is that I can add or remove caps to help tun in the primary frequency.

LargeMouthBassThe MadScientist

Answer 8 years ago

1 uF would be fairly large for a tank capacitor. Again, the actual value needed will depend on the rest of the design, but coils your size would us a lower value.

With a rating of 2kV, several of them would need to be placed in series, to create a capacitor with a higher voltage rating. The total capacitance of capacitors in series is like resistors in parallel, where the equivalent is a lower value. If you had 20 1uF caps in series, that would reduce the overall capacitance to about 0.05 uF, which is getting into the range that you would actually need.

Another thing to look out for is whether the microwave cap is polarized. They may well be, as I believe that the high voltage transformer output is rectified and then the cap is used to filter the DC voltage. If they are a polarized type of capacitor, then you would not want to apply AC voltage to them.

The MadScientistLargeMouthBass

Answer 8 years ago

The microwave capacitors are used in a voltage multiplier circuit to get 4kv dc therefore they would need to be ac. Anyway I will be driving the tank circuit with dc, I don't want to go through the trouble of using ac because I don't have a large access to HV capacitors.