Re: The death of a classic

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

Original poster: "Finn Hammer by way of Terry Fritz <twftesla-at-qwest-dot-net>" <f-h-at-c.dk>

Perhaps this is bending the numbers to the advantage of the
circomstances, but I did just check the data sheet for the capacitors,
and the AC rating is not 600 volta as I recalled, but 500 volts.
This puts the expected lifetime to 3 hours.

I am using a formula which Terry made sometime, and are axcessible
somewhere.

It says "10^6((Cap AC rating * no. of caps in string)/transformer RMS
voltage)^15"

There are 20 caps in a string, and the transformer puts out 20kV.


Finn Hammer 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://wimshurst-dot-com/mmc1.jpg
> 
> http://wimshurst-dot-com/mmc2.jpg
> 
> What went wrong?
> 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