Tesla coil (Physics Dept) 2006

  (click to enlarge)

This is the University of Western Australia TC which dates back 40 years. Made in Germany according to the nameplate.  Apparently runs at 1 MHz but lots of problems with the Leyden jar caps.  Not really sure of the performance or if it is working now.  They wanted a new one so I put my hand up.  Not sure if the wiring forms the best theoretical transmission line at 1 MHz.

(click to enlarge)

Above shows the TC I made up for the Physics Dept at the Uni of Western Australia. I tried to incorporate the historical aspects of their 40 year old coil such as the wooden bases with original manufacturers plate and the antique terminals and some of the solid wiring. 
I really wasn't able to get much performance out of the the old setup so I have used the wooden bases and antique terminals in a hybrid acrylic/antique setup. The coil is conventional and was intended to be powered by one or two 12 kV 30 mA NST's but they found an 11 kV 110 mA NST in storage. Secondary is only 840 turns. Caps are standard CD .15 uF, two strings of 15 ie 20 nF and the gap is a static 5 gap copper tube array.
Sparks are 36 inches but it does need to be contained with smaller sparks in a Faraday cage for public safety. I have also made it on a large aluminium sheet counterpoise to allow operation in a non earthed environment.

(click to enlarge)

The left photo above shows the primary detail. The center photo shows the gap behind the red acrylic. A fan was added later. The right photo shows a fully shielded MO interference suppression circuit in a commercial "Lightning Protector unit" which I have modified and is used for the spark gap fan.  HV leads are heavy 75 ohm cable with shield present.

(click to enlarge)

Above shows the power supply which is a 12 kV, 110 mA NST which I have crammed in to a microwave oven (MO) shell. It uses the original MO mains interference suppression, 5V supply, light, fan and lock out switch when the door is opened. I have added a solid state relay, large indicator lights, switch and there is a remote on switch with a flashing red LED on a 6 foot lead. There is a mains outlet which is switched which can run the fan for the coil and also have an optional variac inserted.
There is an inrush limiter and a few MOV's in different areas.
I have included a 3.5mm headphone type socket which requires a shorted 3.5mm plug to be inserted before the unit will activate. (in lieu of a key switch).
There is a Terry filter of sorts with 360 ohms 15 W and a 440 pF 40 kV cap on each leg of the HV . There is also similar circuitry inside the Faraday cage to the coil.

(click to enlarge)

Photo above shows 36 inch sparks from the 16 inch coil.  My design was not meant to be stressed like this and used relatively thin PVC which punctured through several times with charring of the interior. Fortunately when used in the Faraday cage the sparks are constrained and this doesn't happen.

Point to run for AVI video (1.5M) of the Physics Dept Tesla coil

I have predictably had to replace the secondary for one with thicker PVC (schedule 40).

Can crusher (Physics Dept) 2006
This is an upgraded version of Cancrusher 3 that I built up for the Physics Department at the Uni of Western Australia. The previous defibrillator capacitors did not last long and I have now installed a "proper" pulse rated Maxwell capacitor rated at 131 uF, 8 kV, 100 kA, 80% reversal which stores 4 kJ. Typically it will only be used to 2 kJ so even though it is second hand with unknown history, it will hopefully not be particularly stressed and have a reasonable lifespan. Physically it bolts nicely on the bottom of the microwave shell and I can still keep the wiring path fairly short. In view of the 70 kg weight, I have built it onto a furniture removal trolley. Simpler and cheaper than anything I else I could come up with.

(click to enlarge)

The left photo above shows the completed unit bolted to the trolley. The center photo shows the can positioned to be ejected with the base of the can halfway into the coil.  For normal can crushing the block is removed and the can inserted fully.  The right photo shows a close up of the heavy workcoil.

   (click to enlarge)

The left photo above shows the measurement of the current on the ground return wire using a Rogowski coil.  It also shows the heavier coil that is not as efficient as the wire core is not as close to the can surface.  The center photo shows the current reading on the CRO with 10 kA/div scale vertically and 20 us/div horizontally with a 6 kV shot (= 2.1 kJ).  The peak current in the 3 turn coil is 40 kA which corresponds to a current within the can of about 80 kA. Resonant frequency is 13 kHz with the large cap and longer wiring.  The right photo shows the capacitor specifications of 131 uF, 8 kV and 0.08 uH.  It is rated at 100 kA and 80 % reversal.

Performance is good with easy crushing of the can at 4 kV, 860 J or tearing it apart with 6 kV, 2000 J. By positioning the can just out of the coil, it can be propelled 15+ feet into the air.  This is in effect a Thompson gun.

  (click to enlarge)

The left photo shows the deformed Coke can 15 feet in the air (basketball backboard is 12ft). The right photo shows the red Coke can from the first photo showing the deformity. The black Coke can has a goblet shape as it was a little too far into the coil to project properly.

Further improvements could include faster charging with switchable energies. Also I have had requests for a microwave oven like "ping" when it is cooked!  I have a large LED digital display that I had hoped to adapt to a large voltmeter.

