Re: The MMC debate continues . . . . . .

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sparktron01@xxxxxxxxxxx 

Hi DC, Ed

SNIP
-------------------------------------
> The two paths from the nst to it's center-tapped ground, the winding
> resistance is perhaps 10K at maximum.  Using a 5RC time constant the
> reduces the cap discharge time to under 10 seconds for most small and
> medium nsts with their respective small cap bank values.  Perhaps
> this is why our coils have never shocked anyone.  We always run on AC
> and never DC.  Also, at higher potentials, the small dia of the cap
> leads and any single sharp point on the cap bank board will bleed off
> charge as corona in much the same manner as a high potential Van de
> Graaff generator, even with it's symmetrical well-rounded terminal,
> will bleed off over 400 kV into the ambient air, without being
> discharged with a ground wand, in under 60 seconds.  The MMC caps are
> at much lower potential but with their nst resistance path directly
> to ground and any slightly sharp point on the cap board or
> connections dangerous potentials are quickly bled off
---------------------------------------------------
Only time I was shocked was while working with a PT powered Tesla
Equidrive configuration.  At high power (IMHO), the caps ARE NOT
perfectly balanced.  This will lead to an unavoidable voltage delta
between the two sides.  Even with a 5% imbalance with 14kVrms
(typical) would result in ~1kV (20kVpk *.05) available in series circuit ;
and up to several times that amount could be dynamically transfered
based on SG operation etc.  I know on Ed's magnifier, easily 5kV or
more has been seen when the caps are discharged (guess, never been
measured).  Richard Hull's 20kV magnifier 11E and Alex Tajnsek's
"dynamite" magnifier also had to be manually discharged.  Note that
Richard's machine, one side of 20kV PT's was tied to ground; and
ground path did not impair C delta charge build up.

As an additional footnote, I also have never been shocked by NST powered
TC's with equidrive circuit.  Also additional footnote: National Electric Code
1999 and later editions, Article 665 (Dielectric/Induction Heating).
Paraphrasing:  All capacitors 0.1uF or larger operating at voltages of
240V or more WILL have bleeder resistors installed.  This includes
VT bias or keying (modulation/staccato control) power supplies.

0.1uF @ 250VDC ~ 0.003J (3 millijoules).  This level probably
chosen due to involuntary startle reaction resulting in secondary
injuries (lacerations/cuts) or throwing limb onto HV or power circuits
which could result in additional severe / lethal trauma.  3mJ is not
trivial, IT HURTS!!!   10J and above is generally considered a
LETHAL hazard.

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA