Re: Are these maxwell caps OK?

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Sure, in TC use, we tend to use parts beyond their mfr specs... but note, 
rated voltage reversal is only 15% and max is 50%.  Design life is 3E8- 1E9 
cycles, but running them at 90% VR will cut that a bunch.. 
(http://home.earthlink-dot-net/~jimlux/hv/caplife.htm
  has equations from Maxwell Labs on this)
VR = 15% >> Q = 1.3 (approx)
TC Q... 10 (for grins..)
life goes as 1.6 power... a factor of about 26..
However, as Ed mentions, he's going to run them two in series with a 15 kV 
supply (assuming 21kV peak..).  The life is much more a function of voltage 
(7.5 power)... These are rated at 35kV, so 2 in series is 70kV.. A ratio of 
3.33 for a life increase of 8300...

The net would be a life change of 8300/26 or about 320 times longer life 
than the rated 3E8.

What's that really mean?  At 120 cycles/second, it's a long long time (half 
a billion seconds?)

If you've got to count each RF cycle, a lot less... at a Q of 10, you get 
about 10 cycles per bang, so 1200 cycles/second. 320*3E8/1200 seconds... 
about 8E7 seconds...
Hmmm at 86400 seconds per day (call it 8E4)...  I think you'll get a few 
years continous out of it.



Note also the dissipation factor of 0.20%... Run a kilowatt through these 
babies, and you'll be dissipating 2 Watts internally (that's also probably 
assuming the very small voltage reversal at 120 Hz... I'll bet that the 
.002 dissipation is going to be somewhat higher with more VR (more 
mechanical movement/stress internally).

This is probably a bigger factor than the rest of the stuff above.


And, remember that 7.5 exponent for voltage... A bit more voltage, and the 
life drops like a rock.


At 11:21 AM 10/11/2002 -0600, you wrote:
>Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><Esondrmn-at-aol-dot-com>
>
>In a message dated 10/10/02 6:31:38 AM Pacific Daylight Time, tesla-at-pupman-dot-com
>writes:
>
>
> >
> > Hello all,
> >
> > I am interested in buying Dan's maxwell caps. The specs can be found
> > at:
> >
> > http://www.alltronics-dot-com/download/20P005.pdf
> >
> > I'm worried about the maximum voltage reversal of only 50%. Are these
> > caps OK for tesla coil use? Other than that, they look pretty good
> > with their 25kA max current rating.
> >
> >
> > Cheers,
> >
> > Greg.
>
>
>
>Greg,
>
>I bought two of these last year.  I am also concerned about the voltage
>rating.  I have not used them but when I do, it will be with two in series 
>with
>a 14 or 15 kv power supply.  If anyone has used these I would be interested in
>the details - especially if any have failed.
>
>Ed Sonderman