Re: Maxwell AC vs. DC ratings

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

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net> 

Hi Christopher,

The spec sheet for this cap indicates that the impregnant is "IPBP", or 
isopropyl biphenyl (CAS Registry Number 25640-78-2). With a flash point of 
about 300F, it is somewhat flammable, but it has a higher flash point than 
mineral oil (275F). The MSD sheet can be found here:
http://www.whitakeroil-dot-com/images/Sure%20Sol-250%20MSDS.pdf

BTW, Maxwell uses a number of impregnants in their capacitors. The symbols 
that Maxwell uses on their spec sheets and the equivalent chemical names are:
CO  = castor oil (vegetable oil)
RSO = canola oil (vegetable oil)
IPB, IPBP, MIPB = isopropyl biphenyl
PXE = phenyl xylyl ethane
SO  = silicone oil, (polydimethyl siloxane)
MO  = mineral oil (petroleum-based)
EPX = proprietary - contact factory
TCP = tricresyl phosphate
DOP = ethyl hexyl phthalate
DRY = no oil

Best regards,

-- Bert --

Tesla list wrote:

>Original poster: "Christoph Bohr" <cb-at-luebke-lands.de>
>Hello all.
>This is only a little bit related to the topic, but anyway:
>Is the impregnant in the 37667 caps flammable?
>I wanted to mount the caps right above th RSG but now I
>fear this might be a serious fire hazard in case the caps spill oil mist
>during a cap failure.
>I have run these caps with a 6MOT ( guestimated 12KV ) without failure
>but I had only short runs ( < 30 sec ) with this setup.
>regards
>Christoph Bohr
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Saturday, April 03, 2004 11:38 PM
>Subject: Re: Maxwell AC vs. DC ratings
>
>  > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
>  >
>  > Hi Bert,
>  >
>  > At 11:21 AM 4/3/2004, you wrote:
>  > >Tesla list wrote:
>  > >>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
>  > >>
>  > >>.
>  > >
>  > >Hi Terry,
>  > >
>  > >I'd strongly suggest that the tank cap's DC rating be a MINIMUM of 3X the
>  > >HV transformer's faceplate RMS voltage, and I personally use a minimum of
>  > >4X RMS to provide margin for "the unexpected" and long life. The above
>  > >factors take into account peak versus RMS voltage, voltage
>  > >reversal/ringing, and overdriving at 140 or 280 volts. A 3X factor
>  > >is  marginal, while 4X provides comfortable margin, especially for used
>  > >caps with an unknown history:
>  > >
>  > >Estimating the peak voltage stress seen by the capacitor's dielectric
>  > >system (with no additional cap/ballast resonance effects):
>  > >15 kV*1.414*(140/120)*2 (for voltage reversal) ~ 49,500 volts
>  > >
>  > >Designing a system with no/negative margin is a recipe for premature
>  > >capacitor failure. Some coilers have blown these "eBay special" caps in
>  > >their 15 kV NST-driven systems. Pairs of these caps should connected in
>  > >series for use in 15-20 kV RMS systems.
>  > >
>  > >Best regards,
>  > >
>  > >-- Bert --
>  > >--
>  >
>  > I never realized these caps were so fragile!!  I sold those two I have
>from
>  > that Lichtenberg figure experiment (wouldn't have worked...) to Kreso and
>  > we were wondering about this.  I have always played with MMCs, not
>  > commercial caps ;-)
>  >
>  > Cheers,
>  >
>  >          Terry
>  >
>  >
>  >
>
>.