Re: MMC question

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

At the risk of Gerry poisoning me at supper at his place next Tuesday night 
(feed Terry, and he spills Tesla coiling secrets ;-)))   I guess I will 
very respectfully disagree.

One area where you can really push MMC caps is voltage.  I use 10 x 5 X 
1600 volt caps in my big coil that I run at like 135 volts to the NST for 
23865 volts.  That is 49% over the DC voltage  for my 10 cap strings 
:o)))  I am I worried?  Naw.  I once ran that coil on just four MMC 
caps.  They really break down at 3500 volts.  Then they just self 
heal...  In the case of the 942 caps.  They bust at around 5700 volts:

http://hot-streamer-dot-com/TeslaCoils/MMCInfo/GeekCaps/GeekCaps.htm

Ten in series is like 50000+ volts!!!  "I" generally do not worry at all 
with 25% over the DC voltage rating.  "I" tend to run at 50% over, just so 
I "feel good" about recommending 25% over ;-))

One area where you never want to push your luck with MMCs is RMS or peak 
current.  Too much RMS current overheats the poly and they burn up.  Too 
much peak current blows out the plate connections...  So watch out for 
current.  But "mild" over voltage ratings excursions can be ignored ;-))

Cheers,

         Terry




At 09:52 PM 1/16/2004, you wrote:

>Hi Luke,
>
>The 942C series of caps are great.  However, with a 15KV NST (this is RMS
>voltage), the peak voltage will be just over 21000 volts not counting other
>effects such as resonant rise and inductive kick.  A 10 cap string, IMO,
>will be insufficient for this transformer.  I would say a minimum of 12 and
>propose a 14 cap string instead.  LTR for SRSG will certainly keep resonant
>rise down and the SRSG will take advantage of inductive kick.  Also, for a
>given operating voltage, going to a larger string will reduce the peak and
>RMS currents in that particular string with everything else the same (BPS
>and Lp).
>
>Gerry R
>
>
> > Original poster: "Luke" <Bluu-at-cox-dot-net>
> >
> > I have decided on the capacitors that the geek group recommend.
> > The ones I have on order are the 0.15 micro farad and rated at 2KV.
> > If I run these with sets of 10 in series they would have a voltage rating
> > of 20KV
> > I will be using a 15KV NST.
> > The cap size will be LTR and I am going to use a SRSG
> > Does it seem like I am cutting the voltage rating a bit close or will
>these
> > caps hold up to that?
> > Any one have any experience with these.
> > I would rather drop my capacitance a little and put another one in series
> > for a 22KV rating if it is needed
> > But if I feel VERY confident they will hold up with 10 in series I want to
> > go that way.
> > I don't want performance at the expense of needed up keep due to cap
>failures.
> >
> > Luke Galyan
> > Bluu-at-cox-dot-net
> >
> >
> >