The "Twins"

(A chronicle)

R. Scott Coppersmith - November 24, 2002 Update

Two Windows Media Video Files Available (.wmv)

8ft White Hot Arcs (1,115KB)Click Here To View
The Elusive 10ft-ers (1,284KB)Click Here To View

First Light July 8, 2002

The Twins were not working together at all. Racing sparks up and down each side, and sparks not attracted to each other.

Second Light July 13 2002

After an attitude adjustment (actually an altitude adjustment for each secondary of +3-in), and a change in Twin2 primary wiring, the racing sparks ended and the Twins started co-operating.

Longest Sparks (Toroid-to-Toroid 8ft)

AutoCad Design



Primary Transformer

Input Voltage Measured (VAC) 237
Input Current Measured (A) 103
Output Voltage (VAC) 14400

Primary Coils

Inside Diameter (IN) 16.00
Wire Diameter (IN) 0.610
Wire Spacing (IN) 0.500
Total Turns Each Side (Turns) 8.0
Each Primary Tapped At (Turns) 4.625
Inductance Each Side Calculated (mH) 0.0169
Diameter Each Side(IN) 32
Wire Length Each Side(FT) 50
Secondary Frequency Measured(kHZ) 65.79
Primary Capacitor (uF) 0.1800

Secondary Coils

Coil Form Diameter (IN) 12.75
Coil Winding Length (IN) 60
Wire Diameter (IN) 0.043
Wire Size (AWG) 18
Total Turns Each Side (Turns) 1395
Inductance Calculated(mH) 116.37
Inductance Measured Twin1(mH) 114.7
Inductance Measured Twin2(mH) 116.0
Medhurst K 0.77
Radius (IN) 6.38
Circumference (IN) 40.06
Wire Length (FT) 4579.52
Self-Capacitance (pF) 24.89


  • Tuesday 6/11/02:

Stopping by a construction company on the way home from work, I asked if they had any large diameter (12-in or larger) scrap water pipe. After some scrounging in the piles and handing over a crisp new $20 bill, a 12-foot length of dirty old 12.75-inch diameter SCH40 pipe was on its way to its new home bouncing around in the back of my truck. The Twins are conceived.

  • Wednesday 6/12/02:

After some thought � but not too much, a call to Essex wire corporation results in the order for a tad bit of wire � 16,000+ feet to be approximate.

  • Thursday 6/13/02:

Took a half day vacation to drive down to Superior-Essex in Ft. Wayne and pick up a pallet of magnet wire - $250 for a 12-inch spool of GP/MR-200 weighing in at 80 lbs (but no shipping charges!)

  • Spent the next week sectioning the pipe, and designing a winding jig.


The winding apparatus.


How to wind a Tesla coil secondary

  • Get a lathe (or use someone else�s)
  • Get a length of 1.25-inch pipe to chuck in the lathe.
  • Cut end disks at O.D. drill out the center at 1.25 and then turn them in the lathe for I.D.
  • Mount a hub/bearing assembly at the other end for support.
  • Clamp everything down.
  • Spend a few hours sanding all the contamination off the pipe (or get your son to do it), find out it doesn�t sand well (after using about $10 worth of sandpaper) and put some white paint on it instead ($4 a can).
  • Lay strips of double-sided tape ($3 per roll) on the pipe to help hold the wire in place.
  • Find a way to suspend an 80 lb spool of wire.
  • Try and wind the coil (on a 90 degree humid-as-hell day).
  • Fix the winding apparatus with a New Improved Nichols Clamp

  • Try winding the second coil.
  • Coat the wound coil with Pour-On 2 part epoxy mix ($18 per kit � need 2) and spend the rest of the day picking stuck bugs off the "will-this-stuff-ever-dry" coil while at the same time turning it every few minutes to keep the epoxy from sagging (this is a three-beer procedure, at least).
  • Give up and do the next one tomorrow (also on a 90 degree humid-as-hell-with-just-as-many-sticky-bugs day).

The "Twins"


  • Sunday 6/23/02:

Both "Twins" secondary coils are wound and epoxy coated. Time to start on the primary coils. Found some �-inch copper tubing about a year ago rummaging around an old relative�s garage � "Sure, go ahead and get that [stuff] out of here" they said. (that�s two 50-foot rolls still in the [original but slightly mouse-chewed-soggy-old] cardboard boxes.) The copper has been sitting around for a while (30-years?) and is slightly (understatement) discolored.

  • Monday 6/24/02:

After trying anything and everything you can think of to clean the copper tubing, went out and bought some ZAP (sulfuric and muratic acid � nasty stuff) and a small kiddie-pool and soaked the copper until pink again (also took care of any bugs/snakes/who knows what might have been still lurking inside).

Before ZAP

After ZAP

  • Tuesday 6/25/02:

Design and build a cool clamp for tapping/tuning the primary coil.


Then Build

  • Wednesday 6/26/02:

Time to go shopping�..let's see....4 8-ft sections of 8-inch AL flex duct ($10 each), 2 8-ft sections of 4-inch AL flex duct ($6 each), 2 more rolls of AL tape ($6 each), 2 18-inch plastic flower pots ($8 each), 2 36-inch dia plastic tables ($40 each)

  • Saturday 6/29/02:

Time to build some toploads. Cover the flower pots with AL tape, and roll the ductwork around them...looks with some drywall screws, and there you have it - instant (almost) toploads!

  • Tuesday 7/2/02:

More shopping....4 12-inch by 12-inch by 1/2-inch slabs of HDPE ($40) to make the primary coil stand-offs. Cut each in half on the table saw for 8 total, then drill 5/8-inch holes for tubing, then slice off the tops using the table saw.

Primary Coils "Snap-in"

Then Bolt on the Tops

  • Wednesday 7/3/02:

Not much left to do - still may be able spark-up the Twins by tomorrow night?????

  • Saturday 7/6/02:

Didn't make it by the 4th....oh well....Twin One complete.

Primary One

Primary Taps

Twin One