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Re: MMC Question.

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>


At 09:56 PM 8/8/2006, you wrote:
Now, one caveat to the below is that I did spill beer on my calculator. But a little barley never hurt anything.

Wasted beer is never good!

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

Actually you should multiply that by pi/2 for the "LTR" value of 15.9nF.



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?

I would drop down to 9 or ten caps...  The exact value is not super critical.

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)

They take about 200 amps. That is where they "really" break. But they will work "awhile" in any case. A 15/60 will be real hard on them, but party hardy while they last ;-))

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.

The wire size is fine.  There is a list of formulas here:


And a big program that figures out everything here:


About the only thing that can go wrong is that you might not have enough turns on the primary coil to "tune" it. I don't know your secondary diameter so I can't guess for you. But you want to find the frequency of the secondary coil and top terminal and be sure that it will match up to the primary coil and cap. They MUST match. You can't really have too many turns on the primary, but you can have too few which can be a real pain. If the primary does not have enough inductance you might have to resort to something funky like this:


So it is worth figuring out at least to that point.



This is the trickiest part for me. If anybody could shed some light on this aspect it would help a great deal.

On 8/8/06, Tesla list <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx> wrote:
Original poster: "Gerry Reynolds" <<mailto:gerryreynolds@xxxxxxxxxxxxx>gerryreynolds@xxxxxxxxxxxxx>

Hi Matt,

The issue isn't the 60ma charging the caps. The issue is when the
spark gap fires, the only thing limiting the current is the reactance
of the TC primary inductance.  Any resistance in the cap, copper
tubing, and spark gap plasma will be insufficient to prevent very
very high currents.  The resistance of the CU tubing and caps (esr)
is in milliohms.  The SG plasma may be 2 to 5 ohms.  If this was all
limiting the current, you would have 4000-10000 amps.  It is the
inductance that really limits the current.

Ipeak = Vfire / sqrt (Lp/Cp)

Hope this helps,
Gerry R.

>Original poster: <mailto:Mddeming@xxxxxxx>Mddeming@xxxxxxx
>In a message dated 8/8/06 3:18:05 P.M. Eastern Daylight Time,
><mailto:tesla@xxxxxxxxxx> tesla@xxxxxxxxxx writes:
>Original poster: "Glen McGowan" <<mailto:glen.mcgowan@xxxxxxxxx>glen.mcgowan@xxxxxxxxx>
>Thanks for the extra effort regarding the caps.
>Regarding the peak current, both Charts show the same values for peak
>current. I must be missing something(?). I'm not building a beast by
>any means. But,this is my first coil and plan to power it with a
>15/60 NST. My MMC will use 16 of the STK's in series.
>Wouldn't the current remain at 60mA throughout the tank?
>I'm all ears, still learning so everything is educational at this
>point. As long as I don't stop my heart I consider it a learning
>experience. I would like to avoid the "power up and run for the
>hills" avenue as much as possible.
>Hi Glen,
>     I believe you are confusing the charging current with the
> discharge current. and the rms value with the peak values. Let us
> consider an idealized Tesla Coil running at 150 KHz and 120 BPS.
> True, the cap is charged 120 times per second (60Hz supply) at a
> rms current of 60 mA. However, when the gap fires, all those
> electrons that accumulated on the plates of the capacitor in 1/120
> of a second are now removed in 1/300000 sec - 2500 times faster.
> Since current is coulombs per second, The discharge current for
> that first half cycle could be 2500 times higher than the charging
> current. In this case 150 Amps if only for a few usec. It is this
> kind of slamming that eats up all but the most rugged caps.
>Matt D.