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Re: Maxwell AC vs. DC ratings & failure modes
Original poster: "Scott Hanson" <huil888-at-surfside-dot-net>
Mike -
Thanks for the additional info on the failed Maxwell capacitors. As I
suspected, there were no measurements made on the actual operating voltage
when the caps failed.
Just because the system was connected to a 15 KV NST does NOT mean that the
voltage across the capacitor was 15 KV; it may have actually been 2X or 3X
or higher, depending on resonance effects, safety gaps, etc, etc. Please
post the results of your failure analysis when you open up the capacitors.
If you like, I'll pay shipping costs for you to send one of the failed caps
to me and I'll perform an intensive failure analysis in my lab at work, and
post the photomicrographs & findings at hot-streamer-dot-com for everyone to
review. We've seen several failure analyses of MMC caps that died in Tesla
coil service, but nothing on a commercial pulse cap that died under similar
conditions.
As for the Tesla coil driven by the 90 KV X-ray transformer, a posting to
this list from Mike.Marcum-at-zoomtown-dot-com dated Sat, 04 Oct 2003
05:09:29 -0600 went into great detail describing the system, with the X-ray
transformer cooled by a car radiator & pump system, driving a giant MMC
array of five-hundred (!!!) Cornell-Dubilier 943 capacitors, with the whole
system drawing 24KVA (!!!!) and being capable of operation at this power
level for a period of 10 minutes before "the neighborhood browns out". This
posting is archived at www.pupman-dot-com.
Likewise, the claim of a 50 KVA Jacob's ladder running in your backyard (two
34.5 KV, 50 KVA pole pigs):
"Don't know what the actual power draw was, but it was popping 800A worth of
breakers (!!!!) in 5 seconds or so (made the drop wire from the pole quite
warm in the process). The arc spread over 17 feet before the breakers popped
(which was over 4" thick and bright as a welder". This also is archived at
Pupman-dot-com, posted by Mike Marcum -at- zoomtown-dot-com, on Sun, 23 Nov 2003
22:04:59 -0700.
Are there somehow TWO different Mike Marcums -at- zoomtown-dot-com? Could there
somehow be an "imposter" posting incredible claims under your name?
Regards,
Scott Hanson
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, April 04, 2004 1:48 PM
Subject: RE: Maxwell AC vs. DC ratings & failure modes
> Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
>
> Some information about the operating voltage might be inferred if you
> could supply just a few more details. What size NST was used (voltage
> AND current), what size cap was used (I assume just the single
> .03uf/35kV), gap type (sync/async), and safety gap/MOV used?
>
> Thanks, Gary Lau
> MA, USA
>
>
> Original poster: "Virtualgod" <mike.marcum-at-zoomtown-dot-com>
>
> I've had 2 fail. Never measured the particulars but it was running on a
> single 15/60 nst. After the second I gave up and went to 12kv nst's (no
> problems with same coil). My only personal experience with these. Heard
> of
> others problems with 15kv nst's, as well as several mentionings on TC
> websites. The primary L was about 22uH. Possible overcurrent, but
> unlikely
> since it was only 120bps ( these can take 25Arms if I remember right). I
> still have the corpses, haven't got around to dismantling them yet. As
> for
> the x-ray TC/giant JL you must have me confused with someone else. I
> live in
> an apartment building with a "backyard" that probably couldn't handle it
> (at
> least not without the neighbors/police/etc complaining). That would be
> something nice to see, though. I might attempt it if I can find a place
> to
> put it and have the cash. I have a small (~75 lbs with just the core and
> coil, 37.5kVA intermittent) unpotted x-ray unit i got off ebay, but I
> have
> to clean it up and put in oil before anything. Up to now all I've done
> is
> smallish stuff (~3-4kVA from a PT, all my breaker will handle
> (unfortunately
> my whole apartment is on that single breaker til I figure something else
> out).
>
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Saturday, April 03, 2004 8:03 PM
> Subject: Re: Maxwell AC vs. DC ratings & failure modes
>
>
> > Original poster: "Scott Hanson" <huil888-at-surfside-dot-net>
> >
> > Mike -
> >
> > Earlier today, replying to an inquiry on Maxwell model 37667
> capacitors,
> you
> > wrote: "Nope, they usually fail at 15kV".
> >
> > The wording "usually" seems to imply that you have experienced
> multiple
> > failures with these particular capacitors, and that you were
> carefully
> > monitoring the peak voltages in the circuit at the time the
> capacitors
> > failed.
> >
> > Can your provide some additional information on the following:
> > 1. How many of these capacitors have you personally had fail at 15
> KV?
> > 2. Was this 15 KV RMS or 15 KV peak-to-peak?
> > 3. What was the total inductance in the circuit the capacitors were
> > discharging into?
> > 4. What leads you to believe the capacitors failed from overvoltage
> rather
> > than overcurrent?
> > 5. Did you perform a post-mortem of the failed capacitors to see if
> they
> all
> > failed in the same manner?
> > 6. If yes, what were the results of the failure analysis?
> > 7. Are the "blown" capacitors available for examination?
> >
> > (Pardon me if any of this indicates an degree of skepticism, but we
> never
> > did get any response to requests for further information on your
> Tesla
> coil
> > directly powered by the 90 KV X-ray transformer, or your giant
> Jacob's
> > ladder that generated 17 foot arcs.)
> >
> > I have a personal interest in these capacitors, as I have four of
> them
> that
> > I intended to use in a small bipolar-twin coil setup. If anyone has
> any
> > VERIFIABLE information about failure modes or breakdown
> susceptibility of
> > these capacitors, I would be very interested in reviewing the data.
> >
> > Regards,
> > Scott Hanson
> >
> >
> >
> > ----- Original Message -----
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > To: <tesla-at-pupman-dot-com>
> > Sent: Saturday, April 03, 2004 1:19 PM
> > Subject: Re: Maxwell AC vs. DC ratings
> >
> >
> > > Original poster: "Virtualgod" <mike.marcum-at-zoomtown-dot-com>
> > >
> > > Nope, they usually fail at 15kV. 12-12.5kV is about as high as you
> can
> go
> > > and have them last any significant length of time. Those are
> tested at
> > > 40kvdc for 1 minute, but probably wouldn't last much longer if
> constantly
> > > ran at that.
> > >
> > > ----- Original Message -----
> > > From: "Tesla list" <tesla-at-pupman-dot-com>
> > > To: <tesla-at-pupman-dot-com>
> > > Sent: Saturday, April 03, 2004 12:31 PM
> > > Subject: Maxwell AC vs. DC ratings
> > >
> > >
> > > > Original poster: Terry Fritz
> <teslalist-at-twfpowerelectronics-dot-com>
> > > >
> > > > Hi All,
> > > >
> > > > Although we commonly use DC ratings as AC ratings in MMCs, I
> was
> > wondering
> > > > about commercial caps like the Maxwell 37667. We are running
> about
> > 60Hz
> > > AC
> > > > across them and they probably have far fewer caps in series
> internally
> > > than
> > > > an MMC. They are rated for "35 kV". I was wondering what
> people
> > thought
> > > > about the voltage they should be run at for Tesla coil use?
> > > >
> > > > I would guess that 15kV RMS or 21kV peak ( 42kV peak-to-peak)
> would
> be
> > ok?
> > > >
> > > > Cheers,
> > > >
> > > > Terry
> > > >
> > > >