RE: First Light for 10" Coil.

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

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Peter -

Congratulations, you have reached the ultimate goal in Tesla coil research.
That is to attain the following

     1. Build a good coil
     2. Test it properly
     3. Have it agree with the theory

These 3 steps are not easy to achieve but they will give a coiler some very
valuable information about Tesla coils. I will mention only one important
parameter and that is the toroid capacitance reduction when it is placed on
the TC secondary. This is very important because it determines the true
toroid capacitance when placed on the TC secondary. This capacitance is much
less than the toroid capacitance calculated by the standard equations. Why??

For example with your coil the 12"x42.5" toroid capacitance using the
standard toroid equations is about 47.4 pf. This will not agree with the
actual toroid capacitance when it is located on the secondary. The actual
toroid capacitance is 34 pf which gives the 84.8 KHz (you measured). The
only way to find this actual toroid capacitance when it is on the secondary
is by measuring the operating frequency with and without the toroid after
the coil is built. You then calculate the resonant frequencies with and
without the toroid. All of the surrounding conditions that affect the toroid
and secondary capacitances will then be accounted for.

You can use a computer program to verify the above. Go to the following
website and click the following:

      http://www.mgte-dot-com

Click on Tesla, then on JHCTES (Books),
Go to the bottom of the Book page and click on JHCTES Ver3.42

Enter for the
Primary  0.15    11.30    0.00    9.90

Secondary  5.00  1130    27.20    0.00   34pf

The computer output will give you 84.43 KHz (with toroid) operating
frequency as you measured. If you enter zero (no toroid) for the Secondary
terminal pf the operating frequency will be 145.49 KHZ as you measured. The
primary turns are shown as 6.08 which is close to what you are using. Ignore
the spark length because it is broken.

The toroid reduction is 34/47.4 = .717      1-.717 = .283 = 28.3% reduction

I do not believe anyone has ever explained this Toroid reduction with Tesla
coils. It should be an increase because the toroid is closer to other
objects. Maybe Paul or Antonio will look into it.

Note that the computer program and similar programs eliminated many
calculations to find the actual toroid capacity of 34pf.
However, if you can do the calcs manually you have a firm grasp of how a
Tesla coil operates.

Comments welcomed

John Couture

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




-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, December 23, 2003 2:54 PM
To: tesla-at-pupman-dot-com
Subject: First Light for 10" Coil.


Original poster: "Peter Reid" <peter-at-reidconsulting-dot-com.au>

Hello Everyone on the Tesla Coil Mailing List.

I have just finished building my new MOT powered 10” Coil and managed to
tune it somewhat. I am quite happy with the results so far, however I am
wondering if anybody could shed some light onto areas I should work on In
order to improve the spark length and power handling capabilities of this
coil. So far I have managed occasional 8.5ft Power Arcs to a grounded rod.
However I feel that the coil is still capable of a lot more. Initially the
spark output was quite poor until I increased the coupling between the
primary and secondary. (I don’t think I’ve gone too far).

I will list the specifications below. With the current setup I am getting
quite powerful arcs to the strike rail and ground with-in about a 3ft
radius around the coil.

I have posted some photos on my website for anyone that’s interested. I
also have some pretty good video footage, but that isn’t on the
webpage.
<http://tesla.reidconsulting-dot-com.au/>http://tesla.reidconsulting-dot-com.au
Any input / help with improving the current setup would be greatly
appreciated, I am just a little worried about burning up my secondary if I
try and pump any more power though it.



Coil Specs are as follows..

Primary
Flat Spiral, Wound with ½ In Copper tubing, spaced but ½ inch.
ID = 12.7in
OD = 32.5in
Turns = 10.25, tapped at about turn 6.15
Primary sits 1.5ft above the ground on a specially made wooden platform.
Strike Rail = 1/2copper tube raised by ½ inch around outside of primary.

Secondary
Wound on a 10” PVC pipe, which has been baked and sealed with many coats of
polyurethane.
Winding length = 41in
Wire Diameter = 0.9mm B&S Gauge 19
The bottom turn of the secondary is elevated 1 inch above the top of the
primary winding.

Toroid
12” x 42.5” (Tube Diameter x Outside Diameter of Toroid)
Mounted 12in above the top winding on the secondary.

Measured Res Frequency of Secondary is 84.8kHz, and primary has been tuned
to exactly that. (Can someone please tell me if its worth trying to detune
it by 1/3 of a turn to account for streamer loading etc?.)

Capacitor
              0.15uF MMC Cap Bank made up of 144, 942C20P15K caps.

Power Supply
              6 MOT Supply, Currently Ballasted to 40A -at- 240V (Using a
Sliding Choke Balast)
              Maximum line draw current of 80A -at- 220v when the ballast is
removed. That’s 17.6kVA J
              Approx 12kV output.

Spark Gap.
              200bps Sync Gap, with a Remote Phase Adjuster.
              Single Gap, Tungsten static electrodes, and 4 x 8mm brass
threaded rod (moving electrodes) Spinning on a 12in
G-10 disc (3000 rpm) Gap spacing is about 1-2mm total.


BTW, Thanks to everybody who has contributed to the mailing list, the help
I have received from you guys has been invaluable.


Regards

Peter Reid.