Tank Capacitor

The tank capacitor is probably the most stressed component of all in the Tesla coil system.  It has the highest failure rate and can be the most expensive component to replace.   Only the capacitor used in 5 kW or higher Tesla Coil system will be discussed on this page.   I have not done much research on this matter, they are treated as my opinion.

Possible cause of tank capacitor's failure:

1. Corona discharge produce heat and UV light source.  Both destroys the dielectric insulation property.
2. The partial charges remain in the dielectric itself, when the polarity of the capacitor voltage changes at a high rate, causing over-voltage stress on the dielectric insulation.
3. High repetition peak current generates excessive heat as a result of the dielectric/conduction loss, causing thermal stress on the insulation.

How can the corona discharge, partial charges in dielectric, and high current heating problem be reduced?  Suggested items listed below to improve the capacitor construction design.

1. Multiple capacitor stack in series to divide voltage for the lowest possible voltage stress for each capacitor, while meeting the design and cost goal. 5kV (RMS) is the suggested maximum voltage for corona reason.
2. Place capacitor assembly under oil with all air bubbles removed.  It can be done by vacuuming most of air out and then use vacuum pressure for back-fill oil in. 
3. Round off all sharp corners on each conductor plates.  A radius of 1/8" will work for voltage range of 5 kV.
4. Use LDPE plastic for lowest loss for its price range and availability.

Suggested Capacitor:

  • MMC

  • Maxwell Pulse Capacitor

  • Mica Transmitter Capacitor

  • Rolled LDPE/Aluminum Foil Capacitor

  • Stacked LDPE/Aluminum Foil Plate Capacitor