Re: Garry's MMC cap failure explained.

["Tesla list" <tesla-at-xxxxxxxxxx>]

Original poster: "Steve" <seric48-at-yahoo-dot-com> 


 Hi Terry, all,

  These caps are supposed to be of metallized polypropylene
 construction, according to CDE. The 940C-series data is at

     http://www.cornell-dubilier-dot-com/h940.htm

 and detailed data on Garry's .033uF/2000v cap is at

     http://www.cornell-dubilier-dot-com/9402000.htm


  Robin Copini has used (1600v) 940C-series caps sucessfully
 in an MMC. Maybe someone at CDE actually did 'spill pop in
 the cap winder', or loaded it with polyester film by mistake?

  Steve Copeland


--- from Tesla List ---

>Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>Hi All,
>
>	I received Garry's MMC cap that kept wildly blowing up
> on him tonight by mail and I immediately set to work on it.  
>
-snip-
>
>  I then got out the RF power supply and ran a little current
> through each.  I found two caps were open and removed them.
> I then took one and then another and ran 1 amp through them.
> After about 30 seconds they puffed up and melted down.  They
> are NOT polypropylene!!  Comparing to my other caps they must
> have about 20X the dissipation!  Tearing them apart, the 
> internal construction is basically good but they are built
> rather weakly.
>
>  So, The caps had a real high dissipation factor and they burn
> up under 1 amp of RF current in about 30 seconds.  A Panasonic
> cap with twice the current seem to run stone cold after a few
> minutes.  So these are high voltage "DC" caps (fairly good ones)
> with very poor AC characteristics.  The caps are white wrapped
> tubular types that are 1 1/4 inches long and a little under one
> inch in diameter.  The markings on them are:
>
> 940C  20533K
> .033MFD+-10%
> 2000VDC  CDET.
>
> There are a bunch of pictures at:
>
> http://hot-streamer-dot-com/TeslaCoils/Misc/blownMMC/
>
> Unfortunately, there is nothing that can be done to fix the
> cap.  But I'll get it sent back to Garry on Monday.
>
> Cheers,
>
>        Terry

------------------------------------------------------------------

> Original poster: "Robin Copini" <rcopini-at-merlin-dot-net.au>
>
> Hi Gary,
>
>  The cap code you give '940C' implies a CDE part, i.e. 
> Cornell-Dubilier. Well..... I have to say I disagree with
> your assessment of these caps. I have a mmc built with
> CDE 940C caps (7x(33x0.33uF)) rated at 1600Vdc. The caps 
> are fairly plain looking with a cheap white stick-on label
> but... I run a pole pig rated at 33Kv/220Vin and I overdrive
> it with 270Vin, at over 80amps, the coil throws arcs over
> 4 metres and I cannot get these caps even warm.
>
> Best Regards
>
>  Robin Copini, Australia.
>