Re: Maxwell AC vs. DC ratings & failure modes

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

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
 >  >
 >  >
 >  >