Re: Magnifier Primary Capacitors - EQUIDRIVE vs. STANDARD

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

Original poster: David Sharpe <sccr4us-at-erols-dot-com> 

Hi Dan!

Tesla list wrote:

 > Original poster: dhmccauley-at-spacecatlighting-dot-com
 >
 > Ed, Richard, List,
 >
 > I have a question regarding the two most common primary capacitor
 > arrangments in magnifier systems.
 >
 > 1.  STANDARD - Single capacitor as most commonly used in classic tesla coil
 > systems.
 >
 > 2.  EQUIDRIVE - Two capacitors used in the primary circuit.  One on either
 > side of the primary and connected in series with the primary.
 >
 > I'm currently designing my system using the EQUIVDRIVE arrangment on the
 > basis that the two great magnifier builders, Richard Hull and Ed Wingate,
 > state this
 > arrangement is superior over the other arrangement.
 >
 > However, I'm not sure and can't see right away what the advantage is.
 >
 > Does anyone have the nitty gritty details of why the EQUIVDRIVE arrangement
 > is superior over the STANDARD arrangement.

Having used both topologies here are my spins on them
1. Standard:
     PROS: - one capacitor
                 - self discharging _if_in_parallel_ with powering transformer
     CONS: - one capacitor absorbs total stress of impulse excitation

2.  Equidrive
     PROS:  - two capacitors share voltage stress of tank circuit
                 -  modest tank tuning possible by "shifting" capacitor value
                    of one capacitor in relation to other (realizing smallest
                    capacitor sees highest voltage drop)
    CONS:  - DANGEROUS, e field variation while tank is being
                    impulse excited will result in residual charge on 
capacitors

                    in series.  If you touch the primary with machine off and
are
                    touching ground at the same time ZZAAPP!!  (Guess how
                    I know about this...   :^C )  Caps MUST be discharged 
either

                    by shorting rods or resistors prior to making tune
adjustments
                    to primary.
                  - Two capacitors are needed at 2X single capacitor value
                    (series C = C/2) for a given resonant Fo.

My guess is since Tesla was using glass capacitors at Colorado Springs,
the series connection allowed more voltage hold off versus a singular
capacitor bank.  Plus he reconnected interior high voltage windings of
Westinghouse Transformer from 50kV to 25kV for most of his experiments,
due to the fact of in masse capacitor blow ups while attempting to run
his magnifier at 40-50kV (refer to the CSN for further details).

Tesla postulated that the equidrive circuit since it was symmetrical would
have faster drive characteristics then a single capacitor configuration.
I find it hard to believe that there is any significant advantage to one
capacitor versus the Tesla equidrive configuration, except in one condition.
IF one was using very high voltage input (>30kV arbitrary), equidrive
would very effectively reduce voltage stress on capacitor(s), but now you
need (4) of a given size (2 in parallel + 2 in series) to equal a singular
capacitor for a given primary frequency.  Another possible advantage
is fine primary tune control by adjusting relative capacitor values relative
to each other.

A comparison of both circuits set to same frequency using appropriate
capacitor values (same construction, ESR, connections, etc.) would be
an excellent experiment to determine if there is any difference
between the two topologies...

 >
 > Thanks
 > Dan

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA