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Re: MMC Question.

Original poster: "Gerry  Reynolds" <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: Mddeming@xxxxxxx
In a message dated 8/8/06 3:18:05 P.M. Eastern Daylight Time, tesla@xxxxxxxxxx writes: 
Original poster: "Glen McGowan" <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.