Re: TC Questions

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

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi George, John,

When the gap fires, the gap remains conducting until it quenches. During 
this conducting time, energy is transferred from the primary to the 
secondary. Sparks fly! Any energy remaining in the secondary then transfers 
back across the gap to the primary. This mode of transfer continues as long 
as there is sufficient energy to keep the gap conducting. At some point, 
the primary will transfer the last breath of energy and the gap will stop 
conducting. The secondary will then ring down. This all occurs pretty fast 
in the low microseconds (say 1 half of 1 percent of 1 mains 1/2 cycle). 
Once quench occurs, the cap begins it's charging cycle (again, since we 
were obviously already charged). During the charge, the gap is open and 
there is no "wasted" power.

George, the mains frequency is related to the charge of the cap. The 
discharge is related to what I said above. In essence, the coils only exist 
when the gap is closed (if it helps to think of it that way although 
strange analogy I guess).

In an AC circuit,

V = Vs(1-e^-t/tc) = Vs(e^-t/tc), where:
V=cap voltage(volts)
Vs=supply voltage(volts)
e=natural log
t=time(seconds)
tc=RC time constant(seconds)

The thing to note here, is Vs is "varying" up and down every 90 degrees (it 
isn't a constant value). Thus, you cannot apply the transformer peak 
voltage to the equation unless you use the time when the voltage is at peak 
(90 degrees). In a 60Hz system, 90 degrees occurs at 8.33ms (peak voltage). 
So, at that "point in time", it would be appropriate to use Vp and 
calculate the cap voltage. All looks good until the charge time of the cap 
is extended. This is where the time constant plays a vital role. In 
essence, at 90 degrees, it can show you the voltage at the cap in view of 
the time constant which has been reached in 8.33ms. For example, if the cap 
is large in comparison to the current charging it, the cap may reach full 
charge in say twice the time (16.33ms). It would take 1 full cycle to fully 
charge the cap.

The mains frequency as you know is constant, but the breakrate varies 
(RSG's 120bps, 240bps, etc..). In an RSG, the breakrate, mains frequency, 
current source, and cap size are all requirements for cap voltage analysis. 
In a static gap system, the same applies, except the breakrate will be at 
the mains frequency (it can however go below this). In the RSG case, a cap 
could be overcharged if the breakrate is really slow and the cap charge 
time is really fast! In a static gap, the same can occur if the gap width 
is huge! However, if properly adjusted, this wouldn't be a problem.

John, can you reiterate on what I said (as shown below)? If it was a short 
time ago, then my memory is getting really short. It doesn't make sense to 
me. Is it possible we were talking apples and oranges?

Take care,
Bart



>I discussed this problem a short time ago with Bart Anderson. He believed
>the primary capacitor charge was a complete half cycle. I don't agree
>because the cycle ends in zero volts and no charge. I have been too busy to
>get back to him. This may be the time to dig deeper into this question.
>
>Bart or other coilers what are your comments regarding the cycle ending with
>zero volts and no charge on the primary capacitor? Note that the charging is
>different with fixed compared to rotary spark operating gaps! Forget about
>the inductance L for the time being.
>
>John
>
>--------------------------------
>
>
>-----Original Message-----
>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>Sent: Tuesday, January 06, 2004 9:48 AM
>To: tesla-at-pupman-dot-com
>Subject: Re: TC Questions
>
>
>Original poster: "gtyler" <gtyler-at-drummond-dot-org.za>
>
>Hi,
>      I am involved in electronic design but I see that that does not
>qualify me to build a TC! There are many things to learn before I can
>even begin. Can some one explain this to me please.
>      What happens after the spark gap "fires"? does the arc continue for
>the rest of the mains 1/2 cycle? If so there will be 1 pulse of HV every
>1/2 cycle, and the current flowing after the spark gap fires is waisted.
>Also the repetition rate will be 100 or 120 hz.?
>
>George
>
>
>
>