Re: Lifetime of CD942C20P15K is ~75 hours

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>

Hello Terry.

> Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

>>  i knew that no "self healing" would save them! :-)))

> Unlike say mica caps, they don't break easily.  But
> if accidents are avoided, the mica cap might live much longer...

with the same sort of abuse? %-)

> I tend to break caps from dropping them on the floor long
> before they wear out anyway :o)

%%%-) you must be a very tall guy, Terry, _very_ tall :-)))
or the temperature at your house is lower that in siberia :-)))

> There are little electronic timers, but they might cost more than the
> MMC!

the timer on my RF generator is  on the mercury based - i don`t think
it costs more than $1 :-)

> Maybe best to use the caps at lower voltage.  But I don't know
> how much that helps.  They will always ionize beyond 630VAC...

you wanna say that they mentioned just the ionisation threshold here:

"Available Ratings."
http://www.cornell-dubilier.com/misc/h942.htm

?

>>  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.

sorry - i told that, had been mentioning our (russian - k78) caps -
750VAC for 1000VDC and 1600VDC, 1100VAC for 2000VDC - it`s true for them :-)

> Or, if they last 2 hours at 2500V and 10000 hours at 1500....
> I don't know  the curve shape...

you don`t need to know - just run them at 2Vpeak=VDC, coz anyway
decreasing the voltage more is very expensive, at least for the 942C20 ;-)

> If say 50% more money would give us 5000% more life, then it could
> get real interesting ;-))  But we don't have the data or the life
> graphs to plug into the spreadsheets and equations.  It is all too
> goofy to just guess at...

read above - "just run them" %-)
btw - at Vpeak=1000V the time of the 500V overshoot would decrease in
1.54 times, and if we`d take the 630V threshold - in 2.353 times.

> I have never seen any data on capacitors operated in such regions...

> As far as I can tell, manufacturer's data on such issues is "zero"...

and it`s can be very bad, coz it can mean that the capacitor in such
mode is unpredictable. for example, for the electrolytic caps it`s
often mentioned - how much would the lifetime decrease depending from
the voltage increase above rating value.

> Right now, I have to take down the equipment to play with the
> OL-DRSSTC stuff...  But I should return to this

i`ve got at least 6 months, so no problemo, just don`t forget about
people, who don`t have 942 at hand yet :-D

p.s.

btw - 75 hrs - it`s for the cw mode - then my coil would work
continuously _approximately_ 15000 hrs (first notch quenching -
unlikely), or 5000 hrs (second notch quenching) - it`s 208 days
_continuously_! not bad, right? maybe then it`s no need to decrease
voltage at all?  %-D
low bps rulez :-)))