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Re: Capacitors
Original poster: "Tim by way of Terry Fritz <twftesla-at-uswest-dot-net>" <warpath-at-wtp-dot-net>
Much and many Thanks, I am just learnig to "walk" and it sure is nice to have
someone hold my hand for a while. With the money that is going to be
invested, I
don't want to make any costly mistakes. You and others have been extremely
helpful.
I have downloaded your pics about the protection circuit for my NST and I am a
little unsure about where to start. I am not even sure what perf board is.
However,
I am going to make friends with the local Radio Shack and I will learn.
I do have a question in regards to the capacitance of the capacitors-Am I
supposed
to keep the capacitance in balance with the output of the transformer or
something
like that-that is- the transformer puts out 15K and the caps store it until
they
can't store anymore and then they release the voltage/energy to the spark
gap? I
won't get into the spark gap yet as I am "crawling" in that area. I am
reading all
the postings in this group(some 300 so far) to get a feel for what is going
on and
how to do things. I appreciate your patience in directing me. Again, I want
to say
thankyou.Later, Tim
Tesla list wrote:
> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>
> At 12:44 PM 12/22/2000 -0700, you wrote:
> >Hi Mike, Herein lies the question-what size cap do I need? I have tons of
> >information on computing
> >cap size but for the life of me, I can't make sense of it. Any and all help
> >is truly appreciated.My
> >transformer is a 15000volt nst with output of 450VA at 30MA. So far this is
> >all I know except that I
> >won't make a plate stack cap. Later, Tim
> >
> >Tesla list wrote:
> >
>
> Hi Tim,
>
> There are three common choices for cap size:
>
> 1. The "resonant" size. This is the value that will cancel the current
> limiting of your transformer allowing a lot of power to be drawn. It is
> also the most risky and safety gaps are a big must.
>
> For a 15/30 NST, that is 0.0053Uf or 5.3nF.
>
> 2. The Larger Than Resonant (LTR) size. At around 9-11nf Well say
10nF.
> This size is far safer and cause less strain on the parts but you still
> have very good power.
>
> 3. LTR for a rotary sync gap. Since rotary gaps can precisely
control when
> the gap fires, we can play tricks (inductive kick effects) to pull more
> power out of them. That would be at 14nF for your NST.
>
> I could babble on for hours about how these numbers are arrived at but I'll
> spare you :-))
>
> I assume you want #2 since you probably don't have a rotary gap for a first
> time coil and I hate to recommend resonant caps to first time coilers since
> that is how many blow their first NST =:O
>
> I think you are contemplating an MMC so let's try MMCCalc3 with my 0.056uF
> MMC caps.
>
> ==============================
> MMC Calculator Ver. 2.2 9/12/2000 Terry Fritz
> Transformer voltage = 15000
> Transformer current = .03
> Firing voltage = 21213.15
> Fo = 250000
> Break rate = 120
> Thermal dissipation constant = 40
> Individual cap value = 5.6E-08
>
> Strings Caps/Str Capacitance Voltage Temp C Cost I Arms
> 2 11 10.18 17600 6.37 39.60 :-| :-) 4.96
> 3 17 9.88 27200 2.67 91.80 :-)) :-)) 4.82
> --------------------------------------------------------------------
>
> The key number I use is the current which is about 5 amps. Two stings will
> do that (the program is a little conservative) so a 2 string by 11 cap MMC
> would work. You will note that even the "expensive" MMC caps here only add
> up to $40 ;-))
>
> Hope that give you an idea of how it all works. MMCs are pretty new and
> there are not any super well polished tools for figuring this stuff out
> yet. If you have any ideas about how to make this easier for a new coiler
> I am all ears.
>
> I am going to be bulk buying 0.056uF 1600V caps next month so stay tuned.
> I am also working on a newer style MMC cap too but that is yet to be tested
> but it is well directed for things like this.
>
> Cheers,
>
> Terry