Re: First coil I built worked great !

To: tesla-at-pupman-dot-com
Subject: Re: First coil I built worked great !
From: "John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Sat, 03 Oct 1998 15:21:39 -0600
Approved: terryf-at-verinet-dot-com
At 04:59 AM 10/3/98 -0600, you wrote:
>Original Poster: "Barton B. Anderson" <mopar-at-uswest-dot-net> 
>
>Richie,
>First let me say congrats!!! It's always great to hear of a first timer doing
>
---------------------  snip

>Bart
>
>Tesla List wrote:
>
>> Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk>
>>
>> First coil I built worked great !
>>
>> Hi everybody,  I have just finished building a small (medium) sized
>> tesla coil after seeing one demonstrated on an American TV programme
>> about lighting.  I am a qualified electrical engineer and have read
>> lots of information from the many Internet sites and would like to say
>> two things:-
>>
>> 1. I was very impressed with the performance of my first Tesla Coil.
>>
>> 2. The information on the Internet sites is VERY good so use it.

-----------------   snip

>> My point is that the spark length seems high for the relatively low 6Kv
>> neon transformers,  small primary capacitor  and LOW CALCULATED POWER !
>> I have heard figures like 500 to 1000 Watts per foot mentioned before,
>> does anyone have any feelings on this ? (Are my calculations wrong ?)

-----------------  snip
>>                                 Cheers,
>>
>>                                         Richie,
>>                                         in sunny Newcastle (England.)

-------------------------------------

  Richie -

  Your calculations for the 70.4 watts/ft of spark are correct, however,
they leave out the large losses of the input circuit. These losses are
taken into consideration with the 500 to 1000 watt/ft of spark. Also, the
type of spark is considered, either streamers in air or controlled sparks.
A controlled spark is a continuous horizontal spark to a ground point. This
has the advantage of a being a constant load on the secondary that can be
compared accurately with the input wattage unlike streamers in air.

  I ran your coil numbers on the JHCTES computer program which showed a
1.72 foot controlled spark giving 698 watts/ft of spark using 1200 watts
input or 5 amps? at 240 volts input. The resonant frequency was 290.26 Khz
with 13.62 mh secondary coil and 12.85 pf toroid. This equated to 6.69
primary turns with a 22 nf pri cap. Can you find what the computer used for
the sec coil self capacity and the primary inductance?

  The secondary Q factor was 57.54 and log dec .0546 giving a dampened
waveform of 42.2 cycles to 10% amplitude. Note that the Q factor can be
found from   Q = pi/log dec  and also from the 10% cycles (more difficult).
This is the dampened waveform of the secondary coil when the TC is
operating without sparks. This apparently is the only way to find the
secondary Q factors of an operating TC. The K factor is .17 but may not be
accurate because you did not give enough info regarding the primary coil so
I had to estimate the dimensions. The half cycles of the primary waveform
are 1/K factor. You may want to check this with your scope.

  Your coil appears to be doing very well for a beginner. I was happy to
see that you were also interested in doing the calculations.

  John Couture