Vortex cannon 2006
This was made for the Physics Dept after they saw my other vortex cannon in action and felt it would be good for school displays. Features of this one:
Portability - well it is a wheelbarrow so easy to get around. Uses a 220 liter compost container.
Large rear diaphragm (70 cm) to shift a good amount of air.
Diaphragm is more flexible and lower for kids to use.
All up cost with new parts was AU$220 (apart from 4 old bike tubes). No screws and can be disassembled in a flash (well sort of falls apart).
It uses a commercial fog generator such as used in discos.  The fog is a proprietary mix of propylene glycol and triethylene glycol in water. 
But the best part is that it looks mean with a light inside it and sights.

  (click to enlarge)

My interest and involvement was sparked (pun intended) by its Tesla coil which was made by Stan Deyo in around 1988. It has functioned reliably with little modification since. The black and white double exposure publicity shot at the time is shown below on the left.

Original coil  2003
I was able to see the Tesla coil in Feb 2003, but found that it was not performing well with perhaps 2 foot streamers despite using a 5 kVA pole transformer.  Truly, here was a noble cause worthy of assistance. 

  (click to enlarge)

The best picture I could get showing only small streamers (above right). Despite retuning, doubling the topload, and doubling the capacitance only about 3 foot sparks could be obtained.  The staff were keen to upgrade and I gave a demo of my 4 inch coil and micro wave oven transformer supply, which gave sparks up to 4 1/2 feet.

(click to enlarge)

On the wrong side of the Faraday cage (above), doing the demo in Feb 2003. An earthed PVC rod with steel wool on the end gives a sparkler effect if the sparks are hot enough. To the right in the photo is Scitech's TC which needs some work.

Upgraded coil  2003

(click to enlarge)

In June 2003, my 6 inch coil was installed with a significant improvement in performance (above).  The sparks are now a lot hotter and are out to around 4 feet.  The length can be estimated by the 36 inch length of the secondary to the base of the toroid.  Still less than hoped for but a much noisier and more impressive display.

Specifications (original) 2003
The original Scitech TC components included a 5KVA pole transformer 250 V to 12.5 KV with a soft start and extensive mains filtering and monitoring. It is ballasted with 3 paralleled heater elements which glow red hot after a minute or so of continuous operation.  It has fuse limiting to 16A.
The motor is an ARSG running on DC 180 V with 8 tungsten 1/2 inch rotating electrodes and 2 stationary. 
The 2 tank capacitors are each 20 nF mylar (total 40 nF at 20 kV). 
The previous primary was around 2-3 turns and the secondary is 6 x 30 inch with around 420 turns.
The topload was a 5 x 12 inch gold plated copper toroid.

The construction of this coil and the Faraday cage was of very high quality and the long service a testament to this.

Specifications (upgraded) 2003

  (click to enlarge)

The coil during modifications (above) with the new double layer primary and new secondary.  The double layer was needed to accommodate the larger number of primary turns (8 above, 5 below) in the same physical space as the previous 3 turn coil.
My changes were to:
          1  Replace the secondary with 6 x 32 inches with 1280 turns (previously 6 x 30 with 400 turns).
          2  Replace the primary now tapped at 8 of the 13 turns.
          3  Use a larger topload of a 12 x 29 inch toroid with a smaller 8 x 20 toroid beneath it.
          4  Add my Cornell Dubilier MMC capacitor of 45 nF to the existing capacitor (total 89 nF). 
          5  Run the motor from 200v DC (previously 180 V).
          6  Fit low profile strike rails.
          7  Use an inductive ballast (below) instead of the resistive one.

   (click to enlarge)

The inductive ballast (above) made from a modified 440V to 240V transformer rated at 5 KVA bought at a junk yard. It weighs 30 kg and has a core iron cross section area of 47 cm² (= 7.3 in²). The four 'C' cores were taken apart with gentle persuasion from a large hammer, and an 'air gap' made by using a cardboard or acrylic spacer between the cores. By using 0 to 6mm spacers the current draw on the 240 V winding can be adjusted from 1 A to 30 A. This corresponds to an inductance of 1.0 down to 0.04 Henries.
I plan to replace the resistive ballast with this inductive ballast soon. See Ritchie Burnett's site for comparative information.
The resonant charging capacitors (also shown above) of 74 uF is the sum of the 7 polypropylene capacitors that I had.  It is in series with the ballast and in parallel with the pole transformer.  Using these capacitors results in a higher voltage across the pole transformer input.  Testing with a 10 KVA transformer as a load with a 240V supply resulted in 280 V across the transformer with the capacitors compared with 195 V without. In other words this arrangement gives a higher voltage than the supply and will limit total current draw which generally sounds like a good thing.  In practice, however, it did not improved the performance or current draw and has been left out.

  (click to enlarge)

University Open day for Physics Dept 2006
I demonstrated the Tesla coil which  brought people in with the noise who then got to see the can crusher, ferrofluid, laser lissajous figures or just get free shocks.  The big vortex ring generator was the biggest attraction and few people went past without seeing or feeling it.

 (click to enlarge)

A spectator (Robin Wong) took some videos and posted them on YouTube which I happened to see by chance.

