Re: Math help...

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Luc,

It can be shown that if a capacitor is charged through a resistor, and if
the charge time is sufficient to virtually fully charge the cap (Tcharge >
3RC), then the series resistor will dissipate the SAME amount of energy as
the energy that ends up being stored in the capacitor. Knowing this
simplifies the problem a bit. 

If the Energy/bang = 0.5*C*(V^2) Joules and the break rate = X
bangs/second, then, the power transferred to the TC primary circuit will be
0.5*X*C*V^2 Watts, and the power dissipated by the series water resistors
will be the SAME (for 50% efficiency by the charging system):

   Presistors = 0.5*X*C*(V^2) Watts

Because of the significant inefficiency (only 50% max), pure RC charging
systems are seldom used for higher power pulse work, and reactive (LC)
charging systems are preferred instead. Note that the above analysis
assumes that the primary cap is fully recharged between breaks irrespective
of the break rate. This means that the time between breaks must be at least
3*R*C:

  1/X = 3*R*C

For 400k ohm water resistors, and 120 BPS, this means that the maximum tank
circuit capacitance can only be about 0.007 uF. If you want to use larger
tank caps, you'll need to reduce the value of the charging resistors.


-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Luc by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<ludev-at-videotron.ca>
> 
> Hi guy
> 
> I presently build a DC power supply for coil. I want to be able
> to use it for big coil but mostly for small one, you could see
> the circuit at:
> http://pages.infinit-dot-net/luc2/ps_mot_3.gif
> 
> Some of you will tell me to use a variarc for power control; I
> have some but I choose to use variable water resistor for many reason.
> 
> Any way I need to have an equation to know at different value of
> power how much power will be dissipated in the variable resistor
> and the primary circuit ( power in the V. resistance + power in
> the primary circuit ), I already know some equation : capacitive
> energy J=C*V^2/2, ohm law V=I*R, P=V*I, P-V^2/R, transient
> V-(Vf-Vi)*e^-T/RC, but can't merge them in a big equation...:-((.
> 
> What I want to have is an equation where variable are PS voltage,
> cap value, break rate, value of my variable resistor, one of the
> unknown will be the power dissipated in the variable resistance
> when the SG conducted, it could be estimated like a short of the
> PS across the V. resistance for the time the gap conduct, but an
> approximation will do the job. The output of the equation will be
> the power use in primary circuit and power dissipated in the
> variable resistor.
> 
> If one of you could help me with that or make a small excel file
> I'll be eternally thankful ;-) .
> 
> Cheers,
> 
> Luc Benard
> 
> *This post and an other one was send friday at 1:00 PM but both
> never make it to the list...???