# Re: DC Tesla Coil

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From: 	Bill Lemieux[SMTP:gomez-at-netherworld-dot-com]
Sent: 	Monday, January 05, 1998 12:48 PM
To: 	Tesla List
Subject: 	Re: DC Tesla Coil

Tesla List wrote:

>     Can you help me to understand how a spark gap which is probably closed
> for several tens of cycles of the resonant frequency can be considered in
> resonance? And how is this different from periodically (and not at the
> resonant frequency) *banging* the primary?

The spark gap isn't "in resonance", the LC circuit is!  The SG just
connects the C to the L when C is charged to the breakdown voltage of
the SG.

When I say "banging" the primary, I'm referring to simply pulsing it
from a capacitor, dicharging through a spark gap switch, where the LC
circuit formed will not resonate at any frequency of interest... such as
the resonant frequency of the secondary, for example.

> >>  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.
>
> >Have another look at the sine wave that you're feeding that cap.  The
> period
> >of time your cap has "no" charge on it, is almost infinitessimally small.
>
>     There is a significant amount of time each 60th of a second when the
> capacitor will be no where near its maximum charge.

I agree, but that's a very different statement from your first- see what
you wrote, above.

> >Um, last I checked, transformers steadfastly refused to operate on DC.  If
> >you've got one that will, I will make you very, very rich!
>
>         A chopped DC sine wave (that you get thru a rectifying bridge) fed
> into a primary of a transformer will cause a constantly changing field that
> should induce a similar wave form in the secondary.

Square wave AC != DC.  Also, feeding square waves (with their very high
harmonic content) will overheat (and possibly also saturate) a
transformer intended for sine wave AC.  It sounds like you're talking
about building a switching power supply for tens of kilovolts- a