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Re: Double Throw Spark Gap (fwd)



---------- Forwarded message ----------
Date: Tue, 09 Oct 2007 23:10:39 -0500
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Double Throw Spark Gap (fwd)

Hi Adam,

I suspect the tank cap will charge almost completely. Let's plug in some 
reasonable "guesstimate" numbers and see...

Chris didn't indicate the size of his tank cap, so let's take an 
educated guess that it's 0.02 uF. We can always change this to the 
actual cap size Chris is using later if necessary. The starting voltage 
on the DC storage cap (when driven by a 12/30 NST and FWB rectifier) 
will be about 17,000 volts. With a 25 mH charging choke, the resonant 
charging frequency of the combination of the charging choke (Lc), tank 
cap (Cp), and DC storage cap (Cs) will be about 7300 Hz. If allowed to 
fully complete, the charging current will be a half sine wave lasting 
for 1/2 cycle, or about 69 usec, peaking at about 14.5 amperes. For 
complete resonant charging cycle, we must see a minimum effective dwell 
time of about 69 usec in th charging gap.

Now, when the charging gap initially fires, the rotating contacts are 
approaching each other. Let's assume that the gap fires when the 
approaching electrodes reach a minimum separation of 0.25", the gap 
electrodes are 0.125" in diameter, and the DC charging current arc can 
be drawn out at least another 0.375" before being extinguished. YMMV. 
With these parameters, the estimated total distance over which the 
charging current would be connected (via arcing) would be about 0.75".

Let's further assume that the ARSG rotor speed is 3000 RPM, and the 
electrode radius of rotation is 4" (8" diameter for electrode rotation). 
The effective "dwell" angle is about 10.7 degrees, and at 3000 RPM this 
translates to about 42 usec of total effective dwell time versus 69 usec 
to fully charge the tank cap. Does this mean that the gap will 
prematurely interrupt the charging cycle?

I suspect the answer is - NO.

Since the peak charging current is a robust 14.5 amps, I suspect that 
(at least for the relatively short arc distances we're discussing) the 
gap will be unable to interrupt the charging cycle until the charging 
current has dropped significantly - perhaps down to an ampere or less. 
Instead of prematurely terminating the charging cycle, I suspect that 
we'll see trailing arcs in the gap that effectively "stretch out" the 
dwell time so that the tank cap can achieve nearly 2 x Vsupply.

It will be interesting to see the actual results that Chris sees...  :^)

Bert

Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Tue, 9 Oct 2007 03:46:42 -0700 (PDT)
> From: Yurtle Turtle <yurtle_t@xxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: Double Throw Spark Gap
> 
> I haven't really been following this thread, so
> forgive me if this comment has already been addressed.
> 
> 
> Regarding the following circuit:
> 
> http://tangent.cluenet.org/~chules/hv/tesla/dtsg.html
> 
> Does everyone think the cap can charge adequately in
> the same amount of time it can discharge? Without
> doing the math, I gotta believe that if one set of
> flying electrodes zooms around at several hundred rpm,
> the presentation time for the charging portion will be
> too short to fully charge the cap. After all, most rsg
> coils are charging the whole time they aren't
> presenting (well not exactly). I guess you gotta know
> the dwell time and the size of the pig feeding this.
> 
> Adam
> 
> 
>        
> ____________________________________________________________________________________
> Boardwalk for $500? In 2007? Ha! Play Monopoly Here and Now (it's updated for today's economy) at Yahoo! Games.
> http://get.games.yahoo.com/proddesc?gamekey=monopolyherenow  
> 
> 
> 
> 


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