Re: Safety gap resistor?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 8/6/01 3:12:12 AM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

<< 
 >Do you current limit your primary to keep the discharge current from
 damaging your cap?
 >I have NEVER seen a cap destroyed by a safety gap yet. I HAVE however
 seen many caps go to the great beyond for the lack of a safety gap!
 >The first question I ask someone who has just blown a capacitor is "were 
 >you running a safety gap on the cap?", and almost invariably the answer is 
 >no. I personally will use a safety gap every time!
 
 
 
 Someone please straighten me out on this! It makes since to use a current 
 limiting resistor for the MMC caps, but... WHERE should I put the resistor? 
 Are we talking about the resistors in the Terry filter (that I am using), or 
 should there be another resistor in series with the cap gap, or a resistor 
 in series with the primary coil? And if so, WHAT value and wattage resistor 
 should I use? Save my caps! Kevin
  >>
There seems to be some confusion on safety gaps for the primary tank 
capacitor.  Having lost an expensive commercial cap due to a lack of a safety 
gap, I speak from experience.  My opinion:

If your system uses a static gap for the main primary spark gap, you need a 
safety gap at the H.V. transformer output terminals and no safety gap for the 
tank capacitor.  The main tank circuit spark gap already serves this purpose 
- just be careful not to open it up too far.

For a rotary gap system things are different.  Due to gap phase control 
settings, rotary gap speed, or undesireable primary resonance problems, you 
definitely need a safety gap to protect the primary tank capacitor.  This 
safety gap should be installed directly across the rotary gap.  When it 
fires, all the current goes through the primary inductance and no current 
limiting systems or impedance matching components are required.  Just don't 
mount a safety gap directly across the main tank capacitor - which I had 
originally done.  It goes off like a rifle shot and is really hard on the 
capacitor.

Ed Sonderman