Re: New three TC finished! but i need some help

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 3/7/03 11:19:10 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:


>Hello Everyone,
>
>      Well  I finished a new coil, it is a 3in system that runs on a single
>depotted 7.5/60 francfomer, it used to be one of the transformers with
>ground fault protection. I use my new PSU its noting fancy just a variac
>with a few switches. Well I need some help again I have been trying to
>figure out were to tap the primary coil by visual observation of streamer
>length and behavior and it is quiet perplexing. My problem is I think I
>have to much topload for break out, see when I taped the coil -at- 9.25 with a
>break out point it produces long bright strikes to near by pair of metal
>crutches.  Now when I remove the break out point the tesla coil wont run
>even at full power, then I need to tap it around 7.5 turns to get any break
>out from the toroid, and there are allot streamers that are short(around 1.5
>feet) very pail, with the break out point I get 40-44 inch sparks regularly
>to the crutches. Now Ed Sondermans Tesla Cal says it needs to be taped
>around 10 turns. I think when I taped it -at- 9.4 or beyond the sparks
>shortened and then will stop when tapped around 9.6turns. Ok how do you tune
>by visual
>inspection?? Is it in proper tune when the break out is on but there are
>streams COMING off the toroid on a few random places despite having a break
>out point were most of the streamers go, also streamers not quite as bright
>when they strike the crutches?? OR is it in tune when streamers only come
>from the break out point and are slightly more intense when they hit the
>crutches and slightly more frequently?? I REALLY would appreciate if some
>one could answer those question and describe exactly how to determine
>whether the coil is in tune by visual observation of streamers.
>
>Here I'll give you a run down of my coils specs.
>
>Topload
>Two toroids made from flexo Al ducting
>#1=19in wide by 3.375in across for 19.83pF
>#2=12in wide by3.375in across for 13.35pf
>So then what's is the total?? Its 33.18pF CORRECT???? That's a question
>cause am not sure!
>There spaced aprox .5in away from the top and bottom of each other btw the
>smaller one is on the bottom.
>
>Secondary
>Length=17.25in wound with 28awg enamled wire
>Diameter= 3.5in pvc pipe coated with polyurathane
>L=24.7mH (Measured) That makes it 71.25 turns per inch
>
>Primary
>IND=6.5in
>OD=15.375in
>Spaceing=Turns out to be around .29 on average between turns
>Wire= 0.162in
>Max turns=10.125 Measured 32uH max but Calculated its 34.2uH i think my New
>DMM is off cause the lowest seting is 2mH
>
>Capacitor= Maxxwell pulse rated 35KV at 30nF Measued value=30.2nF
>With a satfey gap set at 0.28125in wich fires ocasonaly
>
>Spark Gap
>Spaced total 0.1875in with 3 gaps and 4 copper pipe peices 2in wide by
>1.125in diamither enclosed in a box fabricated from plastic cuting board
>cooled by a 3in fan
>
>Transfromer
>Depotted Fance modified for matching to the capcitor, Some of the shunts
>were removed, and i actualy submerged and soaked the tran in semi-gloss
>polyurathane then let dry several times
>I out=87.8mA
>When the tesla coil is runing the amp meter waves backanforth between
>8-13amps
>
>      Ok i have tryed to figure out were to tap the primary coil by puting
>figures in to the formula F(KHz)=1/(2*pi*(sqrt(L*C))).  When I put in the
>numbers for the secondary with out the adding on the self capacitance of the
>secondary only the topload I get 176.17KHz secondary resonance, and when I
>change the figures for the primary coil to match the secondary I used the
>figures 30.2nF for the tank cap and it would take 27uH to match the
>secondary.  According to Ed's tesla cal it would take 9.03 turns to get 27uh
>of inductance, also it says I would need to used a 41nf tank capacitor witch
>is not the value of mine, so what is going on?  Also according to Ed's tesla
>cal I would need 10.4 turns to match my 30nF capacitor, which is bad cause I
>only have 10.1 turns max and when I tap it there it doesn't even resonate
>and the spark gap wont fire, id have to say it appears to operate best when
>tapped from 8.6 turns to 9.25 turns. Is this because of my topload?? Is it
>too bigg?? or is it that there is some formula to figure out the total
>capacitance of the two toroids?? Like would it be the average of the series
>and parallel values??  So could some one help me!! I would like to have it
>in perfect tune before trying to maximize the spark length.
>
>      Also I was wondering if there is a formula to figure out the voltage
>need to breakdown across the space in the spark gap, so that I know what
>voltage the spark gap will fire at regularly. So far this system has been
>very
>agreeable and well behaved, there have been no racing sparks or secondary to
>primary strikes, and streamer length and power is quite impressive. I have
>also taken some terrific pictures Ill post some of them in a folder at
>http://hot-streamer-dot-com/nolan/threeintc/ I really need some help on this so
>I appreciate your help greatly. Thanks.
>
>
>
>Sincerely,
>
>Nolan Moore


Nolan,

I have done some calculations on your coil.  I come up with the primary 
being tuned at 8.6 to 9.1 turns for best tune.  The effective capacitance 
of two stacked toroids is not the sum of the individual calculations of 
each toroid.  My two toroids individually calculate to 8.5 pf and 17.0 
pf.  The sum would be 25.5 pf.  Knowing all the parameters of my system 
quite well, from calculations and measurements - I input the secondary 
information and the primary data with the number of turns set at the best 
tap point for performance, then adjust the toroid capacitance input to 
produce the capacitance value that I am actually using (solving for primary 
tank capacitor). i.e., knowing everything quite well except for the toroid 
capacitance - plug all the numbers into the spreadsheet and find out what 
the equivalent toroid capacitance actually is.  In my case, it ends up 
being about 18 pf which is about 70% of the sum of the individual toroid 
capacitance.  I believe this 70% number agrees with other coiler's findings.

Your two toroids combined would be 33.18 pf and 70% of that would be 23 
pf.  If I run the numbers on your system using 23 pf for the toroid, I get 
best tap point at about turn 8.6.  It is not unusual to find the best 
performance up maybe one half turn from here at full power - which is about 
exactly where you find your best performance.  I agree, I think you just 
have too much toroid for that coil.  If you get longest sparks with a break 
out wire on the toroid (and nice performance by the way) and no or few 
breakouts without the wire, I think your toroid is just a little too large.

Ed Sonderman