Re: DC Tesla Coil

From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
Sent: 	Sunday, January 04, 1998 5:23 AM
To: 	Tesla List
Subject: 	Re: DC Tesla Coil

Alfred C. Erpel wrote:

>     If my tank capacitor is charged with DC only, it seems to me that it
> would be much easier to get a solid resonance occuring in the tank circuit
> with a fixed spark gap (well quenched).

The dynamics of the resonance are only sensitive to
the instantaneous Vcap at the time of firing, and not
how that voltage got there, whether by AC or DC charging.

>     For instance, lets say my TC is resonant at 100 khz, it seems to me that
> all that is necessary to get a solid resonance is a fixed spark gap that
> will quench and fire 100,000 times per second, and capacitor power supply
> combination that exactly replenishs at this same rate.  

You are essentially describing a Class-C tube-powered coil, 
where an electron tube performs the quench and fire at 
100,000 times per second.  They work well, but don't yield
anywhere near the peak power of impulse-driven coils.

> DC avoids having to
> have your spark synchronous with a (AC fed) capacitor that 60 times (USA
> 60hz) every second has *no* charge on it.

This is true, and is one of the advantages of running DC.
However, the primary advantages of DC charging are better
power factor, and the ability to use three-phase power,
which keeps the mains balanced.

>     Can a fixed spark gap be quenched at that rate?  
No. Quench times are usually many 10's to 100's of usecs.

> To get DC into the tank
> capacitor, is it as simple as feeding rectified AC into your transformer?

??!!??  Only the AC component of the ripple would make it 
through, assuming the core wasn't saturated... 
The DC component would simply treat the transformer as
a space heater.  Rectification must occur after the xfmr.