Re: Maxwell AC vs. DC ratings & failure modes

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

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
 >  >  >
 >  >  >
 >  >  >
 >
 >