Re: MMC cap bank - ion inception testing

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

Original poster: "Mark Broker by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mbroker-at-thegeekgroup-dot-org>

Jeepers!  Barely a whisper of MMCs for months, and then the perverbial 
"stuff" hits the fan during *THE* first, real vacataion I've had in about 3 
years....  Which also happened to be my honeymoon, too!  8^)

Although not quoted, I'd like to mention I completely agree with Gary Lau's 
comments on his Thursday post.  Dr. R, as a commercial supplier of Tesla 
Coils for museums, schools, etc, has to design for complete reliability for 
many years.  Us "hobbyists" probably won't use the same coil setup for more 
than a few years (or even months!), and may only acrue a few tens of hours 
of total runtime on one particular TC component.  IMO, designing something 
that will definately fail isn't by default "bad" if we design the failure 
at 1000 hours and expect only 10 hours of use.  In fact, it's fairly common 
engineering practice to do so.

With all due respect, of course, perhaps a less strongly worded reply from 
Dr R. in the begninning would have lessened this firestorm to merely a 
back-yard bonfire?  I know *I* read his replies as "it's going to fail; it 
won't work; you have to do it this way...."

<snip>

>Since Geek Group caps are so common, a simple test would be to string say 
>5 of them together and run 7.07kV across them from an NST (be sure the cap 
>value is not resonant with a given NST!).  Then just sit and wait... to 
>see how long it takes for them to fail.  One has to be careful since it 
>may burn one's house down if they flame out when your not there and there 
>is a big electrical hazard and all that.  But that test would pretty well 
>define the lifetime.  It is interesting to note that at first they will 
>just self-heal.  But eventually, they will obviously go "bad".  As far as 
>I know, no MMC has ever failed from ionization.  Just to hard to get 1000+ 
>hours of run time on a coil ;-))  Perhaps your coils get run much more, so 
>you may have to worry far more than most.  Of course, you buy caps most of 
>us can't afford too ;-))
>
>I am not sure if Mark Broker is looking for a science experiment ;-) but 
>maybe the Geek group could run this test safely.  It would be interesting 
>to really know...

<snip>

I think it's a good idea, and will discuss logistics and such with Chris 
Boden.  I think that the hardest part of the test will be to "hurry up and 
wait"....

We should define "failure" and agree on testing conditions.  We (TGG) have 
"many" MOTs on hand, so wiring up 2 caps in series across a 2kV MOT is my 
preferred setup.  The cap is much larger than resonant, and will self-limit 
the MOT.  I think we have at least one old laptop around that can be set up 
with some form of data aquisition to monitor voltage and current, and shut 
things down automatically if "bad things" happen.

Regards,

Mark Broker
Chief Engineer, The Geek Group