blown caps was rotary question

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

Original poster: "bob golding by way of Terry Fritz <twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>

Hi terry all,
    Thanks for your analysis. I think I might modify the design of my
adjustable cap to allow more space to lift the resistors up off the caps. At
the moment they are stuck inside 22 mm tubes without much spare room. As well
as giving more room for the resistors this should make it easier to tell if
they are getting hot. For the moment while I  am trying  to get the coil in
tune and finding the best break rate  I will reduce the gap on the ballast to
limit the current. From my tests with the Jacob's ladder across the output of
the tranny if I use a 1 mm gap this should limit the current to around 5 amps.
I have plenty of  100 nF arcotronics caps so I will make up some more strings
to add to the ones I already have. I think I am pushing the voltage as well as
the current s I will make them up into strings of 20 this time. Must go and buy
more solder. I think this failure was due more to my carelessness  by thowing
too much power at it  too quickly before I had the coil in tune. I don't think
running it with the primary disconnected helped much either. Must resist the
temptation to keep winding the variac up ;-)

Cheers
bob golding

Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>
> Hi Bob,
>
> At 03:04 AM 2/26/2001 +0000, you wrote:
> snip...
> >above forula is right this is only 140 BPS. If this is the case I must
> >be really hammering my caps,They are getting warm.
> >
> >Can someone tell me how to work this out please before I fry all my
> >caps. Killed a string of caps today. I think this was due to the inside
> >primary connection coming off rather  than the break rate, I ran the
> >coil up, no sparks,  thought it was out of tune tried again and noticed
> >smoke and flames coming from the cap. Opps, only damaged one cap in the
> >middle of the string closest to the connections. some photos  of the
> >fried cap will appear on hot streamer soon I hope.I must warn you they
> >don't make pleasant viewing  :-(( well not to me anyway.
>
> The photos are at:
>
> http://hot-streamer-dot-com/temp/blown%20cap1.jpg
> to
> http://hot-streamer-dot-com/temp/blown%20cap9.jpg
>
> I would worry that the drain resistors are laying directly on the cap cases
> as in picure:
>
> http://hot-streamer-dot-com/temp/blown%20cap2.jpg
>
> The cap cases cannot stand off much voltage and corona may form between the
> resistor and the cap case if the underlying plates are of opposite
> polarity.  Perhaps bending the resistors up a bit off the cases would help
> prevent corrona damage and possible arcing.
>
> You caps seem to be getting pretty hot as shown by the rough "corregation"
> or rippling in the bodies as shown at:
>
> http://hot-streamer-dot-com/temp/blown%20cap9.jpg
>
> The caps almost have a tiger strip pattern espicially when they blow and
> soot is blown into the stripes as in:
>
> http://hot-streamer-dot-com/temp/blown%20cap8.jpg
>
> As the caps heated, the dielectric started to melt and arcing began in the
> internal floating layer at the edges.  Since they were hot and going down,
> the self healing was no help and they catostophically arced in the center
> as shown in:
>
> http://hot-streamer-dot-com/temp/blown%20cap3.jpg
>
> So the current is too high.  You need more strings,  Probably 4 times more!
>  your caps are listed as good at:
>
> http://hot-streamer-dot-com/TeslaCoils/MMCInfo/good-bad.txt
>
> I have seen these caps and they are fairly good with a dissipation only
> slightly less than the Panasonics.
>
> You can ohm out and measure the value of the remaining caps to check for
> hidden damage to the others.  Sometimes they read as shorted or the value
> is way off if there is internal damage.
>
> Cheers,
>
>         Terry
>
> >
> >cheers
> >bob golding
> >