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Registered Member #1772
Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71
Hi all. I recently decided to build a new SGTC. I built my first one several years ago but I've been out of the game for a while. When I was researching to build the first one, I remember finding a web site (or maybe it was a forum post that I found links to?) that listed a bunch of different brands and model numbers for caps that people had tried out and evaluated their performance and durability for use with a TC. Does anybody know the web page I'm talking about and could you post a link please? I've gotten married since I built the last coil so I have to be a bit more budget conscious. If I can find a good alternative to the 942's that's cheaper but lasts at least a little while I'll be satisfied. I'm not planning on running the coil a lot, probably just when friends bring their kids over or on the 4th of July.
In case anybody is wondering, I've just purchased two more NST's to add to the two that I already had so this new toy is going to be powered by four 12kv 30ma transformers! Twice the power of my last one! I can't wait!
The best capacitors to use for Tesla Coils are polypropylene film capacitors. They come in both axial leaded and radial (both in a rectangular box or epoxy dipped) packages and are usually used by hobbyists.
There are two main types - Metal Foil caps and Metallized film caps, such as the CDE 942 series or 940 series respectively that you mentioned. However, I've used a wide variety of different bands and they all work well. Good brands to look out for include CDE, Panasonic, Epcos, Kemet, AVX to list a few.
For example the 940C series 2kV 100nF capacitors go for $4.73 on digikey (down to 3.21 in 100qnty), or $6.48 for the 942C series (cheaper to buy from for $4.99 since EVR buys them in bulk). I've also seen people use multiple cheap 100nF 1kV or similar blue Epcos film caps which occasionally pop up on ebay for cheap in bags of 50s or 100s. I've also used RS-branded and GE branded film capacitors (100nF 1.5kV) and they've been running in my coil for just about a decade.
942C20P15K-F - 150nF Metal Foil capacitors. Best, but expensive. 940C20P15K-F - 150nF Metallised Film capacitors. Essentially identical, but lower dV/dt capability; still an excellent alternative. ECW-HA3C473J - 47nF Panasonic dipped capacitors. Works great as well.
There's also always the option of finding a good deal for snubber capacitors on ebay (but those usually are more cost effective for solid state coils which tend to run at lower voltages but require more capacitance), or making salt bottle capacitors, though I'd recommend just going for the Polypropylene (you don't want anything else!) film capacitors.
[Edit] If you're running a 12kV 120mA power supply at 60Hz, it looks like you'll need around 40nF for the standard LTR cap bank size for static spark gaps. I'd say anything between 26.5 (resonant) to 40nF will work well, with preferably 20kV or higher rating. Using the 150nF 2kV capacitors, the smallest I would size the capacitor bank would be two strings of 10 capacitors forming a 30nF 20kV bank, which should set you back about $100 which is reasonable for a coil of this power.
Registered Member #1772
Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71
Thanks loneoceans. I think I actually found the list I was looking for. I posted the url below. I used the 940C20P15K-F caps on my last coil and got good results but they didn't last very long. I had two blow their ends off, then I had one catch fire. I don't really have any experience with the 942's or anything else so it's hard for me to compare but I sort of expected them to last longer than they did. If the price is right though I might give them another shot.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
oucivileng wrote ...
Found this list too:
I made this list from the original old list of "good and bad mmc capacitors", I added some newer types used, found out more specifications and integrated them all in my MMC calculator where you an select the in the drop down menu:
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SGTC Capacitor List
