Re: static "sucker" gap / cap stress

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I suggest that you take a look at:
http://home.earthlink-dot-net/~jimlux/hv/caplife.htm which has the basic 
principles of estimating real capacitor life based on Maxwell's info.

While 500 pps is comparable to the bang rate for your TC, the real issue is 
that the rated life/pps is based on 15% voltage reversal: i.e. a single 
shot discharge into a basically resistive load. Your TC is discharging into 
an inductor, and will typically see more like 90+% voltage reversal.  As 
the energy flows back and forth between the L and C, each half cycle looks 
like a charge/discharge cycle (i.e. a "shot") to the capacitor.  It's not 
as bad as a full power shot, though, and since cap life is very strongly 
dependent on voltage (7.5 power), you're a lot better off.  The link above 
has an equation that rolls all those things together...

You might also take a look at the RMS current rating.. 20A... calculate the 
real RMS current in your setup.. The peak currents are high in a TC, but 
the duty factor is low, so the RMS current is probably within reason.


At 11:28 AM 4/25/2003 -0600, you wrote:
>Original poster: "Christoph Bohr by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <cb-at-luebke-lands.de>
>
>Hi!
>
>Good to find someone who knows the cap, although I think I have seen them on
>some coils on the net.
>I got mine from alltronics on ebay for 50$, think this was OK. It came
>without a label but with the catalog number scratched into the housing.
>I thought about buying another one, Tesla Systems Research is offering them
>for 73$ I think...wonder if the price is OK.... I initially bought this one
>because I was looking for extra security, hearing that they can blow up too
>is really disappointing....I have to do most coiling indoors.
>At the moment I am transferring roughly 5 KVA through the system, maybe that
>is too much for a single cap, but your Idea with the "emergency shut off "
>via temperature sensing seems really good and I'll probably build something
>like this and with the new information shielding will surely be installed
>next time.
>Do you think I should buy another cap? or is any other maxwell type better
>suitable? or MMC.....at least MMCs seem to be "blow up friendly" for indoor
>use.
>BTW: I checked my spec paper again and its really has a line in it which
>says: max continuos rep rate: 500 PPS....I thought this means 500 shots per
>second....but that was probably wrong after what you said....or I might have
>the wrong spec sheet.
>My sheet can be seen at http://www.luebke-lands.de/media/20P005.pdf  maybe
>you can have a llok at it or hand me a link to your paper....
>
>Thanks for your support!
>
>sincerely
>
>Christoph
>
>  ----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Thursday, April 24, 2003 7:26 AM
>Subject: Re: static "sucker" gap / cap stress
>
>
> > Original poster: "Jeremy Scott by way of Terry Fritz
><teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>
> >
> > Hi,
> >
> > I use the exact same Maxwell cap in my systems,
> > however I double them up, that is, I use four
> > in a parallel series configuration. .03uf, 70Kv
> > for nice long runs. They are oil filled which makes
> > them nice bombs when they do blow up. I'm thinking
> > of enclosing mine in a nice hardwood box with a fan
> > and maybe one of those CPU temperature display
> > thingys.
> > (Idea: wire a thermistor into relay circuit that
> > controls power to the transformer.)
> >
> > If you look at the spec sheet from Maxwell you'll
> > find that they aren't rated for continuous stress.
> > (They're really designed for the occasional one shot
> > brief discharges: X rays, MRI's and that sorta thing.)
> >
> > The fact that they even last in a tesla circuit is
> > testament to Maxwell quality. I've seen one cut
> > up and there were plenty of black little holes
> > that were the result of a puncture, but the cap
> > fixed itself and before disassembly remained fairly
> > close to it's original value.
> >
> >
> > --- Tesla list <tesla-at-pupman-dot-com> wrote
> >  > Original poster: "Christoph Bohr by way of Terry
> >  > Fritz <teslalist-at-qwest-dot-net>" <cb-at-luebke-lands.de>
> >  >
> >  > Hello everybody.
> >  >
> >  > After experimanting with RSG's I made a little
> >  > excursion back to static gaps.
> >  >
> >  > I built a sucker gap with 2 elektrodes and attached
> >  > an ordinary vacuum
> >  > cleaner to it. ( ordinary design....t-shaped sewer
> >  > tube and 2 copper tubes )
> >  > The results with my current magnifier were
> >  > disappointing as the quenching
> >  > seems not to be too good.
> >  > But with the ordinary 5" setup I got really hot
> >  > white steamers to the
> >  > ceiling space-limited by the walls to 4 feet.
> >  > The power in the arcs must have been really big,
> >  > they almost looked like a
> >  > time-exposure.....only real ;-)
> >  > This mus be due to the high current the MOT-Supply
> >  > can deliver.
> >  > The break rate seemed very high, estimated between
> >  > 400 and 800 bps.
> >  > Only problem that occoured: THe tank cap got warm,
> >  > nit really hot but
> >  > palpable after some 20 second runs at roughly 5KVA (
> >  > no PFC ).
> >  > I use a Maxwell 37667 Type cap, 30nF and 35KV. Is
> >  > this cap to weak for this
> >  > arrangment or do I do something wrong that puts
> >  > stress an the cap.
> >  > Tuning was done at 1KVA before I turned to higher
> >  > power levels....but the
> >  > effect of streamer-loading shouldn't affect the
> >  > tuning too much.
> >  >
> >  > My personal results:
> >  >
> >  > Pros: The sucker gap really performs well and is
> >  > extremely cheap and easy
> >  > to build and seems to be very robust, a good choice
> >  > and a really good
> >  > performer in my                system at least.
> >  >
> >  > Cons: the noise really requiers hearing protection,
> >  > I loosend one of my
> >  > earmuffs for a moment an was really
> >  > shocked.....luckily noone was at home
> >  > at this time.
> >  >            Bad performance with my magnifiers
> >  > although I read about people
> >  > using them succesfully with maggies. I will go for
> >  > high bps RSG with that I
> >  > think, perhaps with
> >  >            sucker gap in series to aid quenching.
> >  >
> >  > Questions to be solved: Cap heating.....is it bad or
> >  > not......dont want to
> >  > destroy it as its my only professional pulse cap.
> >  >
> >  > I hope I don't mess up the list with such "low-level
> >  > posts" but I like to
> >  > share results as sometimes it might be usefull for
> >  > other users,too ...
> >  >
> >  > happy coiling
> >  >
> >  >
> >  > Christoph
> >  >
> >  >
> >
> >
> >
> >