Re: Capacitive Ballasting

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Jim,

Since all that is being handled is low frequency mains current,
virtually any suitable high voltage oil filled caps will work. For your
4200 volt transformer, I'd recommend using current limiting/doubling
caps with a voltage rating of at least 8 kV, sized to at least 10-20X
the capacitance of the tank cap, but no larger than 2 uF to prevent
excessive diode current. The diode chain PIV rating should be 4X the
transformer's RMS voltage and 1A minimum. 

BTW, this circuit is NOT a true voltage doubler circuit, since it
delivers a half-wave rectified output voltage that's 2X the peak output
of the transformer. A true voltage doubler would provide a more or less
steady DC output voltage. While you could use a classic voltage
multiplier circuit, you'd then need to combine it with a different DC
charging technique to prevent short-circuiting the DC supply's output
capacitor when the main gap fires. Various options include:

1. Resistive charging (see Ritchie Burnett and Kevin Ottalini's sites):
http://WWW.RICHIEBURNETT.CO.UK/dcresist.html#resistive
http://www.mindspring-dot-com/~ottalini/DC%20Driven%20Tesla%20Coil.htm

2. Resonant charging (see Richie Burnett's site):
http://WWW.RICHIEBURNETT.CO.UK/dcreschg.html#resonant

3. A specially designed SPDT or even a DPDT H-bridge switching rotary
spark gap. These gaps will alternately charge the tank cap, disconnect
it from the charging source, and then fire the primary gap. See Steve
Young's and Larry Robertson's recent postings in the "DC Power" thread
and an earlier "Solving the DC coil mystery" thread from July of 2001. 

Good luck, Jim!

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com
  

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<HomerLea-at-aol-dot-com>
> 
> Bert
> Thanks. You talked me into cancelling the eBay sale of my 4200v 300 ma xfmr.
> What value of cap would be good to use with this for a multiplier? Maybe I
> should make a tripler. Second Q: If you use caps on the hv side as a limiter
> will oil filled ones get too hot?
> jim
> 
> > Original poster: "Bert Hickman by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <
> > bert.hickman-at-aquila-dot-net>
> >
> >  Jim,
> >
> >  When used on the LV side, capacitive ballasting may not work nearly as
> >  well as inductive ballasting. It also gives you a leading power factor
> >  (current leads voltage) which may cause problems elsewhere in your
> >  home's power distribution system.
> >
> >  Where capacitive current limiting really seems to pay off is in the HV
> >  side in DC coils that use the voltage doubling circuit originated by
> >  Marco and discussed by Greg in a recent posting (See the "How to tame a
> >  Wild MOT" thread).
> >
> >  Best regards,
> >
> >  -- Bert --
> >  --
> >  Bert Hickman