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Re: Commercial cap specs for tesla cap

At 08:46 AM 05/06/2000 -0400, you wrote:
>High Terry,
>Thanks for the info regarding cap specs. Im going to use some of those
>specs to fill out NWL,s cap form. As for my coil specs, I have several
>in various stages of completion. The coil that I want this cap for is
>approx. 11.25 inch in dia. 900 turns of # 18 , Primary: 14 turns of .375
>inch dia tubing spaced .375 between turns. topload is 40by7. Ive been
>experimenting with different size toploads. A 0-5000 rpm 7 inch dia.
>rotory 12 spinning 2 stationary designed and built by Ed Wingate and a
>series vacuum gap. I was using a .05 30kv/ac rms from Plastic Capacitors
>Inc. The cap failed so I sent it back for warranty replacement. I plan
>on having Plastic Capacitors build me another .05 so I have 2 of them
>that I plan on using in a magnifier system. Anyways I wanted to compare
>prices Between the 2 companies. The nice thing about Plastic Capacitors
>is they do all that stuff for you as they offer a line of tesla caps.
>About this mmc cap are these suitable for high power coils 5-10 kva as
>Ive always used commercial caps. Id be willing to build this mmc if they
>will work at 14.4KV/5-6KVA and I could have a .05-.06 mfd-at-30KV/ACrms or
>close to it. Sorry for the long Post.
>Best Regards Jeff 
>

Hi Jeff,

	Thanks for the additional info.  One of the most critical things to know,
in this case, is the gap's maximum break rate.  BPS is directly
proportional to the RMS current and how hot the caps get.  You are using a
fairly small cap at a high break rate.  

Assuming you pull maybe 10kVA out of your transformer, you will have 10000
joules available to charge your 50nF cap to say 20kV.  Each cap charge will
be 1/2CV^2 or 10 joules.  So you should not be able to have a BPS higher
than 1000.  

Using MMCCalc2 and setting it to do big caps.  I get an array of about 22 x
24 caps that would cost about $870.  the voltage is no problem but the RMS
current is.  Recently we have found that Panasonic style caps can take
about 4 amps RMS each at your frequency.  Your should be running about 70
amps RMS in the primary which implies about 18 strings.  You could probably
use 16 x 18 caps at about $420 to get 50nF, 29kV, 70 Arms.

So an MMC would cost 500-800 dollars.  If you run your coil closer to 5kVA
that cost would be cut in half.  MMCs work very well on smaller coils but
when the power and BPS gets high they start to loss their advantage.

I would ask for a 100 amp RMS cap for a 10kVA system and 50Arms for a 5kVA
set up.  It would be interesting to know what the cap that failed at was
rated for in Amps RMS?

So that's my best guess...

Hope this helps...

Cheers,

	Terry