Re: Spark Gap Sustaining Current (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 04 Oct 2007 10:52:06 -0500
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Spark Gap Sustaining Current (fwd)

Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Wed, 03 Oct 2007 15:57:21 -0500
> From: Crispy <crispy@xxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Spark Gap Sustaining Current (fwd)
> 
> On Wed, 2007-10-03 at 07:59 -0600, Tesla list wrote:
>> ---------- Forwarded message ----------
>> Date: Tue, 02 Oct 2007 23:23:51 -0500
>> From: Bert Hickman <bert.hickman@xxxxxxxxxx>
>> To: Tesla list <tesla@xxxxxxxxxx>
>> Subject: Re: Spark Gap Sustaining Current (fwd)
>>
>> Hi Christopher,
>>
>> Tesla list wrote:
>>> ---------- Forwarded message ----------
>>> Date: Sat, 29 Sep 2007 16:28:45 -0500
>>> From: Crispy <crispy@xxxxxxxxxxx>
>>> To: Tesla list <tesla@xxxxxxxxxx>
>>> Subject: Re: Spark Gap Sustaining Current (fwd)
>>>
<snip>
>> And, for a given bang size, overall spark length no longer increases 
>> after you reach several hundred breaks per second... the discharges may 
>> get hotter and more "frantic", but they get no longer.
> 
> Ah, Ok.  Why is this?  I guess there's another factor than what I
> described, but what is this factor?

The other factor is the maximum output voltage of the coil. Eventually, 
the electrical field at streamer tips becomes insufficient (due to 
voltage drop along the leader-streamer channels) to support further 
growth no matter how fast your break rate. Since the maximum coil 
voltage (for a spark gap coil) is ultimately limited by bang size, 
merely increasing the number of bangs per second eventually helps keep 
keep existing spark channels hot, but does not aid in lengthening the 
streamers once they have reached a certain limiting length. The 
increased power from using higher break rates goes into making leaders 
and streamers hotter, and spreading streamer tip activity over a larger 
volume (i.e., generating more "frantic" streamer activity).

<snip>
> 
> Yes, I know that I need a deQ-ing diode.  The PIV should be about the
> peak voltage of the power supply, and with proper overrating, I think a
> string of 30 1N4007 diodes should work (which I have already built for
> the purpose).  They are rated for 1A continuous current, but much more
> peak.  With a charging inductor of about 25mH, I think this should work.
> Also, because my charging inductor won't be very large, dwell time won't
> be an issue (I've calculated it before and there's a significant
> margin).

OK... but I'd recommend at least 1.5 - 2X margin on the dequeing diode.

> 
> You seem to misunderstand exactly what gap I was referring to and what I
> meant by sustaining current.  The gap to which I was referring was not
> the gap that was part of the charging circuit in the rotary gap.  it is
> a separate static gap would be in series with the charging circuit.  I
> want this gap to fire at a certain voltage (approximately the peak
> voltage of the electrolytic capacitor), but not quench until the voltage
> is about half that.  Since arcs are sustained by current, my worry was
> that the breaks in the charging circuit by the rotary gap would cause
> this separate static gap to quench very quickly, maybe even after the
> first firing, which would entirely defeat the purpose.  I want to keep
> it firing for a number of rotations of the rotary gap, during which the
> electrolytic cap will not charge to its peak voltage again.

OK. Is what you are proposing something like this, where gap "A" is a 
static gap and "B" is your main ARSG gap?


                 |\ |  =====   A            | |
    + -------o---| >|--OOOOO---X------o-----| |--------
             |   |/ |                 |     | |        |
             |    DQ    Lc            |     Cp         O
    HV     + |                        |                O
  DC In    -----                   B  X                O
           -----                      |             Lp O
          Cs | 0.44uF                 |                O
             |                        |                O
             |                        |                |
    - -------o------------------------o----------------
> 
<snip>
> 
> What's the acid test?

It's slang for the real thing - running it in a TC at minimum and 
maximum break rates to see what breaks first...  :^)

> 
>>> While watching these
>>> discharges, I came up with an idea - what if this same "smoothing"
>>> capacitor was discharged in impulses into the whole primary circuit?
>> Directly firing the electrolytic bank into the primary would not be a 
>> good idea. Electrolytics do NOT like the voltage reversals that occur 
>> when "ringing" with a primary.
> 
> No, I do not want to directly fire the electrolytic capacitor into the
> primary.  I know that electrolytics will not stand voltage reversals,
> and it is only ever charged in one way.  The electrolytic is similar to
> a DC smoothing capacitor, with the difference that it is periodically
> discharged fully by the aforementioned static gap to provide
> instantaneous power boosts.

OK... I think I see what you are tying to do (at least conceptually). I 
need to see just how you physically plan to do this via a schematic (if 
different from the above).

Bert
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