Re: DC Tesla Coil

From: 	Alfred C. Erpel[SMTP:aerpel-at-op-dot-net]
Sent: 	Saturday, January 03, 1998 9:03 PM
To: 	Tesla List
Subject: 	Re: DC Tesla Coil 

>From: Gomez[SMTP:gomez-at-netherworld-dot-com]
>Reply To: gomez-at-netherworld-dot-com
>Sent: Saturday, January 03, 1998 3:48 PM
>To: Tesla List
>Subject: Re: DC Tesla Coil
>Tesla List 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
>> with a fixed spark gap (well quenched).
>>     For instance, lets say my TC is resonant at 100 khz, it seems to me
>> 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.

>That just isn't going to happen.  In fact, when your spark gap fires, it
>_not_ quench and stop conducting with each cycle of the RF- in fact, you
>_want_ the spark gap to continue conducting for at least long enough to
>establish a "ringing" at the resonant frequency of your tank circuit.
>If all one had to do was bang the primary periodically and let the
>ring, we wouldn't need to make the tank resonant.  But in fact, RF
>resonance in the tank is the only efficient way to transfer energy into the

    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?

>>  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
>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.


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

>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.

Alfred Erpel