RE: MMC advice

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

Original poster: Thomas <tom-at-pwrcom-dot-com.au> 

Have you tried the MMC calculation spreadsheet?:

http://www.pupman-dot-com/listarchives/2002/April/msg00146.html


I use identical capacitors (RS 114-468) in an 18 x 18 array with 10M
bleeders, this is (nearly) resonant with an 11kV 80mA NST (50Hz).

This slightly over engineered, depending on the single static (air blast)
gap setting .

After about 30 minutes of operation (not continuous) with about a 5 to 6mm
gap I can detect little if any temperature rise, and the capacity has not
reduced at all from my initial measurement (no punch through of the
dielectric).

According to the excel sheet you would require ~16nF for resonance and at
least 5 strings of 7 caps for reliable operation.

Regards,

Tom L.


 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Wednesday, 1 October 2003 08:48
 > To: tesla-at-pupman-dot-com
 > Subject: MMC advice
 >
 >
 > Original poster: "Mudford, Chris" <chris.mudford-at-agresearch.co.nz>
 >
 > Hi everyone
 >
 > Still playing with my little coil (NST 6/30) and wound a new secondary
 > (90 mm PVC, aspect ratio of 6, 1600 turns).  Connected
 > everything up and
 > retuned to what looked to be pretty good at turn 13.5 (this is what I
 > wanted, as my previous secondary lead to a tap point of 3.5).
 >  However,
 > my MMC let out smoke again.  To refresh, my MMC utilises arcotronics
 > 0.022 uF 1500V (RS 114-468) which are meant to be 1800V/us.
 > Although I
 > haven't heard of anyone using these exact ones, somebody on
 > the list was
 > using .047 uF.  Across each capacitor is a 33 mOhm 0.5W resistor.  It
 > has been running in a 6x4 array and periodically sets fire to the odd
 > capacitor.  Admittedly I have been running at resonant 50Hz and I did
 > have a safety gap across the capacitor (now removed).  I do
 > run a filter
 > (as per greg hunters page) and a safety gap to ground (set to fire at
 > 105% mains voltage).
 >
 > On pulling the blown capacitors apart they comprise of two seriesed
 > rolls and there is no aparent damage within the rolls but a lot of
 > damage between them.  Would this suggest too much current?
 >
 > When running a safety gap where each HV leg is to "jump" to
 > an electrode
 > which is connected to the NST case, where is the NST case
 > connected to?
 > Should it be mains earth, a separate ground, RF ground?  On
 > writing this
 > I realise I have disconnected my mains earth from the NST case having
 > had a few electrical mishaps on home appliances.  In which case my
 > safety gap is probably ineffectual.
 >
 > Look forward to peoples ideas.
 >
 > Cheers, Chris (NZ).
 >
 > PS  I have 72 WIMA FKP1 1600 V (650 V AC) 68 nF caps which I could
 > utilise for a new MMC.  Would people agree to go for 1.5 x
 > resonance and
 > to still use peak ac supply voltage divided by DC cap voltage for the
 > number of caps per string?
 > ==========================================================
 >
 >