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Re: [TCML] Need new cap(s) for my coil

Brandon -

First of all, there may be some confusion about the correct capacitor value you need. What type of spark gap are you using with your 15/30 NST?

If you are using a simple static spark gap, the correct capacitor value is around .008uF, not .015uF.

If you are using a synchronous rotary spark gap, then you will need a capacitor value around .014-.015uF.

You also need to learn how capacitance and voltage ratings are calculated change when individual capacitors are connected in series or parallel. See: http://www.allaboutcircuits.com/vol_1/chpt_13/4.html

for an easily understood explanation.

The film capacitors you have found at tedss.com are NOT suitable for Tesla coil use because: 1) They use polyester dielectric that is very "lossy" at high frequencies and will quickly overheat and fail; 2. They cannot handle the high current pulses present in a Tesla coil circuit and will quickly "burn up" internally.

There is a tremendous amount of information on Tesla coil capacitors in the TCML archives at www.pupman.com. Use the "Search the archives" option.

The bottom line is that the simplest, least-expensive and most-reliable capacitors you can use in an MMC for a small Tesla coil are Cornell-Dubilier 942 series hybrid film-foil capacitors. For a Tesla coil using a 15/30 NST with a static spark gap, and using the C-D .15uF, 2000V capacitors, you will need a series string of ~19 capacitors (at about $3.50 each). The .15uF, 2kV caps are the easiest to find; they are frequently offered on eBay. Other capacitance values of the 942 series can be used that may require fewer total capacitors, but you need to know how to calculate the capacitance value of series-connected caps.

Herr Zapp

----- Original Message ----- From: "Brandon Hendershot" <mrbrandman@xxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, October 24, 2009 11:05 AM
Subject: [TCML] Need new cap(s) for my coil

I'm running a 15/30 NST. the recommended capacitor farad rating for that is 0.015uF. I've found this capacitor; 0.015uF 10,000V Film Capacitor (http://www.tedss.com/MPE11H-.015-10000-10/). Could I wire 4 of these in series to get a total voltage rating of 40,000V ( 2.6 times the NST output voltage) and still have a 0.015uF capacitance rating?
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