Re: term understanding: voltage reversal.

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

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net> 

Hi Christopher,

You are probably OK. You may be operating close to the limits of the cap, 
and you may see some shortening of the capacitor's life depending on your 
main gap setting. Since these caps are typically "pulls", it's hard to say 
how much stress they've seen in their previous life and how much remaining 
life they'll have in your system.

Unlike capacitors packaged in cylindrical cases or smaller metal cased 
caps, caps using this package style normally do not fail explosively when 
used in a TC tank circuit. If you overheat the capacitor during long runs 
or get a sudden buildup of gas due to internal arcing, the soft 
polypropylene cases are designed to bulge outwards to help relieve internal 
pressure. Obviously, if you kept running your system under these conditions 
it may be possible to blow the oil-fill plug or perhaps even rupture the 
case. I've not heard of any coiler actually experiencing this problem with 
this style package. However, it may still be a good idea to put the cap 
inside an inexpensive plastic container to catch the oil in case you do 
have a messy failure. BTW, some commercial pulsed laser systems use a 
microswitch that monitors one side of the capacitor's case so that the 
system can be shut down if the case begins to bulge outwards.

Good luck and best regards,

-- Bert --
-- 
--------------------------------------------------------------------
We specialize in UNIQUE items! Coins shrunk by Ultrastrong Fields,
Lichtenberg Figures (electrical discharges in acrylic), & Scarce OOP
Technical Books. Stoneridge Engineering -- http://www.teslamania-dot-com
--------------------------------------------------------------------

Tesla list wrote:

>Original poster: "Christoph Bohr" <cb-at-luebke-lands.de>
>Hello All who replied.
>First thanks a lot for your explanations, I think I got that now.
>  >This is why 35 kV Maxwell caps that are continually offered on eBay have
>  >been observed to prematurely fail when used in 15 kV RMS systems:
>  >http://cgi.ebay-dot-com/ws/eBayISAPI.dll?ViewItem&item=2595652751
>Thats not so good nows. I use these caps with my 6MOT supply for
>aproximately 30 Minutes in intermitted short runs with no problems. Of
>course this is 12 and not 15KV but that will probably not change much.
>More important to me: how do these caps fail? I heard a lot ranging from
>internal shorting to explosions....
>If it just breaks its OK, but when it should be spitting burning oil I
>really have a problem as I do my coiling indoors. I check the temperature of
>the caps regulary and they never heat up significantly.
>Thanks for your replies
>regards
>Christoph Bohr
>
>.