Re: static "sucker" gap / cap stress

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

Original poster: "Christoph Bohr by way of Terry Fritz <teslalist-at-qwest-dot-net>" <cb-at-luebke-lands.de>

 > There was an array for sale on ebay that had six of
 > them. Went for $220 ... I missed it unfortunately.
 > I got mine anywhere from $50 - $70 so that's
 > pretty typical. Consider they go retail for
 > several hundred dollars each.

Yes, saw that one, too. I saw the auktion end "live" and couldn't act
because of a serious lack of money ( why the heck don't pupils earn anything
;-)
But the deal was pretty good....happy bidder whoever it was.

 > I would be very careful using just one of these
 > in a 5KVA coil. I'm guessing here, that you're
 > using a pole pig right? You'll especially
 > want an array if you're using resonant charging.

My Transformer is a 4MOT-Supply. I should deliver 8,4KV RMS ( never
measured ) and draws 25 amps at 240Volts ( 6kva ). Thats all I can state
about the supply. But I hoped with calclated 11879,28 Volts peak I could get
away with it. But the dokument on cap-life really shows that safety margin
is really worth to invest into.

 >
 > Considering that in a 15Kv system the cap's
 > voltage is 21Kv, one or two successive misfirings
 > of your gap will drive the capacitor over it's 35KV
 > rating if you fail to have any other safety gaps.

The voltage with the 4MOT-Supply  is way lower than in an average piggie I
think, but still your assumption is right of course.
I use a very "conservative" set safety gap across the cap and it almost
never fires. ( in fact it fires more often when I go resonant with my 1KVA
OBIT array )

 >
 > I had one in a high power system and it overheated
 > and ejected it's internals out of that little
 > belly button above the connection disc on the side.

Thanks, now I can't sleep at night ;-)
But that brought up another idea: One could mount the cap this screw facing
upwards and then remove the screw ( I know that hurts ;-) and replace it
with some kind of safety valve, maybe even with some spillway. By this the
danger of explosion should be considerably reduced. I know..strange Idea,
but may work.

 > Since I've doubled up the voltage, it's been fine.
 > Hard to go wrong using 70Kv for a 21Kv peak system.

nevertheless: thats right, but with my capacitance cut in half , can I still
handle the power? Or do you refer to your 4-cap array?

 >
 > You might also want to note some values on that
 > spec sheet, specifically those referring to
 > "voltage Reversal." This cap was designed to
 > be a DC capacitor -- it happens to work well
 > for AC if you give it lots of room. (That's
 > 500 pps DC --- AC puts significantly more
 > stress on anything, so it's really less for
 > our usages)

OK, I didn't take that into account though I feared it might be that way...

 >
 > If you do build a box, use some springy bent
 > strips of flat copper to lay against the
 > terminal disks of the capacitor. Ie, design an
 > enclosure that is similar to battery packs.
 > (Sand the copper terminals every once in awhile
 > to get rid of the oxidation) I don't recommend
 > using the small screw hole w/ crimp lugs etc...

I'll give that a try. Currently I use the screws to attach  14" copper
tubing to the cap and cant feel any warming up at this connection, but your
design is a lot more pleasing

 >
 > I like to build things into nice hardwood boxes
 > with routed edges and what not. I'd much rather
 > get hit with a splinter of wood than a chunk of
 > metal/hdpe/hot oil. Also your coil setup will
 > look like furniture if you take the time to sand
 > and stain it :) It won't look as scary and it'll
 > be safer. I guess that's the artist in me. I
 > design my coils to be visually pleasing when
 > turned off,safe and as scary as hell when turned on.


I deeply admire people who do it that way. Fine workmanship is allways
something I like to have a look at.
But I have to admit, I'm rather the kind of guy who wakes up in the morning
with some Idea ( tech, not design ) on mind and than I want to build that as
fast as ( safely ) possible to hold it in my hands to give it a try. Up to
now things usually worked well and I never experienced any life-threatening
disasters ( that's one of my primary aims ). But as I sayd, if I had the
time, money and apropriate tool I'd prefer your way too.

Tank you sofar for your help, now I have a much better view on the cap
situiation.

Greetings

Chistoph