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Re: well, this is interesting

Subject:      Re: well, this is interesting
       Date:  Mon, 05 May 1997 20:26:15 -0700
       From:  Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
         To:  Tesla List <tesla-at-pupman-dot-com>
 References: 
            1


Tesla List wrote:
> 
> Subject:  well, this is interesting
>   Date:   Sat, 3 May 97 05:02:48 UT
>   From:   "William Noble" <William_B_Noble-at-MSN.COM>
>     To:  "Tesla List" <tesla-at-poodle.pupman-dot-com>
> 
> well, I learned a few things tonite - maybe even some make sense.  I
> added
> some capacitance to my new coil - I started from .001 mica and added a
> .001
> 14.5KV capacitor made by Plastic Capacitor company (it's about 1"
> diameter, 8
> inches long, encased in glass) - sparks went from dinky little 3 inch
> sparks
> to really nice looking 18 inch sparks with lots of forking.  So, adding
> capacitance is good, and the little Plastic Capacitor unit is good too -
> it
> warmed up just a bit in a 20 to 30 sec run (about as long as I can run
> with my
> half done RQ spark gap with no fan) - it felt like it raised up about 5
> degrees or so.
> 
> I also learned that the toilet float I used for a top capacitor (a
> plastic one
> with some aluminum foil wrapped around it) keeps a charge - I got a
> small
> shock when I went to dismantle the coil - I don't quite understand this
> since
> I thought it would be grounded through the secondary (the low side of
> which is
> grounded), but the connections were't the best, so maybe there was an
> open
> circuit???
> 
> What I don't understand is the following - when I doubled the tank
> capacitance, I would have thought I would halve the tank inductance to
> keep LC
> about constant and maintain resonance with the secondary.  But I found
> that
> with .002 uf it was best on turn 13 (I only have 14 total turns on a 1/4
> inch
> {50 ft} tubing flat spiral primary), and with just the .001 mica
> capacitor it
> seemed to like fewer turns - my notes say that with the same secondary
> configuration (toilet float on top, etc) I got best performace at turn
> 8, and
> with no top capacitance, best was at turn 13.  does this make any
> sense???
> 
> And, can I expect still better performance by adding more primary
> capacitance?? (input xformer is 15KV 30 ma neon) - it would seem so....

William,

1. Be VERY careful using that glass encased Plastic Caps unit - the
dielectric is more than likely Mylar, and it WILL explode if overheated.
If you must use it, make sure you put it into a container which can
absorb the shock, fragments, and hot spewing oil. That type of capacitor
is used for DC/filtering use, NOT for pulse or RF applications. The fact
that it is heating up after only 30 seconds use is a warning...

2. The frequency changes as the square root of the capacitance. Also,
the inductance on your primary does not change linearly with the number
of turns - the outermost turns add considerably more inductance than the
inner turns.  

3. Assuming you don't change the secondary toroid and coil self-C,
increasing the primary C will increase output voltage, assuming you have
enought supply current to adequately recharge the tank cap. Your 15 KV
30 MA neon can drive about 0.005 uF (5 nF) of tank capacitance.

Again, be VERY careful using that Plastic Capacitors filter cap!!

Safe coilin' to you!

-- Bert --