Re: Lifetime of CD942C20P15K is ~75 hours

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Dmitry,

At 11:00 AM 10/2/2005, you wrote:
> Hello Terry.
>
> > Original poster: Terry Fritz 
> <<mailto:vardin@xxxxxxxxxxxxxxxxxxxxxxx>vardin@xxxxxxxxxxxxxxxxxxxxxxx>
>
> > I finally did the great CD942C20P15K MMC capacitor life test.
> > I ran three of them at 1414 VAC (60Hz) which is 2000Vpeak.
>
> [...]
>
> > So it appears that the CD942C20P15K capacitors can go for 75 hours at
> > 2000Vpeak with little problem.  The next 25 hours will see
> > significant internal arcing with total failure probably at the 100
> > hour mark.
>
>  i knew that no "self healing" would save them! :-)))

Self healing save them from over-voltage accidents and direct 
streamer hits.  It really does little to make them last a long time 
from pure wear.  Unlike say mica caps, they don't break easily.  But 
if accidents are avoided, the mica cap might live much longer...

>  he-he-he - just 75 hours, and imagine what would happen if for
>  example D.C. used them in such mode of operation :-D

That is why he de-rates them much more than "I" do :o)  I still run 
them at say 2500V.  I might run a coil for a total of two hours a 
year, so I am not worried ;-)  Of course, in the case of a DRSSTC, it 
is just no problem at all.  Of course, my DRSSTC caps only cost $10 
anyway ;-)  I tend to break caps from dropping them on the floor long 
before they wear out anyway :o)

However, for a hard long running coil, the issue of MMC life could be 
a big deal!

>  i`m not afraid even of "75" value, but of the fact, that mmc would
>  degrade slowly and rather unpredictably. we need to use a time counter
>  with a coil - like it`s done on the precise devices, plus - several
>  times a year verify the mmc capacitance - that`s suxxx :-)))

There are little electronic timers, but they might cost more than the 
MMC!  Maybe best to use the caps at lower voltage.  But I don't know 
how much that helps.  They will always ionize beyond 630VAC...

> > Sometime I will try to run three at 1000VAC too.
>
>  it would be interesting to test them at 2Vpeak=VDC - almost so called
>  "properly derating" :-D

I am not sure if once the ionization starts if it will always be 
about 75 hours regardless if it is say 1500 or 2500 Vpeak.  Or, if 
they last 2 hours at 2500V and 10000 hours at 1500....  I don't know 
the curve shape...

>  anyway - thanx for current results (though i don`t think it was
>  extremely hard to do technically :-D).

Just hard to get around to doing it.... ;-))

BTW - I put it all into a file at:

http://hot-streamer.com/temp/CD942C20P15K-MMC-Capacitor-Lifetest.pdf

Cheers,

        Terry