My Coil Specs

Hi Richard,

Rod here from Canberra....Long time no talk...but I've been reading.. :-)

Anyway, I thought I'd finally get the latest specs of my 12" coil off to 
the group, and be open to suggestions. I'll also include proposed 
construction specs too.

Secondary Coil: (Current)

Archimedes flat (pancake) coil.
12" diameter PVC pipe (pipe thickness approx 1/4")
Winding wire: 1mm enamel coated copper wire
Winding Length: 47.5"
The coil has been space wound at 20 turns-per-inch, which makes out that 
there are 950 turns.

Primary Coil:  (Current)

Using 3/8" copper pipe for windings.
5 Turns
Spacings: 1" from centre of 1 coil to another -

  ----( )------( )------( )----    <---- Perspex Support
       ^--------^   <------ 1 inch from centres

Or take it as 0.625 inch gap between windings.

Inside diameter (overall coil size): 15.75 inches
Outside diameter                   : 24.5  inches

The coil is mounted on 12 perspex mounts which are 1" high x 0.5" thick 
x 6.5" long, positioned on a circular base of 10/16" chipboard which is 
30" across.
The perspex supports are setup in an analog clock formation (ie, placed 
at positions 1 o'clock, 2 o'clock....etc)

Hence with the height of the supports being 1", the P.coil is 1" from the 
base, also, the first winding on the secondar is 1" from the base of the 

(There are proposals for modifications - see after RSG)

Rotating Spark Gap Assembly:

I am using a 1/4 horsepower 1440 rpm 240VAC motor to drive the gap.
It has 12 rotor electrodes. The rotor disk is made from clear perspex 
which is 10" in diameter, and 1" thick. The spacing from one electrode on 
one side to the corresponding electrode on the otherside is 9" - hence 
the electrodes are placed 0.5" from the edge.

All electrodes are made from 0.5" solid Aluminium rods.
The electrode on the rotor disk are 2" long. They are also screwed in 
from the edge of the disk, inwards.

The stationary electrodes are actually machined from 1.5" solid Al rods 
which have been lathed down to have a long 0.5" shaft, with 4 heat-sink 
fins 0.5" from one end which are 1.5" in diam, 1/8" thick and spaced 1/8" 
apart. This is all 1 piece of metal.
The overall length is approx 6-7" long.

Now, the disk rotates horizontally level, having (same on both sides), 
one electrode above, and one electrode below the disk, such that the 
rotating electrodes pass between the two stationary electrodes, hence 
closing the gap.
The two electrodes below the disk are mounted on a solid block of 
aluminium which is 2.5"x0.75x10" in size - hence the two bottom 
electrodes are joined. 
The electrodes above the disk are connected onto the circuit where the 
gap exists.

             motor shaft
  ----------o    \|/     o----------   <---- wires to the circuit
            |            |    
rotating   ===    ||    ===    (Top stat. electrodes)
 electrodes '     ||     '
           -|-----||-----|-    <---- perspex disk
            .            .
           ===          ===
           _|____________|_       <---- bottom stationary electrodes 
           ----------------            (imagine there are 4 fins, not 2)
	     |_______ base aluminium support (connecting) block.
That's pretty much how it looks.

This coil was designed from a larger 8 foot 12.5KVA 3.5MV Tesla coil 
built by the Tesla Technology Research (Professional Sound Systems UHV division)
who are/were in Monrovia California. This coil exists in our National 
Science and Technology Centre a.k.a Questacon. 
That coil has a 20" secondary with 800 turns of approx 2.5mm wire.
The primary coil is identical to mine, except it is wider.

At these power levels, I can see how 5 turns would be enough.

I will scan a photo very soon.
I also have direct access to this coil, so if more information is wanted 
with this large coil, please ask, I'd be only too happy to oblige.

Proposed Constructions:

New Primary Coil: 

I entend on building a new primary made from 1/2" copper pipe, with 3/8" 
spacing with 12 turns. I am able to construct it on the 30" base I 
already have. The current primary coil is removable.
This will also be a flat pancake coil.

Suggestions? Approvals?

Power Supply:

I entend to run this at low power, only about 2KW.
I will use 2 banked neon-xfromers which are 15KV -at- 60mA each.
Capacitors for this are around 0.025 - 0.03 uF. I will use Richard 
Quick's construction plans of tubular capacitors.

This coil should also be able to be operated in power levels of 10KVA - 
20KVA without problems. 

Tuning still has to be made..


Aluminium Toroids:

I am now able to get a toroid made. 

1) With the current primary coil, what size toroid should be made?
2) With the proposed primary coil, what size toroid should be made?

I am suggesting, for both sizes, a 30"x 10" toroid...


Are the specifications I have outlined suitable for a decent working coil?

I am looking to obtain from 3 - 15 feet sparks.

Suggestions? Queries? Problems? 
I am open for comments...and help...

Thanks Heaps...

Canberra, Australia.

-        Rodney Davies - Computer Science Student Association                -
-        Email: Rodney.Davies-at-Student.anu.edu.au                             -
-        Information Technology Co-ordinator, John XXIII College,            -
-        Australian National University, Canberra.                           -