On 7/4/11 2:52 PM, Quarkster wrote:
There's some discrepancy in your NST voltage ratings that may have affected your tank capacitor callculations. Your schematic shows 7.5KV, while your TeslaMap spreadsheet shows 8.75KV. The ballpark "larger-than-resonant" tank capacitor value for a 7.5KV, 60ma power supply used with a static gap is .032uF, not .025uF.Chris -
7. It looks like you are using C-D 942 series caps in your MMC, probably the .15uF, 2KV rated parts. You only have six caps in your MMC, presumably all connected in a single series string to yield .025uF. Two problems here: not enough current carrying capability, and not enough voltage margin. You need at least two parallel strings, and enough caps in each string to provide a DC voltage rating of at least 18-20KV. Your 7.5KV RMS output voltage creates a peak voltage of 10.6KV, and your cap string is only rated at 12KV. If you use a variac to boost the input voltage to yield an 8.75KV RMS output voltage, the resulting peak voltage is around 12.4KV, exceeding the capacitor's rating.
A quick and dirty bucket cap is sometimes useful as a diagnostic thing. Sure, they're not as low loss as nice caps, but if you swap in the bucket cap, and it works a lot better, then you know your caps have been toasted by a few two many hits.
Bucket caps are a pain on a sustaining basis, but they sure are cheap to build
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