Above, the vortex generator in action. Direct YouTube link is here.

Above, the tesla coil in action. Direct YouTube link is here.

Home open day Nov 2006
To keep the neighbours aware that the noises they hear from my place are friendly, (and not gunshots) I have been having an open day where I run about 20 different Tesla, high voltage, laser and magnetic displays and make a few loud noises.

  (click to enlarge)

Tesla Forum presentation 2007
This was organized by the Tesla Forum of Western Australia.  I gave the after dinner presentation on Tesla coils.

  (click to enlarge)

Hamfest 2007
This was organized by the Northern Corridor Radio Group and is the first one I have been to.  I set up my 4 inch TC in the Faraday cage and also ran the mini coil.  Liability insurance was arranged through the groups policy for the event. Seemed pretty well attended and I picked up a couple of NST's and bits and pieces when I had a spare moment. Setup time for the cage is still almost 2 hours.  There must be an easier way.  I tripped a breaker turning off the variac (from zero volts), presumably the RCD.  They didn't have the keys to the control panel so had to do some creative work on the hinges to get power back.

Nice to have an audience that understands resonance.

  (click to enlarge)

University Open day for Physics Dept 2007
Similar to 2006 with the 4 inch coil in a cage plus the vortex generator.  Popular as before.  Also used the mini-TC.  Getting a lot of mileage from this particularly when people draw sparks to a hand held neon tube. No shocks from the tube setup, but people who want to can have the 2 inch sparks jump onto their hand which does prickle a bit.

(click to enlarge)

Gravity Discovery Center Tesla show  2007
This was a display of my 18 inch coil in a 60 ft wide domed building.  Filmed by the Discovery Channel.  A sample gallery shows the various effects.

(click to enlarge)

Home open day 2007
This year I sent out a few more invites.  This show is mainly for neighbours but in the end none turned up -  still there were about 40 people.  I put out my usual array of displays including ferrofluid, soldering demos, magnets and small power supplies and lights for the kids, Oscilloscope with microphone attached, lasers including HeNe and green scanner, HV displays of sparks, lifter, small TC, Jacobs ladder, smoke ring generator, CD in microwave and magnetic levitation.

The weather was not in my favour with high winds and intermittent showers but I did get to run the big TC and get some shots of people next to it.

(click to enlarge)

Future plans 2006
In public displays I would like to have a big vortex generator mounted on a trailer on a swivel mount so it can be fired. Perhaps hired out. No major public liability issues with this one unlike high voltage stuff where it would cost me $1500 premium for 6 Tesla shows for the standard $10 million cover.

I have thoughts for a small demo Tesla coil for the physics dept which is has a low enough power to be safe to hold a fluorescent light up to. This is a popular demo with kids as it looks like a light sabre.

Big Day Out (Syd Klinge's coil on tour in Australia Jan 2005)
The Big Day Out is a rock concert that tours major Australian cities with over 40 , local and international bands. One of the side attractions (the main one for me) was Syd Klinges's 'Cauac' 16 foot coil running at 100KVA.   I was fortunate enough to meet Syd and his entourage and discuss coil details.   He runs from a portable generator rated at ?170 KVA 3 phase ?480V using if I recall correctly one 11 KV pig for each of the 3 phases each individually ballasted. The out put is rectified using over 1000 1N4007's to DC then through an RF filter to the base of the coil and the  spark gap which is ARSG using 1/2 inch tungsten electrodes.  Tank cap was two 0.1 uF custom made units.  Resonant frequency is 59 kHz.  The secondary is 10 feet tall and 16 feet total height. The winding is crosslinked PVC coated.  Toroid is chicken wire covered.

    (click to enlarge)

Some shots of the day with attendance 44,000 in Melbourne.

  (click to enlarge)

Tesla Exhibition 2006 (from Tesla Museum Belgrade)
This was held at the Western Power World of Energy Museum and has a wealth of Tesla related historical information and models. This is the first visit for the exhibition which will go on and visit Strasbourg, Vienna, Vancouver and Paris.

(click to enlarge)

The Tesla coil above from the new travelling display is a very old style coil with glass plate caps and a serrated wheel gap. It wasn't a great performer despite the Serbian Orthodox blessing.

(click to enlarge)

A good crowd included many Tesla Forum members and various VIP's.  There were various models including the Wardenclyffe tower. The extensive bilingual posters and graphics were included in full in a 60 page booklet

(click to enlarge)

Replica models included the first AC motor, bladeless turbine and Egg of Colombus. The egg display uses 415V 3 phase power of 15A. The last photo is a 1/6 sec exposure to give an idea of the speed of precession.

Tesla Play 2006
A one man play on Tesla with Frank Tabbita performed at the local Uni. The play was a superb acting performance. How anyone remembers a whole performance I find hard to conceive (I have trouble remembering phone numbers).  A dynamic and memorable depiction of Tesla's life.

I took some photos with permission from Jeff, the technical manager who was keen for ideas to incorporate HV into the performance. Audience was about 500.

(click to enlarge)

       (click to enlarge)