Need a simple high voltage capacitor for a Tesla coil or other high voltage device? This is a simple plate capacitor which uses glass, plastic, or even a piece of breadboard for the dielectric. The plates are made from common household aluminum foil (Reynold's Wrap). These can be made in a minute or two (more for the breadboard one). A good piece of glass comes from an old picture frame. This glass is typically 1/16" (about 3mm) thick which should stand up to 20kV easily due to it's high dielectric constant. If you need more capacitance you can hook these in parallel and if you need a high voltage rating you can hook them in series. The capacitance is dependent on a few different things; plate area, dielectric constant, and dielectric thickness. Here are some simple formulas for series/parallel capacitors:

Series:

Ctotal = 1 / ((1 / C1) + (1 / C2) + (1 / C3) + (1 / etc.))
Voltage rating is the rating of the smallest capacitor times the number of capacitors.

Parallel:

Ctotal = C1 + C2 + C3 + etc.
Voltage rating is the rating of the smallest capacitor.

The capacitor must be designed in terms of the amount of voltage it will have to handle. So, make sure you leave enough dielectric border on the capacitor so that it will not flashover. There must also be enough dielectric thickness and it must also have a proper dielectric constant (K) to get the desired capacitance in the desired space. The dielectric material must also be free from defects like holes. Defects may cause failure.

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