Re: Any Geekgroup MMC failures out there??

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

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Yep, possibly had a defect. I was pushing the power the pole pig however 
<big grin>. RMS current was marginal to begin with on that particular 
design, which I knew ahead of time, but just went for it. I've always 
assumed I just over did it on the current.

Take care,
Bart


Tesla list wrote:

>Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
>
>Hi Bart,
>
>Sounds like it failed where the plates meet the end cap.  Could have been 
>from high current, but I suspect it just had a defect in it.
>
>I don't see many cap failures being reported ;-))  Sound like all is well 
>out there in MMC land!!
>
>Cheers,
>
>         Terry
>
>At 10:54 PM 1/17/2004, you wrote:
>
>>Hi Terry,
>>
>>Well, I've had one cap bite the bullet. This happened about a year ago. I 
>>was the 1st to receive caps from The Geek Group many moons ago. These are 
>>the 942C series 0.15uF caps. The one that that died was the cap next to 
>>one of the brass bolts I used for a connection. There's a hole in the cap 
>>about 1/8" from the end. I don't believe it an arc from the bolt to the 
>>cap occurred since the hole is on the opposite side of the cap, however, 
>>something odd occurred. It was "not" from over volting the cap but I 
>>believe RMS current. I believe I was running 5 strings of 12 for 0.0625uF 
>>total at the time. The caps were set on a pcb with 10M resistor soldered 
>>across the cap on the opposite side of the pcb. Each cap from side to 
>>side had at least 1/2" clearance. Plenty of room there. I suspect I 
>>exceeded the rms current capability (25 amps).
>>
>>I've since rebuilt the entire cap bank onto an 8" pvc tube. Each resistor 
>>is now soldered across the cap and each cap is simply placed on screws 
>>protruding from the pvc tube (this way I can maneuver cap arrangements 
>>anyway I like). It is currently 3 strings of 18 caps for a total C of 
>>0.025uF. I haven't had a failure since.
>>
>>I'm not sure why the cap failed. It's still on the pcb board along with 5 
>>neighboring caps. I just threw it up in a cabinet and left it there ever since.
>>
>>Take care,
>>Bart
>>
>>Tesla list wrote:
>>
>>>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
>>>
>>>
>>>
>>>
>>>
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