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Re: why does Capacitor break???

Original poster: "resonance" <resonance@xxxxxxxxxxxx>




Ask the manufacturer.

You need a cap rated for RF duty cycles with 90-95% voltage reversals.

Dr. Resonance


How do I know if the dielectric decent for high frequencies?


Tesla list wrote:

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
It is possible if you can find a brand with a decent dielectric (those not using mylar). I've heard that some microwave caps have better materials and can handle higher frequency, but they may be rare (I haven't looked into them myself). You may just have to test each to find out. Be very careful when testing caps. A low frequency dielectric will heat up quickly and explode due to the internal thermal meltdown. Therefore, use precautions. If I were in your situation, I would certainly check out the internal workings (tear into them and look at internal connections and verify the dielectric) and then if it appears decent for high frequency: test it, safely. 

Take care,
Bart

Tesla list wrote:


Original poster: Tomas Stankevic <Tomas.Stankevic@xxxxxxxx>
Thank you for the answer. I understood that my old russian capacitors are not good for Tesla coil's high frequencies, but it's a problem to find good high voltage capacitors here, in Lithuania :(. Can I make a MMC of microwave oven capacitors? 



Tesla list wrote:


Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Tomas,
Many capacitor dielectrics will heat up with high frequency. Caps should be selected for their rep rates, lead construction techniques, dielectric material, rms current capability, voltage, etc. Even though many caps are rated for high voltage, they are not rated for high frequency. It's best to use caps the coiling community has tried and determined good for coiling. You've probably seen on the TCML the mention of Cornell Dubilier MMC's. There are Cornell's 940C series. They are axial lead film caps which use polypropylene as the dielectric (excellent for high frequency) and they have a high dV/dt rating (high peak currents). The MMC is very simple. It's just a cap bank built of several small capacitors which are series connected for the voltage rating. Strings are then paralleled for the capacitance required. That is at least the basics. You can play with MMC configurations here. 

http://www.classictesla.com/java/javammc/javammc.html
I just saw a post of someone looking to do a bulk buy on MMC's. I usually buy caps as needed and only when it's right for my pocket book. If I need caps, I'll likely contact Dr. Resonance. He uses them for his own business and also puts in requests on his order for those on the list who also need caps. This increases his quantity break down pricing if the extra request quantity is high enough (if the quantity is not high enough, he won't get the pricing break. Standard operating procedure for those who deal with this stuff on a daily basis). However, his MMC needs will vary as will list member needs. Contact Dr. Resonance for pricing. I know he's currently looking for coilers in need of caps. 

Take care,
Bart

Tesla list wrote:


Original poster: Tomas Stankevic <Tomas.Stankevic@xxxxxxxx>
Hi, today I tried my first Tesla Coil. It's 65cm high (secondary), it is powered by 10kV 20mA transformer (a bit too low for him). I used 25kV, 22nF capacitor. It worked perfectly for about 20 minutes, then capacitor went hot and then it was dead. Why?? transformer power supply is 10kV and a capacitor is suitable for 25kV! I know about a resonance... but... :( What capacitor should I use then???