Any Geekgroup MMC failures out there??

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

I was just wonder if anyone had any failures of Geek group caps for "no 
good reason"?  I have not heard of any problems, but it seems like a good 
time to ping the users out there to see if any problems have been 
noted.  Sort of just checking to see if there are any holes or unknown 
problems we need to check into.  Of course, if one does not follow the tips 
or runs them out of what is recommended, that is your problem ;-))  But if 
you think you did everything right and they blew, I would like to hear 
about it to see if any common trends or problems are out there we don't 
know about that need fixing

Perhaps additions to the "tips" too.


Cheers,

         Terry


At 12:15 AM 1/17/2004, you wrote:
>Well, let's put it this way....  We have never heard of a failure of a 
>"Geek Cap" that wasn't directly related to poor design or 
>construction....  The design chart on our mmc page is tried and true.  If 
>you build an MMC using the suggested design on our site and follow our 
>construction guidelines, your MMC should last forever in hobbyist duty.
>
>If you really do feel uncomfortable using an "underated" capacitor, then 
>go ahead and make it more beefy. :)  But, IMO, if "our" caps can hold off 
>5000V, one could argue that 10 in series is plenty overdesigned.  IIR, a 
>second high voltage test with a newer cap held off 5300V at the first 
>breakdown, then more than 6000V at the second (that's a 2.7J bang inside 
>the cap!).  Then the current draw got pretty high.  You have that info 
>handy, Terry, or do I have to go digging?  (one of these days we'll just 
>add that piece of information to our site)
>
>http://www.thegeekgroup-dot-org/mmc/
>
>FWIW, my first MMC was made from 1600V Panasonics (I think I managed to 
>hit Terry's first bulk buy in early 2000), total voltage rating of 
>19.2kV.  After a few hours of runtime, one dead NST, one dead "Terry 
>Filter" (shorted the MOVs), a lot of toasted AOL CDs, and a lot of awed 
>spectators, the MMC caps are still fine.  And IMO I've been gentle on 
>those compared to some of the torture we've put our Geek Group MMCs 
>through!  The Geek Group MMCs have seen many coil setups and many power 
>levels, including running near-resonant value caps with a 14.4kV PDT 
>overvolted to ~280V input on a 360BPS SRSG coil (half the Gemini project) 
>and also running a static gap 12/180 setup with no topload (we tuned at 
>about 2 turns - the gap was much less happy than the MMC).  So all this is 
>just saying that, yeah, these are pretty tough little buggers.
>
>Cheers
>
>Mark Broker
>Chief Engineer, The Geek Group