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Re: MMC advice



Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Chris,
           What is the total value of the MMC and how many strings in
parallel make it up? Also, how many caps per string? What is you
primary inductance? For the record, I use the 47nF Arcotronics caps
and have never blown one.

Malcolm

On 30 Sep 2003, at 16:47, Tesla list wrote:

 > 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?
 > ==========================================================
 >
 >
 >