RE: TC Questions

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

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Bart -

We were talking about the charging of the primary capacitor by a NST. You
showed calculations that included a half cycle of .00833 seconds to arrive
at a fully charged primary capacitor. I now understand that you are saying
the charging time is much less than that amount of time so the cap is not
being charged to full voltage. I believe this is correct and that the cap
seldom gets fully charged with a fixed gap and may never get fully charged
with a rotary gap unless the system is very carefully designed. This is why
the actual test output spark length varies so widely. A similar charging
condition exists with the pole type transformer but voltage regulation
during charging would be less of a problem.

I think matching the pri cap to the NST is much more complicated than
coilers believe. If the coiler builds a TC that gives an extra long spark it
isn't by design. This means that maybe the coiler with proper design could
get a longer spark output. This may or may not be what George was referring
to.

I am having problems with my computer so my replies my have a delay.

John Couture

--------------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, January 08, 2004 3:24 AM
To: tesla-at-pupman-dot-com
Subject: Re: TC Questions


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
 >
 >
 >
 >