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Re: MMC Cap Papers and MMC Life Prediction

Hi Reinhard,

At 04:14 PM 7/11/99 +0200, you wrote:
>Hi Terry,
>
>Thanks for all your work on MMC life prediction. Your
>newest HTML file really proves the gut feel I had about
>those WIMA FKP-1 33nF/6kVdc/700Vac caps. They
>arenīt worth a darn, which is what I also told the GTL
>gang, but... they went ahead and ordered them (and
>caught me off gaurd) anyway. The 100nF/1600Vdc
>/650Vac would have been a *MUCH* better buy. My
>present MMC setup (with those cheaply bought) ERO
>caps has a life prediction of around 2000hrs (of which
>there are now "only" 1996.5 left ;o}).

Of course, this MMC cap thing is in its early stages and we knew there
would be a learning curve.  The big 6000 volt caps do have high current
handling.  Also their rated AC voltage is probably around 800 volts.  I
though a number of other things would catch up to us before the corona
voltage thing, but it is proving to be pretty important...

>
>Very interesting papers, I must say. I DO have to
>disagree with one thing you wrote, tho:
>
>> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>> Hi All,
>
>Sniptīcha
>
>> primary systems.  Since the length of the output arcs is proportional
>>to the input voltage, there is always a desire to use as much primary
>>voltage as possible.
>
>NO, NO and once more NO!! ;o) I have proved this with my 8" coil.
>The length of the output sparks is NOT (!!!) soley dependant on
>the input voltage. Otherwise, how would I be getting 63" sparks
>from a 7500V NST -at-1275VA? I consider the "need-for-high-
>voltage" story to be other one of those myths. True, there are
>limits (either low or high), but it is NOT necessary to use high
>voltages for long spark lengths. Both low and high voltage
>systems (AND vice versa for the current) have their advantages
>and their disadvantages. I think it is safe to say the spark length
>depends almost purely on how much raw power you shovel into
>the coil (VA, BPS, J must all be considered), but if you build
>two systems with equal power (VA, BPS, J) and one having a
>15kV xformer and the other being powered by a 7500V xformer,
>there will be no (or only very little) difference in output arc length.
>Of course there are other things, which determine the spark
>length (like the gap design, toroid size), but these are of a more
>secondary (fine tuning) nature. Another "biggy" (at least from
>my experience) in spark length increase is the size of the
>secondary. Performance improves as the secondary gets larger
>in diameter AND length. For equal input (wall) power, I found
>that my 8" secondary will give me some 40% longer sparks
>(100cm vs 60 cm -at- ~400VA) than my 3.34" coil did.
>
>I donīt mean to flame you, but I just had to say this (from my
>own findings) about high vs. low input voltage. Please, no
>hard feelings! ;o)
>
>
>Coiler greets from Germany,
>(keeping his fingers crossed, that Terry
>takes the words as they are ment).
>Reinhard
>

	Of course, there are many many things that determine arc length.  I was
assuming that if you double the voltage, the stored energy in the primary
cap is quadrupled.  With four times the energy going into the system, the
output arc length should double if one believes that arc length is
proportional to the square root of the energy going in.  Another way to
look at this is if you measure the arc length with the variac setting at
100, and then turn it down to 50, the arc length should be cut roughly in half.

	In the past, it has been very hard to make a high voltage Tesla cap.
However MMCs remove that limitation for those that like to push the primary
voltage to the extreme.

	I have also found that the larger the secondary inductance, the more power
a given coil will pump into the output arcs.  My larger secondaries give
much larger sparks than my smaller secondaries.  The top terminal seems to
give roughly the same sparks no mater what its size but small terminals
seemed to be overwhelmed with power and loose spark length.  Computer
models predict this, but I tried it just to be sure and it appears to be
very true.  I think you want as high of primary voltage as possible with as
large of primary cap as possible running the largest secondary as possible.
 Of course, it is a big balancing match and you can minimize one and make
the others larger to get the same sparks.  

	Considering what we have done with little 1kW systems using all kinds of
careful design and new principles, Imagine what we could do with a
22kV/500mA pig and a matched 0.247uF LTR cap.  That works out to 120 joules
per bang and 14400 watts through put!  I wonder how big the secondary for
such a monster charging system would need to be for the best sparks...  I
imagine the arcs would be around 15 feet...

Of course, moderators or inherently flame proof :-))

Cheers,

	Terry
References: