FW: Paralleledneon inductance.

rom: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Sunday, August 10, 1997 3:15 AM
To: 	Tesla List
Subject: 	Re: Paralleledneon inductance.

Tesla List wrote:
> From:   daniel_hess-at-VNET.IBM.COM[SMTP:daniel_hess-at-VNET.IBM.COM]
> Sent:   Saturday, August 09, 1997 5:26 PM
> To:     tesla-at-pupman-dot-com
> Subject:        Paralleledneon inductance.
> Re; Bert;
> secondaries. Using the resonant approach, I can run off a pair of
> 15-60's with 18 gaps (0.5" total) and still hit 300 - 400 BPS. Without
> the addtional charging current, this would not be possible. However...
> I've also reconciled myself that (per Richard Hull) eventually my neons
> are doomed!
> Safe coilin' to you!
> -- Bert H --
> Bert; The portion of your note I've quoted above poses another question;
> I run two 15/60's, (and sometimes three or four.) How do I compute the
> C/L resonance equation when I have several secondaries paralleled together?
> And while I'm at it, mighten I want to avoid, at least to some degree, too
> much resonance between my neons and Cpri for the purpose of extending their
> lives? I realize that in doing so I may compromise output but then, so does
> a burned-out neon.
> Sincerely,
> Daniel Hess


You get low frequency resonance when the inductive reactance of your
combined neons "neutralizes" the capacitive reactance of your tank cap.
For 15 KV neons, this works out to be just around 0.01 uF for every 60
MA of current from your banked neons. The tank capacitance will need to
be  about 20% higher if you're running off a 50 Hz power source. 

For example, suppose your neon is a 15 KV 60 MA. It's effective output
short-circuit impedance is:
    XL = 15000/0.060 = 250,000 Ohms (reactive).

At an incoming line frequency F, your tank capacitor's capacitive
reactance will be:

    XC = 1,000,000/(2*Pi*F*C) Ohms, where C is in uF
Setting XL = XC, and solving for C:

     C = I/(V*2*Pi*F)  
         I = total sum of faceplate ratings of neon bank in MilliAmps
         V = faceplate RMS in Kilovolt for neon bank
         F = Incoming Line Frequency in Hz
        Pi = 3.14159   
         C = in uFarad

     C = 60/(15*6.28*60) = 60/11,304
       = 0.0106 uF

Using the above relationship, I've generated the table below for 15 KV
neons banks for both 60 and 50 Hz sources. Note that the overall Q of
the neon-cap LC circuit is not exceptionally high, so if you're within
about 10-20% of the ideal tank capacitance you'll still see resonance
effects. A typical effect, for example, is that the point at which the
spark gap JUST begins to fire intermittently is reached at a relatively
low variac setting (about 15% on my system).    

   Bank        (uF)        (uF) 
 Current -at-     60 Hz       50 Hz
   15 KV:    Tank Cap:   Tank Cap:
   ======    =========   =========
   30  MA     0.0053      0.0064
   60  MA     0.0106      0.0127 
   90  MA     0.0159      0.0191
  120  MA     0.0212      0.0255
  150  MA     0.0265      0.0318
  180  MA     0.0318      0.0382
  210  MA     0.0371      0.0446
  240  MA     0.0424      0.0509

As long as your gaps are firing smoothly and your coil's in tune,
running in this manner should not be a problem. Remember to limit
run-times to no more 60 second bursts followed by at least comparable
cool-down times. The real key is to always make sure your gaps break
down before your transformers do... use safety gaps and RF chokes, and
don't open the main spark gaps too widely - it's RF and overvolting that
ends up killing most neons.

Hope this helps!

-- Bert H --