Re: option 1 or option 2.....

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

The difference between the 940 series caps and the 942 series is 
current handling.  From the data sheets at:

http://www.cde.com

http://www.cde.com/filmframe.htm

We can compare the currents:

CAP                     Peak Current    RMS Current
940C20P15K              144             8.9
942C20P15K              432             13.5

The actual destruct point is about 1.5X these rated values:

CAP                     Peak Current    RMS Current
940C20P15K              216             17.8
942C20P15K              864             27.0

If you run the 940 series bellow 216 peak amps and 17.8 amps RMS then 
everything will be just fine.  If you run more, they will burn 
up.  Too much RMS current will overheat them and too much peak 
current will blow the metal connections.

Obviously, a given coil might be very happy with the 940 series so it 
is not surprising that some coils work fine with them.  However, the 
942 series is far stronger and what all the charts are made to 
conform too.  Typically, people watch out for RMS heating so 
overheating is often avoided.  However, end plates blowing out is 
sudden, dramatic, and fatal.

So it all depends on the currents "your" coil is seeing as to which 
cap is best.  Of course, we always recommend the strongest and best as a rule.

Cheers,

        Terry




At 07:10 PM 11/11/2005, you wrote:
> In a message dated 11/11/05 2:56:02 P.M. Eastern Standard Time, 
> tesla@xxxxxxxxxx writes:
> Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>
>
> I disagree with the statement that 940C's don't survive moderate use.
> They aren't as good as 942C's, sure, but I have 4 strands of 10 3Kv
> .1uF 940c's that have withstood a couple years so far. That includes
> many times when the coil was misconfigured (most of the time? ) which
> is worse on the caps than running perfectly tuned, if I am not
> mistaken.
>
>
> Snippp
>
>      When I was much younger, Thor Heyerdahl and his crew 
> successfully crossed the south Pacific on a balsawood raft (Kon 
> Tiki) Years later, they successfully crossed the south Atlantic in 
> a boat made of papyrus.(The Ra expedition). But, if a young sailor 
> had asked him to recommend an ocean-going vessel, I doubt he 
> would  have recommended either one. On the other hand, a friend of 
> mine built a rowboat using tongue and groove lumber which naval 
> acrhitechts agree is a terrible choice. It sank during its 43rd season.
>
> Endorsements drawn from a sample of one experience need to be taken 
> with enough salt to make several bucket caps. A more supportable 
> original statement would have been that 940Cs are much more likely 
> to have a significantly shorter life expectancy in TC service than 942Cs.
>
> But here again, mortality tables do not determine the fate of a 
> single individual, they only point out the better way to place long 
> term bets. My suggestion: If you have the 940Cs, use them, run to 
> failure, then get 942Cs. If you have the funds and a choice, go for the 942s.
> Either WILL work for a while.
>
> Matt D.
>
> Matt D.