Re: Piranha II tuning (was: Re: Dual MOT plans - PIRANHA)

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Original poster: Terrell Fritz <terrellfone@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Dan,

At 11:27 PM 2/14/2007, you wrote:
> Original poster: "Daniel Kline" <daniel_kline@xxxxxxxxxxx>
> > .........
>
> > You would just change it to use "one" of Mark's boards and it would 
> > use a lower input voltage and current.  All the component values 
> > are the same but the caps probably don't need very high current 
> > ratings for just one board.  With its ball terminal toroid (which 
> > works fine*) and PIRANHA-II electronics, it is probably one of the 
> > most advanced Tesla coils on Earth.
>
> Great information! The only thing I don't understand is how the 
> tuning works...is the cap-bank frequency independent?
>
> What I think I would normally have to do is to consider my 
> capacitance as a fixed value and design a matching primary, so that 
> the cap/primary
> Fres would compliment my secondary's Fres. Since I'm only after 18" 
> max, I wouldn't want to have a 3-foot-tall secondary, but rather 
> something more proportional to the spark length. Is there room in 
> the design for different primary/secondary configurations?

The cap size shown is for "optimal" use with a MOT in a dual pumped 
resonant voltage trippler configuration.  Of course, I never thought 
about using "less" power :o))

If you use smaller caps, the energy per bang goes down and the 6 
inches of arc/section rule would no longer apply.  Since the SISG 
boards come in fours, it would be nice to use just one section so 
that caps sizes should probably stay the same.

The peak current needs to stay under say 600 amps and:

Ipeak = Vfire x SQRT(Cp/Lp)  So 600 = 3600 x SQRT(165e-9 / L)  L == 
6uH  Minimum.  Thus, Fo will have to be less than 160kHz for the coil.

Two say 680nF caps in series for each leg (4 total) would do 
it.  Like 942C16P68K-F.  Newark lists them as 12C8852 but you might 
have to call the have them add it to there next OEM order.  Or call 
CD reps...  Or make it with other caps.  If Fo were really low you 
could use 940 series which DigiKey sells for a high price.

I am not sure about what parts you already have but something should 
be doable.  I have a lot of stuff laying around here too so contact 
me off-list and we can see what we can come up with.

Cheers,

        Terry