RE: MMC cap bank

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

The difference between AC an DC ratings is "ion inseption voltage"... At 
about 630 Volts AC, poly tends to get that "pretty blue glow"...  Tears the 
heck out of the poly, but it takes time...  Far more time than us 2 hours a 
year coiler's are concerned with ;-)))

Cheers,

         Terry


At 10:36 PM 7/3/2003 -0400, you wrote:
>I have to concede, you are correct.  The cap will ultimately fail.  The 
>question is when.  But the cap maker is spec'ing that cap for continuous 
>24-7 operation under the most adverse conditions.  In a TC application, we 
>typically demand far less life from a cap.  For most of us, if we run our 
>coils for a couple hours over the course of a year, that's probably all we 
>need.  If a coil were to be run for several hours every day, in a museum 
>perhaps, then a far more conservative design would be required.
>
>For recreational coiling though, the norm has been to design MMC's based 
>on the DC spec.  Folks have been doing that since the advent of MMC's, and 
>it's very rare that a failure is seen.  Certainly less often than with 
>rolled poly/foil/oil caps!
>
>Regards, Gary Lau
>MA, USA
>
>
>Original poster: "Dr. Resonance by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
>
>The manufacturer has spec'd the rating at 900 VAC.  He's running the caps at
>14.4 kV (mfgr rating is only 9 kV AC).  It's not rocket science.  He's
>exceeding the manufacturers ratings severely.
>
>DC ratings have to be completely ignored because RF corona will occur at the
>caps plate edges.  They will fail --- it's only a question of when failure
>will occur.
>
>Dr. Resonance
>
>  >
>  > I'm not sure I agree with this dismal assessment.