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Re: ?kva at 800 bps

Tesla List wrote:
> 
> Original Poster: Cabbott Sanders <cabbott-at-cyberis-dot-net>
> 
> I have been researching these corum experiments and how thier coil setup
> was, and i may have to run my coil at 800 bps!  how much kva do i need to
> charge a .161 ufd cap 800 times a second???  I've heard about 60 kva.  what
> do you think? i simple substation perhaps?

Cabbott,

It depends on the desired energy per bang, and whether you're driving
the system directly off AC or from a DC-resonant charging system. From a
pure energy standpoint,the energy/bang (Ep) will be a function of the
tank cap size (Cp), and the main sparkgap breakdown voltage (Vg):

   Ep = 0.5*Cp*(Vg^2)  Joules  (Watt-Seconds)

The power required to recharge the tank cap to Vg 800 times/second will
be:
   Wp = 800*Ep  Watts

Plugging in Cp = 1.61e-7 Farad:

   Wp = 6.44e-5*Vg^2

   Vg       Wp (KW)    Bang Size (Joules)  
  ====     ====        =================   
12,000      9.3            11.5            
13,000     10.9            13.6
14,000     12.6            15.8
15,000     14.5            18.1
16,000     16.5            20.6
17,000     18.6            23.3 
18,000     20.9            26.1
    
Now a breakrate of 800 BPS means the gap must be fire about every 1.2
mSec. However, the allowable tank cap recharge time will be less than
this, since recharging can only take place after the main gap quenches.
If we assume the gap's "firing" time is about 100 uSec, the estimated
recharge time must be 1.1 mSec or less. 

Also, the time that the HV source voltage spends above |Vg| must
represent a major portion of the incoming HV waveform. This means that
that you will most likely need a higher voltage pig in order to achieve
the desired bang size AND BPS rate. For the sake of argument, assume
that we need to reach Vg in 1.1 mSec after the AC Mains zero crossing,
and the absolute value of the pig's output voltage then stays above Vg
until 1.1 mSec before the NEXT zero crossing. It can be shown that this
implies that the pig's output RMS voltage must be as much as 1.75 times
the desired main gap breakdown voltage(!). Another option might be to
adjust the ballast inductance to resonate at 60 Hz with the "reflected"
impedance of the tank cap. In either case, the tank cap must be very
robust to withstand the severe overvolting effects of a main gap
misfire. 

Obtaining 800 BPS while using a large tank cap directly off the 60 Hz AC
mains is not trivial! Are you sure you really need 800 BPS??

BTW, Cagle's Physics site is really quite interesting... as are his
posts every now and then to sci.physics newsgroup... :^)

-- Bert --