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Re: Capacitors



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

Hi Tim,

	The primary capacitor size is matched to a particular transformer.  The
transformer charges the cap 120 times per second (at the positive and
negative peaks of the 60 Hz AC).  If the cap is too big, the NST will not
be able to fully charge it.  If it is too small, the NST may overcharge the
cap.  A chart with the static gap cases is at:

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm

In the resonant case, the cap may charge faster than 120BPS as the charts
show.  However, LTR coils are always at 120BPS.

Cheers,

	Terry


At 09:24 AM 1/1/2001 -0700, you wrote:
>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
>