Polypropylene Capacitors

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Frequently Asked Questions...

Tesla Coil Capacitors: What do I need?

I'm just getting started with my first Tesla Coil and im fairly confident with both my primary and secondary coils however I'm not too sure about my capacitance. I'm going to run an NST rated at 15kV and 30mA so I believe I need about 30kV of capacitance and I'd like to run a MMC setup but I know nothing about Farad ratings of capacitors and as much as I try I just cant seem to get it figured out so any help is greatly appreciated.


Best Answer...

Answer:

Since you're using an 15 kV 30 mA NST, the maximum size of your primary tank capacitor is 5.3 nF (0.0053 uF). Note that you probably shouldn't use this exact capacitance with an NST because of a condition called resonant rise which causes a resonance producing a high voltage in the primary circuit and that can lead to lethal arcing in your primary circuit. You can use something bigger or smaller. In fact, if you use something bigger, it prevents resonant rise. If you're using a static spark gap, the optimum LTR (larger than resonate) size is 0.0086 uF. If you're using a rotary spark gap, the optimum LTR size is 0.0138 uF.
You'll want to look for capacitors that are metal foil polypropylene capacitors. Avoid ones that are "metallized/metal film" types as the metal film is too thin to handle the Tesla Coil's current. Also avoid polyester caps. Generally, MMC caps have voltage ratings in the 1.5 kV to 2 kV range. Capacitance varies but is normally 0.005 uF - 0.1 uF. Each string is wired in series so the capacitance will be cut down. Because you're using a higher voltage, you may need multiple strings, which is common for medium and larger coils. When you connect multiple strings together, you connect them in parallel so the capacitance is combined.

For series: 1/C = 1/C1 + 1/C2 + ... + 1/Cn
For parallel: C = C1 + C2 + ... + Cn

The capacitors I used in my MMC can be found at Digikey:
ECW-H 16563JV

On the first website listed below, there is a list of good and bad caps to use when building an MMC. Remember to solder a 10M Ohm (1/2 W) resistor across each capacitor. Not doing so could result in electrocution and other electrical hazards. The resistor also prevents charge build up from electrical fields when you're storing them.

Excellent Tesla Coil Resources:

http://www.tb3.com/tesla/capacitors/capacitors.html

http://www.capturedlightning.org/hot-streamer/TeslaCoils/MMCInfo/mmcinfo.htm

http://205.243.100.155/frames/build1.html#Where%20on%20Web

http://deepfriedneon.com/tesla_start.html

http://www.teslamap.com/guide.html

http://www.pupman.com/

If you have further questions, just send me a message.