Re: The death of a classic

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Finn,

At 10:30 PM 8/11/2002 +0200, you wrote:
>Perhaps it is not so good an idea to fit a museum coil with a MMC style
>capacitor.
>
>The capacitor for The Museum Coil is a classic, in that it was one of
>the first really big MMC`s 3 years back. It has put up with all my
>initial mistakes, a lot of abuse, and an estimated 10 hours of total run
>time. I had thought it would last 470 hours, but alas, I must have been
>treating it worse than I thought I did.
>
>Recovering from a Weekend bicycle race yesterday (160 miles -at-9h22min)the
>museum manager called me this morning to tell me, that the coil was
>smelling.
>"Red Alert"
>So I hurried down to the museum, carrying with me the cap from the
>Ambassador coil in order to have something to rig up, so the visitors
>could get what they came for.
>Now it is gone for good.
>
>http://www.wimshurst-dot-com/mmc1.jpg
>
>http://www.wimshurst-dot-com/mmc2.jpg
>
>What went wrong?

I understand you will send me the parts were it looks like it might have
started.  I will do all I can to figure it out.  I would be happy to cover
postage and I'll return the parts when done.

Are the strings isolated from each other?  Hard to tell from the second
picture, but it looks like the leads of the parallel strings are connected?
 That normally should not have hurt...  Just have to see when it comes.
Lots of tests to run on it...

Surprising that multiple strings seem to have been affected and the damage
to the bottom of the board suggests arcing...  The "undamaged" caps may
have a story to tell...  Over heating or over voltage will show in them...
Could have started on the back too...  Maybe a drain reistor failure...

Many questions to be answered here...

Cheers,

	Terry


>Perhaps I just pounded it too heavily, I didn`t always hook up the
>fiberprobes, so I really have no idea about how often they were
>overvolted.
>They never were hot, even one time when they ran for an hour, without
>stop, during EMC measurements.
>So probably, one cap gave up, and this lead to heat inside it, being
>transmitted to nearby caps, and the avalance started.
>
>This is the reason that I will not use a MMC again on a professional
>coil: It is not reasonable to ask, that the operator should be able to
>spot that first bulging cap when it pops out amongst the others, A pro
>coil damands a pro cap.
>
>With the caps from the Ambassador, rearranged for 28nF, and 5 strings
>from the original MMC, i managed to get the coil up in an hout or so,
>and am now anxiously awaiting the arrival of the backups, Maxwell 37667,
>that I bought from Tesla Systems Research.
>Got 6 of those, and am going to use 4 in a quad, and 2 as spare. Then it
>is only my hope that they will last untill we get the Maxwell 35309,
>which is a 40nF 100kV cap.
>
>Don`t ever deal with a professional setup without a backup! 
>
>Cheers, Finn Hammer
>