Hello "dunnsept" (it's considered polite to close your post with a name):There is a very significant difference between the Cornell-Dubilier 930C and 942C series capacitors, especially for use in a Tesla coil tank circuit. It might be worthwhile for you to study the TCML archives to get a better understanding of the requirements for a Tesla coil capacitor before you purchase anything. Once you understand the electrical requirements, study the technical information on the Cornell-Dubilier website
http://www.cde.com/catalog/series/#9and look at the differences in internal construction and particularly the current and voltage ratings for the 930C and 942C capacitors. You'll notice that the 930C series have a maximum voltage rating of only 630 volts, vs 2,000 volts for the 942C series. You'd need almost twice an many of the 930C caps per string as you'd need if you used the 942C caps to achieve a given MMC voltage rating.
Most importantly, the 930C series utilize a metallized polypropylene dielectric, and the 942C series use a hybrid metallized film/foil construction. The polypropylene dielectric used in both capacitors has low losses at high frequencies, which is required for successful use in a Tesla coil, but the film/foil caps have a significantly higher peak current rating. The metal foil plates used in the 942C caps can carry much greater peak currents than the micron-thin vapor-deposited aluminum coating used in the 930C series. Both the 930C and 942C series are available in a large number of voltage and capacitance ratings, not just .1uF or .15uF.
The tank capacitor is probably the most highly stressed component in a Tesla coil. More coils fail due to problems with the tank capacitor than any other component. If you don't understand the voltages and currents that will be present in your coil's tank circuit, you won't be able to design a MMC that will survive.
The TCML archives contain all the information you will need to design your coil, including a suitable MMC. If you're new to Tesla coil building, your first stop should be Richie Burnett's exceptional website at http://www.richieburnett.co.uk/tesla.shtml. Here every aspect of tesla coil design, construction and operation will be clearly explained. In addition to conventional spark-gap coils, Richie covers solid-state coils, vacuum-tube coils, and other more complex designs.
Regards, Scott Hanson----- Original Message ----- From: "dunnsept" <dunnsept@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Sent: Monday, December 10, 2007 12:35 PM Subject: Re: [TCML] Intro and questions / MMC
I live close to Midland, about 80 miles north-east of Lansing. Here's another question for the group:In looking at different caps to use for an MMC, it sure seems that the CDE 942C are everybody's favorite, but would it be that big of a deal to go to the 940C? They are 0.1uF 2000 vdc instead of 0.15uFand are less than half the cost ($1.86 per for quant > 10) is there some other rating on these that prefers the 942C20P15K ? thanks!----- Original Message ----- From: <Mddeming@xxxxxxx>To: <tesla@xxxxxxxxxx> Sent: Friday, December 07, 2007 5:47 PM Subject: Re: [TCML] Intro and questionsHi Paul,Welcome! Where in Michigan do you live? You might have a number of othercoilers very close to you. Other comments interspersed below: Matt D.<snip> _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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