RE: Capacitor Sizing for Power

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Loudner, Godfrey by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>

Hi Matt

All your first equation says is that 120 caps with a capacitance of 0.2uF
placed in parallel will be able to store 2700 joules of energy at a
potential of 15,000 volts. This is already enough to lock in the charging
time of a cap, say 5RC = 5(15,000volt/0.240amp)(0.0000002F) = 0.0036sec. =
1/278sec. You are asking for all 120 caps to charge and discharge in 1sec.
This is the same as asking a single cap to charge and discharge in 1/120sec,
or a charging time of 1/240 sec. Now1/240sec. is about 116% of 1/278sec. So
you want to place a 0.2uF cap in a tank circuit that requires 1/278sec. to
charge, but you are asking it to forget all about that and charge in
1/240sec.

Godfrey Loudner
 

> -----Original Message-----
> From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent:	Wednesday, July 18, 2001 5:54 PM
> To:	tesla-at-pupman-dot-com
> Subject:	Capacitor Sizing for Power
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <Mddeming-at-aol-dot-com>
> 
> Hi All! 
>          
>         I just started working up the requirements for my 15/240 NST farm 
> coil and decided to try the P=rate*0.5*C*V^2 method. using a SRSG -at-120
> BPS. I 
> have read that this is a "good ballpark figure" for minimum cap size
> needed 
> to handle the power. 
> Now 15KV*240mA= 2700 W Substituting gives us 
> 2700=120*0.5*15000^2*C  or 
> 2700=60*15*15*1E6*C which reduces to   
> 3/15*1E-6=C  or 
> 0.20uF=C = 200nF 
> 
> Using the resonance relationship to calculate the minimum capacitance: 
> XL=2*pi*f*L=Xc=1/(2*pi*f*C) 
> if R<<XL then Z=E/I ~XL 
> XL=15000/.240=62500=377*L or L=166.8Hy 
> Xc=1/(2pi*f*C) 
> 62500=1/377C or 2.35625*1e7=1/C 
> 4.244*1e-8=C or, 
> C=42.44nF 
> A difference of 470% is not close in my ballpark. Even doubling the value
> for 
> LTR gives an error >230% 
> Am I missing something obvious or am I just brain dead this week? 
> 
> Matt D.
>