Re: why does Capacitor break???

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Tomas Stankevic <Tomas.Stankevic@xxxxxxxx>

Thank you for the answer.

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???