Re: Maxwell AC vs. DC ratings

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

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

Hi Ed,

At 08:36 AM 4/16/2004, you wrote:
>Tesla list wrote:
> >
> > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
> >
> > Hi Ed,
><snip>
>
> > There are probably close to 20,000 MMC caps out there.  Unexplained
> > failures number about 5 ;-))  with a little more time, we will figure out
> > these interesting failures with John's coil too!  Last year we asked
> > everyone if there were any problems they were having with MMC or the
> > resistors and no new or serious problems were reported.
>
>Terry,
>
>Just how many commercial pulse caps do you think are out there working
>just fine without failures? I'd bet it's significantly more than 20,000!

I meant in Tesla coils only.  If we take all uses into account...  Maybe 
someone could guess by the serial numbers how many pulse caps are in use 
for all applications in the world.  Of course, annual sales of poly MMC 
style caps is in the 10's of millions, but only a tiny fraction are in 
Tesla coils...


><snip>
> > You are not a beginner now and you use the caps best for your advanced
> > coils.
>
>My latest "advanced coil" has a secondary that is 4.25" long and 1.125"
>in diameter and is wound with 850 turns of #38 (.004") magnet wire. The
>entire coil with 20 ma kV transformer and 3 gap tungsten stationary gap
>will fit in the palm of your hand. The capacitor on this coil is a 5000
>volt .001Mfd bathtub mica, $2 hamfest special. NO MMC!! The bathtub is
>smaller and neater.

I bet your smaller coil is still better than most of our coils ;-))  Unlike 
a beginner, you know exactly what you are doing.


> > >All that said, I can't wait to fire up the maggy for the first time this
> > >year after I get the lab open and have one of the aforementioned
> > >commercial caps go up in a blaze of sparks and smoke. :^) That would be
> > >just my luck!
> >
> > Chances are very good they will do fine.  If a cap is really going to blow
> > up from stress, chances are it will be within minutes.  After all this
> > time, I bet your coils and caps have proven to be able to live happily
> > together.
>
>Terry, the second sentence isn't really true. The "infant mortality
>rate" that applies to many modern electronic devices doesn't apply to
>the pulse caps I use.

!!  I think it does since we buy the same caps you do too and once in 
awhile they die way too soon.  But those are just manufacturing defect 
things that really don't matter here.

>They have a mean shot life that is calculated from
>dielectric thickness, voltage, pulse rate, etc. Roughly calculated, my
>maggy caps have over 60 million shots on them. How many million shots
>are left in them is an unknown.

I do wonder "what wears out" in them??  Might just be pure mechanical 
stresses as the high current shots pound them.  In that case, a lower peak 
current Tesla coil my not wear them at all.  ESR just burns them up but 
does not really "wear" them.  Dielectric damage due to ionization seems to 
be a big factor from reading data sheets on them where they are so worried 
about voltage reversal.  I am not sure...

Cheers,

         Terry


>Ed Wingate RATCB