# Re: MMC Question.

```Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Glen,

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```Original poster: "Glen McGowan" <glen.mcgowan@xxxxxxxxx>

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Now, one caveat to the below is that I did spill beer on my calculator. But a little barley never hurt anything.
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I'm using an 15kv 60mA NST

z= 15000/60
So my impedance is 250000

c= 1 / (6.2832x250000x0.00006 )
So my NST would seem to prefer a primary cap of .0106uF

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Currently my MMC is using 16 .15uF 2000v caps (.15/16 = 0.009375uF) would the .0012uF difference between .0094uF and .0106uF really cause me huge problems? The peak amps the STK's are rated at I now understand isn't that lovely but aside from that I should get some fairly decent discharges correct? (If the caps hold)
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Calculate the peak current and make sure the current thru the string is less than the STK's spec. If so, I see no problem. If you do run with 9.4 nf (close to mains resonant), you will need to be very careful not to open the gap too wide. The voltage could rise to as high as 80KV if allowed to. If you have a properly set safety gap, the voltage will be controlled but the next potential problem is BPS. running at resonant Cp with the SG set at rated output voltage will result in fairly high BPS. JavaTC will predict this resonably close. If the BPS gets too high, the RMS current thru the cap may become an issue. I recently posted a quick formula for estimating the RMS current and you will need to insure you dont violate the Irms spec of the cap. Alternatively, you can fire up the system and only run it for a minute, shut it down, and see if the caps are getting warm. If not, then check for overheating after say 5 minutes. Just dont shock yourself.
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With all the concern over the caps I'm afraid to ask about the primary and secondary coils. I had originally planned to make my primary around 10-12 turns of 1/4" copper tubing and making the secondary coil winding out of #26 wire with about 20" of actual wound coil length. The wire gauge is not an option. I've got a huge spool of the crap that I really would like to use. I'm not entirely certain what the values should be. This is the trickiest part for me. If anybody could shed some light on this aspect it would help a great deal.
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I think you could benefit from JavaTC.

http://www.classictesla.com/java/javatc.html

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Very accurate and has great help files. It will tell you about the peak current and other things you might find useful. There are many successful combinations of materials. Almost anything can be made to work. I think at 15KV 60ma, your 26 guage wire will be just fine. Many shoot for a height to diameter ratio of 4:1 to 5:1 and 1200 to 1500 turns for the secondary. It is not that critical. The main thing is to choose a secondary size that will be appropriate for your power level and will withstand the top load voltage. At 900 VA, I used a 8x36 secondary. A 6x27 secondary will work fine too. Javatc will tell you how many turns you will need on the primary and it is good to plan on say 50% more to give you some flexability to compensate for streamer loading and allow for larger toroids.
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Good luck,
Gerry R